Primary and secondary mirror combined detection system and method for beam shrinking system

Abstract

The invention discloses a primary and secondary mirror combined detection system and method for a beam shrinking system, and belongs to the technical field of optical detection.The method comprises the steps that a first micro-spherical mirror and a second micro-spherical mirror are arranged, reflection light spots are captured through an interferometer, the position offset is calculated, and a first control instruction for adjusting the pose of a secondary mirror is generated; a dual-band light source is integrated in a detection light path, wavefront data and alignment monitoring data are collected, and temperature drift is corrected to obtain effective combined wavefront; an error separation model is constructed based on the primary mirror compensator parameter and the Zernike aberration coefficient, and a primary mirror surface shape error component and a secondary mirror offset error component are decoupled and separated by using a preset aberration coupling coefficient; feeding the error component back to a polishing process and a displacement table for closed-loop iterative correction until the RMS value and the PV value of the effective combined wavefront meet a preset imaging quality index; through precise positioning, error correction and decoupling separation, the precision and efficiency of primary and secondary mirror combination detection are improved, and targeted correction is realized.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology, specifically a primary and secondary mirror combination detection system and method for beam-shrinking systems. Background Technology

[0002] In the field of optical engineering, the beam-shrinking system, as a core component of high-precision optical equipment, directly determines the imaging quality of the system through the surface accuracy and pose matching degree of its primary and secondary mirror combination. Therefore, accurate detection of both is a crucial step in optical manufacturing and assembly. Existing primary and secondary mirror combination detection technologies have limitations: First, the surface error of the primary mirror is coupled with the translational and tilt misalignment errors of the secondary mirror, making independent separation difficult and resulting in a lack of targeted error correction. Second, changes in ambient temperature can cause temperature drift due to differences in the thermal expansion coefficients of the primary and secondary mirror materials, directly interfering with the accuracy of wavefront detection data. Third, the inherent aberrations of the primary mirror compensator and manufacturing errors form a fixed transmission wavefront error, which existing methods cannot effectively subtract, affecting the extraction of the system's true error. Fourth, the detection and correction process lacks an efficient closed-loop mechanism, resulting in low iteration efficiency and difficulty in meeting the stringent requirements of high-precision imaging for peak-to-valley values ​​and root-mean-square values. Therefore, there is an urgent need for a detection method that can achieve error decoupling and separation, offset the effects of temperature drift, accurately subtract fixed errors, and achieve efficient closed-loop operation, in order to overcome existing technological bottlenecks and ensure the imaging performance of the beam-shrinking system. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a primary and secondary mirror combination detection system and method for beam-shrinking systems. It involves setting up a first and second microspherical mirror, capturing reflected light spots using an interferometer, calculating positional offsets, and generating a first control command to adjust the pose of the secondary mirror. A dual-band light source is integrated into the detection optical path to collect wavefront data and alignment monitoring data, correcting temperature drift to obtain an effective combined wavefront. An error separation model is constructed based on the primary mirror compensator parameters and Zernike aberration coefficients. A preset aberration coupling coefficient is used to decouple and separate the primary mirror surface shape error component and the secondary mirror misalignment error component. The error components are fed back to the polishing process and the displacement stage for closed-loop iterative correction until the RMS and PV values ​​of the effective combined wavefront meet preset imaging quality indicators. This application improves the accuracy and efficiency of primary and secondary mirror combination detection through precise positioning, error correction, and decoupling separation, achieving targeted correction.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for detecting the combination of primary and secondary mirrors in a beam-shrinking system includes:

[0006] S1: Multiple first micro spherical mirrors are evenly distributed around the effective aperture edge of the primary mirror of the beam-shrinking system, and a second micro spherical mirror is set at the center of the secondary mirror. The detection optical path of the interferometer is activated to illuminate the first and second micro spherical mirrors, and the reflected light spots are captured by the detector. The position offset of each reflected light spot is calculated in real time to generate a first control command for adjusting the pose of the secondary mirror.

[0007] S2: A dual-band light source is integrated into the detection optical path of the interferometer. While driving the displacement stage to execute the first control command, the first wavefront data and the second alignment monitoring data obtained by the dual-band light source are simultaneously acquired. Based on the second alignment monitoring data, the temperature drift caused by the difference in thermal expansion coefficients of the primary mirror and the secondary mirror materials is corrected to obtain the corrected effective combined wavefront.

[0008] S3: Input the effective combined wavefront into the preset error separation model, subtract the fixed transmission wavefront error introduced by the primary mirror compensator from the effective combined wavefront through the error separation model to obtain the residual system wavefront, and decouple and separate the independent primary mirror surface shape error component and secondary mirror misalignment error component from the residual system wavefront according to the preset aberration coupling coefficient; the error separation model is constructed based on the optical parameters of the primary mirror compensator of the beam-shrinking system and the Zernike aberration coefficient;

[0009] S4: Feed back the primary mirror surface shape error component to the primary mirror repair and polishing process, convert the secondary mirror misalignment error component into a second control command and feed it back to the displacement stage. After completing the targeted correction, repeat S1 to S3 to obtain a new effective combined wavefront and its decoupled error components. Determine whether the RMS value and PV value of the new effective combined wavefront meet the preset imaging quality index. If yes, the detection is completed; if not, repeat S4 until the imaging quality index is met.

[0010] Specifically, the detection optical path of the start interferometer illuminates the first and second microspherical mirrors, and the reflected light spots are captured by the detector. The positional offset of each reflected light spot is then calculated in real time, including:

[0011] The interferometer is activated so that the emitted detection beam passes through the main mirror compensator in sequence and then simultaneously illuminates all the first microsphere mirrors and the second microsphere mirrors.

[0012] Using an array detector set in the receiving optical path of the interferometer, the independent light spot images formed by reflections from each first microspherical mirror and the second microspherical mirror are captured synchronously;

[0013] The image of the independent light spot is preprocessed; the preprocessing includes at least noise reduction and grayscale normalization.

[0014] A spot center localization algorithm based on circle fitting is used to extract the real-time center pixel coordinates of each spot in the image coordinate system;

[0015] The position offset vector of each light spot is obtained by calculating the difference between the real-time center pixel coordinates of each light spot and the reference center pixel coordinates stored in the database.

[0016] Specifically, the generation of the first control command for adjusting the pose of the secondary mirror includes:

[0017] The calculated position offset vectors of all light spots are input to a preset offset-offset mapping model. The offset-offset mapping model is established through a pre-calibrated experiment, with the translational and tilt offsets of the secondary mirror as input variables and the theoretically calculated position offsets of the reflected light spots of each microsphere mirror as output variables.

[0018] Using the calculated position offset vectors of all light spots as known quantities, a nonlinear least squares optimization algorithm is used to invert and solve the problem based on the offset-offset mapping relationship model. The goal of the inversion solution is to find a set of secondary mirror translation offset and tilt offset such that the overall error between the predicted light spot offset calculated after substituting the corresponding secondary mirror translation offset and tilt offset into the offset-offset mapping relationship model is minimized.

[0019] The optimal translational and tilting misalignments of the secondary mirror obtained by the solution are converted into the first control command for driving the movement of the displacement stage according to the control parameters of each motion axis of the displacement stage; the first control command includes the translational amount of the secondary mirror along the X-axis and Y-axis and the tilting angle around the X-axis and Y-axis.

[0020] Specifically, the dual-band light source includes a first laser source with a first nanometer wavelength and a second laser source with a second nanometer wavelength. The first laser source and the second laser source are combined into a common-path beam by a polarization combiner and incident on the primary mirror compensator, and the first nanometer wavelength is smaller than the second nanometer wavelength; the process of acquiring the first wavefront data and the second alignment monitoring data obtained from the dual-band light source includes:

[0021] From the beam containing two wavelengths returned from the interferometer, a monitoring beam is separated using the first beam splitter;

[0022] The monitoring beam is guided to a beam splitting and filtering module consisting of a dispersive prism and a filter, and separated into a first band beam with a first nanometer wavelength and a second band beam with a second nanometer wavelength.

[0023] The first wavefront sensor is used to receive the first band beam, and the first wavefront data is obtained by solving its phase distribution.

[0024] The second band beam is received using a four-quadrant detector. By calculating the energy distribution differences of the beam spot center in the four quadrants of the detector, second alignment monitoring data characterizing the beam alignment status is obtained.

[0025] Specifically, the step of correcting the temperature drift caused by the difference in thermal expansion coefficients of the primary and secondary mirror materials based on the second alignment monitoring data to obtain the corrected effective combined wavefront includes:

[0026] Real-time monitoring of ambient temperature, and based on the difference in thermal expansion coefficients between the primary mirror material and the secondary mirror material, a temperature-spot offset correction lookup table is established;

[0027] Based on the current ambient temperature and the second alignment monitoring data obtained by the four-quadrant detector, the temperature-spot offset correction lookup table is queried to obtain the theoretical spot center offset compensation amount corresponding to the first nanometer wavelength caused by material thermal deformation under the current temperature conditions.

[0028] Based on the theoretical spot center offset compensation amount and the spatial resolution of the four-quadrant detector, the influence weight of the theoretical spot center offset compensation amount on the specified Zernike aberration term in the first wavefront data is calculated; the specified Zernike aberration term includes at least astigmatism and coma.

[0029] The Zernike polynomial coefficients after the first wavefront data decomposition are compensated based on the calculated influence weights to generate a corrected effective combined wavefront.

[0030] Specifically, the construction process of the error separation model includes:

[0031] Obtain the optical design parameters of the primary mirror compensator; the optical design parameters include the radius of curvature, center thickness, material refractive index, and lens spacing of each lens surface;

[0032] Based on the optical design parameters, the ideal transmission wavefront of the primary mirror compensator at the first nanometer wavelength is simulated using ray tracing software, and the ideal transmission wavefront is expanded into the first N coefficients of the Zernike polynomial to form an intrinsic aberration coefficient vector.

[0033] By conducting actual testing on a standard mirror with a known surface shape, the actual transmitted wavefront data, including the manufacturing error of the primary mirror compensator itself, is obtained. The actual transmitted wavefront data is then expanded into Zernike polynomials of the same order to obtain the actual aberration coefficient vector.

[0034] Subtracting the actual aberration coefficient vector from the inherent aberration coefficient vector yields a difference vector that is defined as the coefficient vector of the fixed transmission wavefront error and stored in the error separation model.

[0035] The step of subtracting the fixed transmission wavefront error introduced by the primary mirror compensator from the effective combined wavefront using the error separation model is as follows: the effective combined wavefront is expanded into a Zernike polynomial coefficient vector of the same order, and the Zernike polynomial coefficient vector is subtracted from the coefficient vector of the fixed transmission wavefront error stored in the error separation model. The resulting difference coefficient vector represents the residual system wavefront.

[0036] Specifically, the preset aberration coupling coefficient is obtained in the following way:

[0037] Based on the design parameters of the primary and secondary mirrors of the beam-shrinking system, a complete optical model of the beam-shrinking system is established in optical design software.

