Detection device for a spot shape

Abstract

A spot shape detection device (1) for detecting a spot shape of a laser beam (LB1) oscillated by a laser oscillator (30), the spot shape detection device (1) comprising: a focus lens (31) for focusing the laser beam (LB1) oscillated by the laser oscillator (30); a rotating body (6) in which a plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) for reflecting the laser beam (LB1) which has passed through the focus lens (31) are arranged on concentric circles; a drive source (7) for rotating the rotating body (6) at a predetermined period; a beam splitter (32) for branching off reverse beams (LB2) of the laser beam (LB1) reflected by the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) of the rotating body (6); a recording unit (33) arranged in a direction in which the reverse beams (LB2) are branched by the beam splitter (32) and records the spot shapes of the reverse beams (LB2); and a display unit (m) for displaying images obtained by recording by the recording unit (33) in relation to the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q), wherein the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) are arranged in the rotating body (6) in such a manner that, when the rotating body (6) is rotated in a predetermined direction, focus points of the return beams (LB2) of the laser beam (LB1) sequentially reflected by the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) gradually approach a pickup position of the pickup unit (33), reach the pickup position, and gradually move away from the pickup position.

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a spot shape detection device capable of detecting an accurate spot shape of a laser beam. Description of the state of the art

[0002] A wafer having a plurality of devices such as integrated circuits (ICs), large-scale integration (LSIs), or light-emitting diodes (LEDs) formed on its front surface divided by dividing lines (streets) is divided into individual devices by a laser processing apparatus for performing ablation by applying a laser beam of such a wavelength to the dividing lines as to be absorbed in the wafer, and the devices are used for electric devices such as mobile phones, personal computers, liquid crystal polymer televisions (TVs), lighting devices, and the like (see, for example, Japanese Patent Laid-Open No. 1998-305420).

[0003] In addition, there is also a proposed laser processing technology in which a laser beam of such a wavelength that is transmitted through the wafer is applied to the wafer along the dividing line, the focal point of the laser beam is positioned in the wafer to form modified layers along the dividing line, and an external force is applied to the wafer to divide the wafer into individual devices, and this technology is practically used in the field of the laser processing apparatus (see, for example, Japanese Patent No. 3408805).

[0004] Furthermore, the spot shape of the laser beam oscillated by a laser oscillator including the above-mentioned laser processing apparatus influences the processing quality. Therefore, to ensure the quality of laser processing, the laser beam should be evaluated either by using the spot shape of the laser beam applied to the wafer or by calculating an M2 factor, which is an index for evaluating the laser beam based on the beam diameter calculated from the spot size. To date, several spot shape detection devices have been proposed (see, for example, Japanese Patent Laid-Open No. 2013-022634, Japanese Patent Laid-Open No. 2013-151002, and Japanese Patent No. 5726999).Note that the M2 factor is an index value that indicates how many times the beam diameter obtained when a laser beam is focused and converged to a calculation limit is equal to the beam diameter obtained when an ideal Gaussian beam is converged to the diffraction limit. Therefore, the index value is expressed as a ratio of at least 1 (one) to the ideal Gaussian beam, and the M2 factor is 1 (one) when the laser beam coincides with an ideal Gaussian beam.

[0005] US 2013 / 0 027 690 A1 relates to a detection method for a point shape of a laser beam. US 2016 / 0 045 980 A1 relates to a detection method for a point shape of a laser beam.

[0006] US 6 313 910 B1 relates to a device for real-time measurement of optical beam parameters. DESCRIPTION OF THE INVENTION

[0007] To evaluate a laser beam by spot shape detection as described above, it is necessary to perform spot shape detection at various points or evaluate the M2 factor obtained based on the spot diameter, etc. Spot shape detection requires a comparatively long time, resulting in low productivity. Additionally, there is a problem regarding the reproducibility of the detected spot shape. Consequently, there is a problem in ensuring the accuracy of the evaluation.

[0008] It is therefore an object of the present invention to provide a spot shape detecting apparatus for efficiently detecting in a short time an accurate spot shape of a laser beam applied from a laser oscillator.

