A surface defect detection device and method for large-aperture optical elements

Abstract

The present invention relates to an optical element surface defect detection device and method, and specifically to a large-aperture optical element surface defect detection device and method, which are used to solve the deficiencies of existing detection methods in the damage detection of large-aperture optical elements. These deficiencies include either being unable to provide a quantitative evaluation standard, having low efficiency and being difficult to effectively meet the large-scale detection requirements, or being unable to obtain the three-dimensional topography information of defects. The large-aperture optical element surface defect detection device utilizes the diffraction characteristics of a binary deformed diffraction grating, and a camera collects diffraction spots of multiple different diffraction orders in a single shot. The surface phase of the large-aperture optical element is calculated through a phase retrieval algorithm, and a two-dimensional translation stage is combined to scan the entire surface of the large-aperture optical element with a laser beam, thereby realizing the detection of surface defects of the large-aperture optical element.

Description

Technical Field

[0001] The present invention relates to an optical element surface defect detection device and method, and more particularly to a large-aperture optical element surface defect detection device and method. Background Art

[0002] In an ultrashort and ultra-intense laser system, due to the high intensity and short-time action of laser pulses, the interaction between the laser and the medium usually leads to some complex non-linear phenomena, among which the self-focusing effect is particularly significant. Self-focusing refers to the fact that under the action of a strong laser field, the light beam itself will focus to a smaller area due to non-linear effects, thereby intensifying the intensity of the light beam, which may cause local damage to the optical element.

[0003] For large-aperture optical elements, under long-term high-intensity laser irradiation, laser damage will occur on the surface and inside. The formation of this damage is closely related to factors such as laser power, focal position, and pulse duration. The damage not only affects the beam quality, causing the focal position to shift, but may also trigger thermal effects, which may ultimately lead to the rupture or local melting of the surface of the optical element. In addition, the beam diffraction effect at the damage point may also cause additional damage to other optical elements, further affecting the system performance.

[0004] Existing detection methods can generally be divided into visual methods and imaging-based detection methods. Visual methods rely on the experience of the detector for damage assessment, but since they rely on manual observation, they cannot provide objective and quantitative detection results. Imaging-based detection methods, such as area array imaging, collimate the light source into large-aperture parallel light and irradiate it on the surface of the optical element, and then obtain images through a camera and an imaging lens; this method is limited by the resolution and sampling frequency of the area array CCD, and since multiple images need to be stitched, the overall detection efficiency is low, especially in the detection of large-aperture optical elements, it is difficult to effectively meet the detection requirements of a large range; while dark field imaging and bright field imaging methods can improve the imaging resolution, but they still face problems such as low detection efficiency and inability to obtain three-dimensional topography information of defects.

[0005] Therefore, existing detection methods are difficult to provide an efficient, accurate, and comprehensive solution when facing the damage detection of large-aperture optical elements. Summary of the Invention

[0006] The object of the present invention is to solve the deficiencies that existing detection methods either cannot provide a quantitative evaluation standard, or have low efficiency and are difficult to effectively meet the detection requirements of a large range, or cannot obtain three-dimensional topography information of defects when facing the damage detection of large-aperture optical elements, and to provide a large-aperture optical element surface defect detection device and method.

[0007] To solve the deficiencies of the above-mentioned existing technologies, the present invention provides the following technical solutions:

[0008] A surface defect detection device for large-aperture optical elements, characterized in that: it includes a laser, a two-dimensional translation stage, and a collimating mirror, a variable magnification beam expander, a binary deformable diffraction grating, a focusing mirror and a camera arranged in sequence along the optical path;

[0009] The laser is used to emit a laser beam to the collimating mirror, and the collimating mirror is used to collimate the laser beam;

[0010] The two-dimensional translation stage is used to place the large-aperture optical element and change the position where the laser beam irradiates on the large-aperture optical element;

[0011] The variable magnification beam expander is used to expand the laser beam passing through the large-aperture optical element or the laser beam directly input into the variable magnification beam expander by the collimating mirror, and output it to the binary deformable diffraction grating; the binary deformable diffraction grating is used to divide the laser beam into diffraction spots of multiple different diffraction orders, and focus them to the detection surface of the camera through the focusing mirror. The detection surface of the camera is located on the rear focal plane of the focusing mirror. Each diffraction order corresponds to a specific phase shift amount, which is used to reconstruct the surface phase of the large-aperture optical element, so as to obtain the surface defect distribution.