[0038] Introduce independent errors of known magnitude into the complete optical model; these independent errors include primary mirror shape errors of various types and magnitudes, as well as secondary mirror translation and tilt misalignments of various directions and sizes.

[0039] For each introduced independent error or error combination, wavefront analysis is performed using the ray tracing function of optical design software to calculate the corresponding wavefront error distribution at the system exit pupil. The wavefront error distribution is then decomposed into Zernike polynomials, and the first M coefficient vectors are recorded.

[0040] Using the category and magnitude of all introduced independent errors as independent variables and the Zernik polynomial coefficient vector of the system wavefront as dependent variables, a coupling relationship matrix is ​​fitted through multiple linear regression analysis. The coupling relationship matrix is ​​used to describe the contribution weight of each type of primary mirror shape error or secondary mirror pose misalignment to each Zernik aberration in the overall wavefront of the system. The elements in the coupling relationship matrix are the aberration coupling coefficients.

[0041] Specifically, the step of decoupling and separating the independent primary mirror shape error component and secondary mirror misalignment error component from the residual system wavefront according to a preset aberration coupling coefficient includes:

[0042] Using the Zernike polynomial coefficient vector representing the wavefront of the residual system as input, a system of linear equations is constructed with the coupling matrix as coefficients. The unknowns of the system of equations are the magnitudes of various primary mirror surface shape errors and the translational and tilting misalignments of the secondary mirrors.

[0043] The linear equations were solved using the linear least squares method based on QR decomposition to obtain numerical solutions for the primary mirror surface shape error component and the secondary mirror misalignment error component.

[0044] Specifically, the step of converting the secondary mirror misalignment error component into a second control command and feeding it back to the displacement stage includes:

[0045] The secondary mirror misalignment error components are analyzed to obtain the translation correction and tilt correction amounts to be compensated for by the secondary mirror in the current pose.

[0046] Based on the transmission parameters of each motion axis of the displacement stage, the translation correction amount and tilt correction amount are converted into motor drive pulse number or analog voltage control signal to form a second control command;

[0047] The second control command is sent to the servo controller of the displacement stage to drive the secondary mirror to perform the corresponding displacement motion so that it reaches the corrected target pose.

[0048] Specifically, determining whether the RMS and PV values ​​of the new effective combined wavefront meet the preset imaging quality indicators includes:

[0049] The corresponding wavefront phase distribution map is reconstructed based on the new effective wavefront combination.

[0050] Calculate the root mean square (RMS) value of the phase values ​​at all sampling points of the wavefront phase distribution map to obtain the RMS value.

[0051] Find the maximum and minimum phase values ​​of all sampling points in the wavefront phase distribution map, and calculate their difference to obtain the PV value;

[0052] The imaging quality indicators are set as follows: the PV value is not greater than one-quarter of the system's operating wavelength, and the RMS value is not greater than one-twentieth of the system's operating wavelength.

[0053] The calculated RMS and PV values ​​are compared with the imaging quality indicators. If both are satisfied, the detection is considered complete.

[0054] The primary and secondary mirror combination detection system for beam-shrinking systems includes: a microspherical mirror arrangement module, a spot processing module, a wavefront data processing module, a decoupling module, a detection and judgment module, and a displacement stage module;

[0055] The microsphere mirror arrangement module is used to set the first microsphere mirror and the second microsphere mirror;

[0056] The light spot processing module is used to emit an interference detection beam, capture and process the reflected light spot, invert the secondary mirror misalignment, and generate the first control command for the initial adjustment of the secondary mirror pose.

[0057] The wavefront data processing module is used to simultaneously acquire the first wavefront data and the second alignment monitoring data, correct the temperature drift caused by the difference in thermal expansion coefficients of the primary mirror and secondary mirror materials, and output an effective combined wavefront.

[0058] The decoupling module is used to deduct the fixed transmission wavefront error introduced by the primary mirror compensator and decouple and separate the independent primary mirror surface shape error component and secondary mirror misalignment error component based on the aberration coupling coefficient.

[0059] The detection and judgment module is used to feed back the separated primary mirror surface shape error component and secondary mirror misalignment error component to the corresponding process / mechanism respectively, and generate a second control command;

[0060] The displacement stage module is used to receive the first control command and the second control command, and to perform translation and tilt adjustments of the secondary mirror.

[0061] Compared with the prior art, the beneficial effects of the present invention are:

[0062] 1. This invention proposes a method for detecting the combination of primary and secondary mirrors in a beam-shrinking system. This method involves evenly distributing a first microspherical mirror along the edge of the effective aperture of the primary mirror and placing a second microspherical mirror at the center of the secondary mirror. By combining spot center positioning and nonlinear least squares optimization inversion, the method can accurately capture the pose shift of the secondary mirror and generate a high-precision first control command. By acquiring wavefront data and alignment monitoring data using a dual-band light source and combining a temperature-spot shift correction mechanism, the method effectively offsets the temperature drift caused by the difference in thermal expansion coefficients between the primary and secondary mirror materials, improving the accuracy of the combined wavefront data. By subtracting the fixed transmission wavefront error introduced by the primary mirror compensator through an error separation model, and then using a preset aberration coupling coefficient, the method achieves precise decoupling between the primary mirror surface shape error and the secondary mirror misalignment error, improving the targeting and accuracy of error detection.

[0063] 2. This invention proposes a method for detecting the primary and secondary mirror combinations in beam-shrinking systems. This method employs a closed-loop iterative correction mechanism, feeding back the decoupled error components to the primary mirror polishing process and the displacement stage respectively, achieving targeted optimization and ensuring that the imaging quality gradually approaches the preset indicators. The entire process integrates efficient algorithms such as spot preprocessing, wavefront calculation, and linear equation solving, eliminating the need for complex manual intervention. It balances detection accuracy and efficiency, adapts to the optical characteristics of beam-shrinking systems, and provides a reliable and efficient technical solution for high-quality detection of primary and secondary mirror combinations in beam-shrinking systems. It is suitable for practical engineering applications in the field of optical detection. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of the primary and secondary mirror combination detection method for beam-shrinking systems according to the present invention.

[0065] Figure 2 This is a flowchart illustrating the principle of the primary and secondary mirror combination detection method for beam-shrinking systems according to the present invention.

[0066] Figure 3 This is a diagram of the primary and secondary mirror combination detection system for the beam-shrinking system of the present invention. Detailed Implementation

[0067] Example 1:

[0068] Please see Figure 1 and Figure 2 The present invention provides an embodiment of a method for detecting the combination of primary and secondary mirrors in a beam-shrinking system, comprising the following steps:

[0069] S1: Multiple first micro spherical mirrors are evenly distributed around the effective aperture edge of the primary mirror of the beam-shrinking system, and a second micro spherical mirror is set at the center of the secondary mirror. The detection optical path of the interferometer is activated to illuminate the first and second micro spherical mirrors, and the reflected light spots are captured by the detector. The position offset of each reflected light spot is calculated in real time to generate a first control command for adjusting the pose of the secondary mirror.

[0070] Furthermore, before the first execution of step S1, the method also includes a system calibration step: using a standard spherical mirror with a known radius of curvature of 10000 mm and a surface accuracy of λ / 20 to replace the primary and secondary mirror combination of the beam-shrinking system, and placing it after the primary mirror compensator, where λ is the wavelength and λ = 632.8 nm; executing the detection optical path, acquiring the wavefront data of the standard spherical mirror, and comparing the wavefront data with the theoretically designed wavefront, the difference being used to calibrate and verify the fixed transmission wavefront error in the error separation model, and storing it in the database as a reference coordinate.

[0071] The wavefront refers to the surface formed by points with the same phase in the light field. For example, the wavefront of an ideal plane wave is a plane, and the wavefront of an ideal spherical wave is a sphere. Wavefront data is a digital description of this surface, recording the phase value of each spatial sampling point in the light field. It is usually a two-dimensional matrix, with each element corresponding to the phase value of a sampling point in the light field, fully presenting the shape characteristics of the wavefront.

[0072] Specifically, the detailed steps of system calibration include:

[0073] (1) Fix the standard spherical mirror to the original primary and secondary mirror installation positions of the beam shrinking system using a precision adjustment frame, adjust the translation and tilt degrees of freedom of the precision adjustment frame, and ensure that the coaxiality error between the optical center of the standard spherical mirror and the optical axis of the interferometer detection optical path is less than or equal to 5 μm using a laser collimator, where μm represents micrometer;

[0074] (2) Turn on the phase shift interferometer, set the incident beam diameter to 100 mm and the wavefront type to ideal plane wave, and detect the beam to be perpendicularly incident on the surface of the standard spherical mirror after passing through the primary mirror compensator.

[0075] (3) Ten interferograms are continuously acquired by an array CCD detector. The wavefront phase distribution of each interferogram is calculated by a four-step phase shifting method. The average value of the ten frames is taken as the actual wavefront data of the standard spherical mirror. The four-step phase shifting method is the prior art in this field and is not an inventive solution of this application. It will not be described in detail here.

[0076] (4) Based on the design parameters of the standard spherical mirror, such as a radius of curvature of 10,000 mm, the phase distribution of the ideal wavefront is calculated by the geometric optics formula to generate theoretical design wavefront data. The geometric optics formula is the prior art in this field and is not an inventive solution of this application, so it will not be described in detail here.

[0077] (5) Subtract the actual wavefront data from the theoretically designed wavefront data pixel by pixel to obtain the initial value of the fixed transmission wavefront error, and store the error value and the reference center pixel coordinates of the reflected spot of the standard spherical mirror into the database.

[0078] Furthermore, the interferometer is a ZYGO GPI XP phase-shift interferometer, which has a wavelength stability of less than or equal to 0.005 nm / h and a wavefront measurement accuracy of less than or equal to λ / 100; the detector is an Andor iXon Ultra897 scientific-grade area array CCD camera with a pixel size of 13 μm × 13 μm, a resolution of 1024 × 1024 pixels, a quantum efficiency of greater than or equal to 90%, and features dark field correction and cooling functions, with a minimum cooling temperature of -90 degrees Celsius, which can effectively reduce noise interference.

[0079] Furthermore, the number of the plurality of first microsphere mirrors is four, and they are evenly distributed at 90-degree intervals along the effective aperture edge of the main mirror, i.e., at 0 degrees, 90 degrees, 180 degrees, and 270 degrees along the edge of the main mirror. The surfaces of the first microsphere mirror and the second microsphere mirror are coated with an anti-reflective coating that has high reflectivity in both the 632.8 nm and 1064 nm wavelength bands. High reflectivity means greater than or equal to 99.5%. The anti-reflective coating adopts a multilayer dielectric film system, such as SiO / Ta2O5, and the film thickness is optimized to ensure that the reflectivity fluctuation is less than or equal to 0.3% in the dual-band range.

