Processing optical system, processing device, and processing method

Abstract

[Problem] To provide a processing optical system, a processing device, and a processing method that can form an ideally shaped riblet structure. [Solution] A processing optical system (15) comprises: a first optical system (16) that split a processing light EL0 from a light source (2) into a first processing light EL1 and a second processing light EL2; a second optical system (17) that forms a interference fringe IS on a surface of an object (W) by dividing the second processing light EL2 into a plurality of second processing lights EL2 and irradiating the divided plurality of second processing lights EL2 onto the object (W) from different incident directions; and a third optical system (18) that irradiates the first processing light EL1 from the first optical system (16) toward an interference area IA on the surface of the object (W) where an interference fringe IS has been formed.

Description

Processing optical system, processing device, and processing method

[0001] The present disclosure relates to, for example, the technical fields of a processing optical system, a processing apparatus, and a processing method for processing an object.

[0002] Patent Literature 1 describes a processing device capable of processing an object such as an aircraft fuselage to form riblets on the surface of the object. Such a processing device is required to process the object appropriately.

[0003] U.S. Pat. No. 4,994,639

[0004] According to a first aspect, a processing optical system is provided, which includes: a first optical system that splits processing light from a light source into a first processing light and a second processing light; a second optical system that splits the second processing light into a plurality of second processing lights and irradiates the split second processing lights onto an object from different incident directions, thereby forming interference fringes on the surface of the object; and a third optical system that irradiates the first processing light from the first optical system toward an interference region on the surface of the object where the interference fringes are formed.

[0005] According to a second aspect, there is provided a processing optical system including: an interference fringe forming optical system that divides the second processing light into a plurality of second processing lights, and irradiates the object with the divided second processing lights from different incident directions, thereby forming interference fringes on the surface of the object; and an irradiation optical system that irradiates the first processing light toward the interference region where the interference fringes are formed.

[0006] According to a third aspect, there is provided a processing device that performs riblet processing on the surface of an object using light from a light source, comprising the above-mentioned processing optical system and a positional relationship changing device that changes the positional relationship between the interference fringes formed on the surface of the object by the processing optical system and the surface of the object.

[0007] According to a fourth aspect, a processing method for performing riblet processing on the surface of an object using light from a light source is provided, which includes: branching the processing light from the light source into a first processing light and a second processing light; dividing the second processing light into a plurality of second processing lights; and irradiating the divided plurality of second processing lights onto the object from different incident directions to form interference fringes on the surface of the object; and irradiating the first processing light toward an interference region on the surface of the object where the interference fringes are formed.

[0008] 1 is a cross-sectional view schematically showing the overall structure of the machining system of this embodiment; 2 is a system configuration diagram showing the system configuration of the machining system of this embodiment; 3 is a perspective view showing a riblet structure; 4 is a cross-sectional view showing a riblet structure (a cross-section taken along line III-III' in FIG. 3A ); 5 is a top view showing a riblet structure; 6 is a plan view showing an example of interference fringes; 7 is a configuration diagram showing the configuration of the machining optical system of this embodiment; 8 is a diagram showing the fluence distribution of processing light (interference light) in a comparative example in which interference fringes are formed with multiple second processing light beams without irradiating a first processing light, and the cross-sectional shape of the riblet structure formed by the processing light of the comparative example; 9 is a diagram showing the fluence distribution of processing light in this embodiment in which a first processing light is irradiated in an overlapping manner onto an interference region in which interference fringes are formed with multiple second processing light beams, and the cross-sectional shape of the riblet structure formed by the processing light of this embodiment; 10 is a graph showing the relationship between the fluence of light and the processing amount of a workpiece; 11 is a diagram showing the fluence distribution of processing light (interference light) in a comparative example in which interference fringes are formed with at least the second processing light without irradiating the first processing light, and the cross-sectional shape of the riblet structure formed by the processing light of the comparative example. 1 shows the fluence distribution of processing light in this embodiment, in which a first processing light is superimposed and irradiated onto an interference region where interference fringes are formed by a plurality of second processing light beams, and the cross-sectional shape of the riblet structure formed by the processing light of this embodiment. shows an ideal waveform. shows two waveforms (fundamental frequency waveform and double frequency waveform) obtained by Fourier transforming the ideal waveform. is an explanatory diagram summarizing in a table the irradiation patterns in the irradiation region, interference region, and overlap region in five examples of processing optical systems. is an explanatory diagram showing the structure of the processing optical system of the first example. is an explanatory diagram showing the pattern of the second processing light at the splitting surface, the pattern of the second processing light at the reflecting surface, and the pattern of the second processing light at the passing surface in the special beam splitter of the processing optical system of the first example. is an explanatory diagram showing the structure of the processing optical system of the second example. is an explanatory diagram showing the pattern of the second processing light at the splitting surface, the pattern of the second processing light at the reflecting surface, and the pattern of the second processing light at the passing surface in the special beam splitter of the processing optical system of the second example. is an explanatory diagram showing the structure of the processing optical system of the third example.1 is an explanatory diagram showing the state of the second processing light at the splitting surface, the state of the second processing light at the reflecting surface, and the state of the second processing light at the passing surface in a special beam splitter of a processing optical system of a third example. FIG. 1 is an explanatory diagram showing the structure of a processing optical system of a fourth example. FIG. 2 is an explanatory diagram showing the state of the second processing light at the splitting surface, the state of the second processing light at the reflecting surface, and the state of the second processing light at the passing surface in a special beam splitter of a processing optical system of a fourth example. FIG. 3 is an explanatory diagram showing the structure of a processing optical system of a fifth example. FIG. 4 is an explanatory diagram showing the state of the second processing light at the splitting surface, the state of the second processing light at the reflecting surface, and the state of the second processing light at the passing surface in a special beam splitter of a processing optical system of a fifth example. FIG. 5 is an explanatory diagram showing the structure of a processing optical system of a modified example. FIG. 6 is an explanatory diagram showing two interference regions and two irradiation regions formed on the surface of a workpiece by the second optical system of a modified processing optical system. FIG. 7 is an explanatory diagram showing the structure of a processing optical system as another modified example. FIG. 8 is an explanatory diagram showing the structure of a processing optical system as yet another modified example.

[0009] Hereinafter, embodiments of a machining optical system, a machining apparatus, and a machining method will be described with reference to the drawings. Hereinafter, embodiments of a machining optical system, a machining apparatus, and a machining method will be described using a machining system SYS capable of machining a workpiece W, which is an example of an object. However, the present invention is not limited to the embodiments described below. In the following description, the positional relationships of various components constituting the machining system SYS will be described using an XYZ Cartesian coordinate system defined by mutually orthogonal X, Y, and Z axes. For convenience of explanation, the X-axis and Y-axis directions are each assumed to be horizontal directions (i.e., predetermined directions within a horizontal plane), and the Z-axis direction is assumed to be vertical (i.e., a direction perpendicular to the horizontal plane, essentially an up-down direction). Furthermore, the rotation directions around the X-axis, Y-axis, and Z-axis (in other words, tilt directions) will be referred to as the θX direction, the θY direction, and the θZ direction, respectively. Here, the Z-axis direction may be the direction of gravity. The XY plane may also be assumed to be horizontal.

[0010] (1) Structure of the Machining System SYS First, the structure of the machining system SYS of this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view that schematically shows the structure of the machining system SYS of this embodiment. Figure 2 is a system configuration diagram that shows the system configuration of the machining system SYS of this embodiment.

[0011] 1 and 2 , the processing system SYS includes a processing device 1, a processing light source 2, and a control device 3. The processing device 1 includes a processing head 11 that is attached as an end effector to an articulated robot 102 attached to a self-propelled drive unit 101, and that irradiates processing light EL from the processing light source 2 via a beam transmission optical system 103 toward the surface of a workpiece W placed on a stage 13. The processing head 11, together with the self-propelled drive unit 101, the articulated robot 102, and the processing light source 2, is controlled by the control device 3.

[0012] Here, the beam transmission optical system 103 transmits the processing light EL from the processing light source 2, which supplies the processing light EL to the processing head 11. Based on a command from the control device 3 (see arrow R in FIG. 1 ), the processing head 11 irradiates the processing light EL from the beam transmission optical system 103 toward the surface of the workpiece W placed on the stage 13. Based on a command from the control device 3, the articulated robot 102 changes the position and orientation of the processing head 11 relative to the surface of the workpiece W, thereby changing the position at which the processing light EL is irradiated on the surface of the workpiece W and the irradiation direction of the processing light EL relative to the surface. Based on a command from the control device 3, the self-propelled drive unit 101 changes the position and orientation of the articulated robot 102, and therefore the processing head 11 attached to the articulated robot 102, relative to the surface of the workpiece W, thereby changing the position at which the processing light EL is irradiated on the surface of the workpiece W and the irradiation direction of the processing light EL relative to the surface. The structure of the processing head 11 will be described in detail below with reference to FIGS. 2 to 6 .

[0013] The processing device 1 is capable of processing a workpiece W, which is an object to be processed (which may also be referred to as a base material), under the control of the control device 3. The workpiece W may be, for example, a metal, an alloy (e.g., duralumin, etc.), a semiconductor (e.g., silicon), a resin, a composite material such as CFRP (Carbon Fiber Reinforced Plastic), paint (for example, a paint layer applied to a base material), glass, or an object made of any other material.

[0014] The surface of the workpiece W may be coated with a film made of a material different from that of the workpiece W. In this case, the surface of the film coated on the surface of the workpiece W may be the surface to be processed by the processing device 1. Even in this case, the processing device 1 may be considered to process the workpiece W (i.e., to process the workpiece W coated with the film).

[0015] The processing device 1 irradiates the workpiece W with processing light EL in order to process the workpiece W. The processing light EL may be any type of light as long as it can process the workpiece W when irradiated thereon. In this embodiment, the processing light EL is described using an example in which the processing light EL is laser light, but the processing light EL may be a type of light other than laser light. Furthermore, the wavelength of the processing light EL may be any wavelength as long as it can process the workpiece W when irradiated thereon. For example, the processing light EL may be visible light or invisible light (e.g., at least one of infrared light, ultraviolet light, and extreme ultraviolet light). The processing light EL includes pulsed light (e.g., pulsed light with a pulse width of picoseconds or less). The pulse width refers to the emission time of the pulsed light. However, the processing light EL does not have to include pulsed light. In other words, the processing light EL may be continuous light.

[0016] The processing light EL is supplied to the processing device 1 from a processing light source 2 that generates the processing light EL via an optical propagation member (e.g., at least one of an optical fiber and a mirror, not shown). The processing device 1 irradiates the processing light EL supplied from the processing light source 2 onto the workpiece W. As described above, if the processing light EL is laser light, the processing light source 2 may include a laser light source (e.g., a semiconductor laser such as a laser diode (LD: Laser Diode)). The laser light source may include at least one of a fiber laser, a CO2 laser, a YAG laser, an excimer laser, etc. However, if the processing light EL is not laser light, the processing light source 2 may include any light source (e.g., at least one of an LED (Light Emitting Diode), a discharge lamp, etc.).

[0017] The processing device 1 may perform removal processing to remove a portion of the workpiece W by irradiating the workpiece W with processing light EL. For example, the processing device 1 may perform removal processing to remove a portion of the workpiece W using the principles of thermal processing. Specifically, when the processing light EL is irradiated onto the surface of the workpiece W, the energy of the processing light EL is transmitted to the irradiated portion of the workpiece W irradiated with the processing light EL and to a nearby portion of the workpiece W adjacent to the irradiated portion. When heat caused by the energy of the processing light EL is transmitted, the heat caused by the energy of the processing light EL melts the material constituting the irradiated portion and the nearby portion of the workpiece W. The molten material scatters as droplets. Alternatively, the molten material evaporates due to the heat caused by the energy of the processing light EL. As a result, the irradiated portion and the nearby portion of the workpiece W are removed. Note that when thermal processing is performed, the processing light EL may include pulsed light or continuous light with a pulse width of at least a millisecond.

[0018] On the other hand, depending on the characteristics of the processing light EL, the processing device 1 may perform removal processing to remove a portion of the workpiece W using the principle of non-thermal processing (e.g., ablation processing). That is, the processing device 1 may perform non-thermal processing (e.g., ablation processing) on ​​the workpiece W. For example, when light with a high photon density (in other words, fluence) is used as the processing light EL, the material constituting the irradiated portion and the adjacent portion of the workpiece W instantaneously evaporates and scatters. That is, the material constituting the irradiated portion and the adjacent portion of the workpiece W evaporates and scatters within a time period sufficiently shorter than the thermal diffusion time of the workpiece W. In this case, the material constituting the irradiated portion and the adjacent portion of the workpiece W may be released from the workpiece W as at least one of ions, atoms, radicals, molecules, clusters, and solid fragments. Note that when non-thermal processing is performed, the processing light EL may include pulsed light having a pulse width of picoseconds or less (or, in some cases, nanoseconds or femtoseconds or less). When pulsed light with a pulse width of picoseconds or less (or, in some cases, nanoseconds or femtoseconds or less) is used as the processing light EL, the material constituting the irradiated portion and the adjacent portion of the workpiece W may sublimate without passing through a molten state. Therefore, it is possible to process the workpiece W while minimizing the effect on the workpiece W of heat caused by the energy of the processing light EL.

[0019] In this embodiment, the processing device 1 may perform removal processing to form a riblet structure RB (see FIG. 3 , etc.) on the surface of the workpiece W. The processing to form the riblet structure RB may be referred to as riblet processing. In other words, the processing device 1 may perform riblet processing on the surface of the workpiece W.

[0020] The riblet structure RB may include an uneven structure that can reduce the resistance of the surface of the workpiece W to the fluid (particularly, at least one of frictional resistance and turbulent frictional resistance). For this reason, the riblet structure RB may be formed on a workpiece W that has a member that is installed (in other words, located) in the fluid. In other words, the riblet structure RB may be formed on a workpiece W that has a member that moves relative to the fluid. Note that the term "fluid" here refers to a medium (e.g., at least one of gas and liquid) that is flowing relative to the surface of the workpiece W. For example, when the surface of the workpiece W moves relative to the medium while the medium itself is stationary, this medium may also be referred to as a fluid. Note that the state in which the medium is stationary may refer to a state in which the medium is not moving relative to a predetermined reference object (e.g., the ground surface).

[0021] When a riblet structure RB including a structure capable of reducing the resistance of the surface of such a workpiece W to a fluid (particularly, at least one of frictional resistance and turbulent frictional resistance) is formed on the workpiece W, the workpiece W becomes more easily movable relative to the fluid. This reduces the resistance that hinders the movement of the workpiece W relative to the fluid, leading to energy savings. In other words, it becomes possible to manufacture environmentally friendly workpieces W, such as turbine blades. This will address Goal 7 of the United Nations-led Sustainable Development Goals (SDGs), "Affordable and clean energy," and contribute to Target 7.3, "Double the global rate of improvement in energy efficiency by 2030."

[0022] The riblet structure RB may be formed on a workpiece W other than a turbine blade. An example of the workpiece W on which the riblet structure RB is formed is at least one of a turbine vane, which may also be called a stationary blade, a fan, an impeller, a propeller, and a pump. A fan is a component (typically a rotating body) used in a blower or the like that forms a gas flow. An impeller is a component used in a pump, for example, and is a rotatable impeller that generates a force for the pump to pump (or suck) a fluid. A propeller is a component (typically a rotating body) that converts the rotational force output from a prime mover including at least one of an engine and a motor into the propulsive force of a moving body including at least one of an airplane, a ship, etc. Another example of the workpiece W on which the riblet structure RB is formed is the housing (e.g., an airframe or a ship) of a moving body including at least one of an airplane, a ship, etc.

[0023] Here, the riblet structure RB will be described with reference to Figures 3A, 3B, and 3C. As shown in Figures 3A, 3B, and 3C, the riblet structure RB may include a structure in which a plurality of convex structures 81 extending in a first direction along the surface of the workpiece W are arranged in a second direction that is along the surface of the workpiece W and intersects the first direction. In other words, the riblet structure RB may include a structure in which a plurality of convex structures 81, each formed to extend in the first direction, are lined up in the second direction. In the example shown in Figures 3A, 3B, and 3C, the riblet structure RB includes a structure in which a plurality of convex structures 81 extending in the X-axis direction are arranged in the Y-axis direction.

[0024] The convex structures 81 are structures that protrude along a direction intersecting both the first direction (the direction in which the convex structures 81 extend) and the second direction (the direction in which the convex structures 81 are arranged). The convex structures 81 are structures that protrude from the surface of the workpiece W. In the examples shown in Figures 3A, 3B, and 3C, the convex structures 81 are structures that protrude along the Z-axis direction. Note that the convex structures 81 may include a protruding structure that protrudes from the surface of the workpiece W. The convex structures 81 may also include a convex structure that protrudes from the surface of the workpiece W. The convex structures 81 may also include a mountain-shaped structure that protrudes from the surface of the workpiece W. Between adjacent convex structures 81, groove structures 82 that are recessed compared to the surrounding area are formed. Therefore, the riblet structure RB may include a structure in which a plurality of groove structures 82 extending along a first direction along the surface of the workpiece W are arranged along a second direction that is along the surface of the workpiece W and intersects the first direction. In other words, the riblet structure RB may include a structure in which a plurality of groove structures 82, each formed to extend along a first direction, are lined up along a second direction. In the examples shown in Figures 3A, 3B, and 3C, the riblet structure RB includes a structure in which a plurality of groove structures 82 extending along the X-axis direction are arranged along the Y-axis direction. The groove structures 82 may also be referred to as groove-shaped structures.

[0025] The convex structure 81 may be considered to be a structure protruding from the groove structure 82. The convex structure 81 may be considered to be a structure that forms at least one of a protrusion-shaped structure, a convex-shaped structure, and a mountain-shaped structure between two adjacent groove structures 82. The groove structure 82 may be considered to be a structure that is recessed from the convex structure 81. The groove structure 82 may be considered to be a structure that forms a groove-shaped structure between two adjacent convex structures 81. The groove structure 82 may be referred to as a groove-shaped structure.

[0026] The height H_rb of at least one of the multiple convex structures 81 may be set to a height determined according to the pitch P_rb of the convex structures 81. For example, the height H_rb of at least one of the multiple convex structures 81 may be less than or equal to the pitch P_rb of the convex structures 81. For example, the height H_rb of at least one of the multiple convex structures 81 may be less than or equal to half the pitch P_rb of the convex structures 81. As an example, the pitch P_rb of the convex structures 81 may be greater than 5 micrometers and less than 200 micrometers. In this case, the height H_rb of at least one of the multiple convex structures 81 may be greater than 2.5 micrometers and less than 100 micrometers.

[0027] In order to machine such a riblet structure RB into the workpiece W, the machining device 1, as shown in Figures 1 and 2, is equipped with, in addition to the machining head 11 described above, a head drive system 12 (in the example of Figure 1, a self-propelled drive unit 101 and an articulated robot 102), a stage 13, and a stage drive system 14. The machining head 11 irradiates the workpiece W with machining light EL from the machining light source 2. In order to irradiate the workpiece W with the machining light EL, the machining head 11 is equipped with a machining optical system 15. The machining head 11 irradiates the workpiece W with the machining light EL via the machining optical system 15.

[0028] In this embodiment, the machining optical system 15 may form interference fringes IS (see FIG. 4, etc.) on the surface of the workpiece W, thereby forming a riblet structure RB on the surface of the workpiece W. Specifically, the machining optical system 15 irradiates the workpiece W with multiple processing light beams EL (two processing light beams EL in the example shown in FIG. 1) generated by splitting the processing light beam EL from the machining light source 2, each from a different incident direction. As a result, interference light is generated by the interference of the multiple processing light beams EL. In this case, the machining optical system 15 may be considered to essentially irradiate the workpiece W with interference light generated by the interference of the multiple processing light beams EL. As a result, interference fringes IS due to the interference light are formed on the surface of the workpiece W. Note that the detailed structure of the machining optical system 15 will be described in detail later with reference to FIG. 5, etc., and therefore will not be described here.

[0029] An example of an interference fringe IS is shown in FIG. 4 . The interference fringe IS may be a fringe having a bright portion IL and a dark portion ID. The bright portion IL may include a portion of the interference fringe IS where the fluence is greater than a predetermined amount (i.e., higher). The bright portion IL may include a portion irradiated with a light portion of the interference light that forms the interference fringe IS where the fluence is greater than a predetermined amount. The dark portion ID may include a portion of the interference fringe IS where the fluence is less than a predetermined amount (i.e., lower). The dark portion ID may include a portion irradiated with a light portion of the interference light that forms the interference fringe IS where the fluence is less than a predetermined amount. Furthermore, the fluence at the bright portion IL may be greater than the fluence at the dark portion ID.

[0030] FIG. 4 further illustrates the relationship between the interference fringes IS and the riblet structure RB. The bright portions IL may be used primarily to form the groove structure 82 described above. In this case, the machining optical system 15 may form the groove structure 82 constituting the riblet structure RB on the surface of the workpiece W by forming the bright portions IL included in the interference fringes IS on the surface of the workpiece W and removing a portion of the workpiece W. The machining optical system 15 may form the groove structure 82 on the surface of the workpiece W by irradiating the surface of the workpiece W with the light portion that forms the bright portions IL of the interference light to remove a portion of the workpiece W. The machining optical system 15 may form the groove structure 82 on the surface of the workpiece W by removing a portion of the workpiece W using the processing light EL that reaches the bright portions IL (i.e., using the light portion of the processing light EL that reaches the bright portions IL). In this case, the interference fringes IS may include multiple fringes in which the bright portions IL extending along the extension direction of the groove structure 82 (the X-axis direction in the example of FIG. 4 ) are arranged along the direction in which the groove structures 82 are arranged (the Y-axis direction (fringe pitch direction) in the example of FIG. 4 ). In other words, the interference fringes IS may include multiple bright areas IL extending along the direction in which the groove structures 82 extend (the X-axis direction in the example of Figure 4), and stripes arranged along the direction in which the groove structures 82 are arranged (the Y-axis direction (stripe pitch direction) in the example of Figure 4).

