A method for measuring the ellipticity of point spread function of an optical system

Abstract

The present invention relates to the field of optical detection technology, and specifically proposes a method for measuring the point spread function ellipticity of an optical system. The method builds a star point target imaging optical path through a collimator and an optical system to be measured, and simultaneously builds a simulated optical system consistent with the optical parameters of the actual optical path in optical simulation software, including a simulated collimator and a simulated optical system to be measured, and adds a Zernike surface in the simulated system. Taking the point spread function measured by the actual imaging optical path as the target, and the added Zernike surface as the optimization variable, the intelligent optimization algorithm is continuously iterated and optimized until the difference between the characteristic parameters of the point spread function of the simulated system and the characteristic parameters of the measured point spread function is less than a set threshold, and the optimization is stopped. The Zenrike surface finally optimized and the simulated system to be measured constitute a new system, and the point spread function ellipticity value of the new system is the point spread function ellipticity of the actual system to be measured.

Description

Technical Field

[0001] The invention relates to the technical field of optical detection, and in particular to a method for measuring the point spread function ellipticity of an optical system. Background Art

[0002] The weak gravitational lensing effect will produce a shearing effect on the observed galaxy ellipticity, and its value is much smaller than the intrinsic ellipticity of the galaxy itself. In the industry, large-sample galaxy survey statistics are usually used for detection, which generally requires measuring the average value of at least thousands of galaxy deformations to calculate the shearing signal. However, to achieve the above-mentioned precise astronomical observations, superior detection tools are required.

[0003] With the update and iteration of space astronomical telescopes, their large field of view, high resolution, high energy utilization, ultra-deep space detection and other characteristics enable us to measure the weak gravitational lensing effect more accurately. However, the non-ideal optical properties of the telescope have a great influence on the detection accuracy. According to the analysis results, the weak gravitational lensing effect will cause the shape of the observed galaxy to change, which is equivalent to the change in the ellipticity of the point spread function caused by the non-ideal imaging characteristics of the telescope. Therefore, eliminating the non-ideal imaging characteristics of the telescope is of great significance for achieving high-precision detection of the weak gravitational lensing effect.

[0004] When a space telescope is in orbit, the target galaxy may appear at any point in the telescope's field of view. In order to achieve high-precision measurement of the ellipticity of the target galaxy at any point, it is necessary to obtain the point spread function (PSF) ellipticity of the telescope at that point in advance. Obviously, it is impossible for us to measure the PSF ellipticity of all points within the field of view of the telescope in advance. The usual practice is to select a certain number of characteristic fields of view that cover the entire field of view for precise PSF ellipticity measurement. After entering orbit, the PSF ellipticity of the telescope at any point in the field of view can be obtained by interpolation. Therefore, accurately measuring the PSF ellipticity of the telescope system on the ground is of great significance for achieving high-precision observations of weak gravitational lensing effects.

[0005] At present, there are two main methods for obtaining the point spread function ellipticity: computational simulation method and imaging method.

[0006] The computational simulation method is to set the characteristic field of view in the numerical calculation software, substitute the measured wave aberration of each field of view into the optical system design software and establish a dynamic link, and obtain the point spread function of the optical system according to the design file of the optical system. In this way, by switching different fields of view, the full field of view point spread function data is obtained and the energy center of mass position is extracted. According to the calculation formula, the full field of view point spread function ellipticity value and the two components of the corresponding field of view ellipticity value can be obtained. and This solution has the following disadvantages:

[0007] 1. The accuracy of point spread function ellipticity calculation depends on the accuracy of point spread function calculation, which is affected by the accuracy of wave aberration detection and exit pupil shape.

[0008] 2. For large-aperture, long-focal-length space telescopes, because their detection optical path is too long, the wave aberration measurement accuracy is easily affected by many factors such as atmospheric disturbances, platform micro-vibration, and Zernike fitting errors.