[0080] Furthermore, the first microsphere mirror is configured as follows: the installation position and number of the first microsphere mirror are determined according to the size of the effective aperture of the primary mirror of the beam-shrinking system and the beam diameter of the interferometer detection optical path. It is ensured that the center distance between two adjacent first microsphere mirrors is not greater than half the diameter of the spot formed by the interferometer detection optical path at the edge of the effective aperture of the primary mirror, and the spherical curvature radius of each first microsphere mirror is configured to match the wavefront curvature of the incident beam after passing through the primary mirror compensator, so that the reflected light can return to the interferometer along the original path.

[0081] Specifically, the parameters and installation details of the first microsphere mirror are as follows:

[0082] (1) Optical parameters: radius of curvature 5000 mm, aperture 5 mm, surface accuracy λ / 20, material is fused silica, which has low coefficient of thermal expansion and good stability;

[0083] (2) Installation structure: A three-point support metal bracket is adopted. The bracket is made of titanium alloy. The bracket is fixed to the reserved mounting holes on the edge of the main mirror by M3 screws. The mounting holes are precision machined and the positioning accuracy is less than or equal to ±10μm.

[0084] (3) Attitude adjustment: Adjust the pitch and yaw angle of the first micro spherical mirror by adjusting the micro adjustment screw on the bracket with an adjustment accuracy of 0.01 mm / turn, so as to ensure that the incident angle of the incident beam is less than or equal to 1 degree and the original path return rate of the reflected beam is greater than or equal to 98%.

[0085] Furthermore, the second microspherical mirror is configured as follows: based on the center mounting reference of the secondary mirror and the coaxiality requirement of the interferometer detection optical path, the fixing structure and spherical parameters of the second microspherical mirror are obtained. The second microspherical mirror is fixed to the center of the secondary mirror through a rigid connection structure, and its spherical vertex coincides with the optical center of the secondary mirror. The difference between the reflectivity of the second microspherical mirror and the reflectivity of the first microspherical mirror is controlled within a preset reflectivity tolerance range to ensure the consistency of the light intensity of the reflected light spots of the first and second microspherical mirrors.

[0086] Specifically, the parameters of the second microsphere mirror are as follows: radius of curvature 5000 mm, aperture 3 mm, surface accuracy λ / 20, material is also fused silica, the connection between the connecting rod and the secondary mirror adopts laser welding process, the welding deformation is less than or equal to 2 μm, to ensure the rigidity and stability of the connection structure.

[0087] S2: A dual-band light source is integrated into the detection optical path of the interferometer. While driving the displacement stage to execute the first control command, the first wavefront data and the second alignment monitoring data obtained by the dual-band light source are simultaneously acquired. Based on the second alignment monitoring data, the temperature drift caused by the difference in thermal expansion coefficients of the primary mirror and the secondary mirror materials is corrected to obtain the corrected effective combined wavefront.

[0088] S3: Input the effective combined wavefront into the preset error separation model, subtract the fixed transmission wavefront error introduced by the primary mirror compensator from the effective combined wavefront through the error separation model to obtain the residual system wavefront, and decouple and separate the independent primary mirror surface shape error component and secondary mirror misalignment error component from the residual system wavefront according to the preset aberration coupling coefficient; the error separation model is constructed based on the optical parameters of the primary mirror compensator of the beam-shrinking system and the Zernike aberration coefficient;

[0089] S4: Feed back the primary mirror surface shape error component to the primary mirror repair and polishing process, convert the secondary mirror misalignment error component into a second control command and feed it back to the displacement stage. After completing the targeted correction, repeat S1 to S3 to obtain a new effective combined wavefront and its decoupled error components. Determine whether the RMS value and PV value of the new effective combined wavefront meet the preset imaging quality index. If yes, the detection is completed; if not, repeat S4 until the imaging quality index is met.

[0090] The detection optical path of the start interferometer illuminates the first and second microspherical mirrors, and the reflected light spots are captured by the detector. The positional offset of each reflected light spot is then calculated in real time, including:

[0091] A1: Start the interferometer so that the emitted detection beam passes through the main mirror compensator in sequence and then simultaneously illuminates all the first microsphere mirrors and the second microsphere mirrors.

[0092] In this embodiment, the specific operation is as follows: the wavelength of the detection beam output by the interferometer is set to 632.8 nanometers, the beam divergence angle is less than or equal to 0.1 milliradians, after passing through the primary mirror compensator, the beam is collimated into parallel light, the beam spot diameter is expanded to 100 millimeters, uniformly covering the effective aperture of the primary mirror and the reflection areas of the four first microspherical mirrors and one second microspherical mirror, ensuring that the light-receiving area of ​​each microspherical mirror is greater than or equal to 90%. The primary mirror compensator is composed of two K9 glass lenses with focal lengths of 500 millimeters and -300 millimeters, respectively, and a spacing of 300 millimeters.

[0093] A2: Using an array detector set in the receiving optical path of the interferometer, the independent light spot images formed by reflections from each first microspherical mirror and the second microspherical mirror are captured synchronously;

[0094] In this embodiment, the specific implementation process is as follows: the exposure time of the CCD detector is set to 10 milliseconds, the frame rate is 10 frames / second, and the synchronization trigger function of the interferometer ensures that the time synchronization error between the incident detection beam and the detector exposure is less than or equal to 1 μs; the beam reflected by each microsphere mirror forms an independent circular spot on the CCD target surface after passing through the primary mirror compensator and the interferometer receiving optical path. The distribution position of the five spots in the image corresponds one-to-one with the installation position of the microsphere mirror on the primary and secondary mirrors. The spot diameter is approximately 20 pixels, corresponding to a physical size of 0.26 mm.

[0095] A3: Preprocess the independent spot image; the preprocessing includes at least noise reduction and grayscale normalization, wherein the calculation process of noise reduction and grayscale normalization is the prior art in this field and is not an inventive solution of this application, and will not be described in detail here;

[0096] A4: A spot center localization algorithm based on circle fitting is used to extract the real-time center pixel coordinates of each spot in the image coordinate system;

[0097] Furthermore, the specific steps for A4 include:

[0098] (1) Binarize the preprocessed independent spot image and use the OTSU adaptive threshold algorithm to determine the binarization threshold. The threshold range is usually between 80 and 120 gray levels. Separate the spot area from the background to obtain the binarized image. Then perform connected component analysis on the binarized image. Use the 8-neighborhood connectivity criterion to identify all independent connected regions and assign a unique identifier to each connected region. Then calculate the geometric features of each connected region, including the size of its bounding rectangle and the area enclosed by the outline. Based on the preset area threshold and aspect ratio range, select candidate connected regions that meet the target spot features and exclude invalid regions caused by noise. Finally, for each candidate connected region, select all pixels with gray values ​​higher than the set threshold to form a set of candidate pixels for circle fitting. The preset area threshold is 50 pixels and the aspect ratio range is 0.8 to 1.2.

[0099] (2) Take each candidate pixel set as input and establish a circle fitting optimization model based on the least squares principle. The circle fitting optimization model takes the center coordinates and radius of the circle to be determined as optimization variables and takes the minimum sum of squared algebraic distances from all candidate pixels to the circle as the optimization objective. The iterative optimization algorithm takes the gray centroid coordinates of the candidate pixel set as the initial estimate of the center and the average distance from the pixel to this initial point as the initial estimate of the radius. The iterative calculation begins. In each iteration, the iterative optimization algorithm calculates the gradient of the objective function under the current circle fitting optimization model parameters and updates the center coordinates and radius values ​​along the gradient descent direction until the parameter change between two adjacent iterations is less than the preset convergence threshold. The iteration terminates and the optimal center coordinates and radius are output. The least squares principle and the iterative optimization algorithm are existing technologies in this field and are not the inventive solutions of this application. They will not be elaborated here.

[0100] (3) Using the optimal circle center coordinates and radius obtained by the solution, calculate the fitting residuals of all candidate pixels and the optimal circle fitting optimization model, and calculate the goodness of fit index to evaluate the degree of fit between the circle fitting optimization model and the real light spot shape. Compare the calculated goodness of fit index with the preset qualified threshold. If the goodness of fit is better than the qualified threshold, the positioning result is determined to be valid, and the output optimal circle center coordinates are confirmed as the real-time center pixel coordinates of the light spot. If the goodness of fit does not reach the qualified threshold, the positioning is determined to be invalid, and an error flag is output to trigger the re-execution of the positioning process or the adoption of a backup positioning strategy.

[0101] (4) The real-time center pixel coordinates of each confirmed valid spot, such as the center coordinates of the four first microsphere mirrors (150.234, 150.125), (150.346, 873.892), (873.761, 873.905), and (873.658, 150.213) and the center coordinates of the second microsphere mirror (512.102, 512.087), are stored according to their identification order in the image, such as the coordinates of microsphere mirrors 1#~5# corresponding to coordinates 1~5, and output to the next processing unit for position offset calculation.

[0102] A5: Calculate the difference between the real-time center pixel coordinates of each spot and the reference center pixel coordinates stored in the database to obtain the position offset vector of each spot.

[0103] For example, the reference center pixel coordinates stored in the database are obtained through the system calibration process. For instance, the reference center pixel coordinates of the first microspherical mirror #1 are (150.000, 150.000), and the real-time center pixel coordinates are (150.234, 150.125). Therefore, the position offset vector is (150.234 - 150.000, 150.125 - 150.000) = (0.234 pixels, 0.125 pixels). Similarly, the reference center pixel coordinates of the first microspherical mirror #2 are (150.000, 874.000), and the real-time center pixel coordinates are (150.346, 873.892). The position offset vector is (0.346 pixels, -0.108 pixels). The reference center pixel coordinates of the first microspherical mirror #3 are (874.000, 873.892), and the position offset vector is (0.346 pixels, -0.108 pixels). The reference center pixel coordinates of the first microsphere mirror #4 are (874.000), and the real-time center pixel coordinates are (873.761, 873.905), so the position offset vector is (-0.239 pixels, -0.095 pixels); the reference center pixel coordinates of the first microsphere mirror #4 are (874.000, 150.000), and the real-time center pixel coordinates are (873.658, 150.213), so the position offset vector is (-0.342 pixels, 0.213 pixels); the reference center pixel coordinates of the second microsphere mirror are (512.000, 512.000), and the real-time center pixel coordinates are (512.102, 512.087), so the position offset vector is (0.102 pixels, 0.087 pixels). The calculation precision of all position offset vectors is less than or equal to 0.001 pixels. For example, if the actual offset is 0.2345 pixels, the calculation result is 0.234 pixels, with an error of only 0.0005 pixels, which is much less than 0.001 pixels.

[0104] The generation of the first control command for adjusting the pose of the secondary mirror includes:

[0105] B1: The calculated position offset vectors of all light spots are input to a preset offset-offset mapping model. The offset-offset mapping model is established through a pre-calibrated experiment, with the translational and tilt offsets of the secondary mirror as input variables and the theoretically calculated position offsets of the reflected light spots of each microsphere mirror as output variables.

