A dispersion compensation method for an acousto-optic deflector based on a dispersion prism group

Abstract

The present invention belongs to the field of laser-related technologies and specifically relates to a method for compensating for dispersion in an acousto-optic deflector based on a dispersive prism assembly. The method comprises: configuring a dispersive prism assembly; constraining the monochromatic laser beam spot emitted from the prism assembly to be circular, calculating the incident angles of the laser beam incident on a first dispersive prism and a second dispersive prism when the negative spatial dispersion generated by the prism assembly is equal to or greater than the positive spatial dispersion of the acousto-optic deflector to be compensated; constraining the incident angles of the laser beam incident on the first and second dispersive prisms and the laser beam emitted from the prism assembly to be perpendicular to the receiving surface of the acousto-optic deflector, determining and adjusting the relative spatial position between the two prisms to achieve spatial dispersion compensation; and calculating and adjusting the distance between the center of the dispersive prism assembly and the center of the acousto-optic deflector when the negative temporal dispersion generated by the prism assembly is equal to or greater than the positive temporal dispersion of the acousto-optic deflector to achieve temporal dispersion compensation. The method of the present invention has a wide range of applications for compensating for spatiotemporal dispersion.

Description

Technical Field

[0001] The present invention belongs to the field of laser-related technologies, and more specifically, relates to a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group. Background Art

[0002] The acousto-optic deflector (AOD), an inertia-free, high-speed scanning device, combined with a femtosecond laser, enables high-precision beam control with high accuracy, high speed, and flexible scanning methods, playing a significant role in precision machining, microscopic imaging, semiconductor defect detection, and other fields. However, due to the spectral bandwidth of femtosecond lasers, the inherent material dispersion and diffraction-deflected beam of the AOD will cause spatiotemporal dispersion in the scanning femtosecond laser, resulting in temporal broadening of the laser pulse and a decrease in spatial beam quality. Therefore, it is necessary to effectively compensate for this introduced spatiotemporal dispersion.

[0003] At present, the main compensation schemes for AOD spatiotemporal dispersion include the monochromatic dispersion prism method, the grating method and the acousto-optic modulator (AOM) method.

[0004] The monochromatic dispersion prism method places a monochromatic dispersion prism in front of the AOD to provide spatial dispersion pre-compensation. Simultaneously, the monochromatic dispersion prism and AOD form a pulse compressor, providing temporal dispersion pre-compensation. The advantages of the monochromatic dispersion prism method lie in its high light transmission efficiency and relatively low cost compared to other solutions. However, its disadvantage lies in the inherent structure of the dispersion prism, which causes spatial distortion of the light spot, potentially resulting in an elliptical output. This elliptical distortion alters the laser processing shape and reduces processing accuracy. Even with the introduction of a lens assembly or a custom dispersion prism to suppress spatial distortion, the application remains limited and the cost increases.

[0005] The grating method fixes a grating before the AOD to provide spatial dispersion pre-compensation. Simultaneously, the grating and AOD form a pulse compressor, providing temporal dispersion pre-compensation. The advantage of the grating method is that it lacks spatial distortion. However, the disadvantages are the high cost and customization of the grating. Even with the introduction of a mirror assembly to adjust the dispersion provided by the grating, the application scope is limited and the cost is high.

[0006] The AOM method places the AOM and AOD opposite each other, placing them in front of the AOD to provide spatial dispersion pre-compensation. Simultaneously, the AOM and AOD form a pulse compressor to provide temporal dispersion pre-compensation. The advantage of the AOM method lies in its ease of operation. However, its disadvantages include its limited applicability, the long distance between the AOM and AOD to compensate for the positive temporal dispersion introduced by the AOM, and the resulting large space required and the difficulty of optical path adjustment.

[0007] In summary, the monochromatic prism method, grating method and AOM method currently used for AOD dispersion compensation all have certain defects. Therefore, it is necessary to overcome the many technical difficulties in the existing compensation technology and research more convenient and more applicable compensation technology. Summary of the Invention

[0008] In response to the above defects or improvement needs of the prior art, the present invention provides a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, which aims to solve the problems of limited application range and high customization cost of dispersion compensation devices.

[0009] To achieve the above objectives, according to one aspect of the present invention, a method for compensating dispersion of an acousto-optic deflector based on a dispersive prism group is provided, comprising:

[0010] A dispersion prism group and a rotating stage group are provided; the rotating stage group includes a first rotating stage and a second rotating stage; the dispersion prism group includes a first dispersion prism disposed on the first rotating stage and a second dispersion prism disposed on the second rotating stage; the second dispersion prism is located on a vertical incident path of a laser beam of an acousto-optic deflector to be compensated; the laser beam first passes through the first dispersion prism and then passes through the second dispersion prism;

