Computer-aided adjustment method for variable-attitude wide-temperature-range laser beam expanding system

Abstract

The invention discloses a variable-attitude wide-temperature-range laser beam expanding system computer-aided installation and adjustment method, which comprises the following steps: firstly, acquiring system parameters and working condition requirements, constructing an aberration model under mechanical thermal disturbance based on optical-mechanical thermal integration analysis, then establishing an offset model based on a second-order sensitivity matrix, comprehensively considering working condition change, surface shape error and installation and adjustment error, and finally establishing an offset model based on a second-order sensitivity matrix. And solving the optimal installation and adjustment quantity under physical constraints, and finally, updating model parameters by adopting an iterative convergence installation and adjustment method until the system meets performance indexes of various working conditions, and outputting a final installation and adjustment result to finish system installation and adjustment. The method provided by the invention solves the problems of insufficient precision and poor adaptability of the existing installation and adjustment method under multi-source disturbance, and realizes efficient and robust installation and adjustment of the laser beam expanding system under high precision and multiple working conditions.

Description

Technical Field

[0001] This invention belongs to the field of optical system assembly and adjustment technology, specifically relating to a computer-aided assembly and adjustment method for a variable attitude wide temperature range laser beam expander system. Background Technology

[0002] Laser beam expanders are core components of large-aperture interferometers, collimators, laser communication systems, and are widely used in fields such as interferometers, laser communication, and target tracking.

[0003] With increasing system performance requirements, manual adjustment methods, primarily based on experience, can no longer meet the demands for high-precision adjustment. Computer-aided adjustment (CAA) technology has become a key technological means. CAA is a technique that, based on the difference between measured and ideal values ​​of system performance (such as wavefront aberration, point spread function, and imaging sharpness) during the adjustment process, analyzes the influence of misalignment on system performance and uses misalignment state estimation methods to solve for the actual misalignment, thereby guiding the adjustment process and significantly improving system adjustment efficiency and performance. Existing computer-aided adjustment methods mainly use wavefront sensors to measure system wavefront aberrations to characterize performance and solve for adjustment quantities through misalignment models to achieve efficient adjustment, such as the sensitivity matrix method, inverse optimization method, differential wavefront method, neural network method, and vector aberration method. However, these methods do not consider the system wavefront aberrations caused by mechanical and thermal disturbances, component surface errors, and misalignment under variable attitude and wide temperature range conditions, and cannot effectively guide the adjustment of variable attitude and wide temperature range laser beam expander systems.

[0004] Therefore, there is an urgent need for a computer-aided assembly and adjustment method for laser beam expanders that can adapt to varying orientation and wide temperature range conditions and comprehensively consider the effects of multi-source disturbances, so as to achieve high-precision and high-robustness system assembly and adjustment. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a computer-aided assembly and adjustment method for a variable-attitude, wide-temperature-range laser beam expander system. This method constructs a system aberration characteristic model through optomechanical-thermal integrated analysis, establishes an misalignment model by combining a second-order sensitivity matrix, and employs an iterative convergence assembly and adjustment strategy to achieve optimal assembly and adjustment of the system under multiple operating conditions.

[0006] The technical solution adopted in this invention is: a computer-aided assembly and adjustment method for a variable attitude wide temperature range laser beam expander system, characterized by the following specific steps:

[0007] S1. Obtain the optical parameters, structural parameters, and operating requirements of the laser beam expander system;

[0008] S2. Based on the optomechanical-thermal integrated analysis method, construct a wavefront aberration characteristic model of the system under mechanical and thermal perturbation;

[0009] S3. Establish a system misalignment model based on a second-order sensitivity matrix;

[0010] The misalignment model includes wavefront aberration terms caused by operating condition changes, component surface shape errors, and adjustment errors.

[0011] S4. Based on the aforementioned misalignment model and measured wavefront aberrations, solve for the optimal assembly adjustment under the physical constraints of the assembly adjustment.