[0031] The dark areas ID may be used primarily to form the above-described convex structures 81. In this case, the processing optical system 15 may form the convex structures 81 constituting the riblet structure RB on the surface of the workpiece W by forming the dark areas ID included in the interference fringes IS on the surface of the workpiece W and removing a portion of the workpiece W (or, in some cases, not removing a portion of the workpiece W). The processing optical system 15 may form the convex structures 81 on the surface of the workpiece W by irradiating the surface of the workpiece W with the light portion of the interference light that forms the dark areas ID and removing a portion of the workpiece W. The processing optical system 15 may form the convex structures 81 on the surface of the workpiece W by removing a portion of the workpiece W using the processing light EL that reaches the dark areas ID (i.e., using the light portion of the processing light EL that reaches the dark areas ID). In this case, the interference fringes IS may include a plurality of dark areas ID extending along the extension direction of the convex structures 81 (the X-axis direction in the example of FIG. 4 ) and arranged along the direction in which the convex structures 81 are arranged (the Y-axis direction in the example of FIG. 4 ). In other words, the interference fringes IS may include multiple dark areas ID extending along the direction in which the convex structures 81 extend (the X-axis direction in the example of Figure 4), and stripes arranged along the direction in which the convex structures 81 are arranged (the Y-axis direction in the example of Figure 4).

[0032] As shown in FIGS. 1 and 2 , the head drive system 12 (self-propelled drive unit 101, articulated robot 102) moves the machining head 11 along at least one of the X-axis, Y-axis, and Z-axis directions under the control of the control device 3. The head drive system 12 may also move the machining head 11 along at least one of the θX-axis, θY-axis, and θZ-axis directions in addition to or instead of at least one of the X-axis, Y-axis, and Z-axis directions. When the machining head 11 moves, the positional relationship between the stage 13 (and further, the workpiece W placed on the stage 13) and the machining head 11 changes. As a result, the positional relationship between the interference area IA (see FIG. 4 ), where the machining head 11 forms interference fringes IS on the workpiece W, and the stage 13 and the workpiece W changes. In other words, the interference area IA can be moved on the workpiece W. The workpiece W is placed on the stage 13. The stage 13 does not necessarily have to hold the workpiece W placed on the stage 13. In other words, the stage 13 does not need to apply a holding force to the workpiece W placed on the stage 13 in order to hold the workpiece W. Alternatively, the stage 13 may hold the workpiece W placed on the stage 13. In other words, the stage 13 may apply a holding force to the workpiece W placed on the stage 13 in order to hold the workpiece W. For example, the stage 13 may hold the workpiece W by vacuum suction and / or electrostatic suction. Alternatively, a jig for holding the workpiece W may hold the workpiece W, and the stage 13 may hold the jig that holds the workpiece W.

[0033] The stage drive system 14 moves the stage 13 under the control of the control device 3. Specifically, the stage drive system 14 moves the stage 13 relative to the machining head 11. For example, under the control of the control device 3, the stage drive system 14 may move the stage 13 along at least one of the X-axis direction, the Y-axis direction, the Z-axis direction, the θX direction, the θY direction, and the θZ direction. Note that moving the stage 13 along at least one of the θX direction, the θY direction, and the θZ direction may be considered equivalent to changing the orientation of the stage 13 (and further the workpiece W placed on the stage 13) around at least one of the X-axis, the Y-axis, and the Z-axis. Alternatively, moving the stage 13 along at least one of the θX direction, the θY direction, and the θZ direction may be considered equivalent to rotating (or rotationally moving) the stage 13 around at least one of the X-axis, the Y-axis, and the Z-axis.

[0034] When the stage 13 moves, the positional relationship between the stage 13 (and further the workpiece W placed on the stage 13) and the machining head 11 changes. Furthermore, as a result of machining the stage 13 and the workpiece W, the positional relationship between the interference area IA (see FIG. 4 ) where the machining head 11 forms interference fringes IS on the workpiece W changes, and the stage 13 and the workpiece W. In other words, the interference area IA moves on the workpiece W.

[0035] The machining system SYS may change the positional relationship between the workpiece W placed on the stage 13 and the machining head 11 by moving both the stage 13 and the machining head 11 under the control of the control device 3. The machining system SYS may also move the interference fringes IS relative to the workpiece W without moving the machining head 11 or the stage 13.

[0036] The control device 3 controls the operation of the machining system SYS. For example, the control device 3 may generate machining control information for machining the workpiece W, and control the machining device 1 based on the machining control information so that the workpiece W is machined in accordance with the generated machining control information. In other words, the control device 3 may control the machining of the workpiece W.

[0037] The control device 3 may include, for example, an arithmetic device and a storage device. The arithmetic device may include, for example, at least one of a CPU (Central Processing Unit) and a GPU (Graphics Processing Unit). The control device 3 functions as a device that controls the operation of the machining system SYS by the arithmetic device executing a computer program. This computer program is a computer program for causing the control device 3 (e.g., the arithmetic device) to perform (i.e., execute) the operations to be performed by the control device 3, which will be described later. In other words, this computer program is a computer program for causing the control device 3 to function so as to cause the machining system SYS to perform the operations to be performed later. The computer program executed by the arithmetic device may be recorded in a storage device (i.e., a recording medium) included in the control device 3, or may be recorded in any storage medium (e.g., a hard disk or semiconductor memory) built into or externally attachable to the control device 3. Alternatively, the arithmetic device may download the computer program to be executed from a device external to the control device 3 via a network interface.

[0038] The control device 3 does not have to be provided inside the machining system SYS. For example, the control device 3 may be provided outside the machining system SYS as a server or the like. In this case, the control device 3 and the machining system SYS may be connected via a wired and / or wireless network (or a data bus and / or a communication line). The wired network may be a network using a serial bus interface, such as at least one of IEEE1394, RS-232x, RS-422, RS-423, RS-485, and USB. The wired network may be a network using a parallel bus interface. The wired network may be a network using an Ethernet (registered trademark) interface, such as at least one of 10BASE-T, 100BASE-TX, and 1000BASE-T. The wireless network may be a network using radio waves. An example of a radio wave network is a network compliant with IEEE802.1x (e.g., at least one of wireless LAN and Bluetooth (registered trademark)). A network using infrared rays may be used as the wireless network. A network using optical communication may be used as the wireless network. In this case, the control device 3 and the machining system SYS may be configured to be able to send and receive various information via the network. Furthermore, the control device 3 may be able to send information such as commands and control parameters to the machining system SYS via the network. The machining system SYS may include a receiving device that receives information such as commands and control parameters from the control device 3 via the network. Alternatively, a first control device that performs part of the processing performed by the control device 3 may be provided inside the machining system SYS, while a second control device that performs another part of the processing performed by the control device 3 may be provided outside the machining system SYS.

[0039] A computational model that can be constructed by machine learning may be implemented in the control device 3 by the computation device executing a computer program. An example of a computational model that can be constructed by machine learning is a computational model including a neural network (so-called artificial intelligence (AI)). In this case, learning of the computational model may include learning of parameters of the neural network (e.g., at least one of a weight and a bias). The control device 3 may control the operation of the machining system SYS using the computational model. That is, the operation of controlling the operation of the machining system SYS may include the operation of controlling the operation of the machining system SYS using the computational model. Note that a computational model that has been constructed by offline machine learning using teacher data may be implemented in the control device 3. Furthermore, the computational model implemented in the control device 3 may be updated by online machine learning on the control device 3. Alternatively, the control device 3 may control the operation of the machining system SYS using a computational model implemented in a device external to the control device 3 (i.e., a device provided outside the machining system SYS) in addition to or instead of the computational model implemented in the control device 3.

[0040] The recording medium for recording the computer program executed by the arithmetic unit may include at least one of the following: a CD-ROM, CD-R, CD-RW, or flexible disk; an optical disk such as MO, DVD-ROM, DVD-RAM, DVD-R, DVD+R, DVD-RW, DVD+RW, or Blu-ray®; a magnetic medium such as magnetic tape; a magneto-optical disk; a semiconductor memory such as a USB memory; and any other medium capable of storing a program. The recording medium may also include a device capable of recording the computer program (e.g., a general-purpose device or a dedicated device in which the computer program is implemented in an executable state in at least one of software and firmware). Furthermore, each process or function included in the computer program may be realized by a logical processing block realized within the control device 3 (i.e., a computer) when the control device 3 executes the computer program; by hardware such as a predetermined gate array (FPGA, ASIC) included in the control device 3; or by a combination of logical processing blocks and partial hardware modules that realize some of the hardware elements.

[0041] (2) Processing Optical System 15 (2-1) Overview of Processing Optical System 15 Next, we will explain the processing optical system 15 that forms interference fringes IS on the surface of the workpiece W. As shown in FIG. 5 , the processing optical system 15 has a first optical system 16, a second optical system 17, and a third optical system 18. In the processing optical system 15, the first optical system 16 branches the processing light EL generated by the processing light source 2 into two processing light EL, and the third optical system 18 irradiates one of the two processing light EL onto the workpiece W. In addition, the second optical system 17 splits the other branched processing light EL to generate multiple processing light EL (two processing light EL in the example shown in FIG. 1 ), which are irradiated onto the workpiece W from different directions. At this time, the multiple processing light EL generated by the second optical system 17 interfere with each other to generate interference light. Therefore, the processing optical system 15 can be considered to essentially irradiate the workpiece W with interference light generated by the interference of the multiple processing light EL. In this way, the processing optical system 15 forms interference fringes IS caused by interference light in the interference area IA on the surface of the workpiece W by the second optical system 17, and irradiates the processing light EL from the third optical system 18 onto the interference area IA.

[0042] In the following description, the processing light EL will be distinguished by the following names. First, the processing light EL generated by the processing light source 2 will be referred to as processing light EL0, and the processing light EL0 branched by the first optical system 16 and directed toward the third optical system 18 will be referred to as first processing light EL1. Further, the processing light EL0 branched by the first optical system 16 and directed toward the second optical system 17 will be referred to as second processing light EL2, and the second processing light EL2 split by the second optical system 17 and irradiated onto the workpiece W will be referred to as second processing light EL22. Finally, the first processing light EL1 from the first optical system 16 irradiated onto the workpiece W by the third optical system 18 will be referred to as first processing light EL11.

[0043] Therefore, the first optical system 16 can be referred to as a branching optical system, which splits the processing light EL0 from the processing light source 2 to generate the first processing light EL1 and the second processing light EL2 as pulsed light whose light emission periods at least partially overlap. The second optical system 17 can also be referred to as an interference fringe forming optical system, which splits the second processing light EL2 to generate multiple second processing light beams EL22 and irradiates the workpiece W with each of the multiple second processing light beams EL22 from different incident directions. The third optical system 18 can also be referred to as an irradiation optical system, which irradiates the first processing light EL11 from the first processing light EL1 toward the interference area IA where the interference fringes IS are formed.

[0044] As described above, the processing optical system 15 forms interference fringes IS by irradiating the workpiece W with a plurality of second processing beams EL22 from the second optical system 17 from different incident directions. Here, the number of the plurality of processing beams EL22 may be an integer of 2 or more, as long as the number is sufficient to form interference fringes IS.

[0045] In this embodiment, in addition to the interference area IA formed by the multiple second processing beams EL22, the first processing beam EL11 from the third optical system 18 is irradiated. The fluence distribution of the processing beam in the interference area IA where the interference fringes IS are formed on the surface of the workpiece W is different compared to a comparative example in which the first processing beam EL11 is not irradiated. Specifically, FIG. 6A shows the fluence distribution of the processing beam in the comparative example, and FIG. 6B shows the fluence distribution of the processing beam in this embodiment. As shown in FIGS. 6A and 6B , the minimum fluence of the processing beam is higher in this embodiment than in the comparative example. The minimum fluence may be the minimum value of the fluence of the processing beam at the dark portion ID of the interference fringes IS. The minimum fluence may also be the minimum value of the fluence of the processing beam reaching the dark portion ID of the interference fringes IS. The reason why the minimum fluence of this embodiment is higher than that of the comparative example is that the overlapping irradiation of the multiple second processing beams EL22 and the first processing beam EL11 provides the processing beam with a light component that affects the fluence distribution without affecting the formation of the interference fringes IS. That is, the processing optical system 15 applies a light component that does not affect the formation of the interference fringe IS but affects the fluence distribution (so-called the DC component of the fluence distribution of the interference fringe IS) to the interference light by irradiating a plurality of second processing beams EL22 and the first processing beam EL11 in an overlapping manner. The processing optical system 15 applies a light component that does not affect the formation of the interference fringe IS but affects the fluence distribution (so-called the DC component of the fluence distribution of the interference fringe IS) to the interference light by irradiating a plurality of second processing beams EL22 and the first processing beam EL11 in an overlapping manner.

[0046] Conversely, the processing optical system 15 may superimpose the first processing light EL11 on the multiple second processing light EL22 so as to provide the interference light with a light component that affects the fluence distribution while not affecting the formation of the interference fringes IS. The processing optical system 15 may superimpose the first processing light EL11 on the multiple second processing light EL22 so as to provide the interference light with a light component that increases the minimum fluence while not affecting the formation of the interference fringes IS. Furthermore, the first processing light EL11 (its fluence) superimposed on the multiple second processing light EL22 may be set to provide the interference light with a light component that affects the fluence distribution while not affecting the formation of the interference fringes IS. The first processing light EL11 (its fluence) superimposed on the multiple second processing light EL22 may be determined based on at least one of the characteristics of the processing light EL0, the characteristics of the interference light, the characteristics of the workpiece W, and the characteristics of the riblet structure RB. The first processing light EL11 (its fluence) that is irradiated in overlapping relation with multiple second processing lights EL22 may be determined based on the results of experiments or simulations that form interference fringes IS to form a riblet structure RB on the workpiece W.

[0047] As shown in FIG. 6A , in the riblet structure RB formed in the comparative example, the tip of the convex structure 81 may have a flat shape. This is because, as described above, the minimum fluence is relatively small in the comparative example. Therefore, as shown in FIG. 6A , in the comparative example, there is a relatively high possibility that the fluence of at least a portion of the dark portion ID of the interference fringes IS will be smaller than the lower limit value TH_lowest of the fluence capable of processing the workpiece W (i.e., capable of removing a portion of the workpiece W). As a result, there is a relatively high possibility that at least a portion of the portion of the workpiece W where the dark portion ID of the interference fringes IS is formed will not be processed, resulting in a relatively high possibility that the tip of the convex structure 81 will have a flat shape. Considering the characteristics of the riblet structure RB, when the tip of the convex structure 81 has a flat shape, the effect of reducing the resistance of the surface of the workpiece W to the fluid may be weakened compared to when the tip of the convex structure 81 has a pointed shape.

[0048] On the other hand, as shown in FIG. 6B , in the riblet structure RB formed in this embodiment, the tip of the convex structure 81 is less likely to have a flat shape compared to the comparative example. This is because, as described above, the minimum fluence is relatively large in this embodiment. Therefore, as shown in FIG. 6B , in this embodiment, the fluence of at least a portion of the dark portions ID of the interference fringes IS is relatively less likely to be smaller than the lower limit value TH_lowest of the fluence capable of processing the workpiece W. In other words, the fluence of at least a portion of the dark portions ID of the interference fringes IS is relatively more likely to be set to a fluence capable of processing the workpiece W. As a result, the portion of the workpiece W where the dark portions ID of the interference fringes IS are formed is processed, and as a result, the tip of the convex structure 81 is relatively more likely to approach or match an ideal shape (e.g., a pointed shape). In other words, in this embodiment, the accuracy of the shape of the riblet structure RB is improved compared to the comparative example. As a result, in this embodiment, the possibility of forming a riblet structure RB that is relatively effective in reducing the resistance of the surface of the workpiece W to a fluid is relatively high.

[0049] Thus, the processing apparatus 1 of this embodiment can make the shape of the riblet structure RB closer to or identical to the ideal shape, compared to the comparative example. The processing apparatus 1 can form a riblet structure RB having a shape closer to or identical to the ideal shape, compared to the comparative example. In this case, the processing apparatus 1 can be considered to adjust the shape of the riblet structure RB by irradiating the first processing light EL11 and multiple second processing beams EL22 in an overlapping manner, so that the shape of the riblet structure RB formed on the workpiece W becomes a predetermined shape closer to the ideal shape than the shape of the riblet structure RB formed in the comparative example. As a result, the processing apparatus 1 can enjoy the effect of being able to appropriately process the workpiece W to form a riblet structure RB having a shape closer to or identical to the ideal shape.

[0050] In addition, considering that the above-mentioned effects can be appropriately achieved by making the minimum fluence of the processing light equal to or greater than the lower limit TH_lowest of the fluence capable of processing the workpiece W, the processing optical system 15 may set the first processing light EL11 (its fluence) to be irradiated in a manner superimposed on the plurality of second processing lights EL22 so that the minimum fluence of the processing light is set to equal to or greater than the lower limit TH_lowest. The processing optical system 15 may set the first processing light EL11 (its fluence) to be irradiated in a manner superimposed on the plurality of second processing lights EL22 so that the minimum fluence of the processing light is set to a fluence capable of processing the workpiece W. The first processing light EL11 (its fluence) to be irradiated in a manner superimposed on the plurality of second processing lights EL22 may be set so that the minimum fluence of the processing light is a fluence capable of processing the workpiece W. As a result, the above-mentioned effects can be appropriately achieved.

[0051] Depending on the characteristics of the workpiece W, the relationship between the fluence of the light irradiated onto the workpiece W and the processing amount of the workpiece W (for example, the amount of removal per unit time, e.g., the processing amount per pulse) may vary depending on the fluence. For example, depending on the characteristics of the workpiece W, as shown in Fig. 7, a first relationship between the fluence and the processing amount of the workpiece W when the fluence of the processing light irradiated onto the workpiece W (or the fluence of the plurality of second processing light EL22 that generate interference light and the fluence of the first processing light EL11 superimposed thereon) is smaller than a predetermined threshold Fth may differ from a second relationship between the fluence and the processing amount of the workpiece W when the fluence of the processing light (interference light) irradiated onto the workpiece W is larger than the predetermined threshold Fth. In this case, if the fluence of the processing light varies across both a first range less than the predetermined threshold Fth and a second range greater than the predetermined threshold Fth, as shown in the upper part of FIG. 7 , the amount of processing in a first portion of the workpiece W irradiated with a portion of the processing light having a fluence less than the predetermined threshold Fth will differ from the amount of processing in a second portion of the workpiece W irradiated with a portion of the processing light having a fluence greater than the predetermined threshold Fth. In the example shown in FIG. 7 , the ratio of the increase in processing amount to the increase in fluence in the second relationship is greater than the ratio of the increase in processing amount to the increase in fluence in the first relationship. In this case, the amount of processing in the first portion of the workpiece W irradiated with a portion of the processing light having a fluence less than the predetermined threshold Fth will be less than the amount of processing in the second portion of the workpiece W irradiated with a portion of the processing light having a fluence greater than the predetermined threshold Fth. As a result, the amount of processing in the first portion of the workpiece W may be insufficient and / or the amount of processing in the second portion of the workpiece W may be excessive. This may result in a deterioration in the accuracy of the shape of the riblet structure RB formed on the workpiece W. For example, as shown in the lower part of Figure 8, the shape of the tip of the convex structure 81, which is formed mainly by a light portion of the processing light with a relatively low fluence (for example, a light portion irradiated on the dark portion ID), may become flat.

[0052] Therefore, as shown in the upper part of FIG. 9 , the processing optical system 15 may set the first processing light EL11 (its fluence) to be irradiated in a superimposed manner on the plurality of second processing lights EL22 so that the minimum fluence of the interference light is equal to or greater than a predetermined threshold Fth. Alternatively, the processing optical system 15 may set the first processing light EL11 (its fluence) to be irradiated in a superimposed manner on the plurality of second processing lights EL22 so that the minimum fluence of the interference light is equal to or greater than a threshold obtained by adding a predetermined margin to the predetermined threshold Fth. In other words, the processing optical system 15 may set the first processing light EL11 (its fluence) to be irradiated in a superimposed manner on the plurality of second processing lights EL22 so that the minimum fluence of the interference light is equal to or greater than a threshold set based on the predetermined threshold Fth. In this case, as shown in the lower part of FIG. 9 , the tip shape of the convex structure 81, which is mainly formed by a light portion of the processing light with a relatively low fluence (e.g., a light portion irradiated to the dark portion ID), is relatively likely to have an ideal shape. As a result, the above-mentioned effects can be appropriately achieved.

[0053] In other words, the object (workpiece W in the above example) has the characteristic that the first relationship between the fluence and the processing amount when the fluence of each processing light is smaller than a predetermined threshold value is different from the second relationship between the fluence and the processing amount when the fluence of each processing light is larger than the predetermined threshold value, and the ratio of the increase in the processing amount to the increase in the fluence of the processing light in the second relationship is greater than the ratio of the increase in the processing amount to the increase in the fluence of the processing light in the first relationship, and the second optical system 17 sets the first processing light EL11 from the third optical system 18 so that the minimum fluence of the processing light reaching the dark part of the interference fringes is greater than the predetermined threshold value.

[0054] Here, the riblet structure RB is unlikely to have a clean sinusoidal waveform when it comes to the form of the processing light used to obtain an ideal shape (waveform shape (hereinafter also referred to as the ideal waveform Wi)). However, since the riblet structure RB has a periodic shape, the ideal waveform Wi is also periodic. For this reason, the ideal waveform Wi can be expressed as multiple sinusoidal waveforms by Fourier transforming it. An example of this is shown in Figures 10A and 10B. Figure 10A shows an example of the ideal waveform Wi, and Figure 10B shows two waveforms (fundamental frequency waveform Wb and double frequency waveform Wd) obtained by Fourier transforming the ideal waveform Wi. For this reason, the ideal waveform Wi in Figure 10A is a superposition of the fundamental frequency waveform Wb and double frequency waveform Wd in Figure 10B.

