An optical element surface measurement device and method

Abstract

The present invention discloses an optical element surface measurement device and method. The device includes a light source module, a moving stage, a laser energy monitoring module, a photoelectric detection module, a spatial triangle focus positioning module, a projection module, a binocular vision module, and a processing module. According to the technical solution of the present invention, the laser pulse energy is recorded in real time by the laser energy monitoring module, the radius of the focused light spot is accurately measured by the photoelectric detection module, the focus position is accurately positioned by the spatial triangle focus positioning module, the periodic structure interference fringes are projected onto the surface of the optical element to be measured by the projection module, the change of the interference fringes is captured by the binocular vision module, and combined with the phase-shifting and phase-unwrapping algorithms, the micro-deformation or damage is judged, and the three-dimensional reconstruction of the micro-deformation and damage morphology on the surface of the optical element is realized. The real-time online measurement of the micro-deformation and damage threshold of the optical element is realized, and the damage threshold evaluation process is optimized. The present invention has the advantages of high precision, strong real-time performance, high automation degree, and wide application range.

Description

Technical Field

[0001] The present invention relates to the technical field of optical measurement, and particularly relates to an optical element surface measurement device and method. Background Art

[0002] With the wide application of high-power lasers in fields such as scientific research and industrial processing, the surface quality and damage threshold of optical elements have a significant impact on the performance and lifespan of optical systems. Traditional damage threshold measurement methods mainly conduct qualitative analysis of surface damage through off-line experiments, static evaluations, or optical microscopes. These methods usually have the following problems:

[0003] 1) Limited measurement accuracy: Traditional methods have insufficient accuracy in detecting minute deformations and initial damages on the surface of optical elements, and are unable to comprehensively evaluate various damage mechanisms (such as fatigue, aging, thermal damage, etc.), making it difficult to timely detect potential problems. 2) Poor real-time performance: Most methods require removing the optical element from the test system for off-line measurement, and cannot achieve on-line and real-time monitoring. 3) Limited application scope: For optical elements with complex shapes or uneven surfaces, traditional methods are difficult to obtain accurate measurement results.

[0004] Therefore, there is an urgent need for a device and method capable of measuring the micro-deformation and damage threshold of the surface of optical elements with high precision, in real time, and on-line. Summary of the Invention

[0005] Embodiments of the present invention provide an optical element surface measurement device and method to solve problems such as low measurement accuracy, poor real-time performance, and limited application scope existing in the prior art.

[0006] According to one aspect of the present invention, there is provided an optical element surface measurement device, comprising:

[0007] A light source module, which is used to output a laser beam with adjustable intensity to the optical element to be measured;

[0008] A moving stage, which is used to carry the optical element to be measured, a slit element, or a resolution test board, and is also used to drive the optical element to be measured, the slit element, or the resolution test board to move in multiple directions;

[0009] A laser energy monitoring module, which is used to record the energy of each laser pulse emitted by the light source module during the test of the optical element to be measured;

[0010] A photoelectric detection module, which is used to measure the radius of the laser focused spot by the slit method when the slit element is arranged on the moving stage;

[0011] Spatial triangular focus positioning module, which is used to locate the spatial coordinates of the optical element to be measured when the moving stage adjusts the spatial position of the optical element to be measured to the focus;

[0012] Projection module, which is used to generate periodic interference fringes and project them onto the surface of the optical element to be measured;

[0013] Binocular vision module, which includes a first camera and a second camera. Both the first camera and the second camera are used to acquire interference fringe images on the surface of the optical element to be measured. Among them, the first camera acquires coaxial light beams, and the second camera acquires off-axis light beams;

[0014] Processing module. The light source module, the moving stage, the laser energy monitoring module, the photoelectric detection module, the spatial triangular focus positioning module, the projection module and the binocular vision module are all connected to the processing module. The processing module is used to detect the micro-deformation or damage threshold on the surface of the optical element to be measured according to the interference fringe images;

[0015] The moving stage includes a self-centering bracket, a rotary angular displacement stage, a Z-axis lifting displacement stage, a first X-axis linear displacement stage and a Y-axis linear displacement stage. The self-centering bracket is used to fix the optical element to be measured, the slit element or the resolution test board. The rotary angular displacement stage, the Z-axis lifting displacement stage, the first X-axis linear displacement stage and the Y-axis linear displacement stage are respectively used to adjust the rotation angle, Z-direction position, X-direction position and Y-direction position of the optical element to be measured, the slit element or the resolution test board. Among them, the X-axis, Y-axis and Z-axis are perpendicular to each other in pairs;

[0016] The photoelectric detection module includes a band-pass filter and a photodetector. When the slit element is fixed on the self-centering bracket, the focused light spot passes through the slit of the slit element and the band-pass filter and is received by the photodetector. The first X-axis linear displacement stage is used to drive the slit element to move. The processing module is also used to measure the radius of the focused light spot according to the signal of the photodetector.

[0017] Optionally, the light source module includes a first laser, a half-wave plate, a polarization beam splitter, a dichroic mirror and a first focusing lens group. The first focusing lens group includes at least one focusing lens;

[0018] The output beam of the first laser passes through the half-wave plate and then is incident on the polarization beam splitter and is split into a first beam and a second beam. The first beam is incident on the laser energy monitoring module, and the second beam passes through the dichroic mirror and the first focusing lens group and then converges on the optical element to be measured;

[0019] When rotating the half-wave plate along the optical axis of the half-wave plate, the intensities of the first light beam and the second light beam are adjusted.