[0009] 3. Due to the limitations of the simulation capabilities of optical design software, in order to ensure the accuracy of calculation sampling, it is necessary to strictly limit the sampling interval of the point spread function data, the sampling grid size, the number of light rays passing through the pupil, etc.

[0010] 4. There are certain differences between the simulation calculation method and the actual imaging process of the optical system.

[0011] Point spread function ellipsometry imaging measurement method is obtained on the basis of point spread function detection. Point spread function detection methods mainly include slit detection method, knife edge detection method and star target imaging method. Slit detection method and knife edge method obtain point spread function by performing differential operation on the image formed by the slit or knife edge through the optical system. The scheme has the following disadvantages:

[0012] 1. The slit always has a certain width, and its pulse input does not meet the strict pulse function distribution. If the calculation accuracy is to be improved, the slit width needs to be corrected.

[0013] 2. Quantitative measurement cannot be achieved and the accuracy of the measurement data cannot be guaranteed.

[0014] 3. During measurement, the image of the knife edge or blade edge is usually determined by the observer's judgment, which is subjective and will increase the systematic error of the measurement result.

[0015] 4. When the detection light source is uneven or the noise is large, the noise resistance of the point spread function obtained by differential operation is reduced.

[0016] The star point target imaging method refers to the ideal point light source as a pulse function modulated by the optical system. Due to the diffraction effect and aberration of the system, the image point forms a diffuse spot with a certain size. The energy distribution of the diffuse spot is the point spread function of the optical system. The star point target imaging method is the most direct and effective method to obtain the point spread function, which is closest to the actual working process of the telescope on orbit. However, the measurement results of the traditional star point target imaging method will be significantly affected by the collimator wave aberration. Summary of the invention

[0017] In view of this, an embodiment of the present invention provides a method for measuring the point spread function ellipticity of an optical system, comprising:

[0018] The wavefront aberrations of the collimator and the optical system to be measured are measured respectively, the collimator and the optical system to be measured are adjusted and aligned so that the object plane of the collimator is conjugate with the focal plane of the optical system to be measured, the adjusted collimator and the optical system to be measured are placed in a stable environment as a whole, the star point image formed after the star point target passes through the collimator and the optical system to be measured is measured, and the star point image is used as the target point spread function;

[0019] The ellipticity value of the star point image is obtained by using a point spread function ellipticity calculation method, other characteristic parameters of the star point image are calculated synchronously, and the obtained parameters are used as target parameters;

[0020] Optical simulation software is used to construct a simulated optical system with optical parameters consistent with the actual system, including a simulated collimator and a simulated optical system to be measured. A dynamic data connection is established between the optical simulation software and the numerical calculation software. The wave aberrations measured by the collimator and the optical system to be measured are respectively input into the simulated optical system. A Zernike surface is added to the simulated system. The simulated optical system is optimized with the target parameter as the target value and the Zernike surface as the optimization variable. The point spread function output by the simulated optical system is compared with the measured target point spread function. When the difference between the two meets the set threshold requirement, the optimization is stopped. The Zernike surface finally optimized and the simulated optical system to be measured are combined into a new optical system, and the point spread function ellipticity of the new system is calculated, which is the point spread function ellipticity of the optical system to be measured, and the measurement is completed.

[0021] As an optional solution, the point spread function ellipticity calculation method is used to determine the ellipticity value of the star point image in the current field of view, and the major axis parameter, minor axis parameter, point spread function percentage energy concentration angular radius, Strehl ratio and point spread function morphological parameter are calculated, and the obtained parameters are used as target parameters, including:

[0022] The point image measured by the detector is imported into the numerical calculation software, and the energy centroid is extracted through the image processing algorithm. , the calculation formula (1) (2) is:

[0023] (1)

[0024] (2)

[0025] In the formula, is the Gaussian weighting function, It is the image point Light intensity distribution;

[0026] The determined energy centroid is taken as the center of the circle, and the second-order moment of the point spread function with the weight function is determined according to the preset effective data range. The calculation formula (3) is:

[0027] (3)

[0028] The calculation formula (4) of the major axis parameter e1 and the minor axis parameter e2 is:

[0029] (4)

[0030] The ellipticity value of the point spread function of the current field of view is obtained based on the major axis parameter e1 and the minor axis parameter e2 , the calculation formula (5) is:

[0031] (5)

[0032] Calculate the point spread function percentage energy concentration angular radius based on image processing method Strehlby and point spread function morphological parameters , and use the obtained parameters as the target parameters.