[0012] Further, the binary deformable diffraction grating includes two one-dimensional deformable diffraction gratings orthogonal in the X-axis direction and the Y-axis direction; the direction of the laser beam emitted by the laser is the positive direction of the Z-axis, and the positive direction of the X-axis conforms to the left-handed rectangular coordinate system with the positive direction of the Y-axis vertically upward;

[0013] The grating equation of the one-dimensional deformable diffraction grating in the X-axis direction is as follows:

[0014]

[0015] where, , represent the two-dimensional coordinates with the center of the one-dimensional deformable diffraction grating in the X-axis direction as the origin; represents the wavelength of the laser beam, R is the radius of the grating aperture, is the grating period at the pupil center, is an integer, defines the trajectory of each grating slit of the one-dimensional deformable diffraction grating in the X-axis direction, corresponds to the grating slit passing through the aperture center in the X-axis direction, and decreases one by one along the negative X-axis and increases one by one along the positive X-axis ; represents the amount of grating defocusing ability in the X-axis direction;

[0016] Phase shift in the X-axis direction is:

[0017]

[0018] The grating equation of the one-dimensional deformed diffraction grating in the Y-axis direction is as follows:

[0019]

[0020] wherein, the quantity representing the defocusing ability of the grating in the Y-axis direction; and ; is an integer, defines the trajectory of each grating slit of the one-dimensional deformed diffraction grating in the Y-axis direction, corresponds to the grating slit passing through the aperture center in the Y-axis direction, and decreases one by one along the negative Y-axis and increases one by one along the positive Y-axis ;

[0021] Phase shift in the Y-axis direction is:

[0022]

[0023] Phase shift of the binary deformed diffraction grating is determined by the phase shift in the X-axis direction and the phase shift in the Y-axis direction, and is related to the diffraction order.

[0024] Furthermore, the binary deformed diffraction grating is used to divide the laser beam into diffraction spots of nine different diffraction orders; the nine different diffraction orders are respectively the (0,0) order, (-1,0) order, (+1,0) order, (0,-1) order, (0,+1) order, (-1,+1) order, (+1,-1) order, (-1,-1) order, and (+1,+1) order;

[0025] When the laser beam collimated by the collimating mirror is directly input into the variable magnification beam expander, the detected light intensity received by the camera is , , represent the diffraction order, , , , are all integers, represents the diffraction spot intensity distribution corresponding to the diffraction order , represents the coordinates on the detection surface of the camera;

[0026] When the laser beam collimated by the collimating mirror passes through each scanning position on the large-aperture optical element and then enters the variable magnification beam expander, the detected light intensity received by the camera is , s and t are the row and column of the current scanning position, s , t , s and t are both positive integers, u and v are the total number of rows and columns of the scanning positions respectively, represents the diffraction spot intensity distribution corresponding to the diffraction order .

[0027] Furthermore, the diffraction spot intensity distribution of the (0,0) order is , the phase shift amount is , ;

[0028] wherein, represents the coefficient of phase change, corresponding to the diffraction spot of the diffraction order ;

[0029] The diffraction spot intensity distributions of the (-1,0) order and (+1,0) order are respectively , , and the corresponding phase shift amounts are respectively , , , ;

[0030] The diffraction spot intensity distributions of the (0,-1) order and (0,+1) order are respectively , , and the corresponding phase shift amounts are respectively , , , ;

[0031] The diffraction spot intensity distributions of the (-1,+1) order and (+1,-1) order are respectively , , and the corresponding phase shift amounts are respectively , , , ;

[0032] The diffraction spot intensity distributions of the (-1,-1) order and (+1,+1) order are respectively , , and the corresponding phase shift amounts are respectively , , , .

[0033] Furthermore, the variable magnification beam expander includes a beam reducer and a beam expander arranged in sequence along the optical path, and the magnification change range of the variable magnification beam expander is 1 to 100.

[0034] A method for detecting surface defects of a large-aperture optical element is characterized in that the above-mentioned device for detecting surface defects of a large-aperture optical element is adopted, and it includes the following steps:

[0035] Step 1: Adjust the magnification of the variable magnification beam expander to 1, control the two-dimensional translation stage to move the large-aperture optical element out of the optical path, and the detected light intensity received by the camera is , , represents the diffraction order, , , , are all integers, represents the diffraction spot intensity distribution corresponding to the diffraction order , represents the coordinates on the detection surface of the camera; then calibrate the background phase in the optical path through the phase retrieval algorithm , is the coordinate in front of the binary deformed diffraction grating;

[0036] Step 2: Control the two-dimensional translation stage to scan the laser beam on the surface of the large-aperture optical element; at each scanning position, the detected light intensity received by the camera is , s and t are the row and column of the current scanning position, s , t , s and t are both positive integers, u and v are the total number of rows and columns of the scanning position respectively, represents the diffraction spot intensity distribution corresponding to the diffraction order at the current scanning position; calculate the phase distribution at this scanning position through the phase retrieval algorithm , and then remove the background phase , the surface defect distribution of the large-aperture optical element is , s and t are the row and column of the current scanning position;

[0037] Until the entire scanning process of the surface defects of the large-aperture optical element is completed, obtain the spliced surface defect distribution ;

[0038] Step 3: Move the large-aperture optical element through the two-dimensional translation stage to locate at the target defect, adjust the magnification of the variable magnification beam expander to magnify the target defect, observe the details of the target defect, and use the phase retrieval algorithm to obtain the magnified target defect distribution to complete the detection of the surface defects of the large-aperture optical element.