[0020] Optionally, the laser energy monitoring module includes a first energy meter, a second energy meter, and a second X-axis linear displacement stage, and the second energy meter is fixed on the second X-axis linear displacement stage;

[0021] The first energy meter is used to receive the first light beam. When calibrating the splitting curve of the output light beam of the first laser, the second X-axis linear displacement stage drives the second energy meter to be located in the optical path of the second light beam. When measuring the optical element to be measured, the second X-axis linear displacement stage drives the second energy meter to be located outside the optical path of the second light beam.

[0022] Optionally, the spatial triangular focus positioning module includes a second laser and a third laser. The output light beams of the second laser and the third laser are obliquely incident on the optical element to be measured. The Z-axis lifting displacement stage, the first X-axis linear displacement stage, and the Y-axis linear displacement stage adjust the spatial position of the optical element to be measured, and the spatial triangular focus positioning module positions the spatial coordinates of the optical element to be measured according to the triangulation method.

[0023] Optionally, the projection module includes a fourth laser, a linear polarizer, a polarization grating, and a second focusing lens group. The second focusing lens group includes at least one focusing lens. The output light beam of the fourth laser generates periodic interference fringes after passing through the linear polarizer and the polarization grating, and the periodic interference fringes are converged to the surface of the optical element to be measured through the second focusing lens group.

[0024] Optionally, the processing module includes a motion stage controller, a data synchronous collector, and a computer. The motion stage is connected to the motion stage controller. The laser energy monitoring module, the photoelectric detection module, and the binocular vision module are all connected to the data synchronous collector. The motion stage controller and the data synchronous collector are both connected to the computer.

[0025] According to another aspect of the present invention, there is provided an optical element surface measurement method, which is performed by using the above optical element surface measurement device. The optical element measurement method includes:

[0026] S1. Measuring the splitting curve of the light source module by using the laser energy monitoring module;

[0027] S2. Setting the slit element on the workbench, and measuring the radius of the laser focused spot by using the photoelectric detection module by the slit method;

[0028] S3. Mark the measured focal position through the spatial triangular focal point positioning module, replace the slit element with a resolution test board, and calibrate the system parameters and pixel density of the binocular vision module;

[0029] S4. Fix the optical element to be measured on the workbench, adjust the workbench to position the optical element to be measured at the measured focal position, use the projection module to project periodic interference fringes onto the optical element to be measured, and obtain the corresponding position and pixel intensity information of the interference fringes reflected from the surface of the optical element to be measured in the world coordinate system through the binocular vision module;

[0030] S5. Continuously adjust the light source module, gradually increase the laser energy acting on the optical element to be measured, use the laser energy monitoring module to obtain the laser energy acting on the optical element to be measured, obtain the change of the interference fringes on the surface of the optical element to be measured after the action of the corresponding pulsed laser through the binocular vision module, combine the phase shift algorithm and the unwrapping algorithm to restore the true phase of the interference fringes, and judge whether the optical element to be measured has undergone micro-deformation and damage. If the optical element to be measured has undergone micro-deformation or damage, stop the output of the light source module and give the deformation morphology or damage morphology and the corresponding threshold;

[0031] S6: Repeat S1 to S5 to achieve the one-to-one and S-to-one online testing of the damage threshold of the optical element to be measured;

[0032] Wherein, S is an integer greater than 1, and the fringe function after being reflected by the optical element to be measured is expressed as:

[0033] ;

[0034] ;

[0035] Wherein, is the coordinate point on the image plane, is the light intensity of the projection module, b is the fringe amplitude, is the additional phase modulation, is the phase modulation introduced by the optical element to be measured.

[0036] Optionally, whether the optical element to be measured has undergone micro-deformation and damage is judged according to the following conditions:

[0037] According to the measured phase change and the system noise and the deformation threshold comparison, the state of the optical element to be measured is divided into three categories:

[0038] When it is determined that the optical element to be measured has not undergone deformation;

[0039] When occurs, it is determined that the optical element to be measured has undergone a slight deformation;

[0040] When occurs, it is determined that the optical element to be measured exceeds the deformation threshold;

[0041] Among them, before the damage threshold test, by collecting multiple interference fringe images of the optical element to be measured under the same conditions, the first one is used as the reference initial reference state , calculate the standard deviation of the phase difference of each image point :

[0042] ;

[0043] The system noise is defined as ;

[0044] According to the interference fringe image, as an auxiliary determination basis, when the interference fringe is distorted but still continuous and unbroken, it is determined that the optical element to be measured has deformed, and when the interference fringe is broken and discontinuous, it is determined that the optical element to be measured is damaged; define the deformation threshold according to the material parameters of the optical element to be measured , the phase change corresponding to the deformation threshold is:

[0045] .