[0055] For this reason, the machining optical system 15 forms interference fringes IS (hereinafter also referred to as interference fringes IS1) that indicate the fundamental frequency waveform Wb to machine the workpiece W, and also forms interference fringes IS (hereinafter also referred to as interference fringes IS2) that indicate the double frequency waveform Wd to machine the workpiece W, thereby forming an ideally shaped riblet structure RB. In other words, the machining optical system 15 forms interference fringes IS that substantially indicate the ideal waveform Wi by using the interference fringes IS1 and the interference fringes IS2 to form an ideally shaped riblet structure RB. It can also be said that the machining optical system 15 forms interference fringes IS1 and the interference fringes IS2 instead of forming interference fringes IS that indicate the ideal waveform Wi to form an ideally shaped riblet structure RB.

[0056] The ideal waveform Wi varies depending on the shape desired for the riblet structure RB, and the number and type (frequency multiple, amplitude, etc.) of sinusoidal waveforms obtained by Fourier transform also vary. Therefore, the machining optical system 15 can appropriately set the shape of the fundamental frequency waveform Wb and the number and shape of the n-th frequency waveform Wn to be superimposed on the fundamental frequency waveform Wb in accordance with the ideal waveform Wi set for forming the desired riblet structure RB. Here, the machining optical system 15 can superimpose at least one n-th frequency waveform Wn obtained by Fourier transforming the fundamental frequency waveform Wb obtained by Fourier transforming the ideal waveform Wi. The machining optical system 15 can also superimpose two n-th frequency waveforms Wn obtained by Fourier transforming the fundamental frequency waveform Wb obtained by Fourier transforming the ideal waveform Wi. Furthermore, the machining optical system 15 can superimpose three or more n-th frequency waveforms Wn obtained by Fourier transforming the fundamental frequency waveform Wb obtained by Fourier transforming the ideal waveform Wi.

[0057] For these reasons, the processing optical system 15 splits the processing light EL0 from the processing light source 2 into the first processing light EL1 and the second processing light EL2 using the first optical system 16. The second optical system 17 generates a fundamental frequency waveform Wb and multiple n-th frequency waveforms Wn as the second processing light EL22 from the second processing light EL2, and irradiates the workpiece W with each of these from different incident directions to form interference fringes IS for each frequency. The third optical system 18 then irradiates the first processing light EL1 as the first processing light EL11, overlapping it with the second processing light EL22, onto the interference area IA where each interference fringe IS is formed. This allows the processing optical system 15 to appropriately process the workpiece W using each interference fringe IS, while also forming an ideal riblet structure RB by overlapping the interference fringes IS, similar to the case where the ideal waveform Wi is used.

[0058] Here, the period of the interference fringes IS varies depending on the angle of the interfering second processing light EL22; the smaller the angle, the longer the period; and the larger the angle, the narrower (shorter) the period. Furthermore, the amplitude of the interference fringes IS varies depending on the fluence of the multiple second processing light EL22. Therefore, the second optical system 17 can change at least one of the amplitude and period of the interference fringes IS by changing the incident angle of the multiple second processing light EL22 emitted, thereby forming interference fringes IS of the fundamental frequency waveform Wb and the n-th frequency waveform Wn. Furthermore, the second optical system 17 can adjust at least one of the amplitude and period of the interference fringes IS by changing the incident angle of the multiple second processing light EL22 emitted, thereby optimizing the fundamental frequency waveform Wb and the n-th frequency waveform Wn.

[0059] Next, five examples of processing methods using the processing optical system 15 will be described using FIG. 11. FIG. 11 is a table summarizing the forms (formations) of the first processing light EL11 in the irradiation area RA, the interference fringes IS in the interference area IA, and the overlap area OA (described later) in the processing area PA in the five examples. Here, the processing area PA refers to the area where the riblet structure RB can be processed by the processing optical system 15 (processing head 11), i.e., the area where the first processing light EL11 and the second processing light EL22 can be irradiated. This irradiable area includes both the area where the first processing light EL11 and the second processing light EL22 can be irradiated at once (simultaneously) and the sum of the areas irradiated by the first processing light EL11 and the second processing light EL22 by scanning or sweeping (displacing the irradiation position) the first processing light EL11 and the second processing light EL22 using the galvanometer mirror 21 (see FIG. 12, etc.) described later. In other words, the processing area PA is an area where the workpiece W placed on the stage 13 can be irradiated with the first processing light EL11 and the second processing light EL22 without moving the stage 13 and the processing optical system 15 (processing head 11) relative to each other. In this embodiment, the processing area PA is rectangular with a side extending in the X-axis direction and a side extending in the Y-axis direction. In addition, the area of ​​the processing optical system 15 (processing head 11) where the first processing light EL11 is irradiated by the third optical system 18 is referred to as an irradiation area RA.

[0060] In the following description, when the interference area IA or the irradiation area RA is smaller than the processing area PA, the first processing light EL11 or the second processing light EL22 is used to scan the entire processing area PA (the entire scanning range) using the galvanometer mirror 21 described below. Therefore, the galvanometer mirror 21 functions as an interference fringe moving member that moves the position of the interference area IA relative to the second optical system 17 in a direction that intersects, typically perpendicular to, the optical axis of the second optical system 17. Furthermore, the galvanometer mirror 21 as an interference fringe moving member also has the function of moving the position of the irradiation area RA in a direction that intersects, typically perpendicular to, the optical axis of the second optical system 17. Note that this scanning range may be smaller than the processing area PA (processing only a portion of the processing area PA). Furthermore, the processing area PA may be set smaller than the range that can actually be scanned by the first processing light EL11 or the second processing light EL22. In this case, the scanning range may be larger than the processing area PA (the first processing light EL11 or the second processing light EL22 may be irradiated onto a range wider than the processing area PA).

[0061] 11 shows, from the left, five examples of processing techniques using the processing optical system 15A, the processing optical system 15B, the processing optical system 15C, the processing optical system 15D, and the processing optical system 15E. In addition, in FIG. 11, the upper part shows the state of the irradiation area RA by the first processing light EL11, the middle part shows the state of the interference area IA (interference fringes IS) by the second processing light EL22, and the lower part shows the state of the irradiation area RA and the interference area IA (overlap area OA described later) in the processing area PA.

[0062] In the processing method using the processing optical system 15A, as shown in the upper part, the irradiation area RA (hereinafter referred to as irradiation area RA1) of the first processing light EL11 by the third optical system 18 is made smaller than the processing area PA (see the lower part). More specifically, in the processing method using the processing optical system 15A, the irradiation area RA1 is made equal in size to the processing area PA in the Y-axis direction, but is made rectangular in size smaller than the processing area PA in the X-axis direction.

[0063] In the processing technique using the processing optical system 15A, as shown in the middle, an interference area IA where interference fringes IS are formed by a plurality of second processing beams EL22 from the second optical system 17 is a rectangle having a size substantially equal to that of the irradiation area RA1. In the processing technique using the processing optical system 15A, an interference fringe IS1 (hereinafter referred to as interference area IA1) showing the fundamental frequency waveform Wb and an interference fringe IS2 (hereinafter referred to as interference area IA2) showing the double frequency waveform Wd are formed at different timings (times) in the interference area IA.

[0064] In the processing method using the processing optical system 15A, as shown in the lower part, the interference region IA1, which forms the interference fringes IS1 representing the fundamental frequency waveform Wb, and the irradiation region RA1 formed by irradiation with the first processing light EL11 are overlapped. Hereinafter, the overlapping region of the interference region IA1 and the irradiation region RA1 is also referred to as the overlapping region OA1. In the processing method using the processing optical system 15A, this overlapping region OA1 is scanned over the entire processing region PA. That is, in the processing method using the processing optical system 15A, the interference region IA1 and the irradiation region RA1 are overlapped at one end of the processing region PA in the X-axis direction to form the overlapping region OA1, and the overlapping region OA1 is then moved toward the other end in the X-axis direction to scan the entire processing region PA. Then, in the processing method using the processing optical system 15A, the interference region IA2, which forms the interference fringes IS2 representing the double frequency waveform Wd, and the irradiation region RA1 formed by irradiation with the first processing light EL11 are overlapped to form the overlapping region OA2. In the processing method using the processing optical system 15A, the entire processing area PA is scanned with the overlap area OA2 containing the double frequency waveform Wd, as with the overlap area OA1 containing the fundamental frequency waveform Wb.

[0065] As a result, in the machining method using the machining optical system 15A, the entire machining area PA on the surface of the workpiece W can be illuminated with the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd. In this case, in the machining method using the machining optical system 15A, the first machining light EL11 is irradiated while overlapping the interference fringes IS1 and IS2, so the workpiece W can be properly machined even in areas where the dark areas ID of the interference fringes IS1 and IS2 are formed. Therefore, in the machining method using the machining optical system 15A, an ideally shaped riblet structure RB can be formed on the surface of the workpiece W in the machining area PA.

[0066] In the processing method using the processing optical system 15B, as shown in the upper part, the irradiation area RA (hereinafter referred to as irradiation area RA2) of the first processing light EL11 by the third optical system 18 is made smaller than the processing area PA. More specifically, in the processing method using the processing optical system 15B, the irradiation area RA2 is made equal in size to the processing area PA in the Y-axis direction, but is made rectangular in size smaller than the processing area PA in the X-axis direction.

[0067] In addition, in the processing method using the processing optical system 15B, as shown in the middle section, the interference region IA (hereinafter referred to as the interference region IA3) in which the interference fringes IS are formed by the multiple second processing beams EL22 from the second optical system 17 is a rectangular region approximately equal in size to the irradiation region RA2. In the processing method using the processing optical system 15B, the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd are formed parallel to each other in the X-axis direction in the interference region IA3. That is, in the processing method using the processing optical system 15B, the interference fringes IS2 of the double frequency waveform Wd are formed at one end of the interference region IA3 in the X-axis direction, and the interference fringes IS1 of the fundamental frequency waveform Wb are formed next to each other at the other end of the interference region IA3 in the X-axis direction. In this example, in the interference region IA3, the region where the interference fringes IS1 of the fundamental frequency waveform Wb are formed is the first region, and the region where the interference fringes IS2 of the double frequency waveform Wd are formed is the second region. The order of the first and second regions may be set as appropriate and is not limited to this example.

[0068] In the processing method using the processing optical system 15B, as shown in the lower part, an interference area IA3 formed by arranging interference fringes IS1 and IS2 of two types of frequency waveforms Wb and Wd is overlapped with an irradiation area RA2 formed by irradiation with the first processing light EL11. Hereinafter, the area where the interference area IA3 and the irradiation area RA2 overlap is also referred to as an overlap area OA3. In the processing method using the processing optical system 15B, the overlap area OA3 is scanned over the entire processing area PA. That is, in the processing method using the processing optical system 15B, the interference area IA3 and the irradiation area RA2 are overlapped at one end of the processing area PA in the X-axis direction to form an overlap area OA3, and the overlap area OA3 is moved toward the other end in the X-axis direction to scan the entire processing area PA.

[0069] As a result, in the machining method using the machining optical system 15B, the entire machining area PA on the surface of the workpiece W can be irradiated with the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd. In this case, in the machining method using the machining optical system 15B, the aligned interference fringes IS1 and IS2 are irradiated in an overlapping manner with the first machining light EL11, so the workpiece W can be properly machined even in areas where the dark areas ID of the interference fringes IS1 and IS2 are formed. Therefore, in the machining method using the machining optical system 15B, an ideally shaped riblet structure RB can be formed on the surface of the workpiece W in the machining area PA.

[0070] In the irradiation area RA2 in this example, the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd are formed side by side, i.e., the two interference fringes IS are formed in a positional relationship in which they are in contact in the Y-axis direction. However, the interference fringes IS1 and IS2 may be formed in a positional relationship in which they are separated from each other in the Y-axis direction, or in a positional relationship in which they at least partially overlap each other, and are not limited to the example described above.

[0071] In the processing method using the processing optical system 15C, as shown in the upper part, the irradiation area RA (hereinafter referred to as irradiation area RA3) of the first processing light EL11 by the third optical system 18 is set to be equal in size to the processing area PA. Also, in the processing method using the processing optical system 15C, as shown in the middle part, the interference area IA in which the interference fringes IS are formed by the multiple second processing lights EL22 from the second optical system 17 is set to be smaller than the processing area PA. Specifically, in the processing method using the processing optical system 15C, similar to the processing method using the processing optical system 15A, the interference area IA is set to be equal in size to the processing area PA in the Y-axis direction but smaller in size than the processing area PA in the X-axis direction. Furthermore, in the processing method using the processing optical system 15C, similar to the processing method using the processing optical system 15A, the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd are formed at different times in the interference area IA. That is, in the processing method using the processing optical system 15C, similar to the processing method using the processing optical system 15A, an interference region IA1 is formed in which an interference fringe IS1 representing the fundamental frequency waveform Wb is formed, and an interference region IA2 is formed in which an interference fringe IS2 representing the double frequency waveform Wd is formed.

[0072] In the processing method using the processing optical system 15C, as shown in the lower part, the first processing light EL11 is irradiated onto the processing area PA, where the interference area IA1 due to the interference fringes IS1 of the fundamental frequency waveform Wb and the interference area IA2 due to the interference fringes IS2 of the double frequency waveform Wd are formed, to form an irradiation area RA3. Here, the irradiation area RA3 is equal in size to the processing area PA, and the interference areas IA1 and IA2 are smaller than the processing area PA. Therefore, in the irradiation area RA3 (processing area PA), the area where the interference areas IA1 and IA2 are formed becomes an overlap area OA where the first processing light EL11 and multiple second processing light EL22 (interference fringes IS1, IS2) are overlapped. In the processing method using the processing optical system 15C, the entire processing area PA is scanned with the interference areas IA1 and IA2 while forming the irradiation area RA3. That is, in the processing technique using the processing optical system 15C, an irradiation area RA3 is formed in the processing area PA, an interference area IA1 is formed at one end of the processing area PA in the X-axis direction, and the interference area IA1 is moved toward the other end in the X-axis direction to scan the entire processing area PA and form an overlapping area OA4 throughout the processing area PA. Thereafter, in the processing technique using the processing optical system 15C, an irradiation area RA3 is formed in the processing area PA, an interference area IA2 is formed at one end of the processing area PA in the X-axis direction, and the interference area IA2 is moved toward the other end in the X-axis direction to scan the entire processing area PA and form an overlapping area OA5 throughout the processing area PA.

[0073] As a result, in the machining method using the machining optical system 15C, the entire machining area PA on the surface of the workpiece W can be irradiated with the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd. In this case, in the machining method using the machining optical system 15C, the entire machining area PA is irradiated with the first machining light EL11, so the interference fringes IS1 and IS2 and the first machining light EL11 are reliably superimposed and irradiated, allowing the workpiece W to be properly machined even in areas where the dark areas ID of the interference fringes IS1 and IS2 are formed. Therefore, in the machining method using the machining optical system 15C, an ideally shaped riblet structure RB can be formed on the surface of the workpiece W in the machining area PA.

[0074] In the processing method using the processing optical system 15D, as shown in the upper part, the irradiation area RA3 of the first processing light EL11 by the third optical system 18 is set to be equal in size to the processing area PA, as in the processing method using the processing optical system 15C. Also, in the processing method using the processing optical system 15D, as shown in the middle part, the interference area IA3 in which the interference fringes IS are formed by the multiple second processing light EL22 from the second optical system 17 is set to be smaller than the processing area PA, as in the processing method using the processing optical system 15B. Specifically, in the processing method using the processing optical system 15C, the interference area IA3 is set to be equal in size to the processing area PA in the Y-axis direction, but is rectangular in size smaller than the processing area PA in the X-axis direction. Furthermore, in the processing method using the processing optical system 15D, as in the processing method using the processing optical system 15B, the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd are formed in parallel in the X-axis direction in the interference area IA3. That is, in the processing method using the processing optical system 15D, an interference fringe IS2 of the double frequency waveform Wd is formed at one end in the X-axis direction in the interference area IA3, and an interference fringe IS1 of the fundamental frequency waveform Wb is formed next to it at the other end in the X-axis direction.

[0075] In the processing method using the processing optical system 15D, as shown in the lower part, the first processing light EL11 is irradiated onto the processing area PA, where the interference area IA3, in which the interference fringes IS1 and IS2 of the two frequency waveforms Wb and Wd are arranged, to form an irradiation area RA3. Here, the irradiation area RA3 is equal in size to the processing area PA, and the interference area IA3 is smaller than the processing area PA. Therefore, in the irradiation area RA3 (processing area PA), the area where the interference area IA3 is formed becomes an overlap area OA6 where the first processing light EL11 and multiple second processing light EL22 (interference fringes IS1 and IS2) are overlapped. In the processing method using the processing optical system 15D, the entire processing area PA is scanned with the interference area IA3 while forming the irradiation area RA3. That is, in the processing method using the processing optical system 15D, an irradiation area RA3 is formed in the processing area PA, while an interference area IA3 is formed at one end of the processing area PA in the X-axis direction, and the interference area IA3 is moved toward the other end in the X-axis direction to scan the entire processing area PA and form an overlap area OA6 over the entire processing area PA.

[0076] As a result, in the machining method using the machining optical system 15D, the entire machining area PA on the surface of the workpiece W can be irradiated with the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd. In this case, in the machining method using the machining optical system 15D, the entire machining area PA is irradiated with the first machining light EL11, so the interference fringes IS1 and IS2 and the first machining light EL11 are irradiated in an overlapping manner, and the workpiece W can be properly machined even in areas where the dark areas ID of each interference fringe IS are formed. Therefore, in the machining method using the machining optical system 15D, a riblet structure RB with an ideal shape can be formed on the surface of the workpiece W in the machining area PA.

[0077] In the processing method using the processing optical system 15E, as shown in the upper part, the irradiation area RA3 of the first processing light EL11 by the third optical system 18 is set to be equal in size to the processing area PA, as in the processing methods using the processing optical system 15C and the processing optical system 15D. Also, in the processing method using the processing optical system 15E, as shown in the middle part, the interference area IA in which the interference fringes IS are formed by the multiple second processing lights EL22 from the second optical system 17 is set to be approximately equal in size to the irradiation area RA3, i.e., the processing area PA. Therefore, in the processing method using the processing optical system 15E, the second optical system 17 can form the interference fringes IS throughout the processing area PA without moving the interference area IA. In other words, in the processing method using the processing optical system 15E, the positional relationship between the irradiation area RA3 by the third optical system 18 and the interference area IA formed by the second optical system 17 does not change (they are a constant positional relationship).

[0078] Then, in the processing method using the processing optical system 15E, as shown in the lower part, an interference fringe IS1 (hereinafter referred to as interference region IA4) representing the fundamental frequency waveform Wb and an interference fringe IS2 (hereinafter referred to as interference region IA5) representing the double frequency waveform Wd are formed in the interference region IA at different times (times). At this time, in the processing method using the processing optical system 15E, the interference region IA4 in which the interference fringe IS1 representing the fundamental frequency waveform Wb is formed is overlapped with the irradiation region RA3 formed by irradiation with the first processing light EL11. Hereinafter, the overlapping region of the interference region IA4 and the irradiation region RA3 is also referred to as the overlapping region OA7. Then, in the processing method using the processing optical system 15E, the interference region IA5 in which the interference fringe IS2 representing the double frequency waveform Wd is formed is overlapped with the irradiation region RA3 formed by irradiation with the first processing light EL11. Hereinafter, the overlapping region of the irradiation region RA3 on the interference region IA5 is also referred to as the overlapping region OA8. Here, the irradiation area RA3, the interference area IA4, and the interference area IA5 are all equal in size to the processing area PA. Therefore, the overlapping areas OA6 and OA7 are formed by overlapping the first processing light EL11 and the multiple second processing light EL22 (interference fringes IS1, IS2) over the entire processing area PA.

[0079] As a result, in the machining method using the machining optical system 15E, the entire machining area PA on the surface of the workpiece W can be irradiated with the interference fringes IS1 representing the fundamental frequency waveform Wb and the interference fringes IS2 representing the double frequency waveform Wd. In this case, in the machining method using the machining optical system 15E, the entire machining area PA is irradiated with the first machining light EL11, so the interference fringes IS1 or IS2 and the first machining light EL11 are irradiated in an overlapping manner, and the workpiece W can be properly machined even in areas where the dark areas ID of the interference fringes IS1 and IS2 are formed. Therefore, in the machining method using the machining optical system 15E, a riblet structure RB with an ideal shape can be formed on the surface of the workpiece W in the machining area PA.

[0080] Next, specific configuration examples of the above-mentioned five processing optical systems 15A, 15B, 15C, 15D, and 15E will be described in order with reference to Figures 12 to 21. Note that in Figures 12, 14, 16, 18, and 20, the processing light source 2 is omitted and only the processing light EL0 from the processing light source 2 is shown.

[0081] (2-2) Processing Optical System 15A FIG. 12 shows the structure of the processing optical system 15A, with the processing light source 2 omitted from the illustration. As shown in FIG. 12, the processing optical system 15A includes a galvanometer mirror 21 and a collimator lens 22 to direct the processing light EL0 from the processing light source 2 toward the first optical system 16. As described above, the galvanometer mirror 21 is an interference fringe moving member that moves the position of the interference area IA relative to the second optical system 17 in a direction that intersects, typically perpendicular to, the optical axis of the second optical system 17, and reflects the processing light EL0 from the processing light source 2 toward the beam splitter 23. The tilt of the galvanometer mirror 21 can be changed in the rotational direction around a rotation axis extending in the Z-axis direction. By changing the tilt of the galvanometer mirror 21, the direction of reflection of the processing light EL0 toward the beam splitter 23 can be changed. The range in which the reflection direction of the processing light EL0 can be changed by the galvanometer mirror 21 is set within the range in which the split second processing light EL2 can be incident on the splitting surface 25a of the special beam splitter 25 (described later). That is, the galvanometer mirror 21 can change the direction in which the processing light EL0 travels within the range in which the second processing light EL2 can be incident on the splitting surface 25a. The galvanometer mirror 21 may be driven under the control of the control device 3 or another control device.