[0009] According to one aspect of the present invention, there is provided a spot shape detection device for detecting a spot shape of a laser beam oscillated by a laser oscillator, the spot shape detection device including: a focus lens for focusing the laser beam oscillated by the laser oscillator; a rotary body in which a plurality of mirrors for reflecting the laser beam that has passed through the focus lens are arranged in concentric circles; a drive shaft for rotating the rotary body at a predetermined period; a beam splitter for branching reverse beams of the laser beam reflected by the plurality of mirrors of the rotary body; an imaging unit arranged in a direction in which the reverse beams are branched by the beam splitter and picking up the spot shapes of the reverse beams;and a display unit for displaying images obtained by capturing by the imaging unit in relation to the plurality of mirrors, wherein the plurality of mirrors are arranged in the rotating body in such a manner that, when the rotating body is rotated in a predetermined direction, the focal points of the return beams of the laser beam sequentially reflected by a plurality of mirrors gradually reach an image capturing position of the imaging unit, reach the capturing position, and gradually move away from the capturing position.;

[0010] In the aforementioned aspect of the present invention, a shutter of the imaging unit can be operated in synchronization with the timing of reflection of the laser beam by each mirror of the rotating body. In addition, the brightness of the return beam of the laser beam received by the imaging unit can be controlled by regulating the timing of opening the shutter of the imaging unit in a state where the time when the laser beam is applied and reflected by each mirror is the longest. Furthermore, an attenuation filter can be applied in front of the focus lens.

[0011] The spot shape detection device of the present invention includes: a focus lens for focusing the laser beam oscillated by the laser oscillator; a rotating body in which a plurality of mirrors for reflecting the laser beam that has passed through the focus lens are arranged on concentric circles; a drive shaft for rotating the rotating body at a predetermined revolution; a beam splitter for branching reverse rays of the laser beam reflected by the plurality of mirrors of the rotating body; an imaging unit arranged in a direction in which the reverse rays are branched by the beam splitter and captures the spot shape of the reverse rays; and a display unit for displaying images obtained by capturing by the imaging unit with respect to the plurality of mirrors, wherein the plurality of mirrors are arranged in the rotating body in such a manner that,When the rotating body is rotated in a predetermined direction, focal points of the reversing beams of the laser beam, which are sequentially reflected by a plurality of mirrors, gradually approach a recording position of the imaging unit, reach the recording position, and gradually move away from the recording position. Therefore, the spot shapes of the beam spots formed in an area near the focal point of the laser beam can be easily detected and displayed on the display unit. In particular, for example, in the case where the number of mirrors constituting the rotating body is 17 and 50 images can be captured in one second, the focal points in the areas on both sides of the focal point can be captured and displayed on the display unit in 0.34 seconds. Furthermore, if the spot diameter is determined using the spot shapes thus captured,an evaluation of the beam profile such as the M2 factor can be easily carried out.

[0012] The above and other objects, features and advantages of the present invention and the mode of carrying them out will become clearer and the invention itself best understood by studying the following description and appended claims with reference to the attached figures which show a preferred embodiment of the invention. SHORT DESCRIPTION OF THE CHARACTERS Fig. 1 is a general perspective view of a spot shape detecting device; Fig. Fig. 2 is a block diagram for explaining an optical means of the spot shape detecting device shown in Fig. 1 is shown; Fig. 3 is a schematic view of an encoder of the spot shape detection device shown in Fig. 1 is shown; and Fig. 4 is a graph showing a relationship between the spot diameter detected by the detection device for a spot shape rotated in Fig. 1 and the position at which a mirror is arranged. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013] A spot shape detecting apparatus according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[0014] Fig. 1 and Fig. 2 illustrates an embodiment of a spot shape detecting device. The spot shape detecting device 1 of the present embodiment includes: a base 2 on which main portions of the spot shape detecting device 1 are mounted; a cylindrical rotary body (hereinafter referred to as “mirror holder 6”) in which a plurality of (17 in the present embodiment) reflecting holes 6a to 6q each with a mirror housed therein are arranged on concentric circles; a shaft 5 which is a central shaft of the mirror holder 6 and penetrates the mirror holder 6; and support frames 3 and 4 which support a front end portion 51a and a rear end portion 51b of the shaft 5 and which are raised on the base 2. Note that although not shown in Fig. 1, the spot shape detecting apparatus of the present embodiment is provided with a motor as a drive shaft for rotationally driving the mirror holder 6 at a predetermined period, and an encoder is connected to the motor, the details of which will be described later.