[0011] The method is based on the following steps: constraining the spot of the monochromatic laser beam emitted from the dispersion prism group to be circular, calculating the incident angles of the laser beam incident on the first dispersion prism and the second dispersion prism when the negative spatial dispersion generated by the dispersion prism group is equal to and opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; constraining the incident angles of the laser beam incident on the first dispersion prism and the second dispersion prism and the vertical incidence of the laser beam emitted from the dispersion prism group on the receiving surface of the acousto-optic deflector to be compensated, determining and adjusting the relative spatial position between the two prisms; controlling the laser beam to be incident on the dispersion prism group parallel to the surface of the first rotating stage, and rotating the rotating stage group to fine-tune the incident angles of the first dispersion prism and the second dispersion prism to the calculated incident angles, thereby achieving spatial dispersion compensation;

[0012] The spatial positions of the two prisms are adjusted so that the laser beam is transmitted near the edge area of ​​each dispersion prism. The distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is calculated and adjusted when the negative temporal dispersion generated by the dispersion prism group is equal to or opposite to the positive temporal dispersion of the acousto-optic deflector to be compensated, thereby achieving temporal dispersion compensation.

[0013] Furthermore, when performing temporal dispersion compensation, the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is also fine-tuned to compensate for the temporal dispersion additionally introduced by the dispersion prism group.

[0014] Furthermore, the configuration is implemented as follows:

[0015] The first rotating table is placed vertically, that is, the normal of its table surface is parallel to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table surface of the first rotating table; the second rotating table is placed horizontally, that is, the normal of its table surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table.

[0016] Furthermore, the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0017] The incident angle of the laser beam incident on the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0018] Furthermore, the negative spatial dispersion generated by the dispersion prism group is:

[0019]

[0020] Where, represents the negative spatial dispersion, the value of which is opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; Represents the spatial dispersion produced by a single dispersion prism;

[0021] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass The incident angle of the laser beam incident on the dispersion prism group is obtained, that is, the incident angle of the laser beam incident on the first dispersion prism.

[0022] Furthermore, the acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units, and the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor. The negative temporal dispersion GDD generated by the pulse compressor is:

[0023]

[0024] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the sound field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and is the inverse of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0025] Furthermore, the configuration is as follows:

[0026] The first rotating platform is placed horizontally, i.e., the normal line of the platform surface is perpendicular to the horizontal plane, and a triangular face of the first dispersion prism is attached to the platform surface of the first rotating platform; the second rotating platform is placed horizontally, i.e., the normal line of the platform surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating platform;

[0027] The entire rotating stage assembly is rotated upward by 45° with the central axis of the laser beam perpendicularly incident from the second dispersion prism to the acousto-optic deflector as the rotation axis.

[0028] Furthermore, the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0029] The exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0030] Furthermore, the negative spatial dispersion generated by the dispersion prism group is:

[0031]

[0032] Where, represents the negative spatial dispersion, the value of which is opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; represents the spatial dispersion produced by a single dispersion prism, with subscripts 1 and 2 representing the first dispersion prism and the second dispersion prism, respectively; M represents the magnification of the first dispersion prism;

[0033] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass Obtaining the incident angle of the laser beam incident on the second dispersion prism;

[0034] According to the fact that the exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism, based on the The obtained incident angle value of the laser beam incident on the second dispersion prism is used to calculate the incident angle value of the laser beam incident on the first dispersion prism.

[0035] Furthermore, the acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units, and the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor. The negative temporal dispersion GDD generated by the pulse compressor is:

[0036]

[0037] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the sound field frequency of the AOD scanned in the vertical direction, fx is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and is the inverse of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0038] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0039] 1. The present invention proposes a dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, which uses a double prism to compensate for the spatiotemporal dispersion of the acousto-optic deflector. Prisms are less expensive than other dispersion compensation devices, which controls the system cost. By rotating the dispersion prism group to adjust the incident angle of the light beam, the spatial dispersion of the acousto-optic deflector is compensated while ensuring that the output light beam of the acousto-optic deflector is parallel. There is no need to customize prisms of specific materials and angles, which controls the system cost. In addition, since this solution adopts a prism group solution, the spatial dispersion compensation amount can be continuously adjusted while the light spot does not undergo spatial distortion due to the prism, the adjustment is flexible, and the scope of application is wide. By changing the spacing between the prism group and the acousto-optic deflector, the temporal dispersion of the acousto-optic deflector is compensated. Therefore, the present invention solves the problems of limited application range and high customization cost of dispersion compensation devices.

[0040] 2. During temporal dispersion compensation, the present invention also fine-tunes the distance between the center of the dispersive prism assembly and the center of the acousto-optic deflector to be compensated to compensate for the additional temporal dispersion introduced by the dispersive prism assembly. Because the prism assembly introduces a small amount of additional temporal dispersion, fine-tuning this distance simultaneously compensates for both the temporal dispersion of the acousto-optic deflector itself and the additional temporal dispersion introduced by the prism assembly. This approach addresses the limited applicability and high customization costs of dispersion compensation devices while ensuring compensation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flowchart of a method for compensating for dispersion of an acousto-optic deflector based on a dispersion prism group provided by an embodiment of the present invention;

[0042] Figure 2 Schematic diagram of the principle of compensating for dispersion of an acousto-optic deflector using a prism assembly provided by an embodiment of the present invention;