[0012] S5. Adopt the iterative convergence assembly and adjustment method, update the model parameters and perform assembly and adjustment until the system meets the performance indicators under all operating conditions.

[0013] S6. Output the final assembly and debugging results and system performance report to complete the system assembly and debugging.

[0014] The beneficial effects of this invention are as follows: The method of this invention first obtains system parameters and operating condition requirements, constructs an aberration model under mechanical and thermal perturbation based on optomechanical-thermal integrated analysis, then establishes an misalignment model based on a second-order sensitivity matrix, comprehensively considers operating condition changes, surface shape errors, and assembly errors, and solves for the optimal assembly amount under physical constraints. Finally, an iterative convergence assembly method is used to update the model parameters until the system meets the performance indicators of each operating condition, outputting the final assembly result and completing the system assembly. This invention solves the problems of insufficient accuracy and poor adaptability of existing assembly methods under multi-source perturbation, achieving efficient and robust assembly of laser beam expander systems under high precision and multiple operating conditions. Attached Figure Description

[0015] Figure 1 This is a flowchart of a computer-aided assembly and adjustment method for a variable attitude wide temperature range laser beam expander system according to the present invention.

[0016] Figure 2 This is a schematic diagram of the optomechanical-thermal integrated analysis process in an embodiment of the present invention.

[0017] Figure 3 This is a schematic diagram illustrating the solution for the optimal assembly and adjustment amount in an embodiment of the present invention.

[0018] Figure 4 The flowchart below shows the verification process for the optimal assembly and adjustment method in this embodiment of the invention.

[0019] Figure 5 This is a schematic diagram of the iterative convergence assembly and adjustment process in an embodiment of the present invention. Detailed Implementation

[0020] The method of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] like Figure 1 The diagram shows a computer-aided assembly and adjustment method for a variable-attitude, wide-temperature-range laser beam expander system according to the present invention. The specific steps are as follows:

[0022] S1. Obtain the optical parameters, structural parameters, and operating requirements of the laser beam expander system;

[0023] Specifically, this includes: system diameter, off-axis distance, radius of curvature, material properties, support structure type; operating temperature range (e.g., -20℃ to 50℃), attitude change range (e.g., pitch 0° to 90°); and assembly tolerance index (e.g., wavefront RMS ≤ 0.1λ).

[0024] S2, such as Figure 2 As shown, a wavefront aberration characteristic model of the system under mechanical and thermal perturbation is constructed based on the optomechanical-thermal integrated analysis method.

[0025] Based on the optomechanical-thermal integrated analysis method, the wavefront aberration characteristics of the system under different force and thermal disturbance conditions were obtained, laying the foundation for subsequent misalignment model construction and optimal assembly and adjustment.

[0026] S21. Establish a three-dimensional geometric model of the system in CAD software, and import it into finite element analysis software (such as ANSYS) to establish mechanical and thermal models;

[0027] S22. Set boundary conditions and loads to simulate structural deformation under different combinations of gravity attitudes (e.g., 0°, 30°, 60°, 90°) and temperatures (e.g., -20°, 0°, 25°, 50°).

[0028] S23. Extract the surface nodal displacement data of the optical element and obtain the surface error by Zernike polynomial fitting;

[0029] S24. Import the surface shape and pose change data into optical design software (such as Zemax), calculate the wavefront aberration of the system under each working condition, and fit the aberration coefficient matrix.

[0030] S3. Establish a system misalignment model based on a second-order sensitivity matrix;

[0031] The misalignment model includes wavefront aberration terms caused by operating condition changes, component surface shape errors, and adjustment errors; it realizes the analysis of system aberration characteristics under multi-source disturbances, breaks through the model-driven predictive assembly and adjustment technology, and solves the assembly and adjustment problem under variable attitude and wide temperature range operating conditions.

[0032] S31. Determine the degree of freedom and range of misalignment of the adjustable optical elements of the system;

[0033] The adjustable optical element is a secondary mirror, and its degrees of freedom of misalignment include X-eccentricity, Y-eccentricity, Z-distance, X-tilt, and Y-tilt, with a translation misalignment range of ±1mm and a tilt misalignment range of ±0.25°.