[0046] The optical element surface measurement device provided by an embodiment of the present invention includes: a light source module, a moving stage, a laser energy monitoring module, a photoelectric detection module, a spatial triangulation focus positioning module, a projection module, a binocular vision module, and a processing module. The binocular vision module includes a first camera and a second camera. The light source module, the moving stage, the laser energy monitoring module, the photoelectric detection module, the spatial triangulation focus positioning module, the projection module, and the binocular vision module are all connected to the processing module. A laser beam with adjustable intensity is output to the optical element to be measured through the light source module; the optical element to be measured, the slit element, or the resolution test board is carried by the moving stage, and the optical element to be measured, the slit element, or the resolution test board is driven to move in multiple directions; the energy of each laser pulse emitted by the light source module during the test of the optical element to be measured is recorded through the laser energy monitoring module; when the slit element is arranged on the moving stage, the radius of the laser focusing spot is measured by the photoelectric detection module using the slit method; when the spatial position of the optical element to be measured is adjusted to the focus by the moving stage, the spatial coordinates where the optical element to be measured is located are positioned through the spatial triangulation focus positioning module; periodic interference fringes are generated and projected onto the surface of the optical element to be measured through the projection module; an interference fringe image corresponding to the coaxial beam is acquired by the first camera of the binocular vision module, and an interference fringe image corresponding to the off-axis beam is acquired by the second camera; the surface micro-deformation or damage threshold of the optical element to be measured is detected by the processing module according to the interference fringe image, so as to solve the problems of low measurement accuracy, poor real-time performance, and limited application range existing in the prior art.

[0047] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0049] Figure 1 It is a structural block diagram of an optical element surface measurement device provided by an embodiment of the present invention;

[0050] Figure 2 It is a structural schematic diagram of an optical element surface measurement device provided by an embodiment of the present invention;

[0051] Figure 3 It is a flowchart of an optical element surface measurement method provided by an embodiment of the present invention;

[0052] Figure 4Schematic diagram of the slit element provided by the embodiment of the present invention;

[0053] Figure 5 Schematic diagram of the resolution test board provided by the embodiment of the present invention. Detailed implementation manners

[0054] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0055] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0056] Figure 1 Structural block diagram of an optical element surface measurement device provided by the embodiment of the present invention, Figure 2 Schematic structural diagram of an optical element surface measurement device provided by the embodiment of the present invention, refer to Figure 1 and Figure 2 , the optical element measurement device includes: a light source module 100, and the light source module 100 is used to output a laser beam with adjustable intensity to the optical element 6 to be measured. Optionally, the light source module 100 includes a first laser 1, a half-wave plate 2, a polarization beam splitter 3, a dichroic mirror 4, and a first focusing lens group 5. The first focusing lens group 5 includes at least one focusing lens ( Figure 2 One focusing lens is schematically shown in, which is not a limitation to the embodiment of the present invention); the output beam of the first laser 1 is transmitted through the half-wave plate 2 and then incident on the polarization beam splitter 3 to be split into a first beam a1 and a second beam b1. The first beam a1 is incident on the laser energy monitoring module 300, and the second beam b1 is converged on the optical element 6 to be measured after passing through the dichroic mirror 4 and the first focusing lens group 5; wherein, when the half-wave plate 2 is rotated along its optical axis, the intensities of the first beam a1 and the second beam b1 are adjusted.

[0057] Among them, the first laser 1 can output a laser beam with a constant intensity, and when the half-wave plate 2 rotates along the optical axis, it changes the polarization state of the laser beam. The polarization beam splitter 3 can be a polarization beam splitting prism PBS. For example, it can transmit the horizontally polarized light p and reflect the vertically polarized light s, or reflect the horizontally polarized light p and transmit the vertically polarized light s. When the half-wave plate 2 rotates, the proportions of the p light and the s light are different, and the intensity adjustment of the first beam a1 and the second beam b1 can be realized.

[0058] The moving stage 200 is used to carry the optical element 6 to be measured, the slit element ( Figure 2 (not shown)) or the resolution test board ( Figure 2 (not shown)), and is also used to drive the optical element 6 to be measured, the slit element or the resolution test board to move in multiple directions. Optionally, the moving stage 200 includes a self-centering bracket 7, a rotary angular displacement stage 8, a Z-axis lifting displacement stage 9, a first X-axis linear displacement stage 10, and a Y-axis linear displacement stage 11. The self-centering bracket 7 is used to fix the optical element 6 to be measured, the slit element or the resolution test board. The rotary angular displacement stage 8, the Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, and the Y-axis linear displacement stage 11 are respectively used to adjust the rotation angle, the Z-direction position, the X-direction position, and the Y-direction position of the optical element 6 to be measured, the slit element or the resolution test board, where the X-axis, the Y-axis, and the Z-axis are perpendicular to each other in pairs.

[0059] Among them, the self-centering bracket 7 is mainly used to center the optical element. The maximum size of any optical element can reach the inner diameter of the bracket itself, which is convenient, accurate, fast, and repeatable for placement and fixation. The center position has nothing to do with the diameter size of the optical element. The rotary angular displacement stage 8 is used to rotate the angle of the optical element 6 to be measured to realize the measurement of the damage threshold at different incident angles. The Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, and the Y-axis linear displacement stage 11 can drive the optical element 6 to be measured, the slit element or the resolution test board to realize three-dimensional movement, so that the optical element 6 to be measured, the slit element or the resolution test board can reach the preset position.