[0043] Figure 3 Schematic diagram of an orthogonal prism group and a cascaded prism group provided in an embodiment of the present invention respectively shaping monochromatic light;

[0044] Figure 4 is a schematic diagram of a prism structure provided by an embodiment of the present invention;

[0045] Figure 5Schematic diagram of spatial dispersion of a single prism provided by an embodiment of the present invention;

[0046] Figure 6 Schematic diagram of spatial dispersion introduced by the acousto-optic medium in a single acousto-optic deflector unit provided by an embodiment of the present invention;

[0047] Figure 7 Schematic diagram of temporal dispersion introduced by an acousto-optic medium in a single acousto-optic deflector unit provided by an embodiment of the present invention;

[0048] Figure 8 Schematic diagram of an orthogonal prism group provided by an embodiment of the present invention compensating for spatiotemporal dispersion of an acousto-optic deflector;

[0049] Figure 9 is a graph showing the relationship between the spatial dispersion of the orthogonal prism set provided by an embodiment of the present invention and the incident angle of the femtosecond laser relative to the first dispersion prism;

[0050] Figure 10 Schematic diagram of a cascaded prism group provided by an embodiment of the present invention for compensating for spatiotemporal dispersion of an acousto-optic deflector;

[0051] Figure 11 4 is a graph showing the relationship between the spatial dispersion of the cascaded prism group provided by an embodiment of the present invention and the incident angle of the femtosecond laser relative to the second dispersion prism.

[0052] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0053] 1 is a prism group, 1.1 is a first dispersion prism, 1.2 is a second dispersion prism, 2 is an acousto-optic deflector, 2.1 and 2.2 are two acousto-optic deflector units, 3 is a rotating stage group, 3.1 is a first rotating stage, 3.2 is a second rotating stage; 4 is a femtosecond laser spot, 4.1 is a femtosecond laser spot before passing through the prism group, 4.2 is a femtosecond laser spot after passing through the first dispersion prism, and 4.3 is a femtosecond laser spot after passing through the second dispersion prism; 5.1 is a component with a smaller wavelength in the femtosecond laser beam, and 5.2 is a component with a larger wavelength in the femtosecond laser beam; 6 is an elliptical spot obtained due to spatial dispersion after the femtosecond laser passes through the acousto-optic medium in the acousto-optic deflector unit; 7.1 is an input pulse of the acousto-optic deflector, and 7.2 is an output pulse of the acousto-optic deflector; 8 is a horizontal plane; 9.1 is an acousto-optic medium. DETAILED DESCRIPTION

[0054] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0055] Example 1

[0056] A dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, such as Figure 1 As shown, including:

[0057] A dispersion prism group and a rotating stage group are provided; the rotating stage group includes a first rotating stage and a second rotating stage; the dispersion prism group includes a first dispersion prism disposed on the first rotating stage and a second dispersion prism disposed on the second rotating stage; the second dispersion prism is located on a vertical incident path of a laser beam of an acousto-optic deflector to be compensated; the laser beam first passes through the first dispersion prism and then passes through the second dispersion prism;

[0058] The method is based on the following steps: constraining the spot of the monochromatic laser beam emitted from the dispersion prism group to be circular, calculating the incident angles of the laser beam incident on the first dispersion prism and the second dispersion prism when the negative spatial dispersion generated by the dispersion prism group is equal to and opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; constraining the incident angles of the laser beam incident on the first dispersion prism and the second dispersion prism and the vertical incidence of the laser beam emitted from the dispersion prism group on the receiving surface of the acousto-optic deflector to be compensated, determining and adjusting the relative spatial position between the two prisms; controlling the laser beam to be incident on the dispersion prism group parallel to the surface of the first rotating stage, and rotating the rotating stage group to fine-tune the incident angles of the first dispersion prism and the second dispersion prism to the calculated incident angles, thereby achieving spatial dispersion compensation;

[0059] The spatial positions of the two prisms are adjusted so that the laser beam is transmitted near the edge area of ​​each dispersion prism. The distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is calculated and adjusted when the negative temporal dispersion generated by the dispersion prism group is equal to or opposite to the positive temporal dispersion of the acousto-optic deflector to be compensated, thereby achieving temporal dispersion compensation.

[0060] This embodiment proposes a dispersion compensation method for an acousto-optic deflector based on a dispersive prism assembly. This method employs dual prisms to compensate for the spatiotemporal dispersion of the acousto-optic deflector. Prisms are relatively inexpensive compared to other dispersion compensation devices. By rotating the dispersive prism assembly to adjust the incident angle of the light beam, the spatial dispersion of the acousto-optic deflector is compensated while maintaining parallelism of the output beam. This eliminates the need for custom prisms made of specific materials and angles, thus reducing system costs. Therefore, this invention addresses the high cost of customizing dispersion compensation devices.

[0061] Furthermore, this embodiment employs a prism assembly solution to adjust the amount of spatial dispersion compensation by varying the angle of incidence of the incident light relative to the prism. This allows for continuous adjustment of the amount of spatial dispersion compensation while preventing spatial distortion of the light spot due to the prism. Temporal dispersion compensation can also be adjusted by varying the spacing between the prism assembly and the acousto-optic deflector, providing flexible adjustment of the amount of dispersion compensation. Therefore, this embodiment solves the problem of limited applicability of dispersion compensation devices.