[0015] In the mirror holder 6, a plurality of reflection holes 6a to 6q drilled in an axial direction are provided in this order along a counterclockwise direction, the reflection holes 6a to 6q being arranged at a predetermined interval on the same circumference of the circle with the shaft 5 as a center. As schematically shown in Fig. 2, mirrors 6a' to 6q' for reflecting a laser beam incident from the outside are included in the reflection holes 6a to 6q, wherein the mirrors 6a' to 6q' are positioned and fixed such that their distances differ from each other in a direction indicated by an arrow X from an end surface 61 of the mirror holder 6. The position at which each of the mirrors 6a' to 6q' is arranged and operations or effects based on this position will be described later. Note that although the reflection holes 6k to 6p are not shown in Fig. 1, the reflection holes 6k to 6p are arranged behind the support frame 3 in the figure and are arranged in the mirror holder 6 at the same distance as that of the other reflection holes.

[0016] As in Fig. As shown in Fig. 2, toothed pulleys 52 and 82 formed with the same number of teeth are fixed to a rear end portion 51b on the support frame 4 side of the shaft 5 penetrating the center of the mirror holder 6 and to a tip end portion 81 of the shaft 8 of the motor 7 arranged to rotatably drive the mirror holder 6, respectively. A toothed belt V is arranged around and between the toothed pulleys 52 and 82. Through the toothed pulleys 52 and 82 and the toothed belt V, rotation of the motor 7 is transmitted to the shaft 5 of the mirror holder 6 without slippage, and by the rotational speed of the motor 7 controlled by the control means 20 described later, the rotation period of the mirror holder 6 can be accurately controlled.

[0017] In addition to the configuration described above, an optical means 40 for detecting a spot shape is arranged in the spot shape detecting device 1 of the present embodiment, as shown particularly in Fig. 2. The optical means 40 includes, for example, a laser oscillator 30 as an object to be evaluated; a focus lens 31 for focusing a laser beam LB1 oscillated by the laser oscillator 30; a beam splitter 32 that applies a laser beam LB1, which has passed through the focus lens 31, to a circumference of the circle of the mirror holder 6 formed with the reflection holes 6a to 6q, and reflects the return beams LB2 reflected by the mirrors 6a' to 6q' arranged inside the reflection holes 6a to 6b to change the optical path of the return beams LB2 to the lower side; and a pickup means (image unit) 33 arranged in the optical path of the return beams LB2 reflected by the beam splitter 32 and including therein a pickup element 33a for picking up the spot shapes of the return beams LB2. Note that although not shown in Fig. 1 as shown by the dashed lines in the optical means in Fig. 2, a power control means for controlling the laser beam LB1 to a power suitable for capturing the beam diameter by the capturing means 33 may be provided between the laser oscillator 30 and the focus lens 31, and a light attenuating filter 34 may be arranged as the power control means.

[0018] Here, the encoder 9, which is connected to the motor 7, is used to rotate the mirror holder 6 with reference to Fig. 2 and Fig. 3. As described in Fig. 2 and Fig. 3, the encoder 9 of the present embodiment includes a rotary disk 91 arranged on the shaft 8 of the motor 7, and a trigger generator 92 arranged on opposite sides of a circumferential portion of the rotary disk 91. As shown in the figures, the trigger generator 92 is provided with a light-emitting element 93 for emitting, as an example, infrared (IR) light and a light-receiving element 94 for receiving IR light, which are arranged on opposite sides of the rotary disk 91. When the rotary disk 91 is rotated and infrared light from the light-emitting element 93 passes through the slits 91a to 91q formed at equal intervals in a circumferential portion of the rotary disk 91 and is received by the light-receiving element 94, a trigger signal S, as shown on the lower side in Fig. 2, and the signal is sent to the control means 20. Here, the opening widths of the slits 91a to 91q arranged in the rotary disk 91 are set to be smallest at the slit 91i and become wider as they move away from the slit 91i. Specifically, the signal width (the length of time when the signal is ON) of the trigger signal S is smallest (shortest) at the slits 91f to 91i and largest (longest) on the slits 91a and 91q sides. Control is performed so that when the trigger signal S is transmitted to the control means 20, a shutter (not shown) of the pickup means 33 is opened in synchronization with the trigger signal S.Note that in the present embodiment, by controlling the rotation speed of the motor 7 in the clockwise direction in plan view, the time when the shutter is caused to be turned on by the slits 91f to 91l is set to 1 ms, the time when the shutter is caused to be turned on by the slits 91c to 91e and 91m to 91o is set to 2 ms, and the time when the shutter is caused to be turned on by the slits 91p to 91b is set to 5 ms.