[0034] S32. Based on optical design software and real-time data interaction interface, generate multiple sets of misalignment combinations and corresponding wavefront aberration data;

[0035] This embodiment uses the real-time data interaction interface between Zemax and Matlab (ZOS-API) to generate a large number of misalignment combinations within the misalignment range and obtain the Zernike coefficients of the corresponding wavefront aberrations.

[0036] S33. A second-order polynomial fitting method is used to establish the mapping relationship between the misalignment and the aberration coefficients. The surface shape error aberration term and the working condition change aberration term are combined to form a complete misalignment model.

[0037] Since the wavefront aberrations of the system caused by changes in operating conditions, component surface shape errors, and adjustment errors are independent, and considering the rigid misalignment aberration characteristics of the off-axis two-reflector laser beam expander system, a misalignment model for the variable attitude wide-temperature-range laser beam expander system based on the second-order sensitivity matrix can be constructed, as shown in the following expression:

[0038] (1)

[0039] (2)

[0040] (3)

[0041] Among them, B i and C i These are the second-order and first-order sensitivity matrices, respectively, which can be solved by the misalignment aberration characteristics of an ideal optical model. The surface shape error of the component can be determined in advance by measuring with a laser interferometer. The changes in wavefront aberration of the system under different operating conditions can be determined based on the optomechanical-thermal integrated analysis in step S2. The misalignment model based on equation (1) can construct the mapping relationship between adjustment error and system wavefront aberration under different gravity and temperature conditions and component surface errors, effectively guiding the high-precision assembly and adjustment of the variable attitude wide temperature range off-axis two-reflector laser beam expander system.

[0042] S4. Based on the aforementioned misalignment model and measured wavefront aberrations, solve for the optimal assembly adjustment under the physical constraints of the assembly adjustment.

[0043] S41. Use a laser interferometer to measure the current wavefront aberration of the system and extract the first 9 Zernike coefficients;

[0044] Typically, adjustment errors mainly cause low-order aberrations, such as defocus, astigmatism, coma, and spherical aberration, corresponding to terms 4 to 9 of the Zernike polynomial. As shown in equation (1), solving the adjustment error, which involves five unknowns, through six equations corresponding to low-order aberrations, reveals that this equation is clearly overdetermined, with a non-unique solution. Although this overdetermined equation can be easily solved using methods such as least squares, the corresponding solution is only mathematically correct and may be physically suboptimal or even out of tolerance. For a variable-attitude, wide-temperature-range off-axis two-reflector laser beam expander system, not only is accurate solution of the adjustment error required, but the design requirements must also be met under different operating conditions.

[0045] S42. Within the design tolerance range of the assembly and adjustment quantity, construct a constrained optimization problem:

[0046] To achieve the optimal assembly and adjustment, multiple physical constraints are applied to equation (1), and a single-objective optimization model is constructed, as shown in the following expression:

[0047] (4)

[0048] (5)

[0049] Where, x max y max , z max θ xmax and θ ymax These represent the maximum values ​​of X-eccentricity, Y-eccentricity, Z-interval, X-tilt, and Y-tilt, respectively, which are the design tolerance ranges. W0 and W(X) correspond to the measured wavefront aberration and the wavefront aberration corresponding to the adjustment error, respectively.

[0050] S43. Use a multi-starting-point optimization algorithm (such as global least squares) to solve for the optimal assembly and adjustment amount;

[0051] Since the nonlinear least squares solution of equation (1) is related to the starting point, different combinations of extreme values ​​of the adjustment error are used as the starting point to solve for the adjustment error, resulting in a total of 2 5 =32 solutions. Substituting the solutions within the design tolerance range into the optical model yields the corresponding wavefront aberrations. The solution closest to the measured wavefront aberration (with the smallest RMS) is the optimal assembly adjustment. A schematic diagram of the optimal assembly adjustment solution is shown below. Figure 3 As shown, by applying design tolerance range constraints, the misaligned wavefront aberration is made closest to the measured result, and finally the optimal assembly and adjustment solution of the variable attitude wide temperature range laser beam expander system is obtained.