[0039] Further, in step 1, the process of the phase retrieval algorithm is as follows:

[0040] Step A1: Assume that the optical field to be measured in front of the binary deformable diffraction grating is , is the assumed initial phase value, which is a set of constants or a set of random numbers, is the complex unit; let , ;

[0041] Step A2: Modulate the optical field to be measured through the binary deformable diffraction grating, and calculate the optical field after its diffraction is transmitted to the camera, which is the forward Fraunhofer diffraction calculation;

[0042] Step A3: Keep the phase part of the optical field unchanged, and use the intensity distribution of the corresponding diffraction spot of the camera to update the amplitude part, obtaining the updated optical field ;

[0043] Step A4: Transmit the updated optical field to the front of the binary deformable diffraction grating through inverse diffraction, and remove the phase shift modulation effect, obtaining the optical field updated again;

[0044] Let , ;

[0045] Judge whether it is greater than 1. If so, execute step A5; otherwise, jump to step A2;

[0046] Step A5: Judge whether it is less than 1. If so, let , , and jump to step A2; otherwise, execute step A6;

[0047] Step A6: Judge whether the root mean square error is less than or equal to . If so, stop the iteration and execute step A7; otherwise, let , , and jump to step A2;

[0048] Step A7: Transmit inversely diffracted to the preset position of the large-aperture optical element to obtain the background phase , is the operation of taking the argument, is the inverse angular spectrum calculation.

[0049] Further, in step 2, at each scanning position, the phase distribution at the scanning position is calculated by a phase retrieval algorithm. The process is as follows:

[0050] Step B1. Assume that the current optical field to be measured in front of the binary deformable diffraction grating is , is the assumed initial phase value, which is a set of constants or a set of random numbers, is the imaginary unit; let , ;

[0051] Step B2. Modulate the current optical field to be measured by the binary deformable diffraction grating, and calculate the optical field diffracted and transmitted to the camera, which is a forward Fraunhofer diffraction calculation;

[0052] Step B3. Keep the phase part of the optical field unchanged, and update the amplitude part with the intensity distribution of the corresponding diffraction spot of the camera to obtain the updated optical field ;

[0053] Step B4. Transmit the updated optical field back to in front of the binary deformable diffraction grating through inverse diffraction, and remove the phase shift modulation effect to obtain the further updated optical field ;

[0054] Let , ;

[0055] Judge whether is greater than 1. If so, execute step B5; otherwise, jump to step B2;

[0056] Step B5. Judge whether is less than 1. If so, let , , and jump to step B2; otherwise, execute step B6;

[0057] Step B6. Judge whether the root mean square error is less than or equal to . If so, stop the iteration and execute step B7; otherwise, let , , and jump to step B2;

[0058] Step B7. Transmit it back to the large-aperture optical element through inverse diffraction to obtain at the current scanning position, where It is for inverse angular spectrum calculation.

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0060] (1) For a large-aperture optical element surface defect detection device of the present invention, by utilizing the diffraction characteristics of a binary deformable diffraction grating, a camera collects diffraction spots of multiple different diffraction orders at one time, calculates the surface phase of the large-aperture optical element through a phase retrieval algorithm, and combines a two-dimensional translation stage to scan the entire surface of the large-aperture optical element with a laser beam, thereby realizing the detection of surface defects of the large-aperture optical element; by reconstructing the phase information of the surface of the large-aperture optical element, the three-dimensional topography detection of surface defects can be realized, and at the same time, the self-focusing effect and the interaction between the laser and the medium causing damage to the surface of the optical element are avoided.

[0061] (2) In the present invention, the magnification change range of the variable magnification beam expander is 1 to 100, which can realize a smooth transition from rough scanning to fine detection, making the detection process not only efficient but also accurate; during large-range scanning, a low magnification can quickly locate potential defect areas, while a high magnification can magnify and analyze the target defect in detail to obtain high-resolution three-dimensional defect data.

[0062] (3) The automation and high efficiency of the present invention enable it to perform rapid detection during large-scale production, greatly improving the detection efficiency of the production line and meeting the requirements of high-throughput detection.