[0082] The collimator lens 22 collimates the processing light EL0 from the processing light source 2 reflected by the galvanometer mirror 21 into collimated light (parallel light). That is, the processing light EL0 from the processing light source 2 in this example is made into diffused (divergent) light, and the collimator lens 22 collimates the processing light EL0 into collimated light (parallel light).

[0083] The processing optical system 15A includes a beam splitter 23 as the first optical system 16, which splits the processing light EL0 from the processing light source 2 into the first processing light EL1 and the second processing light EL2. The processing light EL0, collimated by the collimating lens 22, is incident on the beam splitter 23. The beam splitter 23 splits the processing light EL0 into the first processing light EL1 and the second processing light EL2. Specifically, the beam splitter 23 reflects a portion of the processing light EL0 to generate the first processing light EL1 that travels to the third optical system 18, and transmits another portion of the processing light EL0 to generate the second processing light EL2 that travels to the second optical system 17. The beam splitter 23 may transmit a portion of the processing light EL0 to generate the first processing light EL1 and reflect another portion of the processing light EL0 to generate the second processing light EL2. The beam splitter 23 may be an amplitude division type beam splitter or a polarizing beam splitter. The beam splitter 23 causes the second processing light EL2 generated by passing through the beam splitter 23 to travel parallel to the Y-axis direction to the second optical system 17. For this reason, the galvanometer mirror 21 as an interference fringe moving member is disposed in the optical path between the processing light source 2 and the beam splitter 23 as the first optical system 16, which is disposed at a position where the processing light EL0 is split into the first processing light EL1 and the second processing light EL2. As described above, the galvanometer mirror 21 moves the position of the interference area IA relative to the second optical system 17 in a direction intersecting (orthogonal to) the optical axis of the second optical system 17.

[0084] 12 , the processing optical system 15A splits the processing light EL0 from the processing light source 2 into two beams using a diffractive optical element (DOE) or a beam splitter (not shown) before entering the first optical system 16 (its galvanometer mirror 21). The processing optical system 15A also uses optical elements such as lenses to focus the two split processing light EL0 onto a single point or a narrow area at different positions on the galvanometer mirror 21 (its reflecting surface). The first optical system 16 then reflects the two split processing light EL0 off the galvanometer mirror 21 and passes them through a collimator lens 22. One of the split processing light EL0 is then reflected by a beam splitter 23 to become a first processing light EL1, and the other split processing light EL0 passes through the beam splitter 23 to become a second processing light EL2. As a result, the processing optical system 15A can prevent the energy of the processing light EL0 from the processing light source 2 from concentrating in a narrow spot on the beam splitter 23, thereby suppressing damage to the beam splitter 23 by the processing light EL0. Furthermore, since the processing optical system 15A concentrates the two processing lights EL0 at one point on (the reflecting surface of) the galvanometer mirror 21 or in a narrow area close to that point, it is possible to easily and appropriately adjust the change in the traveling direction of the processing light EL0 caused by changing the tilt of the galvanometer mirror 21.

[0085] The processing optical system 15A also includes a second optical system 17, which splits the second processing light EL2 from the first optical system 16 to generate multiple second processing light beams EL22. The second optical system 17 includes a first cylindrical lens 24, a special beam splitter 25, a second cylindrical lens 26, a first mirror 27, an optical deflection member 28, a second mirror 29, a third mirror 31, a third cylindrical lens 32, and a lens 33. The second optical system 17 of the processing optical system 15A does not necessarily include the first cylindrical lens 24, the second cylindrical lens 26, the second mirror 29, and the lens 33. The first cylindrical lens 24 is an optical element that extends in the X-axis direction and has refractive power only in the Z-axis direction, and is a convex lens in a cross section perpendicular to the X-axis direction. The first cylindrical lens 24 focuses the second processing light EL2 from the first optical system 16 in the Z-axis direction without changing its optical power in the X-axis direction. The first cylindrical lens 24 has a rear focal point in the traveling direction of the second processing light EL2 set near a splitting surface 25a (described later) of the special beam splitter 25. Therefore, the first cylindrical lens 24 converts the second processing light EL2 into linear light extending in the X-axis direction on the splitting surface 25a (see FIG. 13).

[0086] The special beam splitter 25 splits the second processing light EL2, which has been converted by the first cylindrical lens 24 into a linear beam extending in the X-axis direction, into multiple second processing light beams EL22. Therefore, the special beam splitter 25 functions as a light splitting component that splits the second processing light EL2 into multiple second processing light beams EL22. For ease of explanation, the following description will discuss an example in which the special beam splitter 25 splits the second processing light EL2 into two second processing light beams EL22 (when individually shown, one is referred to as the second processing light EL221 and the other as the second processing light EL222). The special beam splitter 25 also merges the two split second processing light beams EL22 and directs both second processing light beams EL22 toward the lens 33, i.e., the workpiece W beyond. The focusing position of the second processing light EL2 formed by the first cylindrical lens 24 may be slightly shifted from the special beam splitter 25 in the optical axis direction.

[0087] The special beam splitter 25 is a rectangular plate-like member, and is disposed at a 45-degree angle with respect to the Y-axis around a central axis extending in the X-axis direction. The special beam splitter 25 has a splitting surface 25a, a reflecting surface 25b, and a light-transmitting surface 25c, each of which extends in the X-axis direction (see FIG. 13). In the special beam splitter 25, the splitting surface 25a is located near the central axis in the 45-degree tilt direction. The reflecting surface 25b is located above the tilt direction, on the right side as viewed in FIGS. 12 and 13 (the third cylindrical lens 32 side). The light-transmitting surface 25c is located below the tilt direction, on the left side as viewed in FIGS. 12 and 13 (the first cylindrical lens 24 side). The tilt angle of the special beam splitter 25 is not limited to 45 degrees.

[0088] The splitting surface 25a splits the second processing light EL2, which has been converted by the first cylindrical lens 24 into a linear beam extending in the X-axis direction, into multiple second processing light EL22. This splitting surface 25a is composed of an amplitude-splitting beam splitter or a polarizing beam splitter, and generates the second processing light EL221 by reflecting a portion of the second processing light EL2 and generates the second processing light EL222 by passing another portion of the second processing light EL2. Here, the special beam splitter 25 is disposed at a 45-degree angle with respect to the Y-axis direction, so that the second processing light EL221 generated by reflection from the splitting surface 25a travels parallel to the Z-axis direction toward the second cylindrical lens 26, and the second processing light EL222 generated by passing through the other splitting surface 25a travels parallel to the Y-axis direction toward the third cylindrical lens 32.

[0089] As described below, the reflecting surface 25b reflects the second processing light EL221 reflected by the third mirror 31 and focused by the third cylindrical lens 32 so that the second processing light EL221 travels downward in the Z-axis direction (toward the lens 33). Therefore, the reflecting surface 25b is configured so that the back surface of the special beam splitter 25 facing the third cylindrical lens 32 has optical properties that reflect light. This reflecting surface 25b can be formed by, for example, partially evaporating a coating onto the upper end of the back surface of the special beam splitter 25. The configuration and position of the reflecting surface 25b may be appropriately set as long as it reflects the second processing light EL221 from the third cylindrical lens 32 toward the lens 33, and are not limited to this example.

[0090] As described below, the passing surface 25c transmits the second processing light EL222 reflected by the first mirror 27 and focused by the second cylindrical lens 26 so that it travels downward in the Z-axis direction (toward the lens 33). Here, it is desirable that the passing surface 25c has no optical effect on the second processing light EL222 from the second cylindrical lens 26. For this reason, the passing surface 25c in this example is empty, that is, a portion of the special beam splitter 25 corresponding to the passing surface 25c is cut out. The configuration and position of the passing surface 25c may be appropriately set as long as it allows the second processing light EL222 from the second cylindrical lens 26 to pass through toward the lens 33, and are not limited to this example.

[0091] The second cylindrical lens 26 is an optical element extending in the X-axis direction and having refractive power only in the Y-axis direction, and is a convex lens in a cross section perpendicular to the X-axis direction. The front focal point of the second cylindrical lens 26 in the direction of propagation of the second processing light EL221 is set near the splitting surface 25a of the special beam splitter 25, and the second processing light EL221 is collimated (parallel light) with a predetermined magnitude in the X-axis direction and the Y-axis direction. The second cylindrical lens 26 propagates the collimated second processing light EL221 toward the first mirror 27 parallel to the Z-axis direction. The second cylindrical lens 26 also focuses the second processing light EL222 reflected by the first mirror 27 in the Y-axis direction without changing the second processing light EL222 in the X-axis direction, resulting in a linear light beam extending in the X-axis direction on the transmission surface 25c, as described below (see FIG. 13 ).

[0092] The first mirror 27 is a plate-like member and is disposed at an angle of 45 degrees with respect to the Z-axis direction, centered on a central axis extending in the X-axis direction. The first mirror 27 reflects the second processing light EL221 from the second cylindrical lens 26 and causes it to travel parallel to the Y-axis direction toward the optical deflection member 28. The first mirror 27 also reflects the second processing light EL222 from the second mirror 29 that has passed through the optical deflection member 28 and causes it to travel toward the second cylindrical lens 26.

[0093] The optical deflector 28 is a component that changes (deflects) the traveling direction of light (second processing light EL221, second processing light EL222) traveling between the first mirror 27 and the second mirror 29. The optical deflector 28 is an optical component that has a shape extending in the X-axis direction and has refractive power only in the Z-axis direction, and refracts the traveling direction of light to either the upper or lower side in the Z-axis direction between the first mirror 27 and the second mirror 29. In this example, the optical deflector 28 has a trapezoidal (wedge-shaped) shape in a cross section perpendicular to the X-axis direction, in which the thickness (size in the Y-axis direction) is smallest at the upper side in the Z-axis direction and increases toward the lower side in the Z-axis direction. Therefore, compared to a state in which the optical deflector 28 is not provided, the optical deflector 28 refracts light from one of the first mirror 27 and the second mirror 29 toward the other of the first mirror 27 and the second mirror 29 while refracting the light downward in the Z-axis direction. This optical deflection member 28 can be placed in the optical path between the first mirror 27 and the second mirror 29 or removed from the optical path, and in Example 1 is driven under the control of the control device 3.

[0094] The second mirror 29 is a plate-shaped member, and is tilted about its central axis extending in the X-axis direction at a 45-degree angle relative to the Z-axis direction as a reference position. The second mirror 29 is positioned conjugately with the special beam splitter 25 (its splitting surface 25a). In this example, the second mirror 29 is tilted counterclockwise (opposite to clockwise) around the central axis relative to the reference position in FIG. 12 . The tilt direction from this reference position may also be clockwise, and is not limited to this example. The second mirror 29 reflects the second processing light EL221 that has passed through the optical deflection member 28 to advance toward the third mirror 31, and also reflects the second processing light EL222 reflected by the third mirror 31 to advance toward the optical deflection member 28.

[0095] The third mirror 31 is a plate-like member and is disposed at an angle of 45 degrees with respect to the Z-axis direction around a central axis extending in the X-axis direction. The third mirror 31 reflects the second processing light EL221 reflected by the second mirror 29 to advance to the third cylindrical lens 32, and also reflects the second processing light EL222 that has passed through the third cylindrical lens 32 to advance to the second mirror 29 in parallel with the Z-axis direction.

[0096] The third cylindrical lens 32 is an optical element extending in the X-axis direction and having refractive power only in the Z-axis direction, and is a convex lens in a cross section perpendicular to the X-axis direction. The front focal point of the third cylindrical lens 32 in the direction of propagation of the second processing light EL222 is set near the splitting surface 25a of the special beam splitter 25, and the second processing light EL222 is collimated (parallel light) with a predetermined magnitude in the X-axis direction and the Y-axis direction. The third cylindrical lens 32 propagates the collimated second processing light EL222 toward the third mirror 31 parallel to the Y-axis direction. The third cylindrical lens 32 also focuses the second processing light EL221 reflected by the third mirror 31 in the Y-axis direction without changing the second processing light EL221 in the X-axis direction, forming a linear light extending in the X-axis direction on the reflecting surface 25b, as described below (see FIG. 13 ).

[0097] Here, the focal positions of the second cylindrical lens 26 and the third cylindrical lens 32 may be the same. The second cylindrical lens 26, the third cylindrical lens 32, and the optical deflection member 28 make the splitting surface 25a and the reflecting surface 25b optically conjugate in the YZ plane with respect to the second processing beam EL221. The second cylindrical lens 26, the third cylindrical lens 32, and the optical deflection member 28 also make the splitting surface 25a and the passing surface 25c optically conjugate in the YZ plane with respect to the second processing beam EL222. The optical deflection member 28 displaces the incident position of the second processing beam EL221 incident on the special beam splitter 25 from the splitting surface 25a to the reflecting surface 25b, and displaces the incident position of the second processing beam EL222 incident on the special beam splitter 25 from the splitting surface 25a to the passing surface 25c. That is, the optical deflection member 28 has the function of spatially separating the optical paths of the light from the special beam splitter 25 and the light incident on the special beam splitter 25 .

[0098] The lens 33 focuses the second processing light EL221 reflected by the reflecting surface 25b and the second processing light EL222 transmitted through the transmitting surface 25c, as described below, on the surface of the workpiece W so as to form interference fringes IS on the surface of the workpiece W. That is, the lens 33 causes the central axis of the optical path along which the second processing light EL221 reflected by the reflecting surface 25b travels to coincide with the central axis of the optical path along which the second processing light EL222 transmitted through the transmitting surface 25c travels, on the surface of the workpiece W. In other words, the lens 33 focuses the second processing light EL221 and EL222 incident from positions away from the optical axis, and causes them to obliquely enter the surface of the workpiece W so as to intersect with each other on the surface of the workpiece W. As a result, interference fringes IS are formed in linear regions extending in the Y-axis direction on the surface of the workpiece W, forming an interference area IA.

[0099] Furthermore, the processing optical system 15A includes a third optical system 18 that directs the first processing light EL1 from the first optical system 16 toward the interference area IA. The third optical system 18 includes a fourth mirror 34, a fourth cylindrical lens 35, and a fifth mirror 36. The fourth mirror 34 is a plate-shaped member that is tilted 45 degrees relative to the Z-axis direction around a central axis extending in the X-axis direction. The fourth mirror 34 reflects the first processing light EL1 from the first optical system 16 and directs it toward the fourth cylindrical lens 35 parallel to the Y-axis direction.

[0100] The fourth cylindrical lens 35 focuses the first processing light EL1 in the X-axis direction without changing the light in the Z-axis direction. The fourth cylindrical lens 35 is set at a position where the rear focal point in the traveling direction of the first processing light EL1 forms an interference area IA on the surface of the workpiece W after passing through the fifth mirror 36. Therefore, the fourth cylindrical lens 35 converts the first processing light EL1 into linear light extending in the Z-axis direction and causes it to travel parallel to the Y-axis direction toward the fifth mirror 36.

[0101] The fifth mirror 36 is a plate-shaped member and is disposed at a 45-degree angle with respect to the Z-axis direction, centered on a central axis extending in the X-axis direction. The fifth mirror 36 reflects the first processing light EL1 from the fourth cylindrical lens 35 and causes it to proceed toward the surface of the workpiece W. Therefore, the third optical system 18 causes the first processing light EL1 to pass through the fourth mirror 34 and the fourth cylindrical lens 35, and then reflect off the fifth mirror 36, thereby directing it toward the surface of the workpiece W as the first processing light EL11. This first processing light EL11 is converted into linear light extending in the Z-axis direction by the fourth cylindrical lens 35, and is converted into linear light extending in the Y-axis direction by being reflected toward the surface of the workpiece W by the fifth mirror 36.

[0102] Next, the operation of this processing optical system 15A will be described. First, processing light EL0 emitted from processing light source 2 is reflected by galvanometer mirror 21, passes through collimating lens 22, and is split into first processing light EL1 and second processing light EL2 by beam splitter 23, which serves as first optical system 16. Here, first processing light EL1 and second processing light EL2 are converted into collimated light by passing through collimating lens 22. The first processing light EL1 proceeds to third optical system 18, and the second processing light EL2 proceeds to second optical system 17.

[0103] In the second optical system 17, the second processing light EL2 passes through the first cylindrical lens 24 and travels toward the splitting surface 25a of the special beam splitter 25 as linear light extending in the X-axis direction (see FIG. 13 ). A portion of the second processing light EL2 is reflected by the splitting surface 25a toward the second cylindrical lens 26 to become the second processing light EL221, and another portion passes through (transmits) the splitting surface 25a to become the second processing light EL222 toward the third cylindrical lens 32. The second processing light EL221 passes through the second cylindrical lens 26, is reflected by the first mirror 27, is then reflected by the second mirror 29 and the third mirror 31, passes through the third cylindrical lens 32, and travels toward the special beam splitter 25. The second processing light EL222 passes through the third cylindrical lens 32, is reflected by the third mirror 31 and the second mirror 29, is then reflected by the first mirror 27, passes through the second cylindrical lens 26, and travels toward the special beam splitter 25. At this time, if an optical deflection member 28 is disposed in the optical path between the first mirror 27 and the second mirror 29, the second processing light EL221 and the second processing light EL222 also pass through the optical deflection member 28.

[0104] Here, the special beam splitter 25 (its splitting surface 25a), the first mirror 27, and the third mirror 31 are all plate-shaped members inclined at 45 degrees relative to the Z-axis, and the second mirror 29 is also plate-shaped and has a reference position inclined at 45 degrees relative to the Z-axis. Therefore, in the second optical system 17, the second processing beam EL221 and the second processing beam EL222 basically travel in different rotational directions (clockwise and counterclockwise) from the special beam splitter 25 and then return to the special beam splitter 25. In the second optical system 17, the second mirror 29 is tilted counterclockwise around the central axis relative to the reference position in FIG. 12 . Therefore, the second processing light EL221 reflected by the second mirror 29 travels to a position shifted to the right of the third mirror 31 compared to when it is at the reference position, and is reflected there and travels toward a position shifted upward on the special beam splitter 25, i.e., the reflecting surface 25b (see FIG. 13). The second processing light EL222 reflected by the second mirror 29 travels to a position shifted downward on the first mirror 27 compared to when it is at the reference position, and is reflected there and travels toward a position shifted downward on the special beam splitter 25, i.e., the passing surface 25c (see FIG. 13). As a result, the second optical system 17 can generate a spatial position difference between the second processing light EL221 and the second processing light EL222 while allowing them to pass through essentially the same optical path. Therefore, the second optical system 17 can also be said to constitute a rectangular Sagnac optical system.

[0105] The second optical system 17 reflects the second processing light EL221 off the reflecting surface 25b to travel toward the lens 33, and transmits the second processing light EL222 through the transmitting surface 25c to travel toward the lens 33. In this way, the second optical system 17 reflects the second processing light EL221 reflected off the splitting surface 25a of the special beam splitter 25 by the reflecting surface 25b to travel toward the lens 33, and transmits the second processing light EL222 that has passed through the splitting surface 25a to travel through the transmitting surface 25c to travel toward the lens 33. Therefore, the second optical system 17 can use the second processing light EL2 from the first optical system 16 with extremely high efficiency to generate the second processing light EL221 and the second processing light EL222 that irradiate the workpiece W from different incident directions.

[0106] The second optical system 17 also focuses the second processing beam EL221 and the second processing beam EL222 on the surface of the workpiece W by passing them through a lens 33, thereby forming interference fringes IS. The angle of the second mirror 29 is set in consideration of the arrangement and optical performance of each optical component so that the angle between the second processing beam EL221 and the second processing beam EL222 after passing through the lens 33 forms the interference fringes IS1 of the fundamental frequency waveform Wb. That is, the second optical system 17 sets the angle of the second mirror 29 and the arrangement and optical performance of each optical component to match the period of the interference fringes IS1 of the fundamental frequency waveform Wb. This allows the second optical system 17 to form an interference region IA1 (see FIG. 11 ) of the interference fringes IS1 representing the fundamental frequency waveform Wb on the surface of the workpiece W.

[0107] Furthermore, in the second optical system 17, an optical deflector 28 can be disposed in the optical path between the first mirror 27 and the second mirror 29. The optical deflector 28 refracts light from one of the first mirror 27 and the second mirror 29 downward in the Z-axis direction while directing it toward the other of the first mirror 27 and the second mirror 29, compared to when the optical deflector 28 is not provided. Therefore, by passing through the optical deflector 28, the second processing light EL221 travels to a position shifted downward on the second mirror 29 compared to when the second processing light EL221 does not pass through the optical deflector 28. When reflected there, the second processing light EL221 is shifted more to the right on the third mirror 31, and when reflected there, the second processing light EL221 is shifted more upward (outward) on the reflecting surface 25b of the special beam splitter 25 (see symbol EL221 indicated by a dashed line in FIG. 13 ). Furthermore, by passing through the optical deflection member 28, the second processing light EL222 is shifted downward more on the first mirror 27 than when it does not pass through the optical deflection member 28, and when reflected there, the amount of shifted downward (outward) on the passage surface 25c of the special beam splitter 25 is increased (see symbol EL222 indicated by the dotted line in Figure 13).