[0106] Furthermore, the process of establishing the misalignment-offset mapping model is as follows:

[0107] (1) Apply known translational and tilting misalignment to the secondary mirror through the displacement stage. The translational misalignment range is -0.5 to 0.5 mm with a step size of 0.05 mm, and the tilting misalignment range is -5 to 5 arcseconds with a step size of 0.5 arcseconds. A total of 21×21×21×21=194481 calibration conditions are set.

[0108] (2) For each set of calibration conditions, the propagation path of the detection beam after reflection by the micro spherical mirror is simulated by ray tracing software, and the theoretical position offset of each micro spherical mirror reflected spot in the CCD image coordinate system is calculated.

[0109] (3) A multivariate quadratic polynomial fitting algorithm is adopted to establish the mapping relationship between the input variables and the output variables. The fitting coefficients are solved by the least squares method so that the mean square error between the theoretical position offset and the simulated calculation value is less than or equal to 0.005 pixels and the coefficient of determination of the fitted model is greater than or equal to 0.995. The formula of the multivariate quadratic polynomial fitting algorithm is the prior art in this field and is not an inventive solution of this application. It will not be elaborated here.

[0110] B2: Using the calculated position offset vectors of all light spots as known quantities, a nonlinear least squares optimization algorithm is used to perform inversion solution based on the offset-offset mapping relationship model. The goal of the inversion solution is to find a set of secondary mirror translation offset and tilt offset such that the overall error between the predicted light spot offset calculated after substituting the set of offsets into the offset-offset mapping relationship model is minimized and the measured position offset vector is minimized. The least squares optimization algorithm is prior art in this field and is not an inventive solution of this application, so it will not be described in detail here.

[0111] In this embodiment, the specific steps for inversion solution include:

[0112] (1) Based on the approximate range of the spot offset vector, set the initial estimate of the secondary mirror misalignment, with an initial value of 0;

[0113] (2) The Levenberg-Marquardt algorithm is used for iterative optimization. In each iteration, the Jacobian matrix of the objective function is calculated. The Jacobian matrix has a dimension of 5×4. Each row corresponds to the partial derivative of the offset error of a spot with respect to the four misalignment quantities. The estimated misalignment quantity is updated by calculation. The Levenberg-Marquardt algorithm and the Jacobian matrix are existing technologies in this field and are not the inventive solutions of this application. They will not be described in detail here.

[0114] (3) Calculate the difference between the objective function values ​​of two adjacent iterations. If the difference between the objective function values ​​is less than the preset convergence threshold, such as 1×10 -8 Pixels 2 If the iteration terminates, the optimal offset is output. In this embodiment, the optimal offset obtained by inversion is (0.085, 0.042, 1.2, 0.8).

[0115] B3: The optimal translational misalignment and optimal tilt misalignment of the secondary mirror obtained by solving are converted into the first control command to drive the movement of the displacement stage according to the control parameters of each motion axis of the displacement stage; the first control command includes the specific translational amount of the secondary mirror along the X-axis and Y-axis and the specific tilt angle around the X-axis and Y-axis.

[0116] Furthermore, the specific steps for B3 include:

[0117] (1) Decouple the optimal secondary mirror translation misalignment and the optimal tilt misalignment into four independent degrees of freedom error quantities, namely, the translation error quantity along the X-axis is 0.085 mm, the translation error quantity along the Y-axis is 0.042 mm, the tilt error quantity around the X-axis is 1.2 arcseconds and the tilt error quantity around the Y-axis is 0.8 arcseconds. Then, map these four degrees of freedom error quantities to the four physical motion axes of the displacement stage respectively: assign the translation error quantity along the X-axis to the X-axis linear motion unit of the displacement stage, assign the translation error quantity along the Y-axis to the Y-axis linear motion unit of the displacement stage, assign the tilt error quantity θX around the X-axis to the X-axis rotational motion unit of the displacement stage, and assign the tilt error quantity θY around the Y-axis to the Y-axis rotational motion unit of the displacement stage.

[0118] (2) Using the pre-calibrated and stored control parameters of each motion axis of the displacement stage, the four degrees of freedom error quantities are converted into the underlying digital instructions of each motion axis driver. For the X-axis and Y-axis linear motion units, the linear displacement error quantity is converted into the corresponding drive signal according to its motion conversion parameters. If the unit is driven by a stepper motor, the conversion result is a pulse instruction to drive the stepper motor to run a specific number of pulses. If the unit is driven by piezoelectric ceramics, the conversion result is an analog voltage instruction to apply a specific voltage value. For the rotational motion units around the X-axis and Y-axis, the angle error quantity is first converted into the linear compensation quantity required by the drive point through the kinematic model according to the equivalent arm length from its rotation center to the drive point. Then, according to the drive parameters of the rotational motion unit itself, the linear compensation quantity is further converted into specific digital instructions to drive its piezoelectric actuator or micro motor.

[0119] (3) Perform motion sequence planning on the generated low-level digital instructions of each motion axis, determine whether each axis adopts synchronous motion mode or sequential action mode according to preset order, and set S-shaped motion speed curve to avoid impact. Then, encapsulate all planned motion axis instructions, motion parameters and target position information into a complete executable instruction data packet according to the communication protocol format specified by the displacement stage controller. Before sending the instruction data packet, perform safety limit verification, including verifying whether the instruction value of each axis exceeds its physical travel limit, and whether the overall adjustment amount is within the maximum single adjustment range allowed by the system. Only instruction data packets that pass all safety verifications are finally defined as the first control instruction. The data packet format is: [address code][function code][X-axis steps][Y-axis steps][θX-axis voltage][θY-axis voltage][check code][end symbol]. θX-axis and θY-axis are two independent rotary motion axes on the displacement stage. θX-axis is the rotary motion axis of the displacement stage around the X-axis of the system, and θY-axis is the rotary motion axis of the displacement stage around the Y-axis of the system.

[0120] (4) The first control command that has been generated and verified is sent to the servo controller of the displacement stage. The servo controller parses the first control command and drives each motion axis to perform the corresponding micro-displacement motion. After the displacement stage completes the motion, it queries its controller for the actual position feedback signal of each motion axis. By comparing the command target position with the actual feedback position, it confirms whether the secondary mirror has accurately moved to the target pose.

[0121] The dual-band light source includes a first laser source with a first nanometer wavelength and a second laser source with a second nanometer wavelength. The first laser source and the second laser source are combined into a common optical path beam by a polarization beam combiner and incident on the primary mirror compensator, wherein the first nanometer wavelength is smaller than the second nanometer wavelength; the process of acquiring the first wavefront data and the second alignment monitoring data obtained from the dual-band light source includes:

[0122] C1: From the beam containing two wavelengths returned from the interferometer, a monitoring beam is separated using a first beam splitter. The angle between the beam splitter and the optical axis is set to 45 degrees to ensure that the reflected monitoring beam is perpendicular to the incident beam. The transmitted beam continues to be used for interference signal detection. The first beam splitter is a Thorlabs BS013 with a splitting ratio of 50:50, and the splitting ratio deviation in the 632.8 nm and 1064 nm wavelength bands is less than or equal to 2%.

[0123] C2: The monitoring beam is guided to a beam splitting and filtering module consisting of a dispersive prism and filters, separating it into a first-band beam of 632.8 nm and a second-band beam of 1064 nm. The dispersive prism is made of ZF7 glass with a 60-degree apex angle. The dispersive coefficients in the two bands are n632.8 = 1.755 and n1064 = 1.732, respectively. The refraction of the prism causes the two beams to form a 5-degree angle, achieving spatial separation. The filters include a 632.8 nm bandpass filter and a 1064 nm bandpass filter. The 632.8 nm bandpass filter has a center wavelength of 632.8 nm, a bandwidth of 10 nm, and a transmittance of ≥90%. The 1064 nm bandpass filter has a center wavelength of 1064 nm, a bandwidth of 20 nm, and a transmittance of ≥90%. These filters are placed on the optical paths of the two separated beams to further filter out stray light and ensure that the purity of the single-band beam is ≥99.9%.

[0124] C3: The first wavefront sensor is used to receive the first band beam and the first wavefront data is obtained by solving its phase distribution; wherein, the first wavefront sensor is a Photon etc. SH-WFS-64 Shack-Hartmann wavefront sensor, and its microlens array parameters are: focal length f=10 mm, number of sub-apertures 64×64, microlens diameter 150 μm, sub-aperture spacing 150 μm, matched area array detector resolution 1024×1024 pixels, pixel size 13 μm, frame rate 100 frames / second;

[0125] Furthermore, the specific steps of C3 include:

[0126] (1) The first wavefront sensor performs wavefront segmentation and spatial sampling on the incident first-band beam through its internal microlens array. The microlens array divides the incident wavefront into 64×64=4096 independent sub-aperture regions. The microlens corresponding to each sub-aperture region will converge the local wavefront and form a corresponding light spot on the area array detector located at its focal plane. The diameter of the incident beam is 100 mm, which completely covers the effective area of ​​the microlens array, i.e. 64×150μm=9.6mm, ensuring that each sub-aperture can receive sufficient light energy. The exposure time of the area array detector is set to 5 milliseconds. After the exposure is completed, an original light spot array image containing 4096 light spots is output. The image size is 1024×1024 pixels and the grayscale range is 0~255.

[0127] (2) The acquired original spot array image is preprocessed, including background noise subtraction and detector response non-uniformity correction. Then, based on the known period of 150 μm and regular hexagonal arrangement of the microlens array, each spot region is located on the preprocessed image, and the centroid method is used to calculate the real-time center coordinates of each spot. The calculated real-time center coordinates of each spot are compared with the corresponding spot reference center coordinates stored in advance through ideal reference wavefront calibration, and the two-dimensional offset vector of each sub-aperture spot on the detector plane is calculated. The centroid method is the prior art in this field and is not an inventive solution of this application, so it will not be described in detail here.

[0128] Furthermore, background noise subtraction employs a dark field correction method, which acquires a dark field image without incident light and subtracts the grayscale value of the dark field image from the original image; detector response non-uniformity correction employs a flat field correction method, which acquires a flat field image under uniform light illumination and divides the original image by the grayscale value of the flat field image.

[0129] (3) Based on the two-dimensional offset vector of each light spot, combined with the focal length parameter of the microlens, the average local slope of the wavefront in each sub-aperture region is calculated through geometric optical relations. The local slope includes the slope component in the X direction and the slope component in the Y direction. The geometric optical relations are existing technology in this field and are not an inventive solution of this application. They will not be elaborated here.

[0130] (4) Combine the X-direction slope components of all sub-apertures into a wavefront X-direction slope data field, and combine the Y-direction slope components of all sub-apertures into a wavefront Y-direction slope data field.