[0062] like Figure 2 As shown, the principle diagram corresponding to the method of this embodiment includes: a prism group 1, an acousto-optic deflector 2 composed of two orthogonal acousto-optic deflector units, and a one-dimensional rotating stage group 3;

[0063] The prism group consists of a first dispersion prism 1.1 and a second dispersion prism 1.2. Figure 3 As shown in the upper and lower sub-figures in the figure, it is used to provide spatial dispersion pre-compensation and, together with the acousto-optic deflector 2, forms a pulse compressor to provide temporal dispersion pre-compensation and ensure that the light spot does not suffer spatial distortion due to the prism structure. It should be noted that when the rotating stage assembly is rotated to fine-tune the incident angles of the first and second dispersion prisms to the calculated incident angles to achieve spatial dispersion compensation, the light beam emitted from the acousto-optic deflector is a set of parallel light beams. After passing through the focusing lens, the parallel light beams are focused into a circular light spot. By observing that the light spot on the focusing plane after the parallel light beams pass through the focusing lens is circular, it can be easily determined that spatial dispersion compensation has been achieved.

[0064] The acousto-optic deflector to be compensated is composed of two acousto-optic deflector units 2.1 and 2.2 in an orthogonal manner and is used for scanning femtosecond laser.

[0065] The one-dimensional rotating stage assembly is composed of a one-dimensional first rotating stage 3.1 and a second rotating stage 3.2, and is used for carrying and rotating the dispersion prism assembly.

[0066] In this embodiment, the first dispersion prism 1.1 and the second dispersion prism 1.2 are both standard prisms, and are identical in material and shape. Figure 4 As shown. Taking the first dispersion prism 1.1 as an example, the prism has a deflection effect on the incident light, as shown in Figure 5 As shown, the light beam is incident at an angle of I 11 Entering the prism, the outgoing light has a deflection angle θ relative to the incident light p , the spatial dispersion of the first dispersion prism 1.1 Expressed as:

[0067]

[0068] Among them, I 11 is the incident angle of the laser relative to the first dispersion prism 1.1, α is the prism vertex angle, n is the prism refractive index, λ is the central wavelength of the incident light, is the first-order dispersion rate of the prism material.

[0069] Similarly, the spatial dispersion of the second dispersion prism 1.2 Expressed as:

[0070]

[0071] Among them, I21 is the incident angle of the laser relative to the second dispersion prism 1.2, α is the prism vertex angle, n is the prism refractive index, λ is the central wavelength of the incident light, is the first-order dispersion rate of the prism material.

[0072] In this embodiment, the acousto-optic deflector 2 generates spatial dispersion when scanning the femtosecond laser. Figure 6 As shown, taking the acousto-optic deflector unit 2.1 as an example, there is an acousto-optic medium 9.1 in the acousto-optic deflector unit 2.1, and the light is deflected by an angle θ after entering the acousto-optic medium 9.1. A , which can be expressed as:

[0073]

[0074] Among them, f s is the acoustic field frequency of the acousto-optic deflector, v s is the speed of sound and λ is the wavelength.

[0075] Since femtosecond laser has a certain bandwidth in the spectrum, the deflection angle of each spectral component is different, such as Figure 6 , the component with the larger wavelength 5.2 in the beam has an angle Δθ relative to the component with the smaller wavelength 5.1 in the beam, which can be expressed as:

[0076]

[0077] Here, Δλ is the wavelength difference between the diffracted light 5.2 and the diffracted light 5.1.

[0078] Therefore, the spatial dispersion of the AOD 2 can be expressed as:

[0079]

[0080] Because the diffracted light has different deflection angles and different heights on the receiving surface, the femtosecond laser, after passing through the acousto-optic medium 9.1, forms an elliptical spot 6 on the receiving surface. This elliptical spot changes the laser processing shape and reduces processing accuracy. Therefore, the spatial dispersion of the acousto-optic deflector is compensated, making the output beam parallel. When focused by the focusing lens, the output beam forms a circular spot.

[0081] like Figure 7 After the femtosecond laser pulse passes through the acousto-optic medium 9.1 in the acousto-optic deflector unit 2.1, group velocity dispersion is introduced due to the different propagation speeds of the various spectral components in the acousto-optic medium 9.1, resulting in the broadening of the input pulse 7.1 to the output pulse 7.2.

[0082] Group velocity dispersion GVD A It can be expressed as:

[0083]

[0084] Where λ is the central wavelength of the incident light, c is the speed of light, and n A is the refractive index of the acousto-optic crystal.

[0085] Temporal dispersion GDD of the acousto-optic deflector unit 2.1 A It can be expressed as the product of group velocity dispersion and the thickness of the acousto-optic crystal:

[0086]

[0087] Where l is the thickness of the acousto-optic crystal.

[0088] The stretched pulse τ out It can be expressed as:

[0089]

[0090] Among them, τ in For input pulse width 7.1, τ out The output pulse width is 7.2.