[0108] Therefore, by providing the optical deflection member 28 in the second optical system 17, the distance between the second processing light EL221 and the second processing light EL222 when they travel toward the lens 33 can be increased compared to when the optical deflection member 28 is not provided. As a result, by providing the optical deflection member 28 in the second optical system 17, the angle between the second processing light EL221 and the second processing light EL222 after passing through the lens 33 can be increased compared to when the optical deflection member 28 is not provided. Therefore, by providing the optical deflection member 28 in the second optical system 17, interference fringes IS with a smaller period can be formed on the surface of the workpiece W compared to when the optical deflection member 28 is not provided. The second optical system 17 sets the shape (angle (degree of refraction (optical setting)) of the optical deflection member 28 in consideration of the arrangement and optical performance of each optical member so that the angle between the second processing light EL221 and the second processing light EL222 after passing through the lens 33 when the optical deflection member 28 is arranged can form the interference fringes IS2 of the double frequency waveform Wd. In other words, the second optical system 17 sets the shape of the optical deflection member 28, along with the arrangement and optical performance of each optical member, to match the period of the interference fringes IS2 of the double frequency waveform Wd. As a result, by arranging the optical deflection member 28, the second optical system 17 can form an interference area IA2 (see FIG. 11 ) of the interference fringes IS2 showing the double frequency waveform Wd on the surface of the workpiece W.

[0109] The period (pitch) P of the interference fringes IS1 and IS2 formed on the surface of the workpiece W is given by P = λ / (2n × sinθ), where λ is the wavelength of the second processing light EL221 and EL222, n is the refractive index of the medium on the lens 33 side of the workpiece W with respect to the wavelength λ, and 2θ is the intersection angle of the processing light EL221 and EL222 directed toward the workpiece W.

[0110] Consider a case where a difference in amplitude is required between the fundamental frequency waveform Wb and the double frequency waveform Wd. In this case, a similar amplitude (energy amount) difference must be set between the waveform showing the distribution of the energy amount imparted to the workpiece W by the interference fringes IS1 representing the fundamental frequency waveform Wb and the waveform showing the distribution of the energy amount imparted to the workpiece W by the interference fringes IS2 representing the double frequency waveform Wd. This amplitude (energy amount) difference can be set by changing the time it takes for the interference area IA and the irradiation area RA to overlap to form the overlap area OA, i.e., by changing the scanning speed of the galvanometer mirror 21. Furthermore, the above-mentioned amplitude (energy amount) difference can be set by changing the intensity of the processing light EL0 from the processing light source 2 when forming the interference area IA1 and the interference area IA2. The intensity of this processing light EL0 can be changed by changing the output of the processing light source 2 or by providing an optical element with a dimming effect in the optical path from the processing light source 2 to the first optical system 16.

[0111] In this way, in the second optical system 17, by changing the positions of the second processing beam EL221 and the second processing beam EL222 on the optical deflector 28, the emission positions and emission angles of the second processing beam EL221 and the second processing beam EL222 after passing through the lens 33 from the optical deflector 28 can be changed. Furthermore, the second optical system 17 forms the interference fringes IS1 of the fundamental frequency waveform Wb by removing the optical deflector 28 from the optical path, thereby ensuring the intensity of the interference fringes IS1 and effectively forming the interference fringes IS of the ideal waveform Wi. This is because, in general, the interference fringes IS1 of the fundamental frequency waveform Wb are often required to have a higher intensity than the interference fringes IS of the n-th frequency waveform Wn. Therefore, when a higher intensity is required for the n-th frequency waveform Wn, the second optical system 17 may form the interference fringes IS1 of the n-th frequency waveform Wn by removing the optical deflector 28 from the optical path. When the second optical system 17 superimposes three or more n-fold frequency waveforms Wn, it is sufficient to provide a plurality of optical deflection members 28 having different shapes (refractive angles) from each other, and to make it possible to individually place them in the optical path between the first mirror 27 and the second mirror 29 and remove them from the optical path.

[0112] In the third optical system 18, the first processing light EL1 from the first optical system 16 is reflected by the fourth mirror 34, passes through the fourth cylindrical lens 35, and travels to the fifth mirror 36 as linear light extending in the Z-axis direction. Then, in the third optical system 18, the first processing light EL11 is reflected by the fifth mirror 36 and irradiated as linear light extending in the Y-axis direction at the position where the interference area IA (interference area IA1, interference area IA2) is formed on the surface of the workpiece W, forming an irradiation area RA1 (see FIG. 11). Thus, by removing the optical deflector 28 from the second optical system 17, the processing optical system 15A can form an overlapping area OA1 (see FIG. 11) by overlapping the interference area IA1 and the irradiation area RA1 on the surface of the workpiece W. Furthermore, by positioning the optical deflection member 28 in the second optical system 17, the processing optical system 15A can form an overlap area OA2 (see Figure 11) on the surface of the workpiece W by overlapping the interference area IA2 and the irradiation area RA1.

[0113] The processing optical system 15A sets the fluence of the first processing light EL11 in consideration of the arrangement and optical performance of each optical member in the first optical system 16, the second optical system 17, and the third optical system 18 so that the minimum fluence of the processing light in the overlap area OA2 is a fluence capable of processing the workpiece W. In other words, the processing optical system 15A sets the branch ratio of the processing light EL0 from the processing light source 2 based on the arrangement and optical performance of each optical member in the first optical system 16, the second optical system 17, and the third optical system 18 so that the fluence of the interference fringes IS1 and IS2 is equal to or greater than the lower limit TH_lowest of the fluence capable of processing the workpiece W.

[0114] The machining optical system 15A can move over the surface of the workpiece W by driving the galvanometer mirror 21 while maintaining the overlapping area OA1, i.e., the interference area IA1 and the irradiation area RA1, overlapping each other. Therefore, the area in which the machining optical system 15A can move the overlapping area OA1 by driving the galvanometer mirror 21 becomes the machining area PA. The machining optical system 15A scans the entire machining area PA with the overlapping area OA1 containing the fundamental frequency waveform Wb by driving the galvanometer mirror 21 to move the overlapping area OA1. Then, with the optical deflection member 28 in place, the machining optical system 15A scans the entire machining area PA with the overlapping area OA2 containing the double frequency waveform Wd by driving the galvanometer mirror 21 to move the overlapping area OA2. As a result, the processing optical system 15A can irradiate the entire processing area PA on the surface of the workpiece W with interference fringes IS1 representing the fundamental frequency waveform Wb and interference fringes IS2 representing the double frequency waveform Wd, with the first processing light EL11 superimposed. Therefore, the processing optical system 15A can form a riblet structure RB of an ideal shape on the surface of the workpiece W in the processing area PA. Then, by moving the stage 13, the processing optical system 15A can set any position on the surface of the workpiece W as the processing area PA, and can form a riblet structure RB of an ideal shape at any position on the surface of the workpiece W.

[0115] (2-3) Processing Optical System 15B The processing optical system 15B is similar in basic concept and configuration to the processing optical system 15A described above. Therefore, the same components are designated by the same reference numerals and detailed descriptions are omitted. As shown in FIG. 14 , the processing optical system 15B has the same configurations as the processing optical system 15A, including the first optical system 16 and the third optical system 18. Furthermore, the processing optical system 15B has a second optical system 17B that splits the second processing light EL2 from the first optical system 16 to generate multiple second processing light beams EL22, but this second optical system 17B is different from the second optical system 17 of the processing optical system 15A. Compared to the second optical system 17 of the processing optical system 15A, the second optical system 17B does not have an optical deflection member 28, and the second mirror 29B is different.

[0116] The second mirror 29B is formed by combining two plate-like members in the X-axis direction, and each plate-like member is tilted about its central axis extending in the X-axis direction, with a reference position being a 45-degree inclination with respect to the Z-axis direction. In this second mirror 29B, the back side (negative side (-) of the X-axis direction) in FIG. 14 is the first reflecting portion 29Ba, and the front side (positive side (+) of the X-axis direction) in FIG. 14 is the second reflecting portion 29Bb. For ease of understanding, in FIG. 14, the first reflecting portion 29Ba is indicated by a dashed line, and the second reflecting portion 29Bb is indicated by a solid line. In this second mirror 29B, both the first reflecting portion 29Ba and the second reflecting portion 29Bb are tilted counterclockwise (counterclockwise) about the central axis with respect to the reference position in FIG. 14. The second mirror 29 reflects the second processing light EL221 from the first mirror 27 by both the first reflecting portion 29Ba and the second reflecting portion 29Bb to advance to the third mirror 31, and also reflects the second processing light EL222 from the third mirror 31 by both the first reflecting portion 29Ba and the second reflecting portion 29Bb to advance to the first mirror 27.

[0117] The angle of the first reflector 29Ba is set in consideration of the arrangement and optical performance of each optical component so that the angle between the second processing beam EL221 and the second processing beam EL222 after passing through the lens 33 can form the interference fringes IS1 of the fundamental frequency waveform Wb. That is, the angle of the first reflector 29Ba is set in consideration of the arrangement and optical performance of each optical component so that the angle between the second processing beam EL221 and the second processing beam EL222 after passing through the lens 33 can form the interference fringes IS2 of the double frequency waveform Wd. That is, the angle of the second reflector 29Bb is set in consideration of the arrangement and optical performance of each optical component so that the angle between the second processing beam EL221 and the second processing beam EL222 after passing through the lens 33 can form the interference fringes IS2 of the double frequency waveform Wd. That is, the angle of the second reflector 29Bb is set in consideration of the arrangement and optical performance of each optical component so that the angle between the second processing beam EL221 and the second processing beam EL222 after passing through the lens 33 can form the interference fringes IS2 of the double frequency waveform Wd. Therefore, in the second mirror 29B, the second reflecting portion 29Bb on the near side is inclined more with respect to the reference position than the first reflecting portion 29Ba on the far side.

[0118] Here, the second processing light EL221 and the second processing light EL222 are formed by dividing the second processing light EL2 (see FIG. 15 ), which is a linear light extending in the X-axis direction on the dividing surface 25 a, and then collimated (parallel) light of a predetermined size in the X-axis direction and the Y-axis direction by the second cylindrical lens 26 and the third cylindrical lens 32. Therefore, the second processing light EL221 and the second processing light EL222 proceed to the second mirror 29B in a state of having a predetermined size in the X-axis direction, and therefore a part of the second processing light EL221 and the second processing light EL222 is reflected by the first reflecting portion 29Ba and another part is reflected by the second reflecting portion 29Bb.

[0119] 15, the second processing light EL221 is made into a linear light extending in the X-axis direction at the upper side in the X-axis direction (corresponding to the rear side in the X-axis direction in FIG. 14) on the reflecting surface 25b of the special beam splitter 25, and is made into a linear light extending in the X-axis direction at a position displaced to the right at the lower side in the X-axis direction (corresponding to the front side in the X-axis direction in FIG. 14). Also, the second processing light EL222 is made into a linear light extending in the X-axis direction at the upper side in the X-axis direction (corresponding to the rear side in the X-axis direction in FIG. 14) on the transmitting surface 25c of the special beam splitter 25, and is made into a linear light extending in the X-axis direction at a position displaced to the left at the lower side in the X-axis direction (corresponding to the front side in the X-axis direction in FIG. 14). Here, the difference in length between the upper and lower sides of the second processing light EL221 and the second processing light EL222 is the difference in the time it takes for the interference area IA and the irradiation area RA to overlap to form the overlap area OA, and is set to match the difference between the intensity (amplitude) of the fundamental frequency waveform Wb and the intensity (amplitude) of the double frequency waveform Wd.

[0120] Therefore, a part of the second processing light EL221 and the second processing light EL222 forms an interference fringe IS1 of the fundamental frequency waveform Wb, and another part forms an interference fringe IS2 of the double frequency waveform Wd. Therefore, the second optical system 17B irradiates the surface of the workpiece W with the second processing light EL221 and the second processing light EL222 through the lens 33, thereby forming an interference area IA3 on the surface of the workpiece W where the interference fringe IS1 of the fundamental frequency waveform Wb and the interference fringe IS2 of the double frequency waveform Wd are arranged side by side (see FIG. 11 ).

[0121] Next, the operation of the processing optical system 15B will be described. First, processing light EL0 emitted from the processing light source 2 is reflected by a galvanometer mirror 21, passes through a collimator lens 22, and is split into first processing light EL1 and second processing light EL2 by a beam splitter 23 serving as the first optical system 16. The first processing light EL1 travels to the third optical system 18, and the second processing light EL2 travels to the second optical system 17B. The second optical system 17B converts the second processing light EL2 into linear light extending in the X-axis direction by a first cylindrical lens 24, and splits the second processing light EL221, which travels to the second cylindrical lens 26, and the second processing light EL222, which travels to the third cylindrical lens 32, by a splitting surface 25a of a special beam splitter 25. The second optical system 17B, like the second optical system 17B of the processing optical system 15A, causes the second processing light EL221 and the second processing light EL222 to travel in different rotational directions (clockwise and counterclockwise) and then travels from the special beam splitter 25 toward the lens 33.

[0122] The second optical system 17B focuses the second processing light EL221 and the second processing light EL222 on the surface of the workpiece W to form interference fringes IS by passing the second processing light EL221 and the second processing light EL222 through the lens 33. The second processing light EL221 and the second processing light EL222 are reflected by the first reflecting portion 29Ba on the rear side of FIG. 14 and by the second reflecting portion 29Bb on the front side of FIG. 14. Therefore, the second optical system 17B irradiates the surface of the workpiece W with the second processing light EL221 and the second processing light EL222 after passing through the lens 33 at an angle that can form interference fringes IS1 of the fundamental frequency waveform Wb on the rear side of FIG. 14 (negative side (-) of the X-axis direction), and irradiates the surface of the workpiece W with the second processing light EL221 and the second processing light EL222 on the front side of FIG. 14 (positive side (+) of the X-axis direction) at an angle that can form interference fringes IS2 of the double frequency waveform Wd. As a result, the second optical system 17B forms an interference area IA3 on the surface of the workpiece W, in which an interference fringe IS1 representing the fundamental frequency waveform Wb and an interference fringe IS2 representing the double frequency waveform Wd are arranged side by side.

[0123] The third optical system 18 converts the first processing light EL1 from the first optical system 16 into a linear first processing light EL11 extending in the Z-axis direction by passing it through a fourth cylindrical lens 35. The third optical system 18 then irradiates the first processing light EL11 as linear light extending in the Y-axis direction at the position where the interference area IA3 is formed on the surface of the workpiece W, thereby forming an irradiation area RA2. As a result, the processing optical system 15B can form an overlap area OA3 on the surface of the workpiece W by using the second optical system 17B to overlap the interference area IA3 and the irradiation area RA2.

[0124] The machining optical system 15B can move over the surface of the workpiece W by driving the galvanometer mirror 21 while maintaining the overlap region OA3, i.e., the interference region IA3, and the irradiation region RA3, overlapping each other. By driving the galvanometer mirror 21 to move the overlap region OA3, the machining optical system 15B scans the entire machining region PA with the overlap region OA3, which includes the fundamental frequency waveform Wb and the double frequency waveform Wd. This allows the machining optical system 15B to irradiate the entire machining region PA on the surface of the workpiece W with interference fringes IS1 representing the fundamental frequency waveform Wb and interference fringes IS2 representing the double frequency waveform Wd, with the first machining light EL11 superimposed. This allows the machining optical system 15B to form an ideally shaped riblet structure RB on the surface of the workpiece W in the machining region PA. The machining optical system 15B can then move the stage 13 to set any position on the surface of the workpiece W as the machining region PA, thereby forming an ideally shaped riblet structure RB at any position on the surface of the workpiece W.

[0125] (2-4) Machining Optical System 15C The basic concept and configuration of this machining optical system 15C are similar to those of the machining optical system 15A described above. Therefore, the same reference numerals are used to designate identical components, and detailed descriptions are omitted. As shown in FIG. 16 , the machining optical system 15C has a second optical system 17 configured identically to that of the machining optical system 15A. Furthermore, the machining optical system 15C differs from the first optical system 16 and the third optical system 18 of the machining optical system 15A in that the first optical system 16C, which splits the machining light EL0 from the machining light source 2 into the first machining light EL1 and the second machining light EL2, and the third optical system 18C, which generates the first machining light EL11 from the first machining light EL1 and irradiates the workpiece W with the first machining light EL11. Furthermore, the configuration of the machining optical system 15C from the first optical system 16C to the second optical system 17 differs from that of the machining optical system 15A.

[0126] The processing optical system 15C differs from the processing optical system 15A in that the position (arrangement) of the first optical system 16C (beam splitter 23) relative to the galvanometer mirror 21 and the collimator lens 22 is changed and a new lens 41 is provided. The beam splitter 23 as the first optical system 16C is provided at a position where the processing light EL0 from the processing light source 2 travels, and generates the first processing light EL1 that travels to the third optical system 18 by reflecting a part of the processing light EL0, and generates the second processing light EL2 that travels to the lens 41 by passing the other part of the processing light EL0.

[0127] The lens 41 focuses the second processing light EL2 that has passed through the beam splitter 23 onto the galvanometer mirror 21 (its reflecting surface). In this example, the processing optical system 15C converts the processing light EL0 from the processing light source 2 into approximately collimated light (parallel light), and the first processing light EL1 branched from the processing light source 2 into collimated light (parallel light) of a predetermined magnitude in the X-axis and Y-axis directions. The lens 41 sets the rear focal point of the second processing light EL2 in the traveling direction near the galvanometer mirror 21 (its reflecting surface), and focuses the second processing light EL2 onto the galvanometer mirror 21. The collimating lens 22 converts the second processing light EL2 reflected by the galvanometer mirror 21 into collimated light (parallel light). Furthermore, the second processing light EL2 focused by the lens 41 does not have to be completely focused on the reflecting surface of the galvanometer mirror 21, and the position of the focusing line of the second processing light EL2 by the lens 41 may be slightly off from the reflecting surface of the galvanometer mirror 21 in the optical axis direction.

[0128] The second optical system 17 of the processing optical system 15C, like the processing optical system 15A, reflects the second processing beam EL221 at the reflecting surface 25b of the special beam splitter 25 to cause it to travel toward the lens 33, and transmits the second processing beam EL222 through the transmitting surface 25c to cause it to travel toward the lens 33. Similarly to the processing optical system 15A, the second optical system 17 of the processing optical system 15C changes the distance between the second processing beam EL221 and the second processing beam EL222 at the special beam splitter 25 by switching between a state in which the optical deflector 28 is removed and a state in which the optical deflector 28 is installed (see FIG. 17 ). Similarly to the processing optical system 15A, the second optical system 17 of the processing optical system 15C forms, on the surface of the workpiece W, an interference region IA1 of the interference fringe IS1 representing the fundamental frequency waveform Wb and an interference region IA2 of the interference fringe IS2 representing the double frequency waveform Wd.

[0129] The third optical system 18C differs from the third optical system 18 of the processing optical system 15A in that it does not include a fourth mirror 34 and a fourth cylindrical lens 35, but only a fifth mirror 36. In the third optical system 18C, the first processing light EL1 from the first optical system 16C, i.e., the beam splitter 23, is reflected by the fifth mirror 36 and directed toward the surface of the workpiece W. In the processing optical system 15C, the processing light EL0 from the processing light source 2 is converted into substantially collimated light (parallel light), and the first processing light EL1 branched therefrom is converted into collimated light (parallel light) of a predetermined magnitude in the X-axis and Y-axis directions. Therefore, in the third optical system 18C, the first processing light EL11, which is reflected by the fifth mirror 36 and directed toward the surface of the workpiece W, is converted into collimated light of a predetermined magnitude in the X-axis and Y-axis directions. The processing optical system 15C irradiates the first processing light EL11 to form an irradiation area RA3, and the irradiation area RA3 is equal in size to the processing area PA (see FIG. 11). That is, the processing optical system 15C sets the processing light EL0 from the processing light source 2 so that the irradiation area RA3 is equal in size to the processing area PA.

[0130] Next, the operation of the processing optical system 15C will be described. First, when processing light EL0 is emitted from the processing light source 2, it is split into first processing light EL1 and second processing light EL2 by the beam splitter 23 in the first optical system 16C, and then the first processing light EL1 proceeds to the third optical system 18C. Furthermore, the processing optical system 15C collimates the second processing light EL2 split by the first optical system 16C using the collimating lens 22 before proceeding to the second optical system 17.

[0131] The second optical system 17 removes the optical deflection member 28 from the optical path between the first mirror 27 and the second mirror 29, thereby forming an interference area IA1 of interference fringes IS1 that indicate the fundamental frequency waveform Wb on the surface of the workpiece W. In addition, the second optical system 17 places the optical deflection member 28 in the optical path between the first mirror 27 and the second mirror 29, thereby forming an interference area IA2 of interference fringes IS2 that indicate the double frequency waveform Wd on the surface of the workpiece W.

[0132] In the third optical system 18C, the first processing light EL1 from the first optical system 16C is reflected by the fifth mirror 36, and a first processing light EL11 of a predetermined size is irradiated in the X-axis and Y-axis directions, overlapping the interference area IA (interference area IA1, interference area IA2) formed on the surface of the workpiece W, to form an irradiation area RA3. The irradiation area RA3 is equal in size to the processing area PA. Thus, by removing the optical deflector 28 from the second optical system 17, the processing optical system 15C forms an overlapping area OA4 on the surface of the workpiece W by overlapping the interference area IA1 and the irradiation area RA3 (see FIG. 11). Furthermore, by placing the optical deflector 28 in the second optical system 17, the processing optical system 15C forms an overlapping area OA5 on the surface of the workpiece W by overlapping the interference area IA2 and the irradiation area RA3 (see FIG. 11).

[0133] The processing optical system 15C then forms an irradiation area RA3 in the processing area PA while forming an interference area IA1 at one end of the processing area PA in the X-axis direction. The processing optical system 15C drives the galvanometer mirror 21 to move the interference area IA1 toward the other end of the X-axis direction, thereby scanning the entire processing area PA and forming an overlap area OA4 throughout the processing area PA (see FIG. 11 ). The processing optical system 15C then forms an irradiation area RA3 in the processing area PA while forming an interference area IA2 at one end of the processing area PA in the X-axis direction. The processing optical system 15C then drives the galvanometer mirror 21 to move the interference area IA2 toward the other end of the X-axis direction, thereby scanning the entire processing area PA and forming an overlap area OA5 throughout the processing area PA (see FIG. 11 ). As a result, the processing optical system 15C can irradiate the entire processing area PA on the surface of the workpiece W with the interference fringes IS1 of the fundamental frequency waveform Wb and the interference fringes IS2 of the double frequency waveform Wd superimposed on the first processing light EL11. Therefore, the processing optical system 15C can form a riblet structure RB of an ideal shape on the surface of the workpiece W in the processing area PA. Then, by moving the stage 13, the processing optical system 15C can make any position on the surface of the workpiece W the processing area PA, and can form a riblet structure RB of an ideal shape at any position on the surface of the workpiece W.