[0060] The laser energy monitoring module 300 is used to record the energy of each laser pulse emitted by the light source module 100 during the test of the optical element 6 to be measured. Optionally, the laser energy monitoring module 300 includes a first energy meter 12, a second energy meter 13, and a second X-axis linear displacement stage 14. The second energy meter is fixed on the second X-axis linear displacement stage 14. The first energy meter 12 is used to receive the first beam a1. When calibrating the splitting curve of the output beam of the first laser 1, the second X-axis linear displacement stage 14 drives the second energy meter 13 to be located in the optical path of the second beam b1. When measuring the optical element 6 to be measured, the second X-axis linear displacement stage 14 drives the second energy meter 13 to be located outside the optical path of the second beam b1.

[0061] It is understandable that to measure the damage threshold of the optical element 6 to be measured, it is necessary to know the optical energy incident on the optical element 6 to be measured. Therefore, it is necessary to calibrate the splitting curve of the output beam of the first laser 1. During specific implementation, the first energy meter 12 always receives the first beam a1. Before measuring the element 6 to be measured, the second X-axis linear displacement stage 14 drives the second energy meter 13 to be located in the optical path of the second beam b1 ( Figure 2 shown by the dotted line in the figure). By rotating the half-wave plate 2, the splitting curve can be obtained based on the measurement values of the first energy meter 12 and the second energy meter 13, and the corresponding relationship between the two is established. During subsequent measurements, the second X-axis linear displacement stage 14 drives the second energy meter 13 out of the optical path of the second beam b1. By only monitoring the reading of the first energy meter 12, the laser energy acting on the optical element 6 to be measured can be accurately calculated.

[0062] The photoelectric detection module 400 is used to measure the radius of the laser focusing spot by the slit method when the slit element is arranged on the moving stage 200. Optionally, the photoelectric detection module 400 includes a band-pass filter 15 and a photodetector 16. When the slit element is fixed on the self-centering bracket 7, the focused spot passes through the slit of the slit element and the band-pass filter 15 and is received by the photodetector 16. The first X-axis linear displacement stage 10 is used to drive the slit element to move. The processing module 800 is also used to measure the radius of the focused spot according to the signal of the photodetector 16.

[0063] Among them, the band-pass filter 15 is used to filter out light of non-working wavelengths to ensure that the photodetector 16 only receives the target laser signal. By using the slit method and using the first X-axis linear displacement stage 10 to move the position of the slit element, part of the beam of the focused spot passes through the slit each time and the light intensity signal of the photodetector 16 is recorded to obtain the spot intensity distribution curve. The radius of the focused spot is calculated by curve fitting.

[0064] The spatial triangular focus positioning module 500 is used to locate the spatial coordinates of the optical element 6 to be measured when the moving stage 200 adjusts the spatial position of the optical element 6 to be measured to the focus. Optionally, the spatial triangular focus positioning module 500 includes a second laser 17 and a third laser 18. The output beams of the second laser 17 and the third laser 18 are obliquely incident on the optical element 6 to be measured. The Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, and the Y-axis linear displacement stage 11 adjust the spatial position of the optical element 6 to be measured. The spatial triangular focus positioning module 500 locates the spatial coordinates of the optical element 6 to be measured according to the triangulation method.

[0065] Among them, both the second laser 17 and the third laser 18 can be semiconductor lasers, and their tilt angles can be designed according to actual situations, which are not limited in the embodiments of the present invention. By adjusting the Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, and the Y-axis linear displacement stage 11, the two laser beams are made to coincide on the surface of the optical element 6 to be measured, so as to achieve precise positioning of the focal point position.

[0066] The projection module 600 is used to generate periodic interference fringes and project them onto the surface of the optical element 6 to be measured. Optionally, the projection module 600 includes a fourth laser 21, a linear polarizer 22, a polarization grating 23, and a second focusing lens group 24. The second focusing lens group 24 includes at least one focusing lens ( Figure 2 One focusing lens is schematically shown, which is not a limitation on the embodiments of the present invention). The output beam of the fourth laser 21 generates periodic interference fringes after passing through the linear polarizer 22 and the polarization grating 23, and the periodic interference fringes are converged onto the surface of the optical element 6 to be measured through the second focusing lens group 24.

[0067] Among them, the wavelengths of the output beams of the first laser 1 and the fourth laser 21 can be set to be different. The output beam of the first laser 1 is transmitted when passing through the dichroic mirror 4, and thus enters the optical element 6 to be measured. The output beam of the fourth laser 21 is reflected when passing through the dichroic mirror 4, so that the interference fringe beam reflected by the optical element 6 to be measured enters the first camera 19.

[0068] The binocular vision module 700 includes a first camera 19 and a second camera 20. Both the first camera 19 and the second camera 20 are used to acquire the interference fringe images on the surface of the optical element 6 to be measured. Among them, the first camera 19 acquires coaxial light beams, and the second camera 20 acquires off-axis light beams. In specific implementation, the second camera 20 can be arranged at 45°, that is, the included angle between the optical axis of the second camera 20 and the optical axis of the second light beam b1 is 45°. Both the first camera 19 and the second camera 20 can be CMOS cameras. The binocular vision module 700 acquires the interference fringe images on the surface of the optical element 6 to be measured through the first camera 19 at the coaxial angle with the incident laser, and acquires the interference fringe images on the surface of the optical element 6 to be measured through the second camera 20 at a 45° angle. Combining with the phase deflection algorithm, three-dimensional reconstruction of the micro deformation or damage on the surface of the optical element is realized.