[0033] As an optional solution, a digital twin optical model consistent with the actual measured optical path is established using optical design software, and the model includes a simulated collimator and a simulated optical system to be measured. A dynamic data connection is established between the optical design software and the numerical calculation software, and the wave aberrations actually measured are input to the simulated collimator and the simulated optical system to be measured, respectively, including:

[0034] A dynamic data link is established between the optical design software and the numerical calculation software. The numerical calculation software reads the optical performance parameters of the optical model in real time and resets the calculated new parameters to the optical design software, or independently sets the measured data to the optical design software.

[0035] As an optional solution, a Zernike surface is added to the simulated collimator and the simulated optical system to be measured, and the optical model is optimized with the target parameter as the target value and the Zernike surface as the optimization variable, including:

[0036] A digital twin optical model consisting of a collimator and an optical system to be tested is built in the optical design software, and the wave aberrations actually measured are input into the simulated collimator and the simulated optical system to be tested respectively;

[0037] Adding a Zernike surface to the simulated optical system, the Zernike surface can be a Zernike phase surface or a Zernike sag surface. The parameters of the Zernike surface are determined by Zernike coefficients, which include fringe Zernike coefficients, standard Zernike coefficients, and annular Zernike coefficients;

[0038] The optical design software outputs the point spread function of the optical model under the current field of view state and saves it into a readable file;

[0039] The readable file is imported into the numerical calculation software to obtain simulation parameters, wherein the simulation parameters include the ellipticity value of the simulated point spread function , simulation long axis parameters and simulated short axis , simulated point spread function percentage energy concentration angular radius , Simulated Strehl ratio and simulated point spread function morphological parameters ;

[0040] The simulation parameters are compared with the target parameters, and the evaluation function (6) is constructed as:

[0041] (6)

[0042] The Zernike surface parameters are updated iteratively according to the evaluation function.

[0043] As an optional solution, the simulation parameters output by the optical model are compared with the target parameters obtained by actual measurement, and when the difference reaches a preset threshold requirement, the optimization of the optical model is completed, and a new optical system composed of the optical system model to be measured and the Zernike surface is formed, and the point spread function ellipticity value of the new system is the point spread function ellipticity of the optical system to be measured, including:

[0044] If the current evaluation function value is greater than a specified threshold, the optimization steps are continuously repeated until the evaluation function value is less than or equal to the specified threshold, and the optimization is stopped.

[0045] As an optional solution, at least one Zernike surface is set in the optical model.

[0046] As an optional solution, the Zernike surface set in the optical model is a phase surface or a sag surface.

[0047] An embodiment of the present invention provides a method for measuring the point spread function ellipticity of an optical system. The method is based on an imaging optical path of a star target imaging method and is combined with an intelligently optimized Zernike surface compensation algorithm. The method can reduce the influence of factors such as wave aberration introduced by a parallel light tube in the imaging optical path and atmospheric disturbance on the point spread function ellipticity measurement, thereby improving the ground measurement accuracy of the point spread function ellipticity value of the optical system to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1a A flow chart of a method for measuring the point spread function ellipticity of an optical system is provided in an embodiment of the present invention;

[0049] Figure 1b A flowchart of a method for measuring the point spread function ellipticity of an optical system is also provided in an embodiment of the present invention;