[0019] The control means 20 is formed of a computer including a central processing unit (CPU) for performing arithmetic calculations according to a control program, a read-only memory (ROM) for storing the control program and the like, a random access memory (RAM) for temporarily storing detection values, calculation results, and the like, an input interface, and an output interface (details are omitted from the figures). Not only the signal from the trigger generator 92 but also image data or the like sent from the pickup means 33 are input to the control means 20, the image data being stored in the random access memory (RAM) and, if necessary, displayed on the display means (display unit) m arranged near the spot shape detecting device 1.

[0020] The arrangement positions of the mirrors 6a' to 6q' arranged in the reflection holes 6a to 6q of the mirror holder 6 will be described. A mirror for reflecting the laser beam is arranged in each of the reflection holes 6a to 6q, and the arrangement positions of the mirrors 6a' to 6q' are set so that they are different from each other in the direction indicated by the arrow X in Fig. 2. For ease of explanation, the mirror holder 6 shown in the figure is shown in a transparent state, while the positions of the mirrors arranged in the mirror holder 6 are viewed from a lateral side. From the figure, it is understood that the mirror 6a' is arranged on the side of one end surface 61 of the mirror holder 6 so that its distance from the one end surface 61 is the shortest, the mirror 6b', the mirror 6c', etc. are arranged with a distance from the one end surface 61 that increases, and the mirror 6q' at the lowest position in the reflection mirror is also arranged.

[0021] The arrangement positions of the mirrors 6a' to 6q' will be described in more detail. As already described, the laser beam LB1 oscillated by the laser oscillator 30 is focused by the focus lens 31 and is reflected by each of the mirrors 6a' to 6q' to become the reverse beam LB2, which is reflected by the beam splitter 32 to be guided to the pickup means 33. Here, the position of the mirror 6i, which is located at a middle position in a direction of an arrow X in the figure of the mirror holder 6, is set so that the reverse beam LB2 reflected by the mirror 6i forms a focus point P on the pickup element 33a of the pickup means 33; in other words, the spot shape picked up by the pickup means 33 is smallest for the reverse beam LB2 reflected by the mirror 6i.The focus point P is moved to the lower side of the pickup element 33a while the mirror position (reflection position) of the mirror 6i is moved to the side of the one end surface 61 of the mirror holder 6, and the focus position P is moved to the upper side of the pickup element 33a while the mirror position of the mirror 6i is moved to the side farther from the end surface 61 of the mirror holder 6. In addition, with the mirror 6i as a center, the mirrors 6f' to 6l' are arranged at a pitch of 1 mm in the direction of arrow X, the mirrors 6c' to 6f' and 6l' to 6o' at a pitch of 5 mm, and the mirrors 6a' to 6c' and 6o' to 6q' at a pitch of 20 mm, so that the spot shape can be more accurately recorded near a region where the spot diameter of the laser beam becomes smallest and reaches a diffraction limit.

[0022] The spot shape detecting device 1 of the present embodiment is generally configured as described above, and its operations or effects will be described below with reference to Fig. 2 described.

[0023] To evaluate the quality of a laser beam, an operator prepares the laser oscillator 30 as an object to be evaluated, places it on a predetermined mounting base (not shown), and adjusts the application direction of the laser beam. Next, to start the detection of the spot shape, an instruction to start an operation is given to the control means 20, whereupon the motor 7 starts rotating, the rotational force is transmitted through the toothed pulley 82, the toothed belt V, and the toothed pulley 52, and the mirror holder 6 is rotated at a predetermined rotation period.