[0131] (5) Using the obtained wavefront X-direction slope data field and wavefront Y-direction slope data field as known inputs, the wavefront reconstruction algorithm is used to solve the wavefront phase distribution over the entire aperture. The wavefront reconstruction algorithm establishes a system of linear equations with the sub-aperture phase value as the unknown and the phase difference between adjacent sub-apertures matching the measured slope as the constraint condition, and solves the equations using the least squares criterion. Finally, a discrete wavefront phase distribution map is reconstructed, which is the first wavefront data.

[0132] C4: A four-quadrant detector is used to receive the second band beam. By calculating the energy distribution difference of the beam spot center in the four quadrants of the detector, second alignment monitoring data characterizing the beam alignment status is obtained.

[0133] Furthermore, the specific steps of C4 include:

[0134] (1) The four-quadrant detector converts the optical signals received in the four independent quadrants into four corresponding analog voltage signals. The data acquisition unit synchronously samples these four analog voltage signals and converts them into four digital voltage values ​​through analog-to-digital conversion. Then, the pre-measured background noise offset of each quadrant is subtracted from these four digital voltage values ​​to obtain the purified quadrant energy digital signals, which are recorded as the energy value of the first quadrant, the energy value of the second quadrant, the energy value of the third quadrant, and the energy value of the fourth quadrant, respectively.

[0135] (2) Based on the obtained energy digital signals of the four quadrants, calculate the sum of energy in the horizontal direction and the sum of energy in the vertical direction. When calculating the sum of energy in the horizontal direction, add the energy value of the first quadrant to the energy value of the fourth quadrant to obtain the sum of energy on the right side, and add the energy value of the second quadrant to the energy value of the third quadrant to obtain the sum of energy on the left side. When calculating the sum of energy in the vertical direction, add the energy value of the first quadrant to the energy value of the second quadrant to obtain the sum of energy on the upper side, and add the energy value of the third quadrant to the energy value of the fourth quadrant to obtain the sum of energy on the lower side.

[0136] (3) Calculate the sum of the digital energy signals in the four quadrants, that is, the sum of the energy values ​​in the first quadrant to the fourth quadrant, as the total energy value;

[0137] (4) Calculate the original value of the horizontal deviation, that is, the sum of the energy on the right side minus the sum of the energy on the left side. At the same time, calculate the original value of the vertical deviation, that is, the sum of the energy on the upper side minus the sum of the energy on the lower side.

[0138] (5) Divide the original value of the horizontal deviation by the total energy value to obtain the normalized horizontal deviation signal; divide the original value of the vertical deviation by the total energy value to obtain the normalized vertical deviation signal.

[0139] (6) The generated normalized horizontal deviation signal and normalized vertical deviation signal are combined into a two-dimensional vector, which is the second alignment monitoring data characterizing the beam alignment state.

[0140] The step of correcting the temperature drift caused by the difference in thermal expansion coefficients between the primary and secondary mirror materials based on the second alignment monitoring data to obtain the corrected effective combined wavefront includes:

[0141] D1: Monitor the ambient temperature in real time and establish a temperature-spot offset correction lookup table based on the difference in thermal expansion coefficients between the primary mirror material and the secondary mirror material;

[0142] Furthermore, the process of establishing the temperature-spot offset correction lookup table includes:

[0143] The coverage system operates in a temperature range of 15~35℃ with a temperature step of 0.5℃, totaling 41 temperature points. For each temperature point T, the displacement of the secondary mirror relative to the primary mirror caused by the difference in thermal expansion coefficients is calculated, and then the 632.8 nm band spot center offset caused by this displacement is calculated through ray tracing. The temperature T and the corresponding spot center offset are stored as a lookup table. For example, when T=23℃, the displacement is 7.47μm, and the corresponding spot center offset is (0.057 pixels, 0.038 pixels).

[0144] D2: Based on the current ambient temperature and the second alignment monitoring data obtained by the four-quadrant detector, query the temperature-spot offset correction lookup table to obtain the theoretical spot center offset compensation amount corresponding to the first nanometer wavelength caused by material thermal deformation under the current temperature conditions.

[0145] For example, the current measured ambient temperature is 23.5℃, and the second alignment monitoring data is a two-dimensional vector (0.01236, 0.00829). The temperature-spot offset correction lookup table covers a temperature range of 15℃ to 35℃, with a temperature step of 0.5℃ and a total of 41 temperature points. When querying, the theoretical spot center offset compensation amount is calculated using linear interpolation.

[0146] In summary, the spot center offset is the original calculated value during the basic calibration stage. It refers to the 632.8 nanometers calculated by ray tracing simulation after the secondary mirror's displacement relative to the primary mirror is caused solely by the difference in the thermal expansion coefficients of the primary and secondary mirror materials at any specified temperature. rice The physical offset value of the spot center in the band is the basic data for constructing the temperature-spot offset correction lookup table, and it is the objective offset caused by temperature deformation. The theoretical spot center offset compensation value is the application lookup value in the actual detection stage, referring to the value corresponding to 632.8 nanometers extracted from the calibrated lookup table under the current measured ambient temperature. riceThe theoretical offset of the band is primarily used as a basis for compensating wavefront data, offsetting errors caused by temperature drift. It is a theoretical reference value extracted to correct the offset. Simply put, the spot center offset is the data source for the lookup table, while the theoretical spot center offset compensation value is the application value retrieved from the lookup table for actual correction, and both correspond to the first nanometer wavelength.

[0147] D3: Based on the theoretical spot center offset compensation amount and the spatial resolution of the four-quadrant detector, calculate the influence weight of the theoretical spot center offset compensation amount on the specified Zernike aberration term in the first wavefront data; the specified Zernike aberration term includes at least astigmatism and coma.

[0148] Furthermore, the specific steps of D3 include:

[0149] (1) A correlation model is established in advance, which defines the quantitative relationship between the unit offset of the spot center of the four-quadrant detector and the change in the specified Zernike aberration term caused by it in the optical system;

[0150] Furthermore, the spatial resolution of the four-quadrant detector is 0.01 pixels, and the associated model parameters are set as follows: a unit X-direction offset corresponds to an astigmatic X change of 0.002λ / pixel and an astigmatic Y change of 0.001λ / pixel; a unit Y-direction offset corresponds to a coma X change of 0.0015λ / pixel and a coma Y change of 0.001λ / pixel, where λ is the working wavelength of the first wavefront data, 632.8 nanometers. For example, a unit X-direction offset corresponding to an astigmatic X change of 0.002λ / pixel means that for every 1 pixel of X-direction spot shift, an astigmatic X change of size 0.002λ will be generated.

[0151] (2) Based on the theoretical spot center offset compensation amount obtained by looking up the table at the current temperature, query the associated model to obtain the theoretical astigmatism introduction amount and theoretical coma introduction amount in units of length corresponding to the offset compensation amount;

[0152] (3) Divide the theoretical astigmatism and coma introduced by the working wavelength of the first wavefront sensor respectively, convert the aberration from the length unit to the dimensionless quantity based on the wavelength, and then normalize this dimensionless quantity to the standard aperture defined by the Zernike polynomial used by the first wavefront sensor to obtain the theoretical aberration compensation coefficient for the astigmatism term and the theoretical aberration compensation coefficient for the coma term.

[0153] (4) Obtain the spatial resolution parameter of the four-quadrant detector. The spatial resolution parameter represents the smallest spot displacement that the detector can resolve. Calculate the spatial resolution weighting factor. The spatial resolution weighting factor is inversely proportional to the spatial resolution parameter and is used to map the detector's measurement sensitivity scale to the wavefront aberration correction scale. For example, if the spatial resolution of the four-quadrant detector is 0.01 pixels, the spatial resolution weighting factor is calculated to be 100.

[0154] (5) Multiply the obtained theoretical aberration compensation coefficient by the spatial resolution weight factor. The product is the final influence weight of the theoretical spot center offset compensation amount on the corresponding Zernike aberration term in the first wavefront data. Calculate the influence weight of the astigmatism term and the influence weight of the coma term respectively.

[0155] D4: Based on the calculated influence weights, perform compensation calculations on the Zernike polynomial coefficients after the first wavefront data decomposition to generate a corrected effective combined wavefront.

[0156] Furthermore, the specific steps of D4 include:

[0157] (1) Decompose the wavefront phase distribution represented by the first wavefront data into a linear combination of Zernike polynomials to obtain a set of original coefficients containing each Zernike coefficient. Extract the original astigmatic coefficients corresponding to the astigmatic term and the original coma coefficients corresponding to the coma term from the set of original coefficients.

[0158] (2) Multiply the astigmatism influence weight obtained in advance by the current theoretical spot center offset compensation amount obtained from the temperature-spot offset correction lookup table to obtain the astigmatism coefficient compensation value. At the same time, multiply the coma influence weight obtained in advance by the same theoretical spot center offset compensation amount to obtain the coma coefficient compensation value.

[0159] (3) The extracted original astigmatism coefficients are algebraically added to the calculated astigmatism term compensation values ​​to obtain the corrected astigmatism coefficients;

[0160] (4) Add the extracted original coma coefficients and the calculated coma term compensation values ​​algebraically to obtain the corrected coma coefficients;

[0161] (5) Replace the obtained modified astigmatism coefficients and modified coma coefficients back with the corresponding coefficients in the obtained original coefficient set to form a modified Zernike coefficient set. Then, use the modified Zernike coefficient set to perform Zernike polynomial synthesis to reconstruct the wavefront phase distribution. This wavefront phase distribution is the modified effective combined wavefront and is output for error separation processing.

[0162] The construction process of the error separation model includes:

[0163] E1: Obtain the optical design parameters of the primary mirror compensator; the optical design parameters include the radius of curvature, center thickness, material refractive index, and lens spacing of each lens surface;

[0164] E2: Based on the optical design parameters, use ray tracing software to simulate the ideal transmitted wavefront of the primary mirror compensator at the first nanometer wavelength, and expand the ideal transmitted wavefront into the first N coefficients of the Zernike polynomial to form the intrinsic aberration coefficient vector.

[0165] Furthermore, the specific steps of E2 include:

[0166] (1) In the ray tracing software, based on the optical design parameters of the primary mirror compensator, the curvature radius and spatial orientation of each lens surface, the center thickness of each lens, the air gap between lenses, and the refractive index of each lens material at the first nanometer wavelength are defined in sequence. The diameter and wavelength of the incident beam are set to one nanometer wavelength, and the wavefront type is set to ideal plane wave or ideal spherical wave, thus completing the construction of the virtual model of the optical system.

[0167] (2) Perform ray tracing calculation on the constructed optical system virtual model; the ray tracing calculation simulates the propagation and refraction of light on an ideal optical surface, and finally outputs a two-dimensional data matrix representing the phase distribution of the ideal transmitted wavefront at the exit pupil of the optical system virtual model;

[0168] (3) The two-dimensional data matrix of the ideal transmitted wavefront phase distribution is mapped onto a normalized unit circle. The two-dimensional data matrix is ​​decomposed into a linear combination of the first N terms of the Zernike polynomial using the least squares fitting algorithm. A set of coefficients that minimizes the fitting error is obtained. The coefficients are arranged in the order of the Zernike polynomial terms to form the inherent aberration coefficient vector. The least squares fitting algorithm is a prior art in this field and is not an inventive solution of this application. It will not be described in detail here.