[0050] Figure 2 A schematic flow chart of another method for measuring the point spread function ellipticity of an optical system is provided in an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of an optical path for measuring a point spread function ellipticity by simulating a star point target imaging method in a method for measuring a point spread function ellipticity of an optical system is provided in an embodiment of the present invention;

[0052] Figure 4 A schematic diagram of an optical model in which a zernike surface is added to optical design software in a method for measuring the point spread function ellipticity of an optical system in an embodiment of the present invention is provided; DETAILED DESCRIPTION

[0053] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0054] The terms "first", "second", "third", "fourth", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0055] Combination Figure 1a As shown, an embodiment of the present invention provides a method for measuring the point spread function ellipticity of an optical system, comprising:

[0056] S1. Measure the wave aberration of the collimator and the optical system to be measured respectively, adjust and align the collimator and the optical system to be measured so that the object plane of the collimator is conjugate with the focal plane of the optical system to be measured, place the adjusted collimator and the optical system to be measured as a whole in a stable environment, measure the star point image formed after the star point target passes through the collimator and the optical system to be measured, and use the star point image as the target point spread function.

[0057] S2. Obtain the ellipticity value of the star point image by using a point spread function ellipticity calculation method, simultaneously calculate other characteristic parameters of the star point image, and use the obtained parameters as target parameters.

[0058] S3. Use optical simulation software to construct a simulated optical system with optical parameters consistent with the actual system, including a simulated collimator and a simulated optical system to be measured, establish a dynamic data connection between the optical simulation software and the numerical calculation software, input the wave aberrations actually measured from the collimator and the optical system to be measured into the simulated optical system respectively, add a Zernike surface to the simulated system, optimize the simulated optical system with the target parameter as the target value and the Zernike surface as the optimization variable, compare the point spread function output by the simulated optical system with the actually measured target point spread function, stop the optimization when the difference between the two meets the set threshold requirement, form a new optical system with the finally optimized Zernike surface and the simulated optical system to be measured, and calculate the point spread function ellipticity of the new system, which is the point spread function ellipticity of the optical system to be measured, and complete the measurement.

[0059] Combination Figure 1b As shown, an embodiment of the present invention further provides a method for measuring the point spread function ellipticity of an optical system, comprising:

[0060] S101, using a self-collimating interference detection optical path to measure the wavefront aberration of the collimator and each field of view of the optical system to be measured.

[0061] Specifically, the wave aberrations of the collimator and the optical system to be measured are respectively measured, the collimator and the optical system to be measured are adjusted and aligned so that the object plane of the collimator is conjugate with the focal plane of the optical system to be measured, and after the adjusted collimator and the optical system to be measured are placed in a stable environment as a whole, the star point image formed after the star point target passes through the collimator and the optical system to be measured is measured, and the star point image is used as the target point spread function.

[0062] S102, adjusting the collimator and the optical system to be measured to a coaxial optical path, so that the exit pupil of the collimator matches the entrance pupil of the optical system to be measured, and completing the optical path construction.

[0063] S103. Under the condition of keeping the pupils of the collimator and the optical system to be measured matching, adjust the orientation of the collimator or the optical system to be measured so that the parallel light emitted by the collimator is incident on the optical system to be measured at a preset angle, and image the star point of the object plane of the collimator on the focal plane of the optical system to be measured.

[0064] S104, placing the collimator and the optical system to be measured with adjusted positions into a vacuum tank, and after a stable vacuum environment is formed, measuring a star point image formed on a focal plane after the star point target passes through the collimator and the optical system to be measured, and using the star point image as a target point spread function.

[0065] S105, using the point spread function ellipticity calculation method to determine the ellipticity value of the current field of view under the star point image, and calculate the major axis parameter e1, the minor axis parameter e2, the point spread function percentage energy concentration angular radius, the Strehl ratio and the point spread function morphological parameters, and use the above parameters as target parameters.