[0134] (2-5) Processing Optical System 15D This processing optical system 15D uses the first optical system 16C and the third optical system 18C of the processing optical system 15C, and also uses the second optical system 17B of the processing optical system 15B, as shown in Fig. 18. For this reason, parts having the same configuration as those of the processing optical system 15C are given the same reference numerals, and detailed explanations thereof will be omitted.

[0135] The operation of the processing optical system 15D will be described. First, processing light EL0 is emitted from the processing light source 2. In the first optical system 16C, the beam splitter 23 splits the processing light into first processing light EL1 and second processing light EL2, and the first processing light EL1 then travels to the third optical system 18C. In addition, the processing optical system 15D collimates the second processing light EL2 split by the first optical system 16C using the collimating lens 22 before traveling to the second optical system 17B.

[0136] In the second optical system 17B, the second processing light EL221 is transformed into a linear light beam that extends in the X-axis direction on the reflecting surface 25b but is shifted in the Y-axis direction along the way on the special beam splitter 25, and the second processing light EL222 is transformed into a linear light beam that extends in the X-axis direction on the transmitting surface 25c but is shifted in the Y-axis direction along the way (see FIG. 19). The second optical system 17B irradiates the surface of the workpiece W with the second processing light EL221 and the second processing light EL222 through the lens 33, thereby forming an interference region IA3 on the surface of the workpiece W where an interference fringe IS1 representing the fundamental frequency waveform Wb and an interference fringe IS2 representing the double frequency waveform Wd are arranged side by side (see FIG. 11).

[0137] In the third optical system 18C, the first processing light EL1 from the first optical system 16C is reflected by the fifth mirror 36, and the first processing light EL11 of a predetermined size is irradiated in the X-axis and Y-axis directions so as to overlap the interference area IA3 formed on the surface of the workpiece W, thereby forming an irradiation area RA3 of a size equal to the processing area PA. As a result, the processing optical system 15D can form an overlap area OA6 on the surface of the workpiece W by overlapping the interference area IA3 and the irradiation area RA3 with the second optical system 17B (see FIG. 11 ).

[0138] The processing optical system 15D then forms an irradiation area RA3 in the processing area PA while forming an interference area IA3 at one end of the processing area PA in the X-axis direction. The processing optical system 15D drives the galvanometer mirror 21 to move the interference area IA3 toward the other end in the X-axis direction, thereby scanning the entire processing area PA and forming an overlapping area OA6 throughout the processing area PA. This allows the processing optical system 15D to irradiate the entire processing area PA on the surface of the workpiece W with the interference fringes IS1 of the fundamental frequency waveform Wb and the interference fringes IS2 of the double frequency waveform Wd, superimposed on the first processing light EL11. This allows the processing optical system 15D to form an ideally shaped riblet structure RB on the surface of the workpiece W in the processing area PA. By moving the stage 13, the processing optical system 15D can set any position on the surface of the workpiece W as the processing area PA, thereby forming an ideally shaped riblet structure RB at any position on the surface of the workpiece W.

[0139] (2-6) Processing Optical System 15E As shown in FIG. 20 , this processing optical system 15E includes a first optical system 16E having the same basic concept and configuration as the first optical system 16C of the processing optical system 15C described above. In the following description, parts with the same configuration are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the processing optical system 15E includes a second optical system 17E having the same basic concept and configuration as the second optical system 17 of the processing optical system 15A described above. In the following description, parts with the same configuration are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, since the processing optical system 15E uses the third optical system 18C of the processing optical system 15C, parts with the same configuration are denoted by the same reference numerals, and detailed descriptions thereof will be omitted.

[0140] The machining optical system 15E differs from the machining optical system 15C in that it does not include the galvanometer mirror 21, the collimator lens 22, and the lens 41, but instead includes a mirror 42. The beam splitter 23, which serves as the first optical system 16E, is located at a position where the machining light EL0 from the machining light source 2 travels, and reflects a portion of the machining light EL0 to generate the first machining light EL1 that travels toward the third optical system 18, and passes the other portion of the machining light EL0 to generate the second machining light EL2 that travels toward the mirror 42. The mirror 42 is a plate-shaped member, and reflects the second machining light EL2 that has passed through the beam splitter 23 toward the second optical system 17E (its first cylindrical lens 24).

[0141] The second optical system 17E of the processing optical system 15E differs from the second optical system 17 of the processing optical system 15A in that a fourth cylindrical lens 43 is newly installed instead of the lens 33. The fourth cylindrical lens 43 converts the second processing light EL221 and the second processing light EL222 (see FIG. 21), which are linear light extending in the X-axis direction from the special beam splitter 25, into rectangular light having sides extending in the X-axis direction and sides extending in the Y-axis direction (see FIG. 11). The front focal point of the fourth cylindrical lens 43 in the direction of travel of the second processing light EL221 and the second processing light EL222 is set near the special beam splitter 25 (its reflecting surface). Therefore, the fourth cylindrical lens 43 converts the second processing light EL221 and the second processing light EL222 into collimated light (parallel light) of a predetermined size in the X-axis and Y-axis directions on the surface of the workpiece W.

[0142] The operation of the processing optical system 15E will be described. First, when processing light EL0 is emitted from the processing light source 2, it is split into first processing light EL1 and second processing light EL2 by the beam splitter 23 in the first optical system 16E, and the first processing light EL1 then travels to the third optical system 18C. The processing optical system 15E also reflects the second processing light EL2 split by the first optical system 16E with a mirror 42 and directs it to the second optical system 17E.

[0143] The second optical system 17E causes the second processing light EL221 and the second processing light EL222 from the special beam splitter 25 to pass through a fourth cylindrical lens 43, thereby irradiating the surface of the workpiece W with light of a predetermined size in the X-axis and Y-axis directions. The second optical system 17E removes the optical deflection member 28 from the optical path between the first mirror 27 and the second mirror 29 to form an interference region IA4 of the interference fringe IS1 representing the fundamental frequency waveform Wb on the surface of the workpiece W (see FIG. 11 ). The second optical system 17E also places the optical deflection member 28 in the optical path between the first mirror 27 and the second mirror 29 to form an interference region IA5 of the interference fringe IS2 representing the double frequency waveform Wd on the surface of the workpiece W (see FIG. 11 ).

[0144] In the third optical system 18C, the first processing light EL1 from the first optical system 16E is reflected by the fifth mirror 36, and the first processing light EL11 is irradiated onto the interference area IA4 formed on the surface of the workpiece W, forming an irradiation area RA3 equal in size to the processing area PA. As a result, in the processing optical system 15E, by removing the optical deflector 28 from the second optical system 17, the interference area IA4 and the irradiation area RA3 are overlapped on the surface of the workpiece W, forming an overlap area OA7 equal in size to the processing area PA (see FIG. 11 ). In the third optical system 18C, the first processing light EL1 from the first optical system 16E is reflected by the fifth mirror 36, and the first processing light EL11 is irradiated onto the interference area IA5 formed on the surface of the workpiece W, forming an irradiation area RA3 equal in size to the processing area PA. As a result, by positioning the optical deflection member 28 in the second optical system 17, the processing optical system 15E forms an overlap area OA8 on the surface of the workpiece W by overlapping the interference area IA5 and the irradiation area RA3 (see Figure 11).

[0145] As a result, the machining optical system 15E can irradiate the entire machining area PA on the surface of the workpiece W with the interference fringes IS1 of the fundamental frequency waveform Wb and the interference fringes IS2 of the double frequency waveform Wd superimposed on the first machining light EL11. Therefore, the machining optical system 15E can form a riblet structure RB of an ideal shape on the surface of the workpiece W in the machining area PA. Then, by moving the stage 13, the machining optical system 15E can set any position on the surface of the workpiece W as the machining area PA, and can form a riblet structure RB of an ideal shape at any position on the surface of the workpiece W.

[0146] (2-7) Modified Processing Optical System 15F Next, a description will be given of a processing optical system 15F as a modified example of the above-described processing optical system 15. As shown in Fig. 22, this processing optical system 15F has the same basic concept and configuration as the above-described processing optical system 15A, so that the same components are designated by the same reference numerals and detailed descriptions are omitted. In the processing optical system 15F, the processing light EL0 from the processing light source 2 has high directionality and has components with two different polarization directions.

[0147] The processing optical system 15F differs from the processing optical system 15A in that it does not include a galvanometer mirror 21 and a collimator lens 22. The first optical system 16F of the processing optical system 15F splits the processing light EL0 from the processing light source 2 into a first processing light EL1 and a second processing light EL2 by a beam splitter 23. Specifically, the beam splitter 23 reflects a portion of the processing light EL0 to generate the first processing light EL1 that travels toward the third optical system 18F, and transmits the other portion of the processing light EL0 to generate the second processing light EL2 that travels toward the second optical system 17F.

[0148] Furthermore, in the processing optical system 15F, a second optical system 17F into which the second processing light EL2 from the first optical system 16F is incident is different from the second optical system 17 of the processing optical system 15A in that it does not have the first cylindrical lens 24, the second cylindrical lens 26, the optical deflection member 28, the third cylindrical lens 32, or the lens 33. Furthermore, the second optical system 17F of the processing optical system 15F is different from the second optical system 17 of the processing optical system 15A in that it has a first polarizing beam splitter 44 instead of the special beam splitter 25, and also has a second polarizing beam splitter 45, a first lens 46, and a second lens 47.

[0149] The first polarizing beam splitter 44 splits the second processing light EL2 from the first optical system 16F into multiple second processing light EL22. For ease of explanation, the following description will be given assuming that the first polarizing beam splitter 44 splits the second processing light EL2 into two second processing light EL22 (when individually shown, one is referred to as the second processing light EL221 and the other as the second processing light EL222). The first polarizing beam splitter 44 also merges the two split second processing light EL22 and directs both second processing light EL22 toward the second polarizing beam splitter 45.

[0150] The first polarizing beam splitter 44 is a rectangular plate-shaped polarizing beam splitter, and is arranged with a central axis extending in the X-axis direction and tilted at 45 degrees relative to the Y-axis direction. Therefore, the first polarizing beam splitter 44 has a first polarizing splitting surface 44a tilted at 45 degrees relative to the Y-axis direction. The first polarizing beam splitter 44 generates the second processing light EL221 by reflecting a portion of the second processing light EL2 from the first optical system 16F, and generates the second processing light EL222 by passing the remainder of the second processing light EL2. At this time, the first polarizing beam splitter 44 reflects one of the p-polarized light component and the s-polarized light component at the first polarizing splitting surface 44a and passes the other of the p-polarized light component and the s-polarized light component. Therefore, the second processing light EL2 from the first optical system 16F contains at least the p-polarized component and the s-polarized component at the first polarizing beam splitter 44 when it is incident on the first polarizing beam splitter 44. Therefore, two different polarization directions are set so that the processing light EL0 from the processing light source 2 contains the p-polarized component and the s-polarized component at the first polarizing beam splitter 44 when it is incident on the first polarizing beam splitter 44. Here, the first polarizing beam splitter 44 is disposed at an angle of 45 degrees with respect to the Y-axis direction, so that the second processing light EL221 generated by reflection travels parallel to the Z-axis direction toward the first mirror 27, and the second processing light EL222 generated by passing through the first polarizing beam splitter 44 travels parallel to the Y-axis direction toward the third mirror 31.

[0151] In the second optical system 17F, the relationship between the first mirror 27, the second mirror 29, and the third mirror 31 relative to the first polarizing beam splitter 44 is the same as that of the second optical system 17 of the processing optical system 15A, except that the first cylindrical lens 24, the second cylindrical lens 26, the optical deflection member 28, and the third cylindrical lens 32 are not provided. Therefore, in the second optical system 17F, the second processing light EL221 and the second processing light EL222 basically travel from the first polarizing beam splitter 44 in different rotational directions (clockwise and counterclockwise) and return to the first polarizing beam splitter 44 again. In the second optical system 17F, the second mirror 29 is tilted from the reference position (plane), so that the second processing light EL221 and the second processing light EL222 pass through essentially the same optical path while the emission angles of the second processing light EL221 and the second processing light EL222 are different from each other. The second optical system 17F reflects the second processing light EL221 at the first polarizing beam splitter 44 and causes it to travel toward the second polarizing beam splitter 45, and transmits the second processing light EL222 through the first polarizing beam splitter 44 and causes it to travel toward the second polarizing beam splitter 45. The second processing light EL221 is linearly polarized in one of the p-polarized and s-polarized light (first polarization direction) at the first polarizing beam splitter 44, and the second processing light EL222 is linearly polarized in the other of the p-polarized and s-polarized light (second polarization direction) at the first polarizing beam splitter 44.

[0152] Therefore, the first polarizing beam splitter 44 emits the second processing light EL221 in the first polarization direction and the second processing light EL222 in the second polarization direction so that at least one of the emission angles and emission positions differs. Therefore, in the second optical system 17F, the first polarizing beam splitter 44, the first mirror 27, the second mirror 29, and the third mirror 31 form an upstream optical system that emits the second processing light EL221 in the first polarization direction and the second processing light EL222 in the second polarization direction so that at least one of the emission angles and emission positions differs.

[0153] The second polarizing beam splitter 45 is configured by combining a cube-shaped polarizing beam splitter section 45a with an orthogonal triangular prism section 45b connected to one surface of the polarizing beam splitter section 45a. The polarizing beam splitter section 45a has a second polarizing splitting surface 45c inclined at 45 degrees with respect to the Y-axis direction. This second polarizing splitting surface 45c reflects one of the p-polarized and s-polarized components at the second polarizing splitting surface 45c and transmits the other. The second polarizing beam splitter 45 is rotated about a central axis extending in the Y-axis direction relative to the first polarizing beam splitter 44 so that the second polarizing splitting surface 45c is non-parallel to the first polarizing beam splitting surface 44a of the first polarizing beam splitter 44 (having different surface directions). Here, the surface direction may be the normal direction to the surface. In the second polarizing beam splitter 45 of this modification, the second polarizing splitting surface 45c is angled at 45 degrees with respect to the first polarizing splitting surface 44a when viewed in the direction of rotation about the central axis extending in the Y-axis direction. Therefore, while the plane perpendicular to the first polarizing splitting surface 44a includes (is parallel to) the X-axis direction, the plane perpendicular to the second polarizing splitting surface 45c forms a predetermined angle (45 degrees in this modification) with respect to the X-axis direction.

[0154] The second polarization splitting surface 45c is rotated about a central axis extending in the Y-axis direction relative to the first polarization splitting surface 44a, so that it can split the linearly polarized second processing light EL221 in the first polarization direction and the linearly polarized second processing light EL222 in the second polarization direction from the first polarizing beam splitter 44. That is, the second polarization splitting surface 45c passes a portion of the linearly polarized second processing light EL221 in the first polarization direction to form the second processing light EL221 in the third polarization direction, and reflects the remainder of the second processing light EL221 to form the second processing light EL221 in the fourth polarization direction. The second polarization splitting surface 45c also passes a portion of the linearly polarized second processing light EL222 in the second polarization direction to form the second processing light EL222 in the third polarization direction, and reflects the remainder of the second processing light EL222 to form the second processing light EL222 in the fourth polarization direction. The second polarization beam splitter 45 then emits the second processing light EL221 and the second processing light EL222 polarized in the third polarization direction downward from the second polarization splitter 45c in the Y-axis direction, and causes them to travel toward the first lens 46.

[0155] The orthogonal triangular prism 45b has a reflecting surface 45d arranged in the direction of propagation of the second processing light EL221 and the second processing light EL222 in the fourth polarization direction reflected by the second polarization splitting surface 45c. In this modification, the reflecting surface 45d is parallel to the second polarization splitting surface 45c. Therefore, like the second polarization splitting surface 45c, the orthogonal surface of the reflecting surface 45d forms a predetermined angle (45 degrees in this modification) with respect to the X-axis direction. The reflecting surface 45d reflects the second processing light EL221 and the second processing light EL222 in the fourth polarization direction downward in the Y-axis direction from the reflecting surface 45d, causing them to propagate toward the first lens 46.

[0156] The first lens 46 is paired with the second lens 47 in the Y-axis direction. The first lens 46 cooperates with the second lens 47 to irradiate the first position P1 on the surface of the workpiece W with the second processing light EL221 in the third polarization direction and the second processing light EL222 in the third polarization direction, thereby forming a first interference fringe (interference fringe IS in the interference area IA6 (see FIG. 23 )). The first lens 46 cooperates with the second lens 47 to irradiate the second position P2 on the surface of the workpiece W with the second processing light EL221 in the fourth polarization direction and the second processing light EL222 in the fourth polarization direction, thereby forming a second interference fringe (interference fringe IS in the interference area IA7 (see FIG. 23 )). The first lens 46 cooperates with the second lens 47 to adjust the size of the interference area IA6 at the first position P1 and the size of the interference area IA7 at the second position P2 on the surface of the workpiece W. That is, the first lens 46 cooperates with the second lens 47 to adjust the size of the first interference fringe (interference fringe IS in interference area IA6) formed by the second processing light EL221 and the second processing light EL222 in the third polarization direction and the second interference fringe (interference fringe IS in interference area IA7) formed by the second processing light EL221 and the second processing light EL222 in the fourth polarization direction. This size adjustment not only adjusts the size of the interference areas IA6 and IA7 on the surface of the workpiece W, but also includes adjusting the period of the interference fringe IS on the surface of the workpiece W. Therefore, the first lens 46 and the second lens 47 can be said to constitute an afocal optical system.

[0157] For simplicity of illustration, the first lens 46 and the second lens 47 are each shown as a single lens in FIG. 22 , but the first lens 46 and the second lens 47 may each be composed of a plurality of lenses. Therefore, the first lens 46 and the second lens 47 may be referred to as a first lens group 46 and a second lens group 47, respectively. Furthermore, a reflecting member or a diffractive optical element may be used instead of or in addition to the lenses. Therefore, the first lens 46 and the second lens 47 may be referred to as a first optical member group 46 and a second optical member group 47, respectively.

[0158] The second optical system 17F sets the fringe pitch direction of the first interference fringe (the interference fringe IS of the interference region IA6) and the fringe pitch direction of the second interference fringe (the interference fringe IS of the interference region IA7) to be the same or parallel to each other. The second optical system 17F also sets the fringe pitch of the first interference fringe (the interference fringe IS of the interference region IA6) and the fringe pitch of the second interference fringe (the interference fringe IS of the interference region IA7) to be equal. The second optical system 17F also aligns the light-dark phase of the interference fringe IS of the interference region IA6 and the light-dark phase of the interference fringe IS of the interference region IA7. "Aligning the light-dark phases of both interference fringes IS" means that the positions of the light and dark fringes in the interference fringe IS of the interference region IA6 and the interference fringe IS of the interference region IA7 formed by virtually expanding them are the same, i.e., similar light-dark patterns are formed. In other words, the light and dark phases of both interference fringes IS being aligned can also be said to be aligned in phase with each other between the interference fringes IS formed by virtually expanding the interference fringes IS of the interference area IA6 and the interference fringes IS formed by virtually expanding the interference fringes IS of the interference area IA7.

[0159] Therefore, the second polarizing beam splitter 45 splits the second processing light EL221 of the first polarization direction into the second processing light EL221 of the third polarization direction and the second processing light EL221 of the fourth polarization direction, and splits the second processing light EL222 of the second polarization direction into the second processing light EL222 of the third polarization direction and the second processing light EL222 of the fourth polarization direction. Therefore, in the second optical system 17F, the second polarizing beam splitter 45, the first lens 46, and the second lens 47 form a downstream optical system that forms the first interference fringe (the interference fringe IS of the interference area IA6) at the first position P1 and the second interference fringe (the interference fringe IS of the interference area IA7) at the second position P2.

[0160] The third optical system 18F differs from the third optical system 18 of the processing optical system 15A in that a beam splitter 48 is newly provided instead of the fourth cylindrical lens 35. In the third optical system 18F, a fourth mirror 34 reflects the first processing light EL1 from the first optical system 16F and causes it to proceed to the beam splitter 48.

[0161] When the first processing light EL1 from the first optical system 16F is incident on the beam splitter 48, the beam splitter 48 splits the first processing light EL1 into a first processing light EL111 and a first processing light EL112. Specifically, the beam splitter 48 reflects a portion of the first processing light EL1 to generate the first processing light EL111 that travels toward the surface of the workpiece W, and passes another portion of the first processing light EL1 to generate the first processing light EL112 that travels toward the fifth mirror 36. The area irradiated with the first processing light EL111 is designated as an irradiation area RA4. The beam splitter 48 (third optical system 18F) of this modification is configured to irradiate the first processing light EL111 at a first position P1 on the surface of the workpiece W where an interference area IA6 is formed, so that the irradiation area RA4 and the interference area IA6 overlap (see FIG. 23 ). The beam splitter 48 may be an amplitude-splitting beam splitter or a polarizing beam splitter.

[0162] The fifth mirror 36 reflects the first processing light EL112 from the beam splitter 48 and causes it to proceed toward the surface of the workpiece W. The fifth mirror 36 (third optical system 18F) of this modified example is set so that the first processing light EL112 irradiates a second position P2 on the surface of the workpiece W where an interference area IA7 is formed (see FIG. 23 ). The area irradiated with the first processing light EL112 is referred to as an irradiation area RA5.