[0091] Temporal dispersion of the AOD causes pulse broadening, which results in a decrease in pulse peak power.

[0092] As a preferred embodiment, when performing temporal dispersion compensation, the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is also fine-tuned to compensate for the temporal dispersion additionally introduced by the dispersion prism group.

[0093] As an effective implementation method, the above configuration can be implemented as follows:

[0094] The first rotating table is placed vertically, that is, the normal of its table surface is parallel to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table surface of the first rotating table; the second rotating table is placed horizontally, that is, the normal of its table surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table.

[0095] Further preferably, the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0096] The incident angle of the laser beam incident on the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0097] Further preferably, the negative spatial dispersion generated by the dispersion prism group is:

[0098]

[0099] Where, represents the negative spatial dispersion, the value of which is opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; Represents the spatial dispersion produced by a single dispersion prism;

[0100] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass The incident angle of the laser beam incident on the dispersion prism group is obtained, that is, the incident angle of the laser beam incident on the first dispersion prism.

[0101] Further preferably, the acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units, the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor, and the negative temporal dispersion GDD generated by the pulse compressor is:

[0102]

[0103] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the sound field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and is the inverse of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0104] In this embodiment, Figure 8 Figure 2 is a schematic diagram of the dispersion compensation principle of an acousto-optic deflector based on an orthogonal prism group.

[0105] like Figure 8 As shown, the first rotating stage 3.1 is perpendicular to the horizontal plane 8, and the second rotating stage 3.2 is parallel to the horizontal plane 8. The first dispersive prism 1.1 is placed on the first rotating stage 3.1 and rotates about the axis L1; the second dispersive prism 1.2 is placed on the second rotating stage 3.2 and rotates about the axis L2. The femtosecond laser is incident near the top angle of the dispersive prism and parallel to the surface of the first rotating stage. The incident angle of the femtosecond laser relative to the first dispersive prism 1.1 is equal to the incident angle of the femtosecond laser relative to the second dispersive prism 1.2. The output light from the acousto-optic deflector 2 is a group of parallel light, with the larger wavelength component being 5.2 and the smaller wavelength component being 5.1.

[0106] The orthogonal prism group 1 is used to provide spatial dispersion pre-compensation and form a pulse compressor with the acousto-optic deflector 2 to provide temporal dispersion pre-compensation and ensure that the light spot does not suffer from spatial distortion due to the prism structure;

[0107] The acousto-optic deflector 2 is used to scan the femtosecond laser.

[0108] The orthogonal one-dimensional rotating stage group 3 is used to carry and rotate the orthogonal prism group;

[0109] like Figure 3 In the figure above, when monochromatic light is incident, one axis of light spot 4.1 is first reduced (enlarged) by dispersion prism 1.1, resulting in light spot 4.2. Then, dispersion prism 1.2 reduces (enlarges) the other axis of light spot 4.2, resulting in light spot 4.3. The magnification of the first dispersion prism 1.1 and the second dispersion prism 1.2 is the same, M, so the light spot does not undergo spatial distortion due to the prism structure. The relationship corresponding to the magnification M is:

[0110]

[0111] Among them, I 11 is the incident angle of the femtosecond laser relative to the first dispersion prism 1.1, α is the prism apex angle, and n is the prism refractive index.

[0112] The incident angle I of the femtosecond laser relative to the first dispersion prism 1.1 11 The incident angle I of the femtosecond laser relative to the dispersion prism 1.2 21 The laser beam is controlled to be incident on the dispersion prism group parallel to the first rotating stage surface, and the incident angles of the first dispersion prism and the second dispersion prism are fine-tuned to the calculated incident angle by rotating the rotating stage group to achieve spatial dispersion compensation.

[0113] The first dispersion prism 1.1 and the second dispersion prism 1.2 provide equal spatial dispersion in orthogonal directions, i.e.

[0114]

[0115] in Represents the spatial dispersion produced by a single dispersion prism, with subscripts 1 and 2 representing the first dispersion prism and the second dispersion prism, respectively.

[0116] The spatial dispersion provided by the orthogonal prism set 1 can be expressed as:

[0117]

[0118] in, is the spatial dispersion of orthogonal prism group 1.

[0119] When the spatial dispersion of the prism group 1 is equal to and opposite to the spatial dispersion of the acousto-optic deflector 2, the spatial dispersion of the acousto-optic deflector 2 is compensated.

[0120] The prism group 1 and the acousto-optic deflector 2 form a pulse compressor. The negative temporal dispersion GDD provided by the pulse compressor can be expressed as:

[0121]

[0122] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the sound field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the spatial dispersion of orthogonal prism group 1.

[0123] When the temporal dispersion of the pulse compressor is equal to and opposite to the temporal dispersion of the AOD 2, the temporal dispersion of the AOD 2 is compensated.

[0124] If a femtosecond laser with a wavelength of 1030 nm is used, an orthogonal equilateral dispersion prism set with a vertex angle of 60° and a material of N-SF11 is used to compensate for the spatiotemporal dispersion of the orthogonal acousto-optic deflector.