[0066] S106, using optical design software, constructing a digital twin optical model consistent with the actual detection optical path, wherein the model includes a simulated collimator and a simulated optical system to be tested. Establishing a dynamic data connection between the optical design software and the numerical calculation software, and inputting the wave aberrations actually measured for the simulated collimator and the simulated optical system to be tested, respectively.

[0067] The optical design software is an advanced software with analysis, optimization and tolerance analysis functions that meets industrial standards, and can quickly and accurately complete the optical imaging design. The optical design software mentioned in this embodiment can be ZEMAX optical design software, ASAP advanced optical system analysis software or CODEV imaging system design, and ordinary technicians in this field can flexibly choose, without limitation.

[0068] S107, adding a Zernike surface to the simulated collimator and the simulated optical system to be tested, taking the target parameter as the target value and the Zernike surface as the optimization variable, to optimize the optical model.

[0069] S108, compare the PSF parameters output by the optical model with the target parameters. When the difference reaches a preset threshold, the optimization of the optical model is completed. The simulated optical model to be measured and the Zernike surface are combined into a new optical system, and the point spread function ellipticity value of the new system is calculated, which is the point spread function ellipticity of the optical system to be measured, and the measurement is completed.

[0070] An embodiment of the present invention provides a method for measuring the point spread function ellipticity of an optical system. The method is based on a star target imaging method and combined with an intelligent optimized Zernike surface compensation algorithm. The method can reduce the influence of factors such as wave aberration introduced by a parallel light tube in an imaging optical path and atmospheric disturbance on the point spread function ellipticity measurement, thereby improving the measurement accuracy of the point spread function ellipticity value of the optical system to be measured.

[0071] In S105, the point spread function ellipticity calculation method is used to determine the ellipticity value of the current field of view under the star point image, and the major axis parameter, the minor axis parameter, the point spread function percentage energy concentration angular radius, the Strehl ratio and the point spread function morphological parameter are calculated, and these parameters are used as target parameters, including:

[0072] S1051, importing the point image obtained by the detector into the numerical calculation software, and extracting the energy centroid through the image processing algorithm , the calculation formula (1) (2) is:

[0073] (1)

[0074] (2)

[0075] In the formula, is the Gaussian weighting function, It is the image point light intensity distribution.

[0076] S1052, using the determined energy centroid as the center of the circle, and determining the second-order moment of the point spread function with a weight function according to a preset valid data range, the calculation formula (3) is:

[0077] (3)

[0078] S1053, the major axis parameters and the minor axis parameters The calculation formula (4) is:

[0079] (4)

[0080] S1054, based on major axis parameters and minor axis parameters Obtain the ellipticity value of the point spread function of the current field of view , the calculation formula (5) is:

[0081] (5)

[0082] S1055, calculating the point spread function percentage energy concentration angular radius according to the image processing method Strehlby and point spread function morphological parameters and as the target parameter.

[0083] In S106, the digital twin optical model consistent with the actual detection optical path is constructed, and the model includes a simulated collimator and a simulated optical system to be tested. The optical design software is dynamically connected with the numerical calculation software, and the wave aberrations actually measured are input to the simulated collimator and the simulated optical system to be tested, specifically including:

[0084] A dynamic data link is established between the optical design software and the numerical calculation software. The numerical calculation software reads the optical performance parameters of the optical model in real time and resets the calculated new parameters to the optical design software or independently sets the measured data to the optical design software.