[0163] Therefore, the third optical system 18F splits the first processing light EL1 using the beam splitter 48 into a first processing light EL111 (irradiation area RA4) that irradiates the area on the surface of the workpiece W where the interference area IA6 is formed, and a first processing light EL112 (irradiation area RA5) that irradiates the area on the surface of the workpiece W where the interference area IA7 is formed. The processing optical system 15F can form an overlap area OA8 on the surface of the workpiece W by overlapping the interference area IA6 and the irradiation area RA4, and can form an overlap area OA9 by overlapping the interference area IA7 and the irradiation area RA5 (see FIG. 23). Therefore, the processing optical system 15F defines the area combining the overlap areas OA8 and OA9 as the processing area PA.

[0164] In the processing optical system 15F of this modification, the fluence of the first processing light EL111 and the first processing light EL112 is set in consideration of the arrangement and optical performance of each optical member in the first optical system 16F, the second optical system 17F, and the third optical system 18F so that the minimum fluence of the processing light in the overlapping regions OA8 and OA9 is a fluence capable of processing the workpiece W. That is, in the processing optical system 15F, the branching ratios of the beam splitter 23 of the first optical system 16F and the beam splitter 48 of the third optical system 18F are set based on the arrangement and optical performance of each optical member in the first optical system 16F, the second optical system 17F, and the third optical system 18F so that the fluence of the interference fringes IS between the interference regions IA7 and IA8 is equal to or greater than the lower limit TH_lowest of the fluence capable of processing the workpiece W.

[0165] Next, the operation of the processing optical system 15F will be described. First, when processing light EL0 is emitted from the processing light source 2, it is split into first processing light EL1 and second processing light EL2 by the beam splitter 23 in the first optical system 16F. The first processing light EL1 proceeds to the third optical system 18F, and the second processing light EL2 proceeds to the second optical system 17F.

[0166] In the second optical system 17F, a portion of the second processing light EL2 is reflected by the first polarizing beam splitter 44 (first polarizing splitting surface 44a) toward the first mirror 27 to become the second processing light EL221, and another portion passes through the first polarizing beam splitter 44 (first polarizing splitting surface 44a) to become the second processing light EL222 proceeding toward the third mirror 31. The second processing light EL221 is reflected by the first mirror 27, the second mirror 29, and the third mirror 31 to proceed toward the first polarizing beam splitter 44. The second processing light EL222 is reflected by the third mirror 31, the second mirror 29, and the first mirror 27 to proceed toward the first polarizing beam splitter 44.

[0167] Here, the first polarizing beam splitter 44, the first mirror 27, and the third mirror 31 are all plate-shaped and inclined at 45 degrees relative to the Z-axis. The second mirror 29 is also plate-shaped and has a reference position inclined at 45 degrees relative to the Z-axis. Therefore, in the second optical system 17F, the second processing beam EL221 and the second processing beam EL222 basically travel in different rotational directions (clockwise and counterclockwise) from the first polarizing beam splitter 44 and then return to the first polarizing beam splitter 44. In the second optical system 17F, the second mirror 29 is tilted counterclockwise around the central axis relative to the reference position in FIG. 22. Therefore, the second processing beam EL221 reflected by the second mirror 29 travels to a position shifted to the right of the third mirror 31 compared to the reference position, and is reflected there and travels toward a position shifted upward of the first polarizing beam splitter 44. Furthermore, the second processing light EL222 reflected by the second mirror 29 travels to a position shifted downward on the first mirror 27 compared to when it is at the reference position, and is reflected there to travel toward a position shifted downward on the first polarizing beam splitter 44. As a result, in the second optical system 17F, the second processing light EL221 and the second processing light EL222 can be made to travel along essentially the same optical path while generating a spatial position difference between the second processing light EL221 and the second processing light EL222. Therefore, the second optical system 17F (its upstream optical system) can be said to constitute a rectangular Sagnac optical system.

[0168] The second optical system 17F reflects the second processing light EL221 at the first polarizing beam splitter 44 (first polarizing splitting surface 44a) to make it travel toward the second polarizing beam splitter 45, and transmits the second processing light EL222 through the first polarizing beam splitter 44 (first polarizing splitting surface 44a) to make it travel toward the second polarizing beam splitter 45. As a result, the second processing light EL221 is linearly polarized in the first polarization direction, and the second processing light EL222 is linearly polarized in the second polarization direction.

[0169] The second polarizing beam splitter 45 transmits a portion of the second processing light EL221 having the first polarization direction through the first polarization splitting surface 44a to form the second processing light EL221 having the third polarization direction, and transmits a portion of the second processing light EL222 having the second polarization direction to form the second processing light EL222 having the third polarization direction. The second polarizing beam splitter 45 also reflects the remainder of the second processing light EL221 having the first polarization direction through the first polarization splitting surface 44a to form the second processing light EL221 having the fourth polarization direction, and reflects the remainder of the second processing light EL222 having the second polarization direction to form the second processing light EL222 having the fourth polarization direction. The second polarizing beam splitter 45 then directs the second processing light EL221 and the second processing light EL222 having the third polarization direction toward the first lens 46. The second polarizing beam splitter 45 reflects the second processing light EL221 and the second processing light EL222 in the fourth polarization direction at the reflecting surface 45d and causes them to travel toward the first lens 46. The first lens 46 and the second lens 47 form an interference fringe IS (interference area IA6) at the first position P1 on the surface of the workpiece W using the second processing light EL221 and the second processing light EL222 in the third polarization direction. The first lens 46 and the second lens 47 form an interference fringe IS (interference area IA7) at the second position P2 on the surface of the workpiece W using the second processing light EL221 and the second processing light EL222 in the fourth polarization direction.

[0170] In the third optical system 18F, the first processing light EL1 from the first optical system 16F is reflected by the fourth mirror 34 and then split by the beam splitter 48 into the first processing light EL111 and the first processing light EL112. In the third optical system 18F, the first processing light EL111 is caused to travel from the beam splitter 48 toward the surface of the workpiece W to form an irradiation area RA4 at the first position P1, and the first processing light EL112 is reflected by the fifth mirror 36 and caused to travel toward the surface of the workpiece W to form an irradiation area RA5 at the second position P2. As a result, the processing optical system 15F forms an overlapping area OA8 on the surface of the workpiece W by overlapping the interference area IA6 and the irradiation area RA4 at the first position P1, and forms an overlapping area OA9 on the surface of the workpiece W by overlapping the interference area IA7 and the irradiation area RA5 at the second position P2. In the processing optical system 15F, the light and dark phase of the interference fringes IS in the interference area IA6 is made to coincide with the light and dark phase of the interference fringes IS in the interference area IA7.

[0171] As a result, the processing optical system 15F can irradiate the entire processing area PA on the surface of the workpiece W with interference fringes IS in a state where the first processing light EL111 or the first processing light EL112 is superimposed. The processing optical system 15F sets the fluence of the first processing light EL111 and the first processing light EL112 so that the minimum fluence of the processing light in the overlapping areas OA8 and OA9 is sufficient to process the workpiece W. This allows the processing optical system 15F to form a riblet structure RB with an ideal shape on the surface of the workpiece W in the processing area PA. Furthermore, by moving the stage 13, the processing optical system 15F can set any position on the surface of the workpiece W as the processing area PA, and can form a riblet structure RB with an ideal shape at any position on the surface of the workpiece W. At this time, the machining optical system 15F aligns the light and dark phases of the interference fringes IS in the overlapping areas OA8 and OA9, so that similar riblet structures RB can be formed in both the overlapping areas OA8 and OA9. Therefore, by moving the machining optical system 15F in the direction in which the light and dark areas extend relative to the workpiece W, the riblet structure RB can be formed more efficiently at any position on the surface of the workpiece W.

[0172] In the processing optical system 15F, the upstream optical system of the second optical system 17F outputs the second processing light EL221, which is linearly polarized in the first polarization direction, and the second processing light EL222, which is linearly polarized in the second polarization direction, from the first polarizing beam splitter 44 so that at least one of the exit angles and exit positions differs. In this case, the processing optical system 15F splits the second processing light EL2 into the second processing light EL221 in the first polarization direction and the second processing light EL222 in the second polarization direction using the first polarizing beam splitter 44. Therefore, since the processing optical system 15F splits the second processing light EL2 using the first polarizing beam splitter 44, the loss of light during splitting can be significantly reduced.

[0173] Additionally, in the processing optical system 15F, the first polarization splitting surface 44a of the first polarizing beam splitter 44 and the second polarization splitting surface 45c of the second polarizing beam splitter 45 are rotated about a central axis extending in the Y-axis direction, so that the second polarization splitting surface 45c can split each of the second processing light EL221 and the second processing light EL222, which have been split into p-polarized and s-polarized components on the first polarization splitting surface 44a, into p-polarized and s-polarized components on the second polarization splitting surface 45c. In the machining optical system 15F, the second polarization splitting surface 45c of the second polarizing beam splitter 45 splits the second processing light EL221 of the first polarization direction into the second processing light EL221 of the third polarization direction and the second processing light EL221 of the fourth polarization direction, and splits the second polarization direction into the second processing light EL222 of the third polarization direction and the second processing light EL222 of the fourth polarization direction. In the machining optical system 15F, the second processing light EL221 of the third polarization direction and the second processing light EL222 of the third polarization direction that have passed through the first polarization splitting surface 44a pass through the first lens 46 and the second lens 47 and proceed to the first position P1 on the surface of the workpiece W. In addition, in the machining optical system 15F, a reflecting surface 45d is provided in the reflecting direction of the second polarization splitting surface 45c of the second polarizing beam splitter 45. In the processing optical system 15F, the second processing light EL221 and the second processing light EL222 having the fourth polarization direction reflected by the reflecting surface 45d pass through the first lens 46 and the second lens 47 and proceed to the second position P2 on the surface of the workpiece W. In this way, the processing optical system 15F can align the polarization directions of the second processing light EL221 and the second processing light EL222 by passing them through the second polarization splitting surface 45c and reflecting them at the second polarization splitting surface 45c. As a result, the processing optical system 15F can use the second polarizing beam splitter 45 to make the polarization directions of the second processing light EL221 and the second processing light EL222, which cannot interfere due to their different polarization directions, interfere with each other. Then, the processing optical system 15F forms interference fringes IS using the second processing light EL221 and second processing light EL222 in the third polarization direction that have passed through it, and also forms interference fringes IS using the second processing light EL221 and second processing light EL222 in the fourth polarization direction that have been reflected.Therefore, the processing optical system 15F can form the interference fringes IS by efficiently utilizing the second processing light EL2 emitted toward the second optical system 17F.

[0174] Although the above-described processing optical system 15F forms interference fringes IS of a single frequency, one or more n-th frequency waveforms Wn may be superimposed on the fundamental frequency waveform Wb, as in the processing optical systems 15A, 15C, and 15E. In this case, the processing optical system 15F may be provided with, for example, an optical deflection member 28 in the second optical system 17F, similar to the second optical system 17 of the processing optical system 15A, which can be disposed in or removed from the optical path between the first mirror 27 and the second mirror 29.

[0175] (2-8) Modified Machining Optical System 15G Next, we will explain a machining optical system 15G, which is a modified example of the above-described machining optical system 15. This machining optical system 15G has the same basic concept and configuration as the above-described machining optical system 15A, so the same reference numerals are used for parts with the same configuration and detailed description will be omitted.

[0176] 24, the processing optical system 15G differs from the processing optical system 15A in that it does not include a galvanometer mirror 21 and a collimator lens 22. Therefore, the first optical system 16G splits the processing light EL0 from the processing light source 2 into a first processing light EL1 and a second processing light EL2 using a beam splitter 23. Specifically, the beam splitter 23 generates the first processing light EL1 that travels to the third optical system 18G by passing a portion of the processing light EL0, and generates the second processing light EL2 that travels to the second optical system 17G by reflecting another portion of the processing light EL0.

[0177] Furthermore, in the processing optical system 15G, the second optical system 17G, into which the second processing light EL2 from the first optical system 16G is incident, has a configuration different from the second optical system 17 of the processing optical system 15A. This second optical system 17G includes a beam splitter 51, a mirror 52, and a mirror 53. The beam splitter 51 is a light-splitting component that receives the second processing light EL2 from the first optical system 16G and splits the second processing light EL2 into multiple second processing light beams EL22. The beam splitter 51 splits the second processing light EL2 to generate multiple second processing light beams EL2. For convenience of explanation, the following description will be given of an example in which the beam splitter 51 splits the second processing light EL22 into two second processing light beams EL22 (when individually indicated, one is referred to as the second processing light EL221 and the other is referred to as the second processing light EL222).

[0178] The beam splitter 51 may be an amplitude-division type beam splitter. In this case, a portion of the second processing light EL2 passes through the beam splitter 51 as the second processing light EL221. Meanwhile, another portion of the second processing light EL2 is reflected by the beam splitter 51 as the second processing light EL222. Note that the beam splitter 51 is not limited to an amplitude-division type beam splitter and may be a polarizing beam splitter. In this case, a polarization control member such as a wavelength plate may be disposed in one or more of the optical paths of the multiple processing light beams split by the polarizing beam splitter.

[0179] The second processing light EL221 that passes through the beam splitter 51 is incident on the mirror 52. The mirror 52 reflects the second processing light EL221 toward the workpiece W. The mirror 52 reflects the second processing light EL221 so that the second processing light EL221 is incident on the workpiece W at a predetermined incident angle θ.

[0180] The second processing light EL222 reflected by the beam splitter 51 is incident on the mirror 53. The mirror 53 reflects the second processing light EL222 toward the workpiece W. The mirror 53 reflects the second processing light EL221 so that the second processing light EL222 is incident on the workpiece W at an incident angle θ from a different direction than the second processing light EL221.

[0181] The second processing light EL221 reflected by the mirror 52 and the second processing light EL222 reflected by the mirror 53 are irradiated onto an interference area IA8 set on the workpiece W. The second optical system 17G sets the interference area IA8 to a predetermined size in the X-axis direction and the Y-axis direction. As a result, within the interference area IA8, interference light generated by interference between the second processing light EL221 and the second processing light EL222 forms interference fringes IS.

[0182] The third optical system 18G of the processing optical system 15G differs from the third optical system 18 of the processing optical system 15A in that it does not have a fourth mirror 34 or a fourth cylindrical lens 35, but only a fifth mirror 36. In the third optical system 18G, the first processing light EL1 from the first optical system 16G, i.e., the beam splitter 23, is reflected by the fifth mirror 36 and propagates toward the surface of the workpiece W as the first processing light EL11. The third optical system 18G converts the first processing light EL11 directed toward the surface of the workpiece W into light of a predetermined size in the X-axis and Y-axis directions. The area irradiated with the first processing light EL11 is referred to as an irradiation area RA6.

[0183] Next, the operation of the processing optical system 15G will be described. First, when the processing light source 2 emits the processing light EL0, the first optical system 16G splits the light into the first processing light EL1 and the second processing light EL2 by the beam splitter 23. Then, the first processing light EL1 travels to the third optical system 18G, and the second processing light EL2 travels to the second optical system 17G.

[0184] The second optical system 17G splits the second processing light EL2 from the first optical system 16G into second processing light EL221 and second processing light EL222 using a beam splitter 51, and reflects them onto the surface of the workpiece W using mirrors 52 and 53. As a result, the second optical system 17G forms an interference area IA8 of interference fringes IS on the surface of the workpiece W. The third optical system 18G reflects the first processing light EL1 from the first optical system 16G using a fifth mirror 36, and irradiates the first processing light EL11 of a predetermined size in the X-axis and Y-axis directions so that it is superimposed on the interference area IA8 formed on the surface of the workpiece W, thereby forming an irradiation area RA6.

[0185] As a result, the processing optical system 15G forms an overlapping area OA10 on the surface of the workpiece W by overlapping the interference area IA8 and the irradiation area RA6. Therefore, the overlapping area OA10 becomes the processing area PA. This allows the processing optical system 15G to irradiate the entire processing area PA on the surface of the workpiece W with the interference fringes IS superimposed on the first processing light EL11. The processing optical system 15G sets the fluence of the first processing light EL111 so that the minimum fluence of the processing light in the overlapping area OA10 is sufficient to process the workpiece W. Therefore, the processing optical system 15G can form an ideally shaped riblet structure RB on the surface of the workpiece W in the processing area PA. By moving the stage 13, the processing optical system 15G can set any position on the surface of the workpiece W as the processing area PA, and can form an ideally shaped riblet structure RB at any position on the surface of the workpiece W.

[0186] Although the above-described machining optical system 15G forms interference fringes IS of a single frequency, one or more n-th frequency waveforms Wn may be superimposed on the fundamental frequency waveform Wb, as in the machining optical systems 15A, 15C, and 15E. In this case, the machining optical system 15G may be configured, for example, so that the angle of at least one of the mirrors 52 and 53 can be changed, or a light-refracting optical element can be disposed in or removed from the optical path from the first mirror 27 or the second mirror 29 to the surface of the workpiece W. Furthermore, in the machining optical system 15G, the optical path along which the second processing beams EL221 and EL222 travel toward the workpiece W and the optical path along which the first processing beam EL11 travels toward the workpiece W are located on the same plane, but the optical path along which the first processing beam EL11 travels toward the workpiece W does not have to be located on the same plane as the optical path of the second processing beams EL221 and EL222.

[0187] (2-9) Modified Machining Optical System 15H Next, we will explain a machining optical system 15H, which is a modified example of the above-described machining optical system 15. This machining optical system 15H has the same basic concept and configuration as the above-described machining optical system 15A, so the same reference numerals are used for parts with the same configuration and detailed description will be omitted.

[0188] As shown in FIG. 25 , the processing optical system 15H differs from the processing optical system 15A in that it does not include a galvanometer mirror 21 and a collimator lens 22. Therefore, the first optical system 16H of the processing optical system 15H splits the processing light EL0 from the processing light source 2 into the first processing light EL1 and the second processing light EL2 using a beam splitter 23. Specifically, the beam splitter 23 generates the first processing light EL1 that travels toward the third optical system 18H by passing a portion of the processing light EL0, and generates the second processing light EL2 that travels toward the second optical system 17H by reflecting another portion of the processing light EL0. In this example, the beam splitter 23 causes the second processing light EL2 generated by passing the beam splitter 23 to travel parallel to the Y-axis direction.

[0189] Furthermore, in the processing optical system 15H, the second optical system 17H, into which the second processing light EL2 from the first optical system 16H is incident, has a configuration different from the second optical system 17 of the processing optical system 15A. This second optical system 17H includes a beam splitter 55, an optical deflector 56, a first mirror 57, and a second mirror 58. The beam splitter 55 is a light dividing member that receives the second processing light EL2 from the first optical system 16H and divides the second processing light EL2 into multiple second processing light beams EL22. The beam splitter 55 divides the second processing light EL2, which has been converted into linear light extending in the X-axis direction by the first cylindrical lens 24, into multiple second processing light beams EL22. Therefore, the beam splitter 55 functions as a light dividing member that divides the second processing light EL2 into multiple second processing light beams EL22. In the following description, for convenience of explanation, an example will be described in which the beam splitter 55 splits the second processing light EL2 into two second processing light EL22 (when shown individually, one will be referred to as the second processing light EL221 and the other as the second processing light EL222). The beam splitter 55 also has the function of merging the two split second processing light EL22 and causing both second processing light EL22 to proceed toward the workpiece W.

[0190] The beam splitter 55 is a rectangular plate-like member, tilted 45 degrees relative to the Y-axis around its central axis extending in the X-axis direction. The beam splitter 55 is composed of an amplitude-division beam splitter or a polarizing beam splitter. It generates the second processing light EL221 by reflecting a portion of the second processing light EL2 and generates the second processing light EL222 by passing another portion of the second processing light EL2. Because the beam splitter 55 is tilted 45 degrees relative to the Y-axis direction, the second processing light EL221 reflected by the beam splitter 55 travels parallel to the Z-axis direction toward the optical deflector 56, and the second processing light EL222 passed through another beam splitter 55 travels parallel to the Y-axis direction toward the second mirror 58.

[0191] The optical deflection member 56 is a member that changes (deflects) the traveling direction of light (second processing light EL221, second processing light EL222) traveling between the beam splitter 55 and the first mirror 57. The optical deflection member 56 is an optical member that has a shape that extends in the X-axis direction and has refractive power only in the Y-axis direction, and refracts the traveling direction of light to either the right or left side in the Y-axis direction in FIG. 25 between the beam splitter 55 and the first mirror 57. In this example, the optical deflection member 56 has a trapezoidal (wedge-shaped) shape in which the thickness (size in the Z-axis direction) is smallest on the right side in the Y-axis direction and the thickness increases toward the left side in the Y-axis direction in a cross section perpendicular to the X-axis direction. Therefore, compared to a state in which the optical deflection member 56 is not provided, the optical deflection member 56 refracts light from one of the beam splitter 55 and the first mirror 57 to the left in the Y-axis direction and directs it toward the other of the beam splitter 55 and the first mirror 57.

[0192] The first mirror 57 is a plate-shaped member and is disposed at a predetermined inclination with respect to the Z-axis direction around a central axis extending in the X-axis direction. This predetermined inclination is set so that the second processing light EL221 reflected by the beam splitter 55 and passing through the optical deflection member 56 is reflected toward the second mirror 58, and the second processing light EL222 reflected by the second mirror 58 is reflected toward the optical deflection member 56. The first mirror 57 reflects the second processing light EL221 from the optical deflection member 56 and causes it to proceed toward the second mirror 58. The first mirror 57 also reflects the second processing light EL222 from the second mirror 29 and causes it to proceed toward the optical deflection member 56.

[0193] The second mirror 58 is a plate-like member and is disposed with a predetermined inclination with respect to the Z-axis direction, centered on a central axis extending in the X-axis direction, that is different from that of the first mirror 57. This predetermined inclination that is different from that of the first mirror 57 is set so as to reflect the second processing light EL222 that has passed through the beam splitter 55 toward the first mirror 57, and to reflect the second processing light EL221 reflected by the first mirror 57 toward the beam splitter 55.