[0052] In this embodiment, as Figure 4As shown, the optimal assembly and adjustment solution method proposed is verified by simulation of a variable-attitude, wide-temperature-range off-axis two-reflector laser beam expander system. Four simulation conditions are selected: -20℃ horizontal optical axis, -20℃ vertical optical axis, 50℃ horizontal optical axis, and 50℃ vertical optical axis. The rigid misalignment range (design tolerance) is determined to be ±1mm translation and ±0.25° tilt. First, the parameters of the second-order sensitivity matrix model are determined based on the optical model and the optomechanical thermal analysis structure. Then, the misalignment matrix is ​​randomly generated according to the determined rigid misalignment range and imported into Zemax to obtain the corresponding system wavefront aberration. Second, the wavefront aberration obtained from the simulation is used as the measured wavefront aberration, and the optimal assembly and adjustment amount is solved based on equations (4) and (5). Finally, the solution error is calculated and imported into the ideal optical model to obtain the system wavefront residual to evaluate the system performance after simulation and adjustment.

[0053] S5, such as Figure 5 As shown, an iterative convergence assembly method is adopted to update the model parameters and perform assembly until the system meets the performance indicators under all operating conditions.

[0054] Although the results presented in the previous section indicate that the misalignment model based on the second-order sensitivity matrix can accurately solve for the optimal adjustment amount to ensure that the system aberrations meet the requirements under various operating conditions, the following problems still exist: 1) High wavefront measurement accuracy is required. When the error of the Zernike polynomial coefficients in the wavefront measurement exceeds 0.001, the solution error is too large. However, due to limitations in the measurement environment and equipment, the current Zernike polynomial system measurement is unlikely to meet this accuracy requirement; 2) The optimal adjustment amount solution does not consider the adjustment actuator, which may lead to over-adjustment or under-adjustment problems due to non-orthogonal motion or mechanical backlash, making it impossible to complete the adjustment in one go; 3) The proposed misalignment model requires pre-measurement of component surface data to determine model parameters, resulting in low batch adjustment efficiency. In summary, due to the differences between the misalignment model and reality, the influence of measurement errors and adjustment mechanism errors, it is difficult to meet the target requirements in a single adjustment. However, overall, the system wavefront aberrations converge and decrease with the number of adjustments. To reduce the requirements for wavefront measurement and assembly mechanisms and improve assembly robustness, an iterative convergent assembly method is proposed for batch assembly needs. Its core is to update the misalignment model parameters with the assembly iteration.

[0055] S51. Input the sensitivity matrix model parameters obtained from the theoretical design and the wavefront aberration of the measured system;

[0056] S52. Calculate the adjustment amount based on the measured aberration, and complete the adjustment and wavefront measurement in sequence through the adjustment mechanism and the laser interferometer;

[0057] An offset model based on a modified sensitivity matrix is ​​constructed. Through specific offset combinations, efficient compensation for defocus and astigmatism, as well as iterative convergence adjustment of the system, can be achieved. The calculation expression is as follows:

[0058] (6)

[0059] Wherein, k1~k8 are model parameters, and the initial results are obtained from theoretical design. The assembly and adjustment sequence is first XY translation, then XY tilt, and finally Z translation. Although this misalignment model does not consider the system wavefront aberration caused by component surface errors and changes in operating conditions, the aberrations generated by these two situations are small and can be adjusted iteratively to meet the design requirements.

[0060] S53. Determine whether the wavefront aberration of the system under each working condition meets the index requirements. If the requirements are met, the installation and adjustment are considered to be completed. Otherwise, update the misalignment model parameters according to the installation and adjustment amount and the aberration change amount, and carry out the next round of installation and adjustment until the wavefront aberration of the system under each working condition meets the requirements.