[0125] The refractive index of the prism made of N-SF11 is:

[0126]

[0127] in

[0128] B1=1.73759695

[0129] B2=0.313747346

[0130] B3=1.89878101

[0131] C1=0.013188707

[0132] C2=0.0623068142

[0133] C3=155.23629

[0134] When the wavelength is 1030nm, the refractive index of the dispersion prism 1.1 and the dispersion prism 1.2 is n=1.7549, and the first-order dispersion rate is The relationship between the spatial dispersion of the orthogonal prism set 1 and the incident angle of the femtosecond laser relative to the dispersion prism 1.1 is calculated, as shown in FIG. Figure 9 shown.

[0135] At this time, in order to compensate for the TeO2 acousto-optic deflector with a center frequency of 80 MHz, a sound velocity of 670 m / s, and an acousto-optic crystal length of 20 mm, the incident angle of the first dispersive prism 1.1 is I 11 =51.61°, the incident angle of the second dispersion prism 1.2 is also I 21 =51.61°, and the distance between the orthogonal prism group and the acousto-optic deflector is about 272.15 mm.

[0136] As a preferred embodiment, the above configuration is as follows:

[0137] The first rotating platform is placed horizontally, i.e., the normal line of the platform surface is perpendicular to the horizontal plane, and a triangular face of the first dispersion prism is attached to the platform surface of the first rotating platform; the second rotating platform is placed horizontally, i.e., the normal line of the platform surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating platform;

[0138] The entire rotating stage assembly is rotated upward by 45° with the central axis of the laser beam perpendicularly incident from the second dispersion prism to the acousto-optic deflector as the rotation axis.

[0139] On this basis, it is further preferred that the constraint that the spot of the monochromatic laser beam emitted from the dispersion prism group is circular is specifically:

[0140] The exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

[0141] On this basis, it is further preferred that the negative spatial dispersion generated by the dispersion prism group is:

[0142]

[0143] Where, represents the negative spatial dispersion, the value of which is opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; represents the spatial dispersion produced by a single dispersion prism, with subscripts 1 and 2 representing the first dispersion prism and the second dispersion prism, respectively; M represents the magnification of the first dispersion prism;

[0144] By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass Obtaining the incident angle of the laser beam incident on the second dispersion prism;

[0145] According to the fact that the exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism, based on the The obtained incident angle value of the laser beam incident on the second dispersion prism is used to calculate the incident angle value of the laser beam incident on the first dispersion prism.

[0146] On this basis, it is further preferred that the acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units, the dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor, and the negative temporal dispersion GDD generated by the pulse compressor is:

[0147]

[0148] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the sound field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and is the inverse of the positive spatial dispersion of the acousto-optic deflector to be compensated.

[0149] In this embodiment, Figure 10 Figure 2 shows a schematic diagram of the dispersion compensation principle of an acousto-optic deflector based on a cascaded prism assembly. The cascaded one-dimensional rotating stage assembly 3 is placed at a 45° angle to the horizontal plane 8. A first dispersive prism 1.1 is placed on the first rotating stage 3.1 and rotates about axis L1; a second dispersive prism 1.2 is placed on the second rotating stage 3.2 and rotates about axis L2. A femtosecond laser is incident near the prism apex, parallel to the surface of the first rotating stage. The exit angle of the femtosecond laser relative to the first dispersive prism 1.1 is equal to the incident angle of the femtosecond laser relative to the second dispersive prism 1.2. The output light from the acousto-optic deflector 2 is a set of parallel light beams, with the larger wavelength component at 5.2 and the smaller wavelength component at 5.1.

[0150] The prism assembly 1 is used to provide spatial dispersion pre-compensation and, together with the acousto-optic deflector 2, forms a pulse compressor, providing temporal dispersion pre-compensation and ensuring that the light spot does not suffer spatial distortion due to the prism structure. The acousto-optic deflector 2 is used to scan the femtosecond laser. The cascaded one-dimensional rotating stage assembly 3 is used to carry and rotate the cascaded prism assembly.

[0151] like Figure 3 In the figure below, when monochromatic light is incident, one axis of spot 4.1 is first reduced (enlarged) by dispersion prism 1.1, resulting in spot 4.2. Then, the same axis of spot 4.2 is magnified (reduced) by dispersion prism 1.2, resulting in spot 4.3. The magnification of the first dispersion prism 1.1 is M, and the magnification of the second dispersion prism 1.2 is 1 / M. Therefore, the light spot does not undergo spatial distortion due to the prism structure. The relationship corresponding to the magnification M of the first dispersion prism 1.1 is:

[0152]

[0153] Among them, I 11 is the incident angle of the femtosecond laser relative to the first dispersion prism 1.1, α is the prism apex angle, and n is the prism refractive index.

[0154] The exit angle I of the femtosecond laser relative to the first dispersion prism 1.1 12 The incident angle I of the femtosecond laser relative to the second dispersion prism 1.2 21 Equal, can be expressed as:

[0155]

[0156] Among them, I 11 is the incident angle of the femtosecond laser relative to the first dispersion prism 1.1, I 12 is the exit angle of the femtosecond laser relative to the first dispersion prism 1.1, I 21 is the incident angle of the femtosecond laser relative to the second dispersion prism 1.2, α is the prism apex angle, and n is the prism refractive index.