[0069] The processing module 800, the light source module 100, the moving stage 200, the laser energy monitoring module 300, the photoelectric detection module 400, the spatial triangle focal point positioning module 500, the projection module 600, and the binocular vision module 700 are all connected to the processing module 800 ( Figure 2(Some of the connections in the middle are not shown). The processing module 800 is used to detect the micro-deformation or damage threshold on the surface of the optical element 6 to be measured according to the interference fringe image. Optionally, the processing module 800 includes a stage controller 25, a data synchronous collector 26, and a computer 27. The stage 200 is connected to the stage controller 25. The laser energy monitoring module 300, the photoelectric detection module 400, and the binocular vision module 700 are all connected to the data synchronous collector 26. The stage controller 25 and the data synchronous collector 26 are both connected to the computer 27.

[0070] Specifically, the rotary angular displacement stage 8, the Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, the Y-axis linear displacement stage 11, and the second X-axis linear displacement stage 14 are all connected to the stage controller 25, and are used to accurately control the rotary angular displacement stage 8, the Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, the Y-axis linear displacement stage 11, and the second X-axis linear displacement stage 14 to achieve precise positioning of the optical element 6 to be measured in three-dimensional space. The first energy meter 12, the second energy meter 13, the photodetector 16, the first camera 19, and the second camera 20 are all connected to the data synchronous collector 26, and are used to synchronously collect the data of the energy meter, the photodetector, and the CMOS camera to ensure the temporal consistency of the data of each module. The stage controller 25 and the data synchronous collector 26 are both connected to the computer 27, and are used to control the entire measurement process, perform real-time processing and analysis on the collected data, and generate the three-dimensional topography and damage report of the optical element.

[0071] The technical solution of the embodiment of the present invention records the laser pulse energy in real time through the laser energy monitoring module, accurately measures the radius of the focused light spot through the photoelectric detection module, accurately locates the focus position through the spatial triangle focus positioning module, projects the periodic structure interference fringes onto the surface of the optical element to be measured through the projection module, captures the change of the interference fringes by using the binocular vision module, combines the phase shift and phase unwrapping algorithms to judge the micro-deformation or damage, and realizes the three-dimensional reconstruction of the micro-deformation and damage topography on the surface of the optical element. It realizes the real-time online measurement of the micro-deformation and damage threshold of the optical element and optimizes the damage threshold evaluation process. The present invention has the advantages of high precision, strong real-time performance, high degree of automation, and wide application range.

[0072] Figure 3 It is a schematic flowchart of a method for measuring the surface of an optical element provided by an embodiment of the present invention. This optical element measurement method is executed by using the optical element surface measurement device provided in the above embodiment. Refer to Figure 2 and Figure 3 , this optical element measurement method includes:

[0073] S1. Measure the spectral curve of the light source module by using the laser energy monitoring module.

[0074] Among them, the process of the spectral curve measurement step includes: starting the first laser 1, changing the polarization state of the laser by adjusting the rotation angle of the half-wave plate 2, and then controlling the spectral splitting ratio after passing through the polarization beam splitter 3. Record the readings of the first energy meter 12 and the second energy meter 13 at different angles of the half-wave plate 2. Plot the spectral curve between the first energy meter 12 and the second energy meter 13 to establish the corresponding relationship between the two. In subsequent measurements, only the reading of the first energy meter 12 needs to be monitored to accurately calculate the laser energy acting on the optical element 6 to be measured.

[0075] S2. Set the slit element on the workbench, and measure the radius of the laser focused spot by the slit method using the photoelectric detection module.

[0076] Among them, the process of the focused spot radius measurement step includes: removing the optical element 6 to be measured from the self-centering bracket 7 and replacing it with a slit element. Start the photoelectric detection module 400, and the band-pass filter 15 filters out the light of non-working wavelengths to ensure that the photodetector 16 only receives the target laser signal. Using the slit method, move the position of the slit, record the light intensity signal of the photodetector 16, and obtain the spot intensity distribution curve. Use curve fitting to calculate the radius of the focused spot.

[0077] S3. Mark the measured focal position through the spatial triangulation focal position module, replace the slit element with a resolution test board, and calibrate the system parameters and pixel density of the binocular vision module.

[0078] Among them, the process of the system parameter calibration and pixel density calibration step includes: using the spatial triangulation focal position module 500, adjusting the Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, and the Y-axis linear displacement stage 11 to make the laser beams emitted by the second laser 17 and the third laser 18 coincide at the slit position of the slit element, and accurately locate the focal position. Replace the slit element with a standard resolution test board, which has a pattern with known size and shape. Exemplarily, Figure 4 is a schematic diagram of the slit element provided by the embodiment of the present invention, Figure 5 is a schematic diagram of the resolution test board provided by the embodiment of the present invention. Start the binocular vision module 700, and use the first camera 19 and the second camera 20 to collect images of the resolution test board respectively. Use the computer 27 to process the images, calculate the internal and external parameters of the camera, and calibrate the relationship between the pixel density and the spatial coordinates.