[0063] (4) For a large-aperture optical element surface defect detection method of the present invention, first, a rough scan is performed through a variable magnification beam expander and defects are detected using a phase retrieval algorithm, then the large-aperture optical element is positioned at the target defect position through a two-dimensional translation stage, and then the variable magnification beam expander is adjusted for magnification to observe the details of the defects, and the enlarged defect distribution is obtained through a phase retrieval algorithm; the present invention enables the surface defects of the large-aperture optical element to be quantified with high resolution and accuracy, ensuring the efficiency and accuracy of defect detection. Description of the Drawings

[0064] Figure 1 It is a schematic structural diagram of an embodiment of a large-aperture optical element surface defect detection device of the present invention;

[0065] Description of the reference numerals is as follows: 01 - large-aperture optical element;

[0066] 10 - laser; 20 - collimator; 30 - variable magnification beam expander; 31 - beam reducer; 32 - beam expander; 40 - binary deformable diffraction grating; 50 - focusing lens; 60 - camera; 70 - two-dimensional translation stage. Detailed Embodiments

[0067] The present invention will be further described below in conjunction with the accompanying drawings and exemplary embodiments.

[0068] Referring to Figure 1 , a surface defect detection device for large-aperture optical elements includes a laser 10, a two-dimensional translation stage 70, and a collimator 20, a variable magnification beam expander 30, a binary deformable diffraction grating 40, a focusing lens 50, and a camera 60 arranged in sequence along the optical path.

[0069] The laser 10 is used to emit a laser beam to the collimator 20, and the collimator 20 is used to collimate the laser beam.

[0070] The two-dimensional translation stage 70 is used to place the large-aperture optical element 01 and change the position where the laser beam irradiates on the large-aperture optical element 01, so as to realize the scanning of the large-aperture optical element 01 by the laser beam in the X-axis and Y-axis directions; the positive direction of the Z-axis is the direction of the laser beam emitted by the laser, and the positive direction of the X-axis conforms to the left-handed rectangular coordinate system with the positive direction of the Y-axis vertically upward.

[0071] The variable magnification beam expander 30 is used to expand the laser beam passing through the large-aperture optical element 01 or the laser beam directly input into the variable magnification beam expander 30 by the collimator 20, and output it to the binary deformable diffraction grating 40; the binary deformable diffraction grating 40 is used to divide the laser beam into diffraction spots of multiple different diffraction orders, and focus them to the detection surface of the camera 60 through the focusing lens 50, and each diffraction order corresponds to a specific phase shift amount; the detection surface of the camera 60 is located on the rear focal plane of the focusing lens 50, and is used to reconstruct the surface phase of the large-aperture optical element 01 by analyzing the intensity distribution and phase information of the diffraction spots of multiple different diffraction orders, so as to obtain the surface defect distribution.

[0072] The variable magnification beam expander 30 includes a beam reducer 31 and a beam expander 32 arranged in sequence along the optical path, and the magnification change range is 1 to 100, ensuring that the defect information can be clearly imaged on the detection surface of the camera 60.

[0073] The binary deformable diffraction grating 40 has the diffraction characteristics of a grating, and can divide the laser beam into diffraction spots of nine diffraction orders, and the nine diffraction orders are (0,0) order, (-1,0) order, (+1,0) order, (0,-1) order, (0,+1) order, (-1,+1) order, (+1,-1) order, (-1,-1) order, and (+1,+1) order; the binary deformable diffraction grating 40 includes two one-dimensional deformable diffraction gratings orthogonal in the X-axis direction and the Y-axis direction.

[0074] The grating equation of the one-dimensional deformable diffraction grating in the X-axis direction is as follows:

[0075]

[0076] Where , Represents the two-dimensional coordinates with the center of the one-dimensional deformed diffraction grating in the X-axis direction as the origin; Represents the wavelength of the laser beam, R is the radius of the grating aperture, is the grating period at the pupil center, is an integer, defines the trajectory of each grating slit of the one-dimensional deformed diffraction grating in the X-axis direction, corresponds to the grating slit passing through the aperture center in the X-axis direction, decreasing one by one along the negative X-axis and increasing one by one along the positive X-axis ; The quantity representing the defocusing ability of the grating in the X-axis direction, equivalent to the optical path added to the +1 order diffracted light wavefront at the pupil edge, and the phase shift in the X-axis direction introduced thereby is:

[0077]

[0078] The grating equation of the one-dimensional deformed diffraction grating in the Y-axis direction is as follows:

[0079]

[0080] where, The quantity representing the defocusing ability of the grating in the Y-axis direction, and ; is an integer, defines the trajectory of each grating slit of the one-dimensional deformed diffraction grating in the Y-axis direction, corresponds to the grating slit passing through the aperture center in the Y-axis direction, decreasing one by one along the negative Y-axis and increasing one by one along the positive Y-axis ;

[0081] The phase shift in the Y-axis direction is:

[0082]

[0083] The phase shift applied by the binary deformed diffraction grating 40 is determined by the phase shift in the X-axis direction and the phase shift