[0157] The laser beam is controlled to be incident on the dispersion prism group parallel to the first rotating stage surface. The incident angles of the first dispersion prism and the second dispersion prism are fine-tuned to the calculated incident angles by rotating the rotating stage group to achieve spatial dispersion compensation.

[0158] The first dispersive prism 1.1 provides negative spatial dispersion, and the second dispersive prism 1.2 amplifies (reduces) this dispersion and also provides spatial dispersion itself. Therefore, the spatial dispersion provided by the cascaded prism group can be expressed as:

[0159]

[0160] in, is the spatial dispersion of prism group 1, M is the magnification of the first dispersion prism 1.1, Represents the spatial dispersion produced by a single dispersion prism, with subscripts 1 and 2 representing the first dispersion prism and the second dispersion prism, respectively.

[0161] Since the exit angle of the first dispersion prism 1.1 is equal to the incident angle of the second dispersion prism 1.2, it can be deduced that:

[0162]

[0163] Therefore, the amount of spatial dispersion provided by the cascaded prism set can be expressed as:

[0164]

[0165] When the spatial dispersion of the prism group 1 is equal to and opposite to the spatial dispersion of the acousto-optic deflector 2, the spatial dispersion of the acousto-optic deflector 2 is compensated.

[0166] The cascaded prism group 1 and the acousto-optic deflector 2 form a pulse compressor. The negative temporal dispersion GDD provided by the pulse compressor can be expressed as:

[0167]

[0168] Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f yis the sound field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, v s is the speed of sound, is the spatial dispersion of cascaded prism group 1.

[0169] When the temporal dispersion of the pulse compressor is equal to and opposite to the temporal dispersion of the AOD 2, the temporal dispersion of the AOD 2 is compensated.

[0170] Compared with the orthogonal prism group solution, the incident light spot and the exit light spot of the cascaded prism group are equal in size, no additional beam expansion is required before the dispersion prism 1.1, and the dispersion prism 1.1 and the dispersion prism 1.2 are on the same plane, which makes operation easier.

[0171] If a femtosecond laser with a wavelength of 1030 nm is used and a cascaded equilateral dispersion prism set with a vertex angle of 60° and made of N-SF11 material is used to compensate for the spatiotemporal dispersion of the orthogonal acousto-optic deflector, then the refractive index n of the dispersion prism 1.1 and the dispersion prism 1.2 is n = 1.7549, and the first-order dispersion rate is The relationship between the spatial dispersion of the cascade prism group 1 and the incident angle of the femtosecond laser relative to the dispersion prism 1.2 is calculated, as shown in FIG. Figure 11 shown.

[0172] At this time, in order to compensate for the TeO2 orthogonal acousto-optic deflector 2 with a center frequency of 80MHz, a sound velocity of 670m / s, and an acousto-optic crystal length of 20mm, the incident angle I of the dispersion prism 1.1 11 =68.88°, the incident angle I of the dispersion prism 1.2 21 =55.17°, and the distance between the cascaded prism group and the acousto-optic deflector is about 272.15 mm.

[0173] In general, the present invention uses a double prism to compensate for the spatiotemporal dispersion of the acousto-optic deflector. Prisms are less expensive than other dispersion compensation devices, which controls the system cost. By rotating the dispersion prism group to adjust the incident angle of the light beam, the spatial dispersion of the acousto-optic deflector is compensated while ensuring that the light spot does not undergo spatial distortion due to the prism. There is no need to customize prisms of specific materials and angles, which controls the system cost. In addition, since the present solution uses a prism group to avoid the spatial distortion of the light spot, the spatial dispersion compensation amount is continuously adjustable while the output light spot does not undergo spatial distortion due to the prism. The adjustment is flexible and has a wide range of applications. The temporal dispersion of the acousto-optic deflector is compensated by changing the spacing between the prism group and the acousto-optic deflector. Regarding the compensation for temporal dispersion, it should be noted that because the prism group will introduce a small amount of additional temporal dispersion, by fine-tuning the spacing, the temporal dispersion of the acousto-optic deflector itself and the additional temporal dispersion introduced by the prism group can be compensated at the same time.