[0061] S6. Output the final assembly and debugging results and system performance report to complete the system assembly and debugging.

[0062] The method of the present invention is applicable to laser beam expander systems with circular or rectangular apertures, wherein the circular aperture system uses Zernike polynomials for wavefront aberration characterization, and the rectangular aperture system uses Legendre polynomials for wavefront aberration characterization.

[0063] This embodiment further verified the results through experiments. Taking a one-meter-level off-axis two-reflection laser beam expander system as an example, the method of this invention was used for assembly and adjustment within the operating range of -20℃ to 50℃ and pitch 0° to 90°. After three rounds of iterative assembly and adjustment, the wavefront aberration RMS of the system was better than 0.05λ under all operating conditions, the assembly and adjustment efficiency was improved by about 60%, and the assembly and adjustment consistency was significantly improved.

[0064] This embodiment starts with the rigid misalignment aberration characteristics of a variable-attitude, wide-temperature-range off-axis two-reflector laser beam expander system. It analyzes the wavefront aberration changes under different misalignment conditions. Addressing the limitations of existing linear sensitivity matrix solutions in terms of accuracy and inability to decouple misalignment, a second-order sensitivity matrix is ​​proposed. A misalignment model for the variable-attitude, wide-temperature-range off-axis two-reflector laser beam expander system is constructed by combining aberration terms caused by component surface errors and operating condition variations. Optimal alignment is achieved by designing tolerances and physical constraints that closely approximate the measured wavefront. Furthermore, to reduce the influence of alignment mechanism and wavefront measurement errors, a correlation model between alignment and system wavefront aberrations is directly constructed. An iterative convergent alignment method is used to achieve efficient compensation of individual aberrations through specific misalignment combinations. Combined with iteratively updated model parameters, the robustness of the alignment is significantly improved.

[0065] In summary, the method of this invention combines optomechanical-thermal integrated analysis with second-order sensitivity modeling to achieve high-precision and robust assembly of a variable-attitude wide-temperature-range laser beam expander system, which is suitable for digital assembly applications of various complex optical systems.

[0066] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the implementation methods of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. A computer-aided assembly and adjustment method for a variable-attitude, wide-temperature-range laser beam expander system, characterized in that, The specific steps are as follows: S1. Obtain the optical parameters, structural parameters, and operating requirements of the laser beam expander system; S2. Based on the optomechanical-thermal integrated analysis method, construct a wavefront aberration characteristic model of the system under mechanical and thermal perturbation; S3. Establish a system misalignment model based on a second-order sensitivity matrix; The misalignment model includes wavefront aberration terms caused by operating condition changes, component surface shape errors, and adjustment errors. S4. Based on the aforementioned misalignment model and measured wavefront aberrations, solve for the optimal assembly adjustment under the physical constraints of the assembly adjustment. S5. Adopt the iterative convergence assembly and adjustment method, update the model parameters and perform assembly and adjustment until the system meets the performance indicators under all operating conditions. S6. Output the final assembly and debugging results and system performance report to complete the system assembly and debugging.

2. The computer-aided assembly and adjustment method for a variable attitude wide temperature range laser beam expander system according to claim 1, characterized in that, Step S2 is as follows: S21. Establish a three-dimensional geometric model of the system in CAD software, and import it into finite element analysis software to establish mechanical and thermal models; S22. Set boundary conditions and loads to simulate structural deformation under different combinations of gravity attitude and temperature. Based on multiphysics coupling simulation, the deformation and surface shape changes of optical components under different gravity attitudes and temperature conditions are analyzed. The multiphysics coupling simulation includes mechanical simulation and thermal simulation. In the mechanical simulation, four orientations are set with the angle between the gravity direction and the optical axis being 0°, 30°, 60°, and 90°; in the thermal simulation, four working conditions are set with temperature loads of -20℃, 0℃, 25℃, and 50℃. S23. Extract the surface nodal displacement data of the optical element and obtain the surface error by Zernike polynomial fitting; S24. Import the surface shape and pose change data into the optical design software, calculate the wavefront aberration of the system under each working condition, and fit the aberration coefficient matrix.