[0079] S4. Fix the optical element to be measured on the workbench, adjust the workbench to position the optical element to be measured at the measured focal position, project periodic interference fringes onto the optical element to be measured using the projection module, and obtain the corresponding position and pixel intensity information of the interference fringes reflected from the surface of the optical element to be measured in the world coordinate system through the binocular vision module.

[0080] Among them, the specific process of this step includes: installing the optical element 6 to be measured on the self-centering bracket 7 and placing it on the rotary angular displacement stage 8. Adjust the rotary angular displacement stage 8 to set the required incident angle to meet different experimental conditions. Use the motion stage controller 25 to precisely control the Z-axis lifting displacement stage 9, the first X-axis linear displacement stage 10, and the Y-axis linear displacement stage 11 to position the optical element 6 to be measured at the focal position determined by the spatial triangular focus positioning module 500. Start the projection module 600. The laser emitted by the fourth laser 21 is processed by the linear polarizer 22 and the polarization grating 23 to form a structured light with sinusoidal periodicity, which is projected onto the surface of the optical element 6 to be measured through the second focusing lens group 24, generating interference fringes. The first camera 19 and the second camera 20 of the binocular vision module 700 simultaneously collect the interference fringe images on the surface of the optical element 6 to be measured from different angles.

[0081] S5. Continuously adjust the light source module, gradually increase the laser energy acting on the optical element to be measured, use the laser energy monitoring module to obtain the laser energy acting on the optical element to be measured, obtain the change of the interference fringes on the surface of the optical element to be measured after the action of the corresponding pulsed laser through the binocular vision module, combine the phase-shifting algorithm and the phase-unwrapping algorithm to restore the true phase of the interference fringes, and judge whether the optical element to be measured has undergone micro-deformation and damage. If the optical element to be measured has undergone micro-deformation or damage, stop the output of the light source module and give the deformation morphology or damage morphology and the corresponding threshold value.

[0082] Among them, the fringe function after being reflected by the optical element to be measured is expressed as:

[0083] ;

[0084] ;

[0085] Among them, is the coordinate point on the image plane, is the light intensity of the projection module, b is the fringe amplitude, is the additional phase modulation, is the phase modulation introduced by the optical element to be measured.

[0086] The specific process of this step includes: by gradually increasing the laser energy, monitoring the micro-deformation and damage conditions of the optical element 6 to be measured in real time, and determining its damage threshold. Continuously adjust the angle of the half-wave plate 2 to gradually increase the laser energy acting on the optical element 6 to be measured. After each adjustment, wait for the system to stabilize. Use the first energy meter 12 to record the transmitted energy in real time, and calculate the laser energy actually acting on the optical element 6 to be measured according to the spectral curve of S1. After each laser pulse acts, the binocular vision module 700 synchronously acquires the interference fringe image on the surface of the optical element 6 to be measured. The data synchronization collector 26 ensures the temporal consistency of the data of the energy meter and the camera. Use the phase-shifting algorithm and the unwrapping algorithm to process the acquired interference fringe image and restore the true phase distribution. The phase change reflects the tiny deformation on the surface of the optical element under test. Calculate the phase difference to generate the three-dimensional topography map of the optical element 6 to be measured. By comparing the topography changes under different energies, determine whether micro-deformation or damage has occurred. If the phase change is within the system noise range, it is determined that the optical element under test has not deformed, and continue to increase the laser energy; if a small phase change is detected but no obvious damage appears on the surface, record the corresponding laser energy as the deformation threshold; if the phase change is significant and abnormalities such as fringe breaks and distortions appear in the interference fringe image, it is determined that the optical element under test has been damaged. The system automatically stops the output of the first laser 1 to avoid further damage. The computer 27 records information such as the deformed or damaged topography, the corresponding laser energy and position, and generates a detailed damage report.

[0087] S6: Repeat S1 to S5 to achieve a one-to-one and S-to-one online test of the damage threshold of the optical element to be measured.

[0088] Among them, S is an integer greater than 1. This step includes: repeating the test, replacing the optical element 6 to be measured, repeating S1 to S5, and measuring the damage thresholds of different optical elements. Summarize all test results and analyze the overall performance and quality of the optical element to be measured.

[0089] Optionally, whether the optical element to be measured has micro-deformation and damage is judged according to the following conditions:

[0090] According to the measured phase change and the system noise and the deformation threshold comparison, the state of the optical element to be measured is divided into three categories:

[0091] When it is determined that the optical element to be measured has not deformed;

[0092] When it is determined that the optical element to be measured has undergone a small deformation;

[0093] When When it is determined that the optical element to be measured exceeds the deformation threshold;

[0094] Among them, before the damage threshold test, by collecting multiple interference fringe images of the measured optical element under the same conditions, the first one is used as the reference initial reference state , calculate the standard deviation of the phase difference of each image point :

[0095] ;

[0096] The system noise is defined as ;

[0097] According to the interference fringe image, as an auxiliary determination basis, when the interference fringe is distorted but still continuous without interruption, it is determined that the optical element to be measured has deformed. When the interference fringe is broken and discontinuous, it is determined that the optical element to be measured is damaged; different coating materials and substrate materials have different sensitivities and tolerances to deformation. The deformation threshold is defined according to the material parameters of the optical element to be measured , the phase change corresponding to the deformation threshold is:

[0098] .