[0085] In S107, a Zernike surface is added to the simulated collimator and the simulated optical system to be measured, and the optical model is optimized with the target parameter as the target value and the Zernike surface as the optimization variable, specifically including:

[0086] S1071. Building a digital twin optical model in the optical design software that is consistent with the optical parameters of the actual collimator and the optical system to be measured, and inputting the wave aberrations actually measured for the simulated collimator and the simulated optical system to be measured respectively;

[0087] S1072, adding a Zernike surface to the simulated collimator and the simulated optical system to be measured, wherein the parameters of the Zernike surface are determined by Zernike coefficients, wherein the Zernike surface includes a Zernike phase surface and a Zernike sag surface, and wherein the Zernike coefficients include fringe Zernike coefficients, standard Zernike coefficients, and annular Zernike coefficients, etc.;

[0088] S1073, the optical design software outputs the point spread function of the optical model under the current field of view state, and saves it into a readable file;

[0089] S1074, importing the readable file into the numerical calculation software to obtain simulation system parameters, wherein the simulation system parameters include the ellipticity value of the simulated point spread function , simulated major axis parameter e1 and simulated minor axis e2, simulated point spread function percentage energy concentration angular radius , Simulated Strehl ratio and simulated point spread function morphological parameters ;

[0090] S1075, comparing the simulation parameters with the target parameters, constructing an evaluation function (6) as follows:

[0091] (6)

[0092] S1076. Update iterative Zernike surface parameters according to the evaluation function.

[0093] In some embodiments, the simulation parameters output by the optical model are compared with the target parameters. When the difference reaches a preset threshold, the optimization of the optical model is completed, the optical model and the Zernike surface are combined into a new optical system, and the point spread function ellipticity of the new system is calculated, which is the point spread function ellipticity of the optical system to be measured, including:

[0094] If the current evaluation function value is greater than the specified threshold, the optimization steps are continuously cycled until the evaluation function value is less than or equal to the preset threshold, and the optimization is stopped. The final optimization result of the Zernike surface and the simulated optical system to be tested are combined into a new optical system, and the point spread function ellipticity value of the new system is calculated and used as the point spread function ellipticity of the optical system to be tested.

[0095] In some embodiments, at least one Zernike surface is provided in the optical model, and the number of Zernike surfaces is not limited.

[0096] In some embodiments, the Zernike surface set in the optical model is a phase surface or a sag surface, which is not limited.

[0097] Combination Figure 2 As shown, an embodiment of the present invention further provides a method for measuring the point spread function ellipticity of an optical system, comprising:

[0098] Step S1, using self-collimation interference to detect the optical path, and measuring the wave aberration of each field of view of the collimator and the optical system to be measured;

[0099] Combination Figure 3 As shown, a self-collimating interference detection optical path is built, and the wave aberration of the collimator and the system to be tested in different fields of view is measured by the interferometer. Using the collimator and the optical system to be tested, a star point target imaging optical path is built, which consists of an incoherent light source 1, a filter 2, a pinhole 3, a collimator 4, an optical system to be tested 5, and an image acquisition system 6. A suitable pinhole 3 is selected according to the characteristics of the optical system 5 to be tested.

[0100] Step S2, adjusting the collimator and the optical system to be measured to a coaxial optical path, so that the exit pupil of the collimator matches the entrance pupil of the optical system to be measured;

[0101] Step S3, under the condition that the pupil of the collimator is matched with that of the optical system to be measured, adjusting the direction of the collimator or the direction of the optical system to be measured, so that the parallel light emitted by the collimator is incident on the optical system to be measured at a specified angle, and the star point of the object plane of the collimator is imaged on the focal plane of the system to be measured;

[0102] Step S4, pushing the adjusted collimator and the optical system to be measured into a vacuum tank as a whole, and after a stable high vacuum environment is formed, measuring the star point image of the star point target through the collimator and the optical system to be measured, and taking this as the target point spread function;

[0103] Step S5, based on the point spread function obtained by the actual measurement, the ellipticity value in the current field of view is obtained according to the point spread function ellipticity calculation method, and the major axis parameter and the minor axis parameter, as well as the point spread function percentage energy concentration angular radius, Strehl ratio and point spread function morphological parameters are calculated, and these parameters are used as target parameters;

[0104] Step S6, building a simulated optical system consistent with the actual optical path in step S2 in the optical design software, and establishing a dynamic data connection with the numerical calculation software, and inputting the wave aberration of the collimator and the optical system to be measured measured in step S1 into the optical design software in turn.