[0024] In a state where the rotation period of the mirror holder 6 is stable at a predetermined value, a laser beam having a wavelength of 635 nm, for example, is oscillated at a predetermined power by the laser oscillator 30 and applied to the focus lens 31. Further, the rotary disk 91 of the encoder 9 is rotated together with the shaft 8 of the motor 7, thereby outputting a trigger signal S as described above. The trigger signal S, generated based on the slits 91a to 91q, is set to be turned on in synchronization with the timing at which the laser beam LB1 arrives at each of the reflection holes 6a to 6q.For example, when the trigger signal S based on the slit 91a is turned on at the time the laser beam LB1 is reflected by the mirror 6a, the shutter (not shown) of the pickup means 33 is kept open while the trigger signal S is turned on, the spot shape of the inverted beam LB2 applied to the pickup element 33a is picked up and transmitted to and stored in the control means 20. When the mirror holder 6 is further rotated and the inverted beam LB2 reflected by the mirror 6b' reaches the pickup means 33, the shutter of the pickup means 33 is opened based on the trigger signal S generated based on the slit 91b, the spot shape of the beam formed on the pickup element 33a is picked up, and the image data is transmitted to the control means 20.Subsequently, in the same manner, when the return beams LB2 reflected by the mirrors 6c' to 6q' reach the pickup means 33, the shutter of the pickup means 33 is opened based on the trigger signal S generated based on the slits 91c to 91q, and the spot shapes of the beam spots formed on the pickup element 33a due to the reflection of the mirrors 6c' to 6q' are picked up in the control means 20.

[0025] Note that since the light density of the beam received by the pickup element 33a is higher as the position of the focal point P is closer to the pickup element 33a, the on-time of the trigger signal S generated by the slits 91a to 91q is set to be shorter, and the on-time is set relatively longer as the focal point P is farther from the pickup element 33a, thereby controlling the exposure time so that damage to the pickup element 33a is prevented and the spot shape to be picked up is properly picked up. The on-time due to the slits 91a to 91q is effective only while the laser beam LB1 is reflected by each of the mirrors 6a' to 6q'.Therefore, the time for which the shutter is open or the shutter speed is controlled, and the brightness of the spot shape picked up by the pickup means 33 is controlled in a state in which the reflection time relevant to each of the mirrors 6a' to 6q' is determined by the shape of the hole of the reflection holes 6a to 6q and the rotation period of the mirror holder is the longest.

[0026] When the spot shape of the return beam LB2 reflected by each of the mirrors 6a' to 6q' is picked up and stored in the control means 20 in the manner described above, the picked up spot shapes are displayed with respect to the reflection holes 6a to 6q on the display means connected to the control means 20 (see Fig. 2) is shown.

[0027] Simultaneously with displaying the captured spot shapes on the display means with respect to the reflection holes 6a to 6q, the spot diameters of the spot shapes captured by the capture means 33 are calculated based on the spot shapes stored in the control means 20. For calculating the spot diameter, D4σ determined based on the image captured by the capture means 33 is used. D4σ, which is defined as four times the standard deviation σ of the intensity distribution, is defined by the International Organization for Standardization (ISO) as an international standard for a technique for determining a beam diameter of a laser beam, and the details thereof are known; therefore, the description thereof is omitted.When the spot diameters of the return beams LB2 reflected by the mirrors 6a' to 6q' are detected using the D4σ, the spot diameters are stored in the control means 20 in relation to the mirrors 6a' to 6q'.

[0028] In Fig. 4, the beam diameter d (micrometers) of the spot formed on the pickup element 33a by the return beam LB2 reflected by each of the aforementioned mirrors 6a' to 6q' is plotted on the ordinate axis, whereas the position (millimeters) of the mirror reflecting the laser beam when calculating the beam diameter is plotted on the abscissa, and a line obtained by mapping the spot diameters corresponding to the arrangement position of each of the mirrors and connecting the images is represented by a solid line L1. In representing the position of the mirror, the position of the mirror 6i is set in advance so that the focus point P on the pickup element 33a is taken as a reference point (0), and such a definition is used that the mirror position on the side where the focus point P is on the lower side (see Fig. 2) of the receiving element 33a takes a negative value, while the mirror position on the side where the focal point P is formed on the upper side of the receiving element 33a takes a positive value. Here in Fig.4 also shows a dotted line L2 obtained by assuming the value of the spot diameter of a spot formed when an ideal Gaussian beam is applied from the laser oscillator 30 and connecting the relevant outputs. In the case where the laser beam oscillated by the laser oscillator 30 of the present embodiment is assumed to be a Gaussian beam, and the applied laser beam has converged to the diffraction limit, the spot diameter d0 is 42 μm, as indicated by a point P0 at which the spot diameter is smallest on the dotted line L2. On the other hand, the spot diameter d actually measured when the laser beam oscillated by the laser oscillator 30 has converged to the diffraction limit is 50 μm, as indicated by a point P1 in the diagram.Based on the spot diameters indicated by these points P0 and P1, the M2 factor is calculated.