[0099] The technical solution of the embodiment of the present invention has the following effects:

[0100] 1) Real-time online measurement, improving detection efficiency:

[0101] The embodiment of the present invention can monitor the surface damage process of the optical element under high-energy laser irradiation in real time, avoiding the lag of the traditional offline measurement method. Real-time online measurement enables users to obtain the damage information of the optical element in a timely manner, make a quick response, and improve the detection efficiency and productivity.

[0102] 2) Real-time monitoring and calibration of laser energy, ensuring energy stability:

[0103] The laser energy detection module monitors the energy of each laser pulse in real time and calibrates the spectral curve. The real-time monitoring and calibration of energy ensure the stability of laser output, reduce the measurement error caused by energy fluctuation, and improve the accuracy of damage threshold measurement.

[0104] 3) Accurately measuring the spot radius and accurately evaluating the damage threshold:

[0105] Through the slit method and the photoelectric detection module, using a band-pass filter and a photodetector, accurately measure the radius of the laser focusing spot. The accurate measurement of the spot radius is crucial for calculating the light intensity distribution and evaluating the damage threshold of the optical element, improving the accuracy and reliability of the measurement results.

[0106] 4) Precise focus positioning, adaptable to uneven samples:

[0107] By introducing a spatial triangular focus positioning module, the position of the laser focus can be accurately located. Even for special-shaped optical elements with uneven surfaces, precise focus positioning and measurement can be achieved, expanding the scope of application of the device.

[0108] 5) Automatic protection mechanism to prevent excessive damage to the sample:

[0109] When the photoelectric detection module monitors a significant step in the laser signal (damage occurs on the surface of the optical element), the system can automatically stop the laser output to prevent excessive damage to the sample.

[0110] 6) High-sensitivity detection of minor damage for 3D reconstruction:

[0111] By using a projection module and a binocular vision module, minor deformations and damages on the surface of the optical element can be detected with high sensitivity, and 3D reconstruction of the damaged area can be achieved. This provides data support for in-depth analysis of the damage mechanism and optimization of the optical element design.

[0112] 7) Multi-angle incidence measurement to meet diverse test requirements:

[0113] By adjusting the rotary angular displacement stage, the damage threshold measurement at different incident angles can be realized. The damage characteristics of optical elements may vary at different incident angles. The embodiments of the present invention can meet the needs of users for various test conditions, providing the possibility for comprehensively evaluating the performance of optical elements.

[0114] The above specific implementation manners do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An optical element surface measuring device, characterized in that: include: A light source module, the light source module is used to output a laser beam with adjustable intensity to the optical element to be measured; A motion stage, the motion stage is used to carry the optical element to be tested, the slit element or the resolution test board, and is also used to drive the optical element to be tested, the slit element or the resolution test board to move in multiple directions; A laser energy monitoring module, the laser energy monitoring module is used to record the energy of each laser pulse emitted by the light source module when the optical element to be tested is tested; A photoelectric detection module, wherein the photoelectric detection module is used to measure the radius of the laser focus spot by using a slit method when the slit element is arranged on the moving stage; A spatial triangulation focus positioning module, wherein the spatial triangulation focus positioning module is used to locate the spatial coordinates of the optical element to be measured when the motion stage adjusts the spatial position of the optical element to be measured to the focus; A projection module, the projection module is used to generate periodic interference fringes and project them onto the surface of the optical element to be measured; A binocular vision module, the binocular vision module comprising a first camera and a second camera, the first camera and the second camera are both used to obtain interference fringe images on the surface of the optical element to be measured, wherein the first camera obtains a coaxial light beam and the second camera obtains an off-axis light beam; A processing module, wherein the light source module, the motion stage, the laser energy monitoring module, the photoelectric detection module, the spatial triangulation focus positioning module, the projection module and the binocular vision module are all connected to the processing module, and the processing module is used to detect the micro-deformation or damage threshold of the surface of the optical element to be measured according to the interference fringe image; The motion stage comprises a self-centering bracket, a rotational angular displacement stage, a Z-axis lifting displacement stage, a first X-axis linear displacement stage and a Y-axis linear displacement stage, wherein the self-centering bracket is used to fix the optical element to be measured, the slit element or the resolution test board, and the rotational angular displacement stage, the Z-axis lifting displacement stage, the first X-axis linear displacement stage and the Y-axis linear displacement stage are used to adjust the rotation angle, Z-direction position, X-direction position and Y-direction position of the optical element to be measured, the slit element or the resolution test board, respectively, wherein the X-axis, the Y-axis and the Z-axis are perpendicular to each other; The photoelectric detection module includes a bandpass filter and a photodetector. When the slit element is fixed on the self-centering bracket, the focused light spot is received by the photodetector after passing through the slit of the slit element and the bandpass filter. The first X-axis linear translation stage is used to drive the slit element to move. The processing module is also used to measure the radius of the focused light spot according to the signal of the photodetector.