[0105] Compile the link code through the numerical calculation software, establish a direct dynamic data link with the optical design software, and set the file address of the optical model. According to the above-mentioned measured characteristic field of view range and field of view interval, the optical model in the optical design software is set through the numerical calculation software. The output of the point spread function is preset in the optical design software, including the number of image plane sampling, the number of light rays in the pupil, the image plane sampling interval, the field of view number, the wavelength number, etc. The collimator wave aberration and the wave aberration data of the system to be measured measured in the above step S1 are input into the optical design software through the numerical calculation software. At this point, the optical model is built.

[0106] Step S7, simulating the optical system including simulating the collimator and the system to be tested, and adding the Zernike surface to the simulated system, using the intelligent optimization algorithm edited in the numerical calculation software, taking the target parameters described in step S5 as the target values, and taking the Zernike surface as the optimization variable, the simulated optical system is optimized.

[0107] like Figure 4 As shown, in the optical design software, a Zernike surface 7 is added between the simulated collimator 4 and the simulated optical system to be tested 5 to form a digital twin optical model. The Zernike surface 3 can be one, two or more. For simplicity, a Zernike surface is used as an example for description. Initial parameters are randomly assigned to the Zernike parameters of each order in the Zernike surface. The initial parameters are generated by the numerical calculation software, and their numerical range can be limited. The point spread function of the digital twin optical model is read by the numerical calculation software, and the point spread function ellipticity value, the corresponding major axis parameter and minor axis parameter, the point spread function percentage energy concentration angular radius, Strehl ratio and point spread function morphological parameters are calculated by the method described in formulas (1)-(5). The comprehensive evaluation function formula (6) is constructed to calculate the difference between the current optimization value and the target value. The Zernike coefficients of each order of the Zernike surface are used as optimization variables, and the Zernike surface is optimized by the intelligent optimization algorithm.

[0108] It should be noted that the intelligent optimization algorithm in the present invention is not unique and may include particle swarm algorithm, genetic algorithm, annealing algorithm, neural network algorithm and their extended algorithms, without limitation thereto.

[0109] Step S8, when the point spread function ellipticity value, major axis parameter and minor axis parameter, point spread function percentage energy concentration angular radius, Strehl ratio and point spread function morphological parameters of the simulated optical system in the optical design software are close to the target parameters and the deviation is less than the preset threshold, stop the optimization. The simulated optical system to be tested and the Zernike surface are combined into a new optical system, and the point spread function of the new system is calculated, and its ellipticity value is the point spread function ellipticity of the optical system to be tested.

[0110] The method for measuring the point spread function ellipticity of an optical system provided in an embodiment of the present invention has the following beneficial effects:

[0111] 1. It can significantly reduce the influence of the wavefront aberration of the collimator on the measurement results in the star target imaging method, and can also reduce the influence of factors such as the wavefront aberration measurement error caused by the large aperture and long focal length of the optical system to be measured, thereby improving the measurement accuracy of the point spread function ellipticity value of the optical system to be measured.

[0112] 2. Based on the traditional star point target imaging method, the present invention combines the intelligent optimization Zernike surface compensation method and takes the real image of the optical system to be tested as the basis. Compared with the computational simulation method, it can more realistically reflect the imaging characteristics of the optical system to be tested.