[0084] in the Y-axis direction, and is related to the diffraction order. The detection surface of the camera 60 receives diffraction spots of nine different diffraction orders, corresponding to different phase shift amounts respectively; when the laser beam collimated by the collimator 20 is directly input into the variable magnification beam expander 30, the detected light intensity received by the detection surface of the camera 60 is , , represents the diffraction order, , , 、 are all integers, represents the diffraction spot intensity distribution corresponding to the diffraction order ; represents the coordinates on the detection surface of the camera 60; when the laser beam collimated by the collimator 20 passes through the scanning position on the large-aperture optical element 01 and then enters the variable magnification beam expander 30, the detected light intensity received by the camera 60 is , s and t are the row and column of the current scanning position, s , t , s and t are both positive integers, u and v are the total number of rows and columns of the scanning position respectively, represents the diffraction spot intensity distribution corresponding to the diffraction order ;

[0085] The nine different diffraction orders are as follows: Nine different diffraction orders are:

[0086] (0,0) order: The diffraction spot intensity distribution is , and the phase shift amount is , ;

[0087] represents the coefficient of phase change, corresponding to the diffraction spot of the diffraction order ;

[0088] (-1,0) order and (+1,0) order: The diffraction spot intensity distributions are respectively (-1,0) order and (+1,0) order: The diffraction spot intensity distributions are respectively , , and the corresponding phase shift amounts are respectively , , , ;

[0089] (0,-1) order and (0,+1) order: The diffraction spot intensity distributions are respectively , , and the corresponding phase shift amounts are respectively , , , ;

[0090] (-1,+1) order and (+1,-1) order: The diffraction spot intensity distributions are respectively , , and the corresponding phase shift amounts are respectively , , , ;

[0091] ​​​​​​The (-1, -1) level and the (+1, +1) level: The intensity distributions of the diffraction spots are respectively , , and the corresponding phase shift amounts are respectively , , , .

[0092] The specific working process of the present invention is as follows:

[0093] The laser beam emitted by the laser 10 is collimated by the collimating mirror 20 and then enters the variable magnification beam expander 30 to be expanded according to a preset magnification. Then it enters the binary deformable diffraction grating 40, and the laser beam is divided into diffraction spots of nine different diffraction orders by the binary deformable diffraction grating 40, and is focused onto the detection surface of the camera 60 through the focusing mirror 50;

[0094] By moving the two-dimensional translation stage 70, the laser beam scans the surface of the large-aperture optical element 01. Finally, the surface phase of the large-aperture optical element 01 is obtained by using the intensity distributions of these diffraction spots of different diffraction orders and the phase retrieval algorithm, and the detection of surface defects of the large-aperture optical element 01 can be realized.

[0095] A method for detecting surface defects of a large-aperture optical element, using the above-mentioned device for detecting surface defects of a large-aperture optical element, includes the following steps:

[0096] Step 1: Adjust the magnification of the variable magnification beam expander 30 to 1, control the two-dimensional translation stage 70 to move the large-aperture optical element 01 out of the optical path, and the detected light intensity received by the camera 60 is ;

[0097] Then calibrate the background phase in the optical path through the phase retrieval algorithm , specifically as follows:

[0098] Step A1: Assume that the light field to be measured in front of the binary deformable diffraction grating 40 is , is the assumed initial phase value, which is a set of constants or a set of random numbers, is the complex unit, is the coordinate in front of the binary deformable diffraction grating 40;

[0099] Let , ;

[0100] Step A2: Modulate the light field to be measured through the binary deformable diffraction grating 40, and calculate the light field diffracted and transmitted to the camera 60, which is the forward Fraunhofer diffraction calculation;

[0101] Step A3: Keep the phase part of the optical field unchanged, and use the intensity distribution of the diffraction spot corresponding to the camera 60 to update the amplitude part, obtaining the updated optical field ;

[0102] Step A4: Transmit the updated optical field to the front of the binary deformable diffraction grating 40 through inverse diffraction, and remove the phase shift modulation effect, obtaining the optical field updated again ;

[0103] Let , ;

[0104] Judge whether it is greater than 1. If so, execute Step A5; otherwise, jump to Step A2;

[0105] Step A5: Judge whether it is less than 1. If so, let , , and jump to Step A2; otherwise, execute Step A6;

[0106] Step A6: Judge whether the root mean square error is less than or equal to . If so, stop the iteration and execute Step A7; otherwise, let , , and jump to Step A2;

[0107] Step A7: Transmit inversely through diffraction to the preset position of the large-aperture optical element 01, and obtain the background phase , is the operation of taking the argument, is the inverse angular spectrum calculation;

[0108] Step 2: Scan and move the two-dimensional translation stage 70 along the X-axis and Y-axis directions until the laser beam is incident on the upper left corner of the large-aperture optical element 01, denoted as the initial position; control the two-dimensional translation stage 70 to make the laser beam scan on the surface of the large-aperture optical element 01 from the initial position;