[0169] E3: By actually testing a standard mirror with a known surface shape, the actual transmitted wavefront data including the manufacturing error of the primary mirror compensator is obtained, and the actual transmitted wavefront data is expanded into Zernike polynomials of the same order to obtain the actual aberration coefficient vector.

[0170] Furthermore, the specific steps of E3 include:

[0171] (1) Use high-precision detection equipment to independently measure the standard mirror with known surface shape, obtain the reference wavefront phase distribution of the standard mirror, expand the reference wavefront phase distribution into the first N coefficients of the Zernike polynomial, and form and store the reference coefficient vector of the standard mirror.

[0172] (2) The primary mirror compensator and the standard mirror are integrated into the interferometer detection optical path according to the designed optical path sequence, and optical alignment is performed. The interferometer is started, and the interferogram that is irradiated by the primary mirror compensator and returned is collected. The interferogram is solved by the four-step phase shift method to obtain the integrated transmission wavefront data containing the combined error of the primary mirror compensator and the standard mirror.

[0173] (3) Expand the obtained integrated transmission wavefront data into the same Zernike polynomial coefficients as in (1) to form an integrated aberration coefficient vector;

[0174] (4) Subtract the stored standard mirror reference coefficient vector from the obtained integrated aberration coefficient vector. The resulting difference vector is the actual aberration coefficient vector that characterizes the manufacturing error of the primary mirror compensator itself.

[0175] E4: Subtract the actual aberration coefficient vector from the inherent aberration coefficient vector. The difference vector is defined as the coefficient vector of the fixed transmission wavefront error and stored in the error separation model.

[0176] E5: The method of subtracting the fixed transmission wavefront error introduced by the primary mirror compensator from the effective combined wavefront through the error separation model is as follows: the effective combined wavefront is expanded into a Zernike polynomial coefficient vector of the same order, and then the Zernike polynomial coefficient vector is subtracted from the coefficient vector of the fixed transmission wavefront error stored in the error separation model. The resulting difference coefficient vector represents the residual system wavefront.

[0177] The preset aberration coupling coefficient is obtained in the following way:

[0178] F1: In optical design software, establish a complete optical model of the beam-shrinking system based on the design parameters of the primary and secondary mirrors.

[0179] In this embodiment, the primary mirror is designed with a diameter of 1000 mm, a parabolic surface, a focal length of 5000 mm, and a material of microcrystalline glass; the secondary mirror is designed with a diameter of 170 mm, a hyperboloid surface, a focal length of -850 mm, and a material of single-crystal silicon; the distance between the primary and secondary mirrors is 4150 mm, and the beam ratio is 5.88:1.

[0180] F2: Introduce independent errors of known magnitude into the complete optical model; the independent errors include primary mirror shape errors of various types and magnitudes, as well as secondary mirror translation and tilt misalignments of various directions and sizes.

[0181] In this embodiment, the primary mirror surface shape error types include spherical aberration, astigmatism, and coma, with an amplitude range of 0.0λ to 0.1λ and a step size of 0.01λ; the secondary mirror translation misalignment ranges from -0.5 mm to 0.5 mm in the X and Y axes, with a step size of 0.05 mm; the secondary mirror tilt misalignment ranges from -5 arcseconds to 5 arcseconds around the X and Y axes, with a step size of 0.5 arcseconds.

[0182] F3: For each introduced independent error or error combination, wavefront analysis is performed using the ray tracing function of the optical design software to calculate the corresponding wavefront error distribution at the exit pupil of the system. The wavefront error distribution is then decomposed into Zernike polynomials, and the first M coefficient vectors are recorded. In this embodiment, M=36.

[0183] Furthermore, the specific steps for F3 include:

[0184] (1) Load the parameters of the independent error or error combination to be analyzed into the complete optical model; the parameters include the type and magnitude of the primary mirror surface shape error, or the translational and tilting misalignment of the secondary mirror; update the optical model state to include the currently set error conditions;

[0185] (2) Perform ray tracing analysis on the updated complete optical model. The ray tracing analysis simulates the propagation path of light in the complete optical model containing errors, and calculates the deviation of the wavefront phase formed at the exit pupil of the system from the ideal wavefront, and outputs the discrete data point set of the wavefront error distribution of the system.

[0186] (3) The discrete data point set of the obtained system wavefront error distribution is mapped onto the normalized unit circle aperture. The discrete data point set is decomposed into a linear combination of the first M Zernike polynomials using the least squares fitting algorithm. A set of coefficients that minimizes the fitting residual is obtained, and these coefficients are arranged in the order of terms to form the Zernike coefficient vector corresponding to the current error condition. In this embodiment, the least squares fitting algorithm iterates 1000 times and the convergence threshold is 1×10⁻⁶. -6 ;

[0187] (4) Establish a correspondence between the obtained Zernike coefficient vector and the loaded current error condition parameters, and store them in the database. Then, iterate through all the independent errors and error combinations to be analyzed, and repeat (1)-(4) to generate and store the corresponding Zernike coefficient vector for each error condition.

[0188] F4: Using the categories and magnitudes of all introduced independent errors as independent variables and the Zernike polynomial coefficient vector of the system wavefront as the dependent variable, a coupling relationship matrix is ​​fitted by multiple linear regression analysis. The coupling relationship matrix is ​​used to describe the contribution weight of each type of primary mirror shape error or secondary mirror pose misalignment to each Zernike aberration in the overall wavefront of the system. The elements in the coupling relationship matrix are the aberration coupling coefficients. The multiple linear regression analysis is prior art in this field and is not an inventive solution of this application, so it will not be described in detail here.

[0189] In this embodiment, the number of iterations for the multiple linear regression analysis is set to 1000, and the convergence threshold is set to 1×10⁻⁶. -6 The coupling matrix has a dimension of 36×(3+4)=36×7, where 3 is the number of primary mirror surface error types and 4 is the degree of freedom of secondary mirror misalignment, namely X translation, Y translation, tilt around X, and tilt around Y.

[0190] The step of decoupling and separating the independent primary mirror shape error component and secondary mirror misalignment error component from the residual system wavefront according to the preset aberration coupling coefficient includes:

[0191] G1: Using the Zernike polynomial coefficient vector representing the wavefront of the residual system as input, construct a linear system of equations with the coupling matrix as coefficients. The unknowns of the system of equations are the magnitudes of various primary mirror surface shape errors and the translational and tilting misalignments of the secondary mirrors.

[0192] In this embodiment, the Zernike polynomial coefficient vector dimension of the residual system wavefront is 36×1, the coupling matrix dimension is 36×7, and the unknown vector dimension is 7×1.

[0193] G2: The linear equation system is solved by the linear least squares method based on QR decomposition to obtain the numerical solutions of the primary mirror surface shape error component and the secondary mirror misalignment error component. The linear least squares method based on QR decomposition is the prior art in this field and is not an inventive solution of this application, so it will not be described in detail here.

[0194] Furthermore, the specific steps of G2 include:

[0195] (1) The Zernike polynomial coefficient vector of the residual system wavefront is used as the right-hand vector of the linear equation system, and the coupling relationship matrix formed by the aberration coupling coefficients is used as the coefficient matrix of the linear equation system. The number of equations contained in the linear equation system is greater than the number of unknowns to be solved, thus forming an overdetermined linear equation system. In this embodiment, the dimension of the right-hand vector is 36×1, and the dimension of the coefficient matrix is ​​36×7.

[0196] (2) Perform QR decomposition on the coefficient matrix; the QR decomposition decomposes the coefficient matrix into the product of an orthogonal matrix and an upper triangular matrix. In this embodiment, the orthogonal matrix has a dimension of 36×36, the upper triangular matrix has a dimension of 36×7, and the decomposition precision is set to 1×10. -10 ;

[0197] (3) The transpose of the orthogonal matrix is ​​used to perform a linear transformation on the right-hand vector, transforming the overdetermined linear equation system into a triangular equation system with one or more triangular matrices as coefficient matrices. Then, the back-substitution method is used to solve the triangular equation system to obtain a set of numerical solutions for the unknowns. In this embodiment, the convergence threshold of the back-substitution method is set to 1×10. -8 Specifically, the back-substitution method calculation process is existing technology in this field and is not an inventive solution of this application, so it will not be described in detail here.

[0198] (4) Assign the corresponding physical meaning to the numerical solution of the unknown obtained by solving according to its position order in the solution vector, and output the numerical solution of the primary mirror surface shape error component and the secondary mirror misalignment error component; the physical meaning includes the magnitude category of the primary mirror surface shape error and the translation misalignment and tilt misalignment of the secondary mirror.

[0199] The step of converting the secondary mirror misalignment error component into a second control command and feeding it back to the displacement stage includes:

[0200] H1: Analyze the secondary mirror misalignment error components to obtain the translation correction and tilt correction amounts that the secondary mirror needs to compensate for in the current pose.

[0201] Furthermore, the specific steps of H1 include:

[0202] (1) Receive the secondary mirror misalignment error component data packet output from the error separation algorithm, identify and parse the structure and format of the data packet, and extract the translation error amount of the secondary mirror along the X-axis, the translation error amount of the secondary mirror along the Y-axis, the tilt error angle of the secondary mirror around the X-axis and the tilt error angle of the secondary mirror around the Y-axis.

[0203] (2) The mathematical symbols of each extracted error quantity are converted into a movement direction with clear physical meaning according to the pre-set mapping rules between the optical system coordinate system and the movement direction of the displacement stage; the mapping rules define the correspondence between the mathematical positive and negative signs and the physical direction that the secondary mirror should actually move.

[0204] (3) Input the translation error and tilt error angle with a given direction into the inverse kinematics model of the displacement stage. The inverse kinematics model converts the tilt error angle into the equivalent displacement of one or more linear motion axes according to the specific mechanical structure of the displacement stage. Calculate and output the specific translation correction of the secondary mirror along the X-axis, the specific translation correction along the Y-axis, the correction for tilting around the X-axis, and the correction for tilting around the Y-axis.

[0205] (4) Perform safety limit verification on all calculated corrections; the safety limit verification includes determining whether each correction is within the physical travel range of the corresponding motion axis of the displacement stage, and whether the overall correction magnitude is within the maximum allowable value of a single system adjustment, and outputting the corrections that pass the verification as the final result.

[0206] H2: Based on the transmission parameters of each motion axis of the displacement stage, the translation correction amount and tilt correction amount are converted into specific motor drive pulse numbers or analog voltage control signals to form a second control command;

[0207] Furthermore, the specific steps for H2 include:

[0208] (1) Call the transmission parameters of each motion axis of the displacement stage that are stored in advance; the transmission parameters include the lead screw or piezoelectric ceramic drive coefficient of the X-axis translation axis and the Y-axis translation axis, as well as the angle-displacement conversion coefficient and the corresponding driver parameters of the X-axis tilt axis and the Y-axis tilt axis.