[0113] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0114] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring the point spread function ellipticity of an optical system, characterized in that: include: The wavefront aberrations of the collimator and the optical system to be measured are measured respectively, the collimator and the optical system to be measured are adjusted and aligned so that the object plane of the collimator is conjugate with the focal plane of the optical system to be measured, the adjusted collimator and the optical system to be measured are placed in a stable environment as a whole, the star point image formed after the star point target passes through the collimator and the optical system to be measured is measured, and the star point image is used as the target point spread function; The ellipticity value of the star point image is obtained by using a point spread function ellipticity calculation method, other characteristic parameters of the star point image are calculated synchronously, and the obtained parameters are used as target parameters; By using optical simulation software, a simulated optical system consistent with the optical parameters of the actual system is constructed, including a simulated collimator and a simulated optical system to be measured, a dynamic data connection is established between the optical simulation software and the numerical calculation software, the wave aberrations measured by the collimator and the optical system to be measured are respectively input into the simulated optical system, a Zernike surface is added to the simulated optical system, the simulated optical system is optimized with the target parameter as the target value and the Zernike surface as the optimization variable, the point spread function output by the simulated optical system is compared with the measured target point spread function, when the difference between the two meets the set threshold requirement, the optimization is stopped, the Zernike surface finally optimized and the simulated optical system to be measured are combined into a new optical system, and the point spread function ellipticity of the new system is calculated, which is the point spread function ellipticity of the optical system to be measured, and the measurement is completed.

2. The method for measuring the point spread function ellipticity of an optical system according to claim 1, characterized in that: The method of calculating the ellipticity of the point spread function is used to obtain the ellipticity value of the star point image, and to calculate the major axis parameter, the minor axis parameter, the point spread function percentage energy concentration angular radius, the Strehl ratio and the point spread function morphological parameter, and the obtained parameters are used as target parameters, including: The star point image measured by the detector is imported into the numerical calculation software, and the energy centroid is extracted through the image processing algorithm. , the calculation formula (1) (2) is: (1) (2) In the formula, is the Gaussian weighting function, It is the image point Light intensity distribution; The determined centroid is taken as the center of the circle, and the second-order moment of the point spread function with the weight function is determined according to the preset valid data range. The calculation formula (3) is: (3) The calculation formula (4) of the major axis parameter e1 and the minor axis parameter e2 is: (4) Based on the major axis parameters and minor axis parameters Get the ellipticity value of the point spread function of the current field of view , the calculation formula (5) is: (5) Calculate the point spread function percentage energy concentration angular radius based on image processing method Strehlby and point spread function morphological parameters , and use these parameters as target parameters.

3. The method for measuring the point spread function ellipticity of an optical system according to claim 1, characterized in that: The method of using optical simulation software to construct a simulated optical system consistent with the optical parameters of the actual system, including simulating a collimator and simulating an optical system to be measured, establishing a dynamic data connection between the optical simulation software and the numerical calculation software, and inputting the wave aberrations actually measured by the collimator and the optical system to be measured into the optical simulation software, specifically includes: A dynamic data link is established between the optical simulation software and the numerical calculation software. The numerical calculation software reads the optical parameters of the simulated optical system in real time and resets the calculated new parameters to the optical simulation software or independently sets the measured data to the optical simulation software.

4. The method for measuring the point spread function ellipticity of an optical system according to claim 1, characterized in that: Adding a Zernike surface to the simulated optical system, taking the target parameter as the target value and taking the Zernike surface as the optimization variable to optimize the simulated optical system, comprises: The Zernike surface includes a Zernike phase surface and a Zernike sag surface, and the Zernike coefficients include fringe Zernike coefficients, standard Zernike coefficients and ring Zernike coefficients; Outputting the point spread function of the simulated optical system under the current field of view through the optical simulation software and saving it into a readable file; The readable file is imported into the numerical calculation software to obtain simulation parameters, wherein the simulation parameters include the ellipticity value of the simulated point spread function , simulation long axis parameters and simulated short axis , simulated point spread function percentage energy concentration angular radius , Simulated Strehl ratio and simulated point spread function morphological parameters ; Compare the simulation parameters with the target parameters and construct an evaluation function (6) as follows: （6） The Zernike surface parameters are updated iteratively according to the evaluation function.

5. The method for measuring the point spread function ellipticity of an optical system according to claim 1, characterized in that: The number of Zernike surfaces arranged in the simulated optical system is at least one.

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