[0109] At each scanning position, the detected light intensity received by the camera 60 is , calculate the phase distribution at this scanning position through the phase retrieval algorithm, and then remove the background phase , obtaining the surface defect distribution of the large-aperture optical element 01 as , where s and t are the row and column of the current scanning position;

[0110] Until the entire scanning process of the surface defects of the large-aperture optical element 01 is completed, the stitched surface defect distribution is obtained , where u and v are the total number of rows and columns of the scan respectively;

[0111] The phase distribution at the scanning position is calculated as follows:

[0112] Step B1. Assume that the current optical field to be measured in front of the binary deformable diffraction grating 40 is , is the assumed initial phase value, which is a set of constants or a set of random numbers;

[0113] Let , ;

[0114] Step B2. Modulate the current optical field to be measured through the binary deformable diffraction grating 40, and calculate the optical field diffracted and transmitted to the camera 60;

[0115] Step B3. Keep the phase part of the optical field unchanged, and update the amplitude part with the intensity distribution of the corresponding diffraction spot of the camera 60 to obtain the updated optical field ;

[0116] Step B4. Transmit the updated optical field to in front of the binary deformable diffraction grating 40 through inverse diffraction, and remove the phase shift modulation effect to obtain the optical field updated again;

[0117] Let , ;

[0118] Judge whether is greater than 1. If so, execute Step B5; otherwise, jump to Step B2;

[0119] Step B5. Judge whether is less than 1. If so, let , , jump to Step B2; otherwise, execute Step B6;

[0120] Step B6. Judge whether the root mean square error is less than or equal to . If so, stop the iteration and execute Step B7; otherwise, let , , jump to Step B2;

[0121] Step B7, perform reverse diffraction transmission to the large-aperture optical element 01 to obtain the ;

[0122] Step 3, move the large-aperture optical element 01 through the two-dimensional translation stage 70, position it at the target defect, adjust the magnification of the variable magnification beam expander 30 to magnify the target defect, observe the details of the target defect, and use the phase retrieval algorithm in Step 1 to obtain the distribution of the magnified target defect.

Claims

1. A method for detecting surface defects of large-aperture optical components, characterized in that: A large-aperture optical element surface defect detection device is used, the device comprising a laser (10), a two-dimensional translation stage (70), and a collimator (20), a variable-magnification beam expander (30), a binary deformable diffraction grating (40), a focusing lens (50), and a camera (60) arranged in sequence along an optical path; The laser (10) is used to emit a laser beam to a collimator (20), and the collimator (20) is used to collimate the laser beam; The binary deformed diffraction grating (40) comprises two one-dimensional deformed diffraction gratings that are orthogonal in the X-axis direction and the Y-axis direction; the positive direction of the Z-axis is the direction of the laser beam emitted by the laser (10), and the positive direction of the X-axis conforms to a left-hand rectangular coordinate system with the positive direction of the Y-axis pointing vertically upward; The two-dimensional translation stage (70) is used to place the large-aperture optical element (01) and to change the position where the laser beam irradiates the large-aperture optical element (01); The variable magnification beam expander (30) is used to expand a laser beam that passes through a large-aperture optical element (01) or a laser beam that is directly input into the variable magnification beam expander (30) by a collimator (20), and output the expanded beam to a binary deformable diffraction grating (40); the binary deformable diffraction grating (40) is used to split the laser beam into a plurality of diffraction spots of different diffraction orders, and focus the spots onto a detection surface of a camera (60) through the focusing lens (50); the detection surface of the camera (60) is located on the back focal plane of the focusing lens (50); each diffraction order corresponds to a specific phase shift, and is used to reconstruct the surface phase of the large-aperture optical element (01), thereby obtaining a surface defect distribution; The steps include: Step 1: Adjust the magnification of the variable magnification beam expander (30) to 1, control the two-dimensional translation stage (70) to move the large-aperture optical element (01) out of the light path, and the detection light intensity received by the camera (60) is m, n represent the diffraction order, m∈[-1,+1], n∈[-1,+1], m, n are both integers, I m,n (x f ,y f ) represents the intensity distribution of the diffraction spot corresponding to the diffraction order (m,n), (x f ,y f ) represents the coordinates on the detection surface of the camera (60); then the background phase Φ0(x0, y0) in the optical path is calibrated by a phase recovery algorithm, where (x0, y0) is the coordinate before the binary deformed diffraction grating (40); Step 2: By controlling the two-dimensional translation stage (70), the laser beam is scanned on the surface of the large-aperture optical element (01); at each scanning position, the detection light intensity received by the camera (60) is s, t are the row and column of the current scanning position, s∈[1,u], t∈[1,v], s, t are both positive integers, u, v are the total number of rows and columns of the scanning position, respectively. Indicates the intensity distribution of the diffraction spot corresponding to the diffraction order (m, n) at the current scanning position; the phase distribution Ψ of the scanning position is calculated by the phase recovery algorithm s,t (x0, y0), and then remove the background phase Φ0(x0, y0), the surface defect distribution of the large-aperture optical element (01) is Φ′ s,t (x0,y0)=Φ s,t (x0,y0)-Φ0(x0,y0), s, t are the row and column of the current scanning position; Until the entire scanning process of the surface defects of the large-aperture optical element (01) is completed, the surface defect distribution of the splicing is obtained. Step 3: Move the large-aperture optical element (01) by a two-dimensional translation stage (70) to locate the target defect, adjust the magnification of the variable-magnification beam expander (30), magnify the target defect, observe the details of the target defect, and use a phase recovery algorithm to obtain the distribution of the magnified target defect, thereby completing the surface defect detection of the large-aperture optical element (01).