[0209] (2) Based on the transmission parameters called, the received X-axis translation correction is converted into the target driving amount of the X-axis translation driver, the Y-axis translation correction is converted into the target driving amount of the Y-axis translation driver, the X-axis tilt correction is converted into linear displacement through its angle-displacement conversion coefficient, and then converted into the target driving amount according to the parameters of the corresponding driver. The Y-axis tilt correction is converted into linear displacement through its angle-displacement conversion coefficient, and then converted into the target driving amount according to the parameters of the corresponding driver. The target driving amount is the number of motor rotations to be generated or the analog voltage value to be applied.

[0210] (3) All the calculated target driving quantities are digitally encoded. For driving quantities in units of revolutions, they are converted into pulse quantity and direction signals according to the step angle parameters of the corresponding motor. For driving quantities in units of voltage, they are converted into digital control words according to the range and resolution of the digital-to-analog converter. In this embodiment, the motor step angle is 1.8 degrees, the digital-to-analog converter range is 0~10 volts and the resolution is 16 bits.

[0211] (4) The generated digital drive commands for each motion axis are encapsulated according to the communication protocol specified by the displacement stage controller, and combined into a complete command data packet containing motion information of all axes. This command data packet is defined as the second control command and output to the displacement stage controller.

[0212] H3: Send the second control command to the servo controller of the displacement stage to drive the secondary mirror to perform the corresponding micro-displacement motion so that it reaches the corrected target pose.

[0213] The determination of whether the RMS and PV values ​​of the new effective combined wavefront meet the preset imaging quality indicators includes:

[0214] K1: Reconstruct the corresponding wavefront phase distribution map based on the new effective wavefront combination;

[0215] Furthermore, the specific steps of K1 include:

[0216] (1) Define a two-dimensional Cartesian coordinate grid covering the exit pupil region of the optical system;

[0217] (2) Normalize the physical coordinates of the two-dimensional Cartesian coordinate grid to the unit circle on which the Zernike polynomial definition is based, and calculate the normalized coordinates corresponding to each sampling point in the grid;

[0218] (3) For each normalized coordinate sampling point obtained, calculate the function value of each of the first N terms of the Zernike polynomial under that coordinate;

[0219] (4) Multiply the function value of each term by the coefficient of the same term in the Zernike coefficient vector corresponding to the new effective combined wavefront to obtain the phase component contributed by the term at the sampling point. Then sum the phase components of all terms to obtain the total wavefront phase value at the sampling point.

[0220] (5) Traverse all sampling points in the pupil region grid, repeat the calculation process of (3)-(4), obtain the total wavefront phase value of each sampling point, arrange the total wavefront phase values ​​of all sampling points according to their physical coordinate positions, and generate a two-dimensional wavefront phase matrix;

[0221] (6) The generated two-dimensional wavefront phase matrix is ​​used as the data basis and output as a wavefront phase distribution map; the wavefront phase distribution map intuitively displays the two-dimensional changes of the wavefront phase in grayscale or pseudo-color encoding.

[0222] K2: Calculate the root mean square value of the phase values ​​at all sampling points of the wavefront phase distribution map to obtain the RMS value. The formula for calculating the root mean square value is prior art in this field and is not an inventive solution of this application, so it will not be described in detail here.

[0223] K3: Find the maximum and minimum phase values ​​of all sampling points in the wavefront phase distribution map, and calculate their difference to obtain the PV value;

[0224] K4: Set imaging quality indicators, including: the PV value is not greater than one-quarter of the system operating wavelength, and the RMS value is not greater than one-twentieth of the system operating wavelength. In this embodiment, the system operating wavelength is set to 632.8 nanometers. Accordingly, the PV value threshold is 158.2 nanometers and the RMS value threshold is 31.64 nanometers.

[0225] K5: Compare the calculated RMS value and PV value with the imaging quality index. If both are satisfied, the detection is considered complete.

[0226] Example 2:

[0227] Please see Figure 3 Another embodiment of the present invention provides a primary and secondary mirror combination detection system for beam-shrinking systems, comprising:

[0228] The module includes a microsphere mirror arrangement module, a spot processing module, a wavefront data processing module, a decoupling module, a detection and judgment module, and a displacement stage module.

[0229] A microsphere mirror arrangement module is used to set up the first microsphere mirror and the second microsphere mirror;

[0230] The spot processing module is used to emit an interferometric detection beam, capture and precisely process the reflected spot, invert the secondary mirror misalignment, and generate the first control command for the initial adjustment of the secondary mirror pose.

[0231] The wavefront data processing module is used to simultaneously acquire the first wavefront data and the second alignment monitoring data, correct the temperature drift caused by the difference in the thermal expansion coefficients of the primary and secondary mirror materials, and output an effective combined wavefront.

[0232] The decoupling module is used to deduct the fixed transmission wavefront error introduced by the primary mirror compensator and decouples and separates the independent primary mirror surface shape error component and secondary mirror misalignment error component based on the aberration coupling coefficient.

[0233] The detection and judgment module is used to feed back the separated primary mirror surface shape error component and secondary mirror misalignment error component to the corresponding process / mechanism, generate a second control command, realize targeted correction, and iteratively detect until the preset imaging quality index is met.

[0234] The displacement stage module is used to receive the first control command and the second control command, and to perform translation and tilt adjustments of the secondary mirror to achieve precise positioning of the secondary mirror's pose.

[0235] The spot processing module includes: an interferometer unit, an area array detector unit, a spot preprocessing unit, a center positioning unit, a position offset calculation unit, and an offset inversion unit;

[0236] The interferometer unit is used to emit a detection beam so that the beam passes through the main mirror compensator in sequence and then synchronously illuminates all the first microsphere mirrors and the second microsphere mirrors.

[0237] An array detector unit is placed in the interferometer's receiving optical path to synchronously capture independent spot images formed by reflections from each first microspherical mirror and the second microspherical mirror;

[0238] The spot preprocessing unit is used to perform noise reduction and grayscale normalization on the captured independent spot images to improve the spot center positioning accuracy.

[0239] The center positioning unit is used to extract the real-time center pixel coordinates of each light spot in the image coordinate system;

[0240] The position offset calculation unit is used to calculate the difference between the real-time center pixel coordinates of each spot and the reference center pixel coordinates stored in the database to obtain the position offset vector of each spot.

[0241] The offset inversion unit is used to input the position offset vectors of all light spots into the preset offset-offset mapping relationship model, and to perform inversion solution using a nonlinear least squares optimization algorithm to finally obtain the first control command.

[0242] The wavefront data processing module includes: a dual-band light source unit, a beam splitting and filtering unit, a wavefront sensor unit, a four-quadrant detector unit, and a temperature drift correction unit.

[0243] Dual-band light source unit, containing 632.8 nanometers rice The first laser source with 1064 nanometers rice The second laser source and the two are combined into a common optical path beam by a polarization beam combiner and incident on the primary mirror compensator;

[0244] The beam splitting and filtering unit is used to separate a monitoring beam from the beam containing two wavelengths returned by the interferometer using the first beam splitter, and then guide the monitoring beam to the beam splitting and filtering module composed of a dispersive prism and a filter to separate the first wavelength beam and the second wavelength beam.

[0245] A wavefront sensor unit is used to receive the first wavefront beam and obtain the first wavefront data by calculating its phase distribution.

[0246] The four-quadrant detector unit is used to receive the second-band beam and obtain second alignment monitoring data characterizing the beam alignment status by calculating the energy distribution difference of the beam spot center in the four quadrants of the detector.

[0247] The temperature drift correction unit is used to monitor the ambient temperature in real time. Based on the difference in the thermal expansion coefficients of the primary mirror material and the secondary mirror material, a temperature-spot offset correction lookup table is established to obtain the theoretical spot center offset compensation amount and influence weight. The unit also performs compensation calculations on the Zernike polynomial coefficients after the first wavefront data decomposition to generate the corrected effective combined wavefront.

[0248] The decoupling module includes: a model building unit, an error subtraction unit, a coupling coefficient acquisition unit, and an error decoupling and separation unit;

[0249] The model building unit is used to obtain optical design parameters. Based on these optical design parameters, the ideal transmission wavefront of the primary mirror compensator at the first nanometer wavelength is simulated by ray tracing software and expanded into the first N coefficients of the Zernike polynomial to form an inherent aberration coefficient vector. Then, the actual transmission wavefront data, including the manufacturing error of the primary mirror compensator itself, is obtained by actual testing of a standard mirror with a known surface shape. This data is then expanded into the same order Zernike polynomial to obtain the actual aberration coefficient vector. Finally, the two are subtracted to obtain the coefficient vector of the fixed transmission wavefront error and stored in the error separation model.

[0250] The error subtraction unit is used to expand the effective combined wavefront into a Zernike polynomial coefficient vector of the same order, and then subtract it from the coefficient vector of the fixed transmission wavefront error stored in the error separation model to obtain the difference coefficient vector characterizing the wavefront of the residual system.

[0251] The coupling coefficient acquisition unit is used in optical design software to establish a complete optical model based on the design parameters of the primary and secondary mirrors of the beam-shrinking system. It introduces independent errors such as the surface shape error of the primary mirror and the misalignment of the secondary mirror of known magnitude. For each error / combination, it performs ray tracing to obtain the wavefront error distribution and decomposes it into Zernike polynomial coefficient vectors. Then, it fits the coupling relationship matrix through multiple linear regression, and its coefficients are the aberration coupling coefficients.

[0252] The error decoupling and separation unit is used to construct a system of linear equations with coupling relation matrix as coefficients by taking the Zernike polynomial coefficient vector representing the wavefront of the residual system as input. The unknowns of the system of equations are the magnitudes of various primary mirror surface shape errors and the translational and tilting misalignments of the secondary mirrors. Then, the linear equations are solved by the linear least squares method based on QR decomposition to obtain the numerical solutions of the primary mirror surface shape error components and the secondary mirror misalignment error components.

[0253] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments under the guidance of the present invention without departing from the spirit and scope of the present invention. All of these variations are within the protection scope of the present invention.