3. The computer-aided assembly and adjustment method for a variable attitude wide temperature range laser beam expander system according to claim 1, characterized in that, Step S3 is as follows: S31. Determine the degree of freedom and range of misalignment of the adjustable optical elements of the system; The adjustable optical element is a secondary mirror, and its degrees of freedom of misalignment include X-eccentricity, Y-eccentricity, Z-distance, X-tilt, and Y-tilt, with a translation misalignment range of ±1mm and a tilt misalignment range of ±0.25°. S32. Based on optical design software and real-time data interaction interface, generate multiple sets of misalignment combinations and corresponding wavefront aberration data; S33. A second-order polynomial fitting method is used to establish the mapping relationship between the misalignment and the aberration coefficients. The surface shape error aberration term and the working condition change aberration term are combined to form a complete misalignment model. An offset model for a variable-attitude, wide-temperature-range laser beam expander system based on a second-order sensitivity matrix is ​​constructed, and its expression is as follows: （1）； （2）； （3）； Among them, B i and C i These are the second-order and first-order sensitivity matrices, respectively, which are solved by the misalignment aberration characteristics of the ideal optical model; The surface shape error of the component is determined in advance by measuring with a laser interferometer; The wavefront aberration variation of the system under different operating conditions is determined based on the optomechanical-thermal integrated analysis in step S2.

4. The computer-aided assembly and adjustment method for a variable attitude wide temperature range laser beam expander system according to claim 1, characterized in that, Step S4 is as follows: S41. Use a laser interferometer to measure the current wavefront aberration of the system and extract the first 9 Zernike coefficients; S42. Within the design tolerance range of the assembly and adjustment quantity, construct a constrained optimization problem: By applying multiple physical constraints to equation (1), a single-objective optimization model is constructed, as shown in the following expression: （4）； （5）； Where, x max y max , z max θ xmax and θ ymax These represent the maximum values ​​of X eccentricity, Y eccentricity, Z spacing, X tilt, and Y tilt, respectively, i.e., the design tolerance range; W0 and W(X) correspond to the measured wavefront aberration and the wavefront aberration corresponding to the adjustment error, respectively. S43. Use a multi-starting-point optimization algorithm to solve for the optimal assembly and adjustment amount; The nonlinear least squares solution of equation (1) is related to the starting point. Therefore, different combinations of extreme values ​​of adjustment error are used as the starting point to solve for the adjustment error, resulting in 2. 5 =32 sets of solutions; Substitute the solutions within the design tolerance range into the optical model to obtain the corresponding wavefront aberrations, and the solution that is closest to the measured wavefront aberration is the optimal assembly amount.

5. The computer-aided assembly and adjustment method for a variable attitude wide temperature range laser beam expander system according to claim 1, characterized in that, Step S5 is as follows: S51. Input the sensitivity matrix model parameters obtained from the theoretical design and the wavefront aberration of the measured system; S52. Calculate the adjustment amount based on the measured aberration, and complete the adjustment and wavefront measurement in sequence through the adjustment mechanism and the laser interferometer; An offset model based on a modified sensitivity matrix is ​​constructed. Through specific offset combinations, efficient compensation for defocus and astigmatism, as well as iterative convergence adjustment of the system, can be achieved. The calculation expression is as follows: （6）； Among them, k1~k8 are model parameters. The initial results are solved by theoretical design. The assembly and adjustment order is first XY translation, then XY tilt, and finally Z translation. S53. Determine whether the wavefront aberration of the system under each working condition meets the index requirements. If the requirements are met, the assembly and adjustment are considered complete. Otherwise, update the misalignment model parameters according to the assembly and adjustment amount and the aberration change amount, and carry out the next round of assembly and adjustment until the wavefront aberration of the system under each working condition meets the requirements.

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