[0029] Note that a general M2 factor corresponds to the formula: M2 = Θ d / Θ0 d0 (Θ0 is the beam angle of an ideal Gaussian beam, and Θ is the beam angle of the laser beam actually measured). In the case where the difference between Θ and Θ0 is small, it is possible to assume that Θ / Θ0 is approximately 1, and M2 can be calculated as M2 = d / d0. In the case where Θ cannot be considered equal to Θ0, it is sufficient to determine the angles Θ and Θ0 and substitute them into the above formula to obtain the M2 factor. From the foregoing, it is understood that as the value of the M2 factor is closer to 1 (one), the quality of the laser beam oscillated by the laser oscillator 30 is evaluated higher.

[0030] In the present embodiment configured according to the present invention, as mentioned above, the plurality of mirrors for reflecting the applied laser beam to change the position of the focal point are arranged in the rotating body, and the rotating body is rotated by a drive source, whereby the spot shapes of the beam spots near the focal point can be easily acquired in a short time, and the acquired images can be displayed on a display device. Thereafter, based on the thus detected spot shapes, the laser oscillator can be easily evaluated.

[0031] The present invention is not limited to the aforementioned embodiment, and various modifications can be devised as long as they fall within the technical scope of the present invention. While the spot diameter is calculated from the spot shape captured by the capturing means 33 and the M2 factor is obtained therefrom to evaluate the laser beam in the above-described embodiment, obtaining the M2 factor is not limiting. Instead of calculating the M2 factor, the spot shapes displayed on the display means may be used to evaluate the quality of the laser beam. In that case, the evaluation of the laser beam may be performed based on the spot shape formed when the laser beam is an ideal laser beam.

[0032] While the rotary disk 91 is disposed on the shaft 8 of the motor 7 in the encoder 9 of the present embodiment, this is not limiting, and the rotary disk 91 may be disposed on the shaft 5 of the mirror holder 6. Furthermore, while the spot diameter is calculated by D4σ in the present embodiment, this is not limiting, and the beam diameter may be calculated according to other beam diameter definitions (10 / 90, 20 / 80 knife edge, 1 / (e*e), D86, etc.) that are generally used.

Claims

[1] A spot shape detection device (1) for detecting a spot shape of a laser beam (LB1) oscillated by a laser oscillator (30), the spot shape detection device (1) comprising: a focus lens (31) for focusing the laser beam (LB1) oscillated by the laser oscillator (30); a rotating body (6) in which a plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) for reflecting the laser beam (LB1) which has passed through the focus lens (31) are arranged on concentric circles; a drive source (7) for rotating the rotating body (6) at a predetermined period; a beam splitter (32) for branching off reverse beams (LB2) of the laser beam (LB1) reflected by the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) of the rotating body (6); a recording unit (33) arranged in a direction in which the reverse beams (LB2) are branched by the beam splitter (32) and records the spot shapes of the reverse beams (LB2); and a display unit (m) for displaying images obtained by recording by the recording unit (33) in relation to the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q), wherein the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) are arranged in the rotating body (6) in such a manner that, when the rotating body (6) is rotated in a predetermined direction, focal points of the return beams (LB2) of the laser beam (LB1) sequentially reflected by the plurality of mirrors (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) gradually approach a pickup position of the pickup unit (33), reach the pickup position, and gradually move away from the pickup position. [2] A spot shape detecting device (1) according to claim 1, wherein a shutter of the pickup unit is operated in synchronism with the timing of reflection of a laser beam (LB1) by each mirror (6a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i, 6j, 6k, 6l, 6m, 6n, 6o, 6p, 6q) of the rotary body (6). [3] A spot shape detecting device (1) according to claim 2, wherein the detecting device (1) is arranged so that the brightness of the return beam (LB2) of the laser beam (LB1) picked up by the pickup unit (33) is controlled by regulating the timing of opening the shutter of the pickup unit in a state where the time when the laser beam (LB1) is applied and reflected on each mirror is the longest. [4] A spot shape detection device (1) according to any one of the preceding claims, wherein an attenuation filter (34) is arranged in front of the focus lens (31).

Images