Claims

1. A method for detecting the combination of primary and secondary mirrors in a beam-shrinking system, characterized in that, include: S1: Multiple first micro spherical mirrors are evenly distributed around the effective aperture edge of the primary mirror of the beam-shrinking system, and a second micro spherical mirror is set at the center of the secondary mirror. The detection optical path of the interferometer is activated to illuminate the first micro spherical mirror and the second micro spherical mirror, and the reflected light spots are captured by the detector. The position offset of each reflected light spot is calculated in real time to generate a first control command for adjusting the pose of the secondary mirror. S2: A dual-band light source is integrated into the detection optical path of the interferometer. While driving the displacement stage to execute the first control command, the first wavefront data and the second alignment monitoring data obtained by the dual-band light source are simultaneously acquired. Based on the second alignment monitoring data, the temperature drift caused by the difference in thermal expansion coefficients of the primary mirror and the secondary mirror materials is corrected to obtain the corrected effective combined wavefront. S3: Input the effective combined wavefront into the preset error separation model, subtract the fixed transmission wavefront error introduced by the primary mirror compensator from the effective combined wavefront through the error separation model to obtain the residual system wavefront, and decouple and separate the independent primary mirror surface shape error component and secondary mirror misalignment error component from the residual system wavefront according to the preset aberration coupling coefficient. The error separation model is constructed based on the optical parameters of the primary mirror compensator of the beam-shrinking system and the Zernike aberration coefficient. S4: Feed back the primary mirror surface shape error component to the primary mirror repair and polishing process, convert the secondary mirror misalignment error component into a second control command and feed it back to the displacement stage. After completing the targeted correction, repeat S1 to S3 to obtain a new effective combined wavefront and its decoupled error components. Determine whether the RMS value and PV value of the new effective combined wavefront meet the preset imaging quality index. If yes, the detection is completed; if not, repeat S4 until the imaging quality index is met.

2. The method for detecting the primary and secondary mirror combination in a beam-shrinking system according to claim 1, characterized in that, The detection optical path of the start interferometer illuminates the first and second microspherical mirrors, and the reflected light spots are captured by the detector. The positional offset of each reflected light spot is then calculated in real time, including: The interferometer is activated so that the emitted detection beam passes through the main mirror compensator in sequence and then simultaneously illuminates all the first microsphere mirrors and the second microsphere mirrors. Using an array detector set in the receiving optical path of the interferometer, the independent light spot images formed by reflections from each first microspherical mirror and the second microspherical mirror are captured synchronously; The image of the independent light spot is preprocessed; the preprocessing includes at least noise reduction and grayscale normalization. A spot center localization algorithm based on circle fitting is used to extract the real-time center pixel coordinates of each spot in the image coordinate system; The position offset vector of each light spot is obtained by calculating the difference between the real-time center pixel coordinates of each light spot and the reference center pixel coordinates stored in the database.

3. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 2, characterized in that, The generation of the first control command for adjusting the pose of the secondary mirror includes: The calculated position offset vectors of all light spots are input to a preset offset-offset mapping model. The offset-offset mapping model is established through a pre-calibrated experiment, with the translational and tilt offsets of the secondary mirror as input variables and the theoretically calculated position offsets of the reflected light spots of each microsphere mirror as output variables. Using the calculated position offset vectors of all light spots as known quantities, a nonlinear least squares optimization algorithm is used to invert and solve the problem based on the offset-offset mapping relationship model. The goal of the inversion solution is to find a set of secondary mirror translation offset and tilt offset such that the overall error between the predicted light spot offset calculated after substituting the corresponding secondary mirror translation offset and tilt offset into the offset-offset mapping relationship model is minimized. The optimal translational and tilting misalignments of the secondary mirror obtained by the solution are converted into the first control command for driving the movement of the displacement stage according to the control parameters of each motion axis of the displacement stage; the first control command includes the translational amount of the secondary mirror along the X-axis and Y-axis and the tilting angle around the X-axis and Y-axis.

4. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 1, characterized in that, The dual-band light source includes a first laser source with a first nanometer wavelength and a second laser source with a second nanometer wavelength. The first laser source and the second laser source are combined into a common optical path beam by a polarization beam combiner and incident on the main mirror compensator. The first nanometer wavelength is smaller than the second nanometer wavelength. The process of acquiring the first wavefront data and the second alignment monitoring data obtained from the dual-band light source includes: From the beam containing two wavelengths returned from the interferometer, a monitoring beam is separated using the first beam splitter; The monitoring beam is guided to a beam splitting and filtering module consisting of a dispersive prism and a filter, and separated into a first band beam with a first nanometer wavelength and a second band beam with a second nanometer wavelength. The first wavefront sensor is used to receive the first band beam, and the first wavefront data is obtained by solving its phase distribution. The second band beam is received using a four-quadrant detector. By calculating the energy distribution differences of the beam spot center in the four quadrants of the detector, second alignment monitoring data characterizing the beam alignment status is obtained.

5. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 4, characterized in that, The step of correcting the temperature drift caused by the difference in thermal expansion coefficients between the primary and secondary mirror materials based on the second alignment monitoring data to obtain the corrected effective combined wavefront includes: Real-time monitoring of ambient temperature, and based on the difference in thermal expansion coefficients between the primary mirror material and the secondary mirror material, a temperature-spot offset correction lookup table is established; Based on the current ambient temperature and the second alignment monitoring data obtained by the four-quadrant detector, the temperature-spot offset correction lookup table is queried to obtain the theoretical spot center offset compensation amount corresponding to the first nanometer wavelength caused by material thermal deformation under the current temperature conditions. Based on the theoretical spot center offset compensation amount and the spatial resolution of the four-quadrant detector, the influence weight of the theoretical spot center offset compensation amount on the specified Zernike aberration term in the first wavefront data is calculated; the specified Zernike aberration term includes at least astigmatism and coma. The Zernike polynomial coefficients after the first wavefront data decomposition are compensated based on the calculated influence weights to generate a corrected effective combined wavefront.

6. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 1, characterized in that, The construction process of the error separation model includes: Obtain the optical design parameters of the primary mirror compensator; the optical design parameters include the radius of curvature, center thickness, material refractive index, and lens spacing of each lens surface; Based on the optical design parameters, the ideal transmission wavefront of the primary mirror compensator at the first nanometer wavelength is simulated using ray tracing software, and the ideal transmission wavefront is expanded into the first N coefficients of the Zernike polynomial to form the intrinsic aberration coefficient vector. By conducting actual testing on a standard mirror with a known surface shape, the actual transmitted wavefront data, including the manufacturing error of the primary mirror compensator itself, is obtained. The actual transmitted wavefront data is then expanded into Zernike polynomials of the same order to obtain the actual aberration coefficient vector. Subtracting the actual aberration coefficient vector from the inherent aberration coefficient vector yields a difference vector that is defined as the coefficient vector of the fixed transmission wavefront error and stored in the error separation model. The step of subtracting the fixed transmission wavefront error introduced by the primary mirror compensator from the effective combined wavefront using the error separation model is as follows: the effective combined wavefront is expanded into a Zernike polynomial coefficient vector of the same order, and the Zernike polynomial coefficient vector is subtracted from the coefficient vector of the fixed transmission wavefront error stored in the error separation model. The resulting difference coefficient vector represents the residual system wavefront.

7. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 1, characterized in that, The preset aberration coupling coefficient is obtained in the following way: Based on the design parameters of the primary and secondary mirrors of the beam-shrinking system, a complete optical model of the beam-shrinking system is established in optical design software. Introduce independent errors of known magnitude into the complete optical model; these independent errors include primary mirror shape errors of various types and magnitudes, as well as secondary mirror translation and tilt misalignments of various directions and sizes. For each introduced independent error or error combination, wavefront analysis is performed using the ray tracing function of optical design software to calculate the corresponding wavefront error distribution at the system exit pupil. The wavefront error distribution is then decomposed into Zernike polynomials, and the first M coefficient vectors are recorded. Using the category and magnitude of all introduced independent errors as independent variables and the Zernik polynomial coefficient vector of the system wavefront as dependent variables, a coupling relationship matrix is ​​fitted through multiple linear regression analysis. The coupling relationship matrix is ​​used to describe the contribution weight of each type of primary mirror shape error or secondary mirror pose misalignment to each Zernik aberration in the overall wavefront of the system. The elements in the coupling relationship matrix are the aberration coupling coefficients.

8. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 7, characterized in that, The step of decoupling and separating the independent primary mirror shape error component and secondary mirror misalignment error component from the residual system wavefront according to the preset aberration coupling coefficient includes: Using the Zernike polynomial coefficient vector representing the wavefront of the residual system as input, a system of linear equations is constructed with the coupling matrix as coefficients. The unknowns of the system of equations are the magnitudes of various primary mirror surface shape errors and the translational and tilting misalignments of the secondary mirrors. The linear equations were solved using the linear least squares method based on QR decomposition to obtain numerical solutions for the primary mirror surface shape error component and the secondary mirror misalignment error component.

9. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 1, characterized in that, The step of converting the secondary mirror misalignment error component into a second control command and feeding it back to the displacement stage includes: The secondary mirror misalignment error components are analyzed to obtain the translation correction and tilt correction amounts to be compensated for by the secondary mirror in the current pose. Based on the transmission parameters of each motion axis of the displacement stage, the translation correction amount and tilt correction amount are converted into motor drive pulse number or analog voltage control signal to form a second control command; The second control command is sent to the servo controller of the displacement stage to drive the secondary mirror to perform the corresponding displacement motion so that it reaches the corrected target pose.

10. The method for detecting the primary and secondary mirror combination in a beam-shrinking system as described in claim 1, characterized in that, The determination of whether the RMS and PV values ​​of the new effective combined wavefront meet the preset imaging quality indicators includes: The corresponding wavefront phase distribution map is reconstructed based on the new effective wavefront combination. Calculate the root mean square (RMS) value of the phase values ​​at all sampling points of the wavefront phase distribution map to obtain the RMS value. Find the maximum and minimum phase values ​​of all sampling points in the wavefront phase distribution map, and calculate their difference to obtain the PV value; The imaging quality indicators are set as follows: the PV value is not greater than one-quarter of the system's operating wavelength, and the RMS value is not greater than one-twentieth of the system's operating wavelength. The calculated RMS and PV values ​​are compared with the imaging quality indicators. If both are satisfied, the detection is considered complete.

11. A primary and secondary mirror combination detection system for beam-shrinking systems, used to implement the primary and secondary mirror combination detection method for beam-shrinking systems according to any one of claims 1-10, characterized in that, include: The module includes a microsphere mirror arrangement module, a spot processing module, a wavefront data processing module, a decoupling module, a detection and judgment module, and a displacement stage module. The microsphere mirror arrangement module is used to set the first microsphere mirror and the second microsphere mirror; The light spot processing module is used to emit an interference detection beam, capture and process the reflected light spot, invert the secondary mirror misalignment, and generate the first control command for the initial adjustment of the secondary mirror pose. The wavefront data processing module is used to simultaneously acquire the first wavefront data and the second alignment monitoring data, correct the temperature drift caused by the difference in thermal expansion coefficients of the primary mirror and secondary mirror materials, and output an effective combined wavefront. The decoupling module is used to deduct the fixed transmission wavefront error introduced by the primary mirror compensator and decouple and separate the independent primary mirror surface shape error component and secondary mirror misalignment error component based on the aberration coupling coefficient. The detection and judgment module is used to feed back the separated primary mirror surface shape error component and secondary mirror misalignment error component to the corresponding process / mechanism respectively, and generate a second control command; The displacement stage module is used to receive the first control command and the second control command, and to perform translation and tilt adjustments of the secondary mirror.

Images