2. The optical element surface measuring device according to claim 1, characterized in that: The light source module comprises a first laser, a half-wave plate, a polarization beam splitter, a dichroic mirror and a first focusing lens group, wherein the first focusing lens group comprises at least one focusing lens; The output beam of the first laser is incident on the polarization beam splitter after being transmitted through the half-wave plate and split into a first beam and a second beam, the first beam is incident on the laser energy monitoring module, and the second beam is converged to the optical element to be measured after passing through the dichroic mirror and the first focusing lens group; Wherein, when the half-wave plate is rotated along the optical axis of the half-wave plate, the intensities of the first light beam and the second light beam are adjusted.

3. The optical element surface measuring device according to claim 2, characterized in that: The laser energy monitoring module comprises a first energy meter, a second energy meter and a second X-axis linear translation stage, wherein the second energy meter is fixed on the second X-axis linear translation stage; The first energy meter is used to receive the first light beam. When calibrating the spectroscopic curve of the output light beam of the first laser, the second X-axis linear translation stage drives the second energy meter to be located in the light path of the second light beam. When measuring the optical element to be measured, the second X-axis linear translation stage drives the second energy meter to be located outside the light path of the second light beam.

4. The optical element surface measuring device according to claim 1, characterized in that: The spatial triangulation focus positioning module comprises a second laser and a third laser, the outgoing light beams of the second laser and the third laser are incident on the optical element to be measured at an angle, the Z-axis lifting and translation stage, the first X-axis linear translation stage and the Y-axis linear translation stage adjust the spatial position of the optical element to be measured, and the spatial triangulation focus positioning module locates the spatial coordinates of the optical element to be measured according to the triangulation positioning method.

5. The optical element surface measuring device according to claim 1, characterized in that: The projection module includes a fourth laser, a linear polarizer, a polarization grating and a second focusing lens group, the second focusing lens group includes at least one focusing lens, the output light beam of the fourth laser generates periodic interference fringes after passing through the linear polarizer and the polarization grating, and the periodic interference fringes converge to the surface of the optical element to be measured through the second focusing lens group.

6. The optical element surface measuring device according to claim 1, characterized in that: The processing module includes a motion stage controller, a data synchronization collector and a computer. The motion stage is connected to the motion stage controller. The laser energy monitoring module, the photoelectric detection module and the binocular vision module are all connected to the data synchronization collector. The motion stage controller and the data synchronization collector are both connected to the computer.

7. A method for measuring the surface of an optical element, characterized in that: The optical element surface measuring method is performed by using the optical element surface measuring device according to any one of claims 1 to 6, and comprises: S1. Using a laser energy monitoring module to measure the spectral curve of a light source module; S2, placing the slit element on the workbench, and measuring the radius of the laser focus spot by using the slit method through the photoelectric detection module; S3, marking the focal position measured by the spatial triangulation focal positioning module, replacing the slit element with a resolution test plate, and performing system parameter calibration and pixel density calibration on the binocular vision module; S4, fixing the optical element to be measured on the workbench, adjusting the workbench to position the optical element to be measured to the measured focal position, projecting periodic interference fringes to the optical element to be measured by a projection module, and obtaining the corresponding position and pixel intensity information of the interference fringes reflected from the surface of the optical element to be measured in the world coordinate system by the binocular vision module; S5, continuously adjusting the light source module, gradually increasing the laser energy acting on the optical element to be measured, using the laser energy monitoring module to obtain the laser energy acting on the optical element to be measured, obtaining the change of the interference fringes on the surface of the optical element to be measured after the corresponding pulse laser is acted on by the binocular vision module, combining the phase shift algorithm and the unwrapping algorithm to restore the true phase of the interference fringes, and judging whether the optical element to be measured has micro-deformation and damage. If the optical element to be measured has micro-deformation or damage, the output of the light source module is stopped and the deformation morphology or damage morphology and the corresponding threshold value are given; S6: Repeat S1 to S5 to implement 1-to-1 and S-to-1 online tests of the damage threshold of the optical element to be tested; Wherein, S is an integer greater than 1, and the fringe function after being reflected by the optical element to be measured is expressed as: ； ； in, is the coordinate point on the image plane, is the light intensity of the projection module, b is the fringe amplitude, is the additional phase modulation, The phase modulation introduced by the optical element to be measured.

8. The optical element surface measurement method according to claim 7, characterized in that: Whether the optical element to be tested has micro deformation and damage is determined according to the following conditions: According to the measured phase change and system noise and deformation threshold By comparison, the states of the optical element to be tested are divided into three categories: when When , it is determined that the optical element to be measured has not been deformed; when When the optical element to be measured is determined to have undergone a slight deformation; when When , it is determined that the optical element to be tested exceeds a deformation threshold; Before the damage threshold test is performed, multiple interference fringe images of the optical element are collected under the same conditions, and the first image is used as the baseline initial reference state. , calculate the standard deviation of the phase difference at each image point : ； The system noise is defined as ; According to the interference fringe image, as an auxiliary judgment basis, when the interference fringe is distorted but still continuous, it is judged that the optical element to be measured is deformed, and when the interference fringe is broken and discontinuous, it is judged that the optical element to be measured is damaged; the deformation threshold is defined according to the material parameters of the optical element to be measured , the phase change corresponding to the deformation threshold is: 。

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