2. A method for detecting surface defects of large-aperture optical components according to claim 1, characterized in that: The grating equation of the one-dimensional deformable diffraction grating in the X-axis direction is as follows: Wherein, x and y represent two-dimensional coordinates with the center of the one-dimensional deformed diffraction grating in the X-axis direction as the origin; λ represents the wavelength of the laser beam, R is the radius of the grating aperture, d0 is the grating period at the center of the pupil, n1 is an integer, and n1 defines the trajectory of each grating slit of the one-dimensional deformed diffraction grating in the X-axis direction. n1=0 corresponds to the grating slit passing through the center of the aperture in the X-axis direction, and n1 decreases one by one along the negative direction of the X-axis, and increases one by one along the positive direction of the X-axis; W 20x The amount that indicates the defocusing ability of the grating in the X-axis direction; Phase shift in the X-axis direction φ x (x,y) is: The grating equation of the one-dimensional deformable diffraction grating in the Y-axis direction is as follows: Among them, W 20y represents the amount of grating defocusing ability in the Y-axis direction; and W 20y =3W 20x ; n2 is an integer, and n2 defines the trajectory of each grating slit of the one-dimensional deformable diffraction grating in the Y-axis direction. n2=0 corresponds to the grating slit passing through the center of the aperture in the Y-axis direction. n2 decreases one by one along the negative direction of the Y-axis, and n2 increases one by one along the positive direction of the Y-axis. Phase shift in the Y-axis direction φ y (x,y) is: The magnitude of the phase shift φ(x,y) of the binary deformed diffraction grating (40) is determined by the phase shift φ in the X-axis direction. x (x,y) and the phase shift φ in the Y-axis direction y (x,y) determines the diffraction order.

3. A method for detecting surface defects of a large-aperture optical element according to claim 2, characterized in that: The binary deformable diffraction grating (40) is used to split the laser beam into diffraction spots of nine different diffraction orders; the nine different diffraction orders are respectively (0,0), (-1,0), (+1,0), (0,-1), (0,+1), (-1,+1), (+1,-1), (-1,-1) and (+1,+1); When the laser beam collimated by the collimator (20) is directly input into the variable-magnification beam expander (30), the detection light intensity received by the camera (60) is m, n represent the diffraction order, m∈[-1,+1], n∈[-1,+1], m, n are both integers, I m,n (xf, yf) represents the intensity distribution of the diffraction spot corresponding to the diffraction order (m, n), (x f ,x f ) represents the coordinates on the detection surface of the camera (60); When the laser beam collimated by the collimator (20) passes through each scanning position on the large-aperture optical element (01) and then enters the variable-magnification beam expander (30), the detection light intensity received by the camera (60) is s, t are the row and column of the current scanning position, s∈[1,u], t∈[1,v], s, t are both positive integers, u, v are the total number of rows and columns of the scanning position, respectively. Indicates the intensity distribution of the diffraction spot corresponding to the diffraction order (m, n) at the current scanning position.

4. A method for detecting surface defects of a large-aperture optical element according to claim 3, characterized in that: The intensity distribution of the (0,0) order diffraction spot is I 0,0 (x f ,y f ), the phase shift is k 0,0 φ(x,y),k 0,0 =0; Among them, k m,n The coefficient representing the phase change corresponds to the diffraction spot of the diffraction order (m,n); The intensity distributions of the (-1,0) and (+1,0) diffraction spots are respectively -1,0 (x f ,y f ), I +1,0 (x f ,y f ), the corresponding phase shifts are k -1,0 φ(x,y),k +1,0 φ(x,y),k -1,0 =-1, k +1,0 =1; The intensity distributions of the (0, -1) and (0, +1) order diffraction spots are I 0,-1 (x f ,y f ), I 0,+1 (x f ,y f ), the corresponding phase shifts are k 0,-1 φ(x,y),k 0,+1 φ(x,y),k 0,-1 =-3, k 0,+1 =3; The intensity distributions of the (-1, +1) and (+1, -1) order diffraction spots are respectively -1,+1 (x f ,y f ), I +1,-1 (x f ,y f ), the corresponding phase shifts are k -1,+1 φ(x,y),k +1,-1 φ(x,y),k -1,+1 =-2, k +1,-1 =2; The (-1, -1) and (+1, +1) order diffraction spot intensity distributions are I -1,-1 (x f ,y f ), I +1,+1 (x f ,y f ), the corresponding phase shifts are k -1,-1 φ(x,y),k +1,+1 φ(x,y),k -1,-1 =-4, k +1,+1 =4.