[0194] The beam splitter 55 reflects the second processing light EL221 reflected by the second mirror 58 and causes it to proceed toward the surface of the workpiece W, and also causes the second processing light EL222 reflected by the first mirror 57 and passing through the optical deflector 56 to pass through and proceed toward an interference area IA9 on the surface of the workpiece W. The second optical system 17H sets the interference area IA9 to a predetermined size in the X-axis direction and the Y-axis direction. As a result, within the interference area IA9, interference light generated by interference between the second processing light EL221 and the second processing light EL222 forms interference fringes IS.

[0195] The third optical system 18H of the processing optical system 15H differs from the third optical system 18 of the processing optical system 15A in that it does not have a fourth cylindrical lens 35 but has a fourth mirror 34 and a fifth mirror 36. In the third optical system 18H, the first processing light EL1 from the first optical system 16H, i.e., the beam splitter 23, is reflected by the fourth mirror 34 and then by the fifth mirror 36, and travels toward the surface of the workpiece W as the first processing light EL11. The third optical system 18H converts the first processing light EL11 directed toward the surface of the workpiece W into light of a predetermined size in the X-axis and Y-axis directions. The area irradiated with the first processing light EL11 is referred to as an irradiation area RA7.

[0196] Next, the operation of the processing optical system 15H will be described. First, when the processing light source 2 emits the processing light EL0, the first optical system 16H splits the light into the first processing light EL1 and the second processing light EL2 by the beam splitter 23. Then, the first processing light EL1 travels to the third optical system 18H, and the second processing light EL2 travels to the second optical system 17H.

[0197] The second optical system 17H causes the second processing light EL2 to travel to the beam splitter 55. A portion of the second processing light EL2 is reflected by the beam splitter 55 toward the optical deflection member 56 to become the second processing light EL221, and another portion passes through the beam splitter 55 to become the second processing light EL222 that travels toward the second mirror 58. The second processing light EL221 passes through the optical deflection member 56, is reflected by the first mirror 57, and then is reflected by the second mirror 58 to travel toward the beam splitter 55. The second processing light EL222 is reflected by the second mirror 58 and the first mirror 57, and then passes through the optical deflection member 56 to travel toward the beam splitter 55.

[0198] In the second optical system 17H, the second processing light EL221 reflected by the beam splitter 55, the first mirror 57, and the second mirror 58 travels to the beam splitter 55, and the second processing light EL222 passes through the beam splitter 55 and is reflected by the second mirror 58 and the first mirror 57, and travels to the beam splitter 55. Therefore, in the second optical system 17H, the second processing light EL221 and the second processing light EL222 basically travel in different rotational directions (clockwise and counterclockwise) from the beam splitter 55 and then return to the beam splitter 55. In the second optical system 17H, an optical deflection member 56 is provided between the beam splitter 55 and the first mirror 57.

[0199] Therefore, the second processing light EL221 reflected by the beam splitter 55 travels to a position shifted to the left on the first mirror 57 compared to when the optical deflection member 56 is not present, and by being reflected there, the second processing light EL221 travels to a position on the second mirror 58 and the beam splitter 55 that reflects the shift at the first mirror 57. Furthermore, the second processing light EL222 passing through the beam splitter 55 is reflected by the second mirror 58 and the first mirror 57, then enters the optical deflection member 56, and is refracted there, traveling toward a position shifted to the left on the beam splitter 55 compared to when the optical deflection member 56 is not present. In this way, the second optical system 17H has the optical deflection member 56 provided between the beam splitter 55 and the first mirror 57, so that the direction of the optical path along which the second processing light EL221 and the second processing light EL222 travel after being refracted by the optical deflection member 56 is biased. Therefore, in the second optical system 17H, the influence of refraction by the optical deflector 56 on the second processing beam EL221 and the second processing beam EL222 is different, i.e., the deviation caused by passing through the optical deflector 56 is different. As a result, in the second optical system 17H, the second processing beam EL221 and the second processing beam EL222 can be made to exit in different directions while passing through essentially the same optical path. Therefore, the second optical system 17H can be said to constitute a triangular Sagnac optical system.

[0200] The second optical system 17H reflects the second processing light EL221 by the beam splitter 55 and causes it to travel toward the surface of the workpiece W, and also causes the second processing light EL222 to pass through the beam splitter 55 and travel toward the surface of the workpiece W. The second optical system 17H focuses the second processing light EL221 and the second processing light EL222 on the surface of the workpiece W to form interference fringes IS and form an interference area IA9. The third optical system 18H reflects the first processing light EL1 from the first optical system 16H by the fourth mirror 34 and the fifth mirror 36, and irradiates the first processing light EL11 of a predetermined size in the X-axis and Y-axis directions so that it is superimposed on the interference area IA9 formed on the surface of the workpiece W, thereby forming an irradiation area RA7.

[0201] As a result, the processing optical system 15H forms an overlapping area OA11 on the surface of the workpiece W by overlapping the interference area IA9 and the irradiation area RA7. Therefore, the overlapping area OA11 becomes the processing area PA. This allows the processing optical system 15H to irradiate the entire processing area PA on the surface of the workpiece W with the interference fringes IS superimposed on the first processing light EL11. The processing optical system 15H sets the fluence of the first processing light EL111 so that the minimum fluence of the processing light in the overlapping area OA11 is sufficient to process the workpiece W. Therefore, the processing optical system 15H can form an ideally shaped riblet structure RB on the surface of the workpiece W in the processing area PA. By moving the stage 13, the processing optical system 15H can set any position on the surface of the workpiece W as the processing area PA, and can form an ideally shaped riblet structure RB at any position on the surface of the workpiece W.

[0202] Although the above-described processing optical system 15H forms interference fringes IS of a single frequency, one or more n-th frequency waveforms Wn may be superimposed on the fundamental frequency waveform Wb, as in the processing optical systems 15A, 15C, and 15E. In this case, the processing optical system 15H may be provided, for example, with a second optical system 17H that refracts the traveling direction of light in either direction of the Y-axis, similar to the optical deflection member 56, but has a different refraction angle from the optical deflection member 56, and is replaceable with the optical deflection member 56.

[0203] Therefore, the processing optical system 15, processing apparatus 1, and processing method according to the present disclosure can form a riblet structure with an ideal shape.

[0204] The above has described the processing optical system, processing apparatus, and processing method of the present disclosure based on each example, but the specific configuration is not limited to each of the above-mentioned examples 1, and design changes and additions are permitted as long as they do not deviate from the gist of the invention related to each claim in the scope of the claims.

[0205] In the above description, the processing apparatus 1 is provided with the head drive system 12. However, the processing apparatus 1 does not have to be provided with the head drive system 12. In other words, the processing head 11 does not have to be movable. Also, in the above description, the processing apparatus 1 is provided with the stage drive system 14. However, the processing apparatus 1 does not have to be provided with the stage drive system 14. In other words, the stage 13 does not have to be movable. Or, the processing apparatus 1 does not have to be provided with the stage 13 at all.

[0206] The above description has been given of an example in which the processing apparatus 1 forms riblet structures RB on a metallic workpiece W (a base material object), and an example in which the processing apparatus 1 forms riblet structures RB on a film coated on the surface of the workpiece W. However, the processing performed by the processing apparatus 1 is not limited to the above-described examples. For example, the processing apparatus 1 may form riblet structures RB on the surface of the workpiece W, and the surface of the workpiece W on which the riblet structures RB are formed may be coated with a film. For example, when the processing apparatus 1 forms riblet structures RB on a film coated on the surface of the workpiece W, the film on which the riblet structures RB are formed may be further coated with another film. In either example, the riblet structures RB may be coated with a film. In this case, the thickness of the film may be determined so that the film coated on the riblet structure RB does not reduce the function of the riblet structure RB. For example, if the riblet structures RB are buried in the film, the function of the riblet structure RB may be reduced by the film, so the thickness of the film may be determined so that the riblet structures RB are not buried in the film. The film may be formed along the shape of the riblet structure RB (for example, along the convex structure 81 or groove structure 82) so that the function of the riblet structure RB is not reduced by the film coated on the riblet structure RB.

[0207] In addition to or instead of the subtractive processing, the processing device 1 may perform additional processing, which adds a new structure to the workpiece W by irradiating the workpiece W with processing light EL. In this case, the processing device 1 may perform additional processing to form the above-mentioned riblet structure RB on the surface of the workpiece W. Alternatively, in addition to or instead of at least one of the subtractive processing and the additional processing, the processing device 1 may perform machining, which processes the workpiece W by bringing a tool into contact with the workpiece W. In this case, the processing device 1 may perform machining to form the above-mentioned riblet structure RB on the surface of the workpiece W.

[0208] In the above description, the machining system SYS forms a riblet structure RB that has the function of reducing the resistance of the surface of the workpiece W to the fluid. However, the machining system SYS may form a structure on the workpiece W that has a function different from the function of reducing the resistance of the surface of the workpiece W to the fluid. For example, the machining system SYS may form a riblet structure on the workpiece W to reduce noise generated when the fluid and the surface of the workpiece W move relative to each other. For example, the machining system SYS may form a riblet structure on the workpiece W that generates vortices in the flow of the fluid on the surface of the workpiece W. For example, the machining system SYS may form a structure on the workpiece W to impart hydrophobic properties to the surface of the workpiece W.

[0209] In the above description, the machining system SYS forms a riblet structure RB on the surface of the workpiece W. However, the machining system SYS may form any structure having any shape on the surface of the workpiece W. One example of the arbitrary structure is a structure that generates vortices in the flow of a fluid on the surface of the workpiece W. Another example of the arbitrary structure is a structure for imparting hydrophobicity to the surface of the workpiece W. Another example of the arbitrary structure is a regularly or irregularly formed micro- or nanometer-order fine texture structure (typically, an uneven structure including a mountain structure and a groove structure). The fine texture structure may include at least one of a shark skin structure and a dimple structure that have the function of reducing resistance due to a fluid (gas and / or liquid). The fine texture structure may also include a lotus leaf surface structure that has at least one of a liquid-repellent function and a self-cleaning function (e.g., has the lotus effect). The fine texture structure may include at least one of a micro-protrusion structure having a liquid transport function (see U.S. Patent Publication No. 2017 / 0044002), a concave-convex structure having a lyophilic function, a convex-convex structure having an antifouling function, a moth-eye structure having at least one of a reflectance reducing function and a liquid repellent function, a convex-convex structure that exhibits a structural color by intensifying only light of a specific wavelength through interference, a pillar array structure having an adhesive function utilizing van der Waals forces, a convex-convex structure having an aerodynamic noise reducing function, a honeycomb structure having a droplet collecting function, a convex-convex structure that improves adhesion with a layer formed on the surface, a convex-convex structure for reducing frictional resistance, etc. Even in this case, the convex structures constituting the concave-convex structure may have a structure similar to the convex structures 81 constituting the riblet structure RB described above. The groove structure constituting the concave-convex structure may have a structure similar to the groove structure 82 constituting the riblet structure RB described above. Note that the fine texture structure does not necessarily have a specific function.

[0210] In the above description, the processing system SYS forms the riblet structure RB on the surface of the workpiece W. However, the processing system SYS may also form a mold for transferring the riblet structure RB to the surface of the workpiece W. In this case, the workpiece W may be the surface of a movable body, or may be a film that can be attached to a movable body.

[0211] In the above description, the processing system SYS processes the workpiece W by irradiating the workpiece W with processing light EL. However, the processing system SYS may also process the workpiece W by irradiating the workpiece W with any energy beam other than light. In this case, the processing system SYS may be equipped with a beam irradiation device capable of irradiating any energy beam in addition to or instead of the processing light source 2. Examples of any energy beam include at least one of a charged particle beam and an electromagnetic wave. Examples of a charged particle beam include at least one of an electron beam and an ion beam.

[0212] In the above description, the machining system SYS has a single galvanometer mirror 21 as an interference fringe moving member provided before and after the first optical system 16 (16A, 16C) in the first four machining optical systems 15 (15A to 15D). However, the interference fringe moving member may have any other configuration as long as it moves the position of the interference area IA (interference fringe IS) formed by the second optical system 17 (17A to 17D) in a direction perpendicular to the optical axis of the second optical system 17, and is not limited to the above example. Furthermore, although a single galvanometer mirror 21 as an interference fringe moving member is provided before and after the first optical system 16 (16A, 16C), multiple galvanometer mirrors 21 may be provided on the optical path from the machining light source 2 to the workpiece W via the second optical system 17, or multiple galvanometer mirrors may be provided on the optical path from the machining light source 2 to the workpiece W via the third optical system 18, and are not limited to the above example. As an example, in the machining optical system 15A, another galvanometer mirror may be provided in addition to the galvanometer mirror 21. In such an example, a reimaging optical system can be disposed between the special beam splitter 25 and the lens 33 in the second optical system 17 of the processing optical system 15A, and a galvanometer mirror can be provided between the reimaging optical system and the lens 33 at a position that is approximately conjugate with the special beam splitter 25. In this case, the galvanometer mirror between the reimaging optical system and the lens 33 and the galvanometer mirror 21 function as an interference fringe moving member. In this case, a galvanometer mirror can also be provided in the optical path from the processing light source 2 to the workpiece W via the third optical system 18, if necessary.

[0213] In the above description, the machining system SYS has been shown to have an example of multiple second optical systems 17 (17A to 17H) as the machining optical systems 15 (15A to 15H). However, the second optical system 17 may have other configurations as long as it splits the second machining light EL2 from the first optical system 16 to form multiple second machining light beams EL22 that irradiate the workpiece W from different incident directions to form interference fringes IS. Other examples of the second optical system 17 include a system that splits the second machining light EL2 from the first optical system 16 using a diffractive optical element (DOE) or an optical mask (which partially obstructs the propagation of light) to form multiple second machining light beams EL22 traveling in different directions.

Claims

1. A first optical system that splits processing light from a light source into a first processing light and a second processing light; a second optical system that splits the second processing light into a plurality of second processing lights and irradiates the plurality of split second processing lights onto an object from different incident directions, thereby forming interference fringes on a surface of the object; a third optical system that irradiates the first processing light from the first optical system toward an interference region on the surface of the object where the interference fringes are formed; The processing optical system includes:

2. The third optical system irradiates the object with the plurality of second processing beams and the first processing beam simultaneously. The processing optical system according to claim 1 .

3. By simultaneously irradiating the object with the plurality of second processing lights and the first processing light, at least a minimum fluence in a dark portion of the interference fringes formed on the surface of the object is set to a fluence capable of removing the surface of the object. The processing optical system according to claim 2 .

4. The second optical system forms a first interference fringe on the surface of the object by using at least two of the divided second processing lights, and forms a second interference fringe different from the first interference fringe on the surface of the object by using at least two second processing lights different from the at least two second processing lights.

3. The processing optical system according to claim 1 or 2.

5. The interference region on the surface of the object where the interference fringes are formed includes a first region where the first interference fringes are formed and a second region where the second interference fringes are formed. The processing optical system according to claim 4 .

6. The second optical system is a light splitting member that splits the second processing light into the plurality of second processing lights; a first optical member into which one of the second processing beams split by the beam splitter is incident; a second optical member into which another second processing light different from the one second processing light among the plurality of second processing light split by the light splitting member is incident, Directing the one second processing light from the first optical member to the light dividing member via the second optical member and directing the other second processing light from the second optical member to the light dividing member via the first optical member.

3. The processing optical system according to claim 1 or 2.

7. The first processing light is irradiated onto the surface of the object without passing through the second optical system.

3. The processing optical system according to claim 1 or 2.

8. The second optical system has a light splitting member that splits the second processing light into the plurality of second processing lights, and adjusts at least one of the amplitude and the period of the interference fringes by changing the incidence angle of the plurality of second processing lights that pass through the first and second optical members and are incident on the light splitting member.

3. The processing optical system according to claim 1 or 2.

9. The second optical system forms, on the surface of the object, a first interference fringe and a second interference fringe that is different from the first interference fringe in at least one of an amplitude and a period.

3. The processing optical system according to claim 1 or 2.

10. A first period during which the first interference fringes are formed by the second optical system and a second period during which the second interference fringes are formed by the second optical system at least partially overlap each other. The processing optical system according to claim 9.

11. A first period during which the first interference fringes are formed by the second optical system and a second period during which the second interference fringes are formed by the second optical system do not overlap. The processing optical system according to claim 9.

12. The first and second interference fringes are at least two of a plurality of types of interference fringes obtained by Fourier transforming an ideal waveform for obtaining a riblet structure to be formed. The processing optical system according to claim 11.

13. The second optical system is capable of adjusting at least one of the amplitude and the period of the interference fringes.

3. The processing optical system according to claim 1 or 2.

14. The second optical system forms the interference fringes in at least a part of an interference region within a processing region on the surface of the object, The third optical system increases an integrated value of the light fluence irradiated to at least a part of the processing area.

3. The processing optical system according to claim 1 or 2.

15. At least a part of the interference region formed by the second optical system and an irradiation region in which the first processing light is irradiated onto the surface of the object by the third optical system overlap with each other in an overlap region on the surface of the object, The surface of the object is processed while changing a positional relationship between the processing area and the overlapping area. The processing optical system according to claim 14.

16. The optical fiber further includes an interference fringe moving member that moves the position of the interference region relative to the second optical system in a direction intersecting with the optical axis of the second optical system. The processing optical system according to claim 15.

17. The interference fringe moving member moves the irradiation area, where the first processing light is irradiated on the surface of the object, in the intersecting direction. The processing optical system according to claim 16.

18. The interference fringe moving member includes a scanning mirror that reflects light from the light source, The position of the interference area is moved in a direction intersecting with the optical axis of the second optical system by changing the reflection direction of the scanning mirror. The processing optical system according to claim 16.

19. The interference fringe moving member is disposed in an optical path between the light source and the first optical system. The processing optical system according to claim 16.

20. The interference fringe moving member is disposed in an optical path between the first optical system and the second optical system. The processing optical system according to claim 16.

21. The position of the interference region is changed within an irradiation region in which the first processing light is irradiated onto the surface of the object by the third optical system.

3. The processing optical system according to claim 1 or 2.

22. The interference region is formed at a fixed position relative to an irradiation region where the first processing light is irradiated onto the surface of the object by the third optical system.

3. The processing optical system according to claim 1 or 2.

23. The second optical system changes at least one of the amplitude and the period of the interference fringes formed on the surface of the object.

3. The processing optical system according to claim 1 or 2.

24. The second optical system changes at least one of the amplitude and the period of the interference fringes formed on the surface of the object.

3. The processing optical system according to claim 1 or 2.

25. The second optical system is an upstream optical system including a first polarizing beam splitter that splits the second processing light into a first polarized second processing light and a second polarized second processing light having different polarization directions, and that outputs the first polarized second processing light and the second polarized second processing light so that at least one of an output angle and an output position is different from each other; a downstream optical system including a second polarizing beam splitter that splits the first polarized second processing light into a third polarized second processing light and a fourth polarized second processing light having different polarization directions, and splits the second polarized second processing light into the third polarized second processing light and the fourth polarized second processing light, and that irradiates the third polarized second processing light generated by the first polarized second processing light and the third polarized second processing light generated by the second polarized second processing light at a first position on the surface of the object to form a first interference fringe, and that irradiates the fourth polarized second processing light generated by the first polarized second processing light and the fourth polarized second processing light generated by the second polarized second processing light at a second position on the surface of the object that is different from the first position to form a second interference fringe.

3. The processing optical system according to claim 1 or 2.

26. The processing light from the light source includes pulsed light having a pulse width of nanoseconds or less.

3. The processing optical system according to claim 1 or 2.

27. The interference region on the surface of the object where the interference fringes are formed is ablated.

3. The processing optical system according to claim 1 or 2.

28. The second optical system diffracts the second processing light to generate the plurality of second processing lights.

3. The processing optical system according to claim 1 or 2.

29. an interference fringe forming optical system for dividing the second processing light into a plurality of second processing lights, the first and second processing lights being pulsed lights whose light emission periods overlap each other at least partially, and irradiating the object with the divided plurality of second processing lights from different incident directions, thereby forming interference fringes on the surface of the object; an irradiation optical system that irradiates the first processing light toward an interference region where the interference fringes are formed; The processing optical system includes:

30. The processing apparatus further includes a branching optical system that branches the processing light from a light source into the first processing light and the second processing light. The processing optical system according to claim 29.

31. A processing device that performs riblet processing on a surface of an object using light from a light source, A processing optical system according to claim 1, claim 2, claim 29 or claim 30; a positional relationship changing device that changes a positional relationship between the interference fringes formed on the surface of the object by the processing optical system and the surface of the object; A processing device comprising:

32. The positional relationship changing device changes the positional relationship in a direction intersecting a fringe pitch direction of the interference fringes.

32. The processing device according to claim 31.

33. A processing method for performing riblet processing on a surface of an object using light from a light source, Splitting a processing light from the light source into a first processing light and a second processing light; Dividing the second processing light into a plurality of second processing lights, and irradiating the object with the divided plurality of second processing lights from different incident directions, thereby forming interference fringes on the surface of the object; Irradiating the first processing light toward an interference region on the surface of the object where the interference fringes are formed; A processing method comprising the steps of:

34. The irradiating step includes simultaneously irradiating the object with the plurality of second processing lights and the first processing light, thereby setting at least a minimum fluence in a dark portion of the interference fringes formed on the surface of the object to a fluence capable of removing the surface of the object. The processing method according to claim 33.

35. Forming the interference fringes includes: forming a first interference fringe on the surface of the object using at least two of the divided second processing lights; and forming a second interference fringe different from the first interference fringe on the surface of the object using at least two second processing lights different from the at least two second processing lights. The processing method according to claim 33.

36. The interference region in which the interference fringes on the surface of the object are formed includes a first region in which the first interference fringes are formed and a second region in which the second interference fringes are formed. The processing method according to claim 35.