[0174] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dispersion compensation method for an acousto-optic deflector based on a dispersion prism group, characterized in that: include: A dispersion prism group and a rotating stage group are provided; the rotating stage group includes a first rotating stage and a second rotating stage; the dispersion prism group includes a first dispersion prism disposed on the first rotating stage and a second dispersion prism disposed on the second rotating stage; the second dispersion prism is located on a vertical incident path of a laser beam of an acousto-optic deflector to be compensated; the laser beam first passes through the first dispersion prism and then passes through the second dispersion prism; The method is based on the following steps: constraining the spot of the monochromatic laser beam emitted from the dispersion prism group to be circular, calculating the incident angles of the laser beam incident on the first dispersion prism and the second dispersion prism when the negative spatial dispersion generated by the dispersion prism group is equal to and opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; constraining the incident angles of the laser beam incident on the first dispersion prism and the second dispersion prism and the vertical incidence of the laser beam emitted from the dispersion prism group on the receiving surface of the acousto-optic deflector to be compensated, determining and adjusting the relative spatial position between the two prisms; controlling the laser beam to be incident on the dispersion prism group parallel to the surface of the first rotating stage, and rotating the rotating stage group to fine-tune the incident angles of the first dispersion prism and the second dispersion prism to the calculated incident angles, thereby achieving spatial dispersion compensation; Adjust the spatial position of the two prisms so that the laser beam is transmitted near the edge area of ​​each dispersion prism; The distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is calculated and adjusted when the negative time dispersion generated by the dispersion prism group is equal to or opposite to the positive time dispersion of the acousto-optic deflector to be compensated, thereby achieving time dispersion compensation.

2. The method for compensating dispersion of an acousto-optic deflector according to claim 1, wherein: When performing temporal dispersion compensation, the distance between the center position of the dispersion prism group and the center position of the acousto-optic deflector to be compensated is also fine-tuned to compensate for the temporal dispersion additionally introduced by the dispersion prism group.

3. The method for compensating dispersion of an acousto-optic deflector according to claim 1, wherein: The configuration is implemented as follows: The first rotating table is placed vertically, that is, the normal of its table surface is parallel to the horizontal plane, and a triangular face of the first dispersion prism is attached to the table surface of the first rotating table; the second rotating table is placed horizontally, that is, the normal of its table surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating table.

4. The method for compensating dispersion of an acousto-optic deflector according to claim 3, wherein: The constraints for the circular spot of the monochromatic laser beam emitted from the dispersion prism group are as follows: The incident angle of the laser beam incident on the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

5. The method for compensating dispersion of an acousto-optic deflector according to claim 3, wherein: The negative spatial dispersion produced by the dispersion prism group is: Where, represents the negative spatial dispersion, the value of which is opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; Represents the spatial dispersion produced by a single dispersion prism; By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass The incident angle of the laser beam incident on the dispersion prism group is obtained, that is, the incident angle of the laser beam incident on the first dispersion prism.

6. The method for compensating dispersion of an acousto-optic deflector according to claim 3, wherein: The acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units. The dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor. The negative temporal dispersion GDD generated by the pulse compressor is: in, λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, f y is the sound field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, υ s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and is the inverse of the positive spatial dispersion of the acousto-optic deflector to be compensated.

7. The method for compensating dispersion of an acousto-optic deflector according to claim 1, wherein: The configuration is as follows: The first rotating platform is placed horizontally, i.e., the normal line of the platform surface is perpendicular to the horizontal plane, and a triangular face of the first dispersion prism is attached to the platform surface of the first rotating platform; the second rotating platform is placed horizontally, i.e., the normal line of the platform surface is perpendicular to the horizontal plane, and a triangular face of the second dispersion prism is attached to the second rotating platform; The entire rotating stage assembly is rotated upward by 45° with the central axis of the laser beam perpendicularly incident from the second dispersion prism to the acousto-optic deflector as the rotation axis.

8. The method for compensating dispersion of an acousto-optic deflector according to claim 7, wherein: The constraints for the circular spot of the monochromatic laser beam emitted from the dispersion prism group are as follows: The exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism.

9. The method for compensating dispersion of an acousto-optic deflector according to claim 7, wherein: The negative spatial dispersion produced by the dispersion prism group is: Where, represents the negative spatial dispersion, the value of which is opposite to the positive spatial dispersion of the acousto-optic deflector to be compensated; represents the spatial dispersion produced by a single dispersion prism, with subscripts 1 and 2 representing the first dispersion prism and the second dispersion prism, respectively; M represents the magnification of the first dispersion prism; By assigning the opposite of the positive spatial dispersion of the AOD to be compensated to calculate pass Obtaining the incident angle of the laser beam incident on the second dispersion prism; According to the fact that the exit angle of the laser beam from the first dispersion prism is equal to the incident angle of the laser beam incident on the second dispersion prism, based on the The obtained incident angle value of the laser beam incident on the second dispersion prism is used to calculate the incident angle value of the laser beam incident on the first dispersion prism.

10. The method for compensating dispersion of an acousto-optic deflector according to claim 7, wherein: The acousto-optic deflector to be compensated is composed of two orthogonally placed acousto-optic deflector units. The dispersion prism group and the acousto-optic deflector to be compensated constitute a pulse compressor. The negative temporal dispersion GDD generated by the pulse compressor is: Where λ is the central wavelength of the incident laser, c is the speed of light, L is the distance between the center of the acousto-optic deflector and the center of the dispersion prism group, and f y is the sound field frequency of the AOD scanned in the vertical direction, f x is the sound field frequency of the AOD scanned in the horizontal direction, υ s is the speed of sound, is the negative spatial dispersion generated by the dispersion prism group, and is the inverse of the positive spatial dispersion of the acousto-optic deflector to be compensated.

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