5. A method for detecting surface defects of a large-aperture optical element according to any one of claims 1 to 4, characterized in that: The variable magnification beam expander (30) comprises a beam reducer (31) and a beam expander (32) which are sequentially arranged along an optical path, and the variable magnification beam expander (30) has a magnification variation range of 1 to 100.

6. A method for detecting surface defects of a large-aperture optical element according to claim 1, characterized in that: In step 1, the process of the phase recovery algorithm is as follows: Step A1, assuming that the light field to be measured before the binary deformed diffraction grating (40) is O(x0, y0) = exp[iφ0(x0, y0)], φ0(x0, y0) is an assumed initial phase value, which is a set of constants or a set of random numbers, and i is a complex unit; Let m = -1, n = -1; Step A2: modulate the light field O(x0, y0) to be measured by the binary deformed diffraction grating (40), and calculate the light field U after the light field is diffracted and transmitted to the camera (60). f (x f ,y f )=F fraunhofer {O(x0,y0)exp[i·k m,n φ(x,y)]},F fraunhofer Calculation of Fraunhofer diffraction in the forward direction; Step A3: Maintain light field U f (x f ,y f ) remains unchanged, and the diffraction spot intensity distribution I corresponding to the camera (60) is used m,n (x f ,y f ) to update the amplitude part and get the updated light field Step A4: Reverse diffraction to update the light field U′ f (x f ,y f ) is transmitted to the binary deformable diffraction grating (40), and the phase shift modulation effect is removed to obtain the light field after being updated again Let m=m+1, O(x0,y0)=O′(x0,y0); Determine whether m is greater than 1. If so, execute step A5; otherwise, jump to step A2. Step A5, determine whether n is less than 1, if so, set m=-1, n=n+1, jump to step A2, otherwise execute step A6; Step A6: Determine the root mean square error Is it less than or equal to 10? -5 If yes, stop the iteration and execute step A7; otherwise, set m=-1, n=-1 and jump to step A2; Step A7: Back-diffraction transmission to the preset position of the large-aperture optical element (01) to obtain the background phase angle is the angle-taking operation. Calculate the inverse angular spectrum.

7. A method for detecting surface defects of a large-aperture optical element according to claim 1 or 6, characterized in that: In step 2, at each scanning position, the phase distribution Φ of the scanning position is calculated by the phase recovery algorithm. s,t The process of (x0,y0) is as follows: Step B1, assuming that the current light field to be measured in front of the binary deformed diffraction grating (40) is O s,t (x0,y0)=exp[iφ s,t (x0,y0)],φ s,t (x0, y0) is the assumed initial phase value, which is a set of constants or a set of random numbers, and i is a complex unit; Let m = -1, n = -1; Step B2: using the binary deformed diffraction grating (40) to measure the current light field O s,t (x0, y0) is modulated and its diffraction light field U transmitted to the camera (60) is calculated f (x f ,y f )=F fraunhofer {O s,t (x0,y0)exp[i·k m,n φ(x,y)]},F fraunhofer Calculation for forward Fraunhofer diffraction; Step B3: Maintain the light field U f (x f ,y f ) remains unchanged, and the intensity distribution of the diffraction spot corresponding to the camera (60) is To update the amplitude part, get the updated light field Step B4: Reverse diffraction to update the light field U′ f (x f ,y f ) is transmitted to the binary deformable diffraction grating (40), and the phase shift modulation effect is removed to obtain the light field after being updated again Let m = m + 1, O s,t (x0, y0) = O' s,t (x0, y0); Determine whether m is greater than 1. If so, execute step B5; otherwise, jump to step B2. Step B5, determine whether n is less than 1, if so, set m=-1, n=n+1, jump to step B2, otherwise execute step B6; Step B6: Determine the root mean square error Is it less than or equal to 10? -5 If yes, stop the iteration and execute step B7; otherwise, set m=-1, n=-1 and jump to step B2; Step B7: Back-diffracted light is transmitted to the large-aperture optical element (01) to obtain the current scanning position. angle is the angle-taking operation. Calculate the inverse angular spectrum.

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