A method and system for measuring a radius of curvature

Abstract

A curvature radius measurement method and system can realize high-precision detection of curvature radius by using shorter guide rails, greatly increase the measurement range of the interference method, and reduce the test cost. The method comprises the following steps: (1) building a detection light path, measuring the aperture of a to-be-detected mirror, and moving the to-be-detected mirror to a confocal position; (2) pushing the to-be-detected mirror to move along the optical axis direction, acquiring an axial displacement distance in a displacement measurement interferometer, and acquiring a defocus wave front in a phase measurement interferometer; (3) performing Zernike fitting on the defocus wave front to obtain a defocus coefficient; and (4) accurately modeling the test light path in optical design software, taking the defocus coefficient in system wave aberration as an optimization target of the system, taking the curvature radius of the to-be-detected mirror as an optimization variable, and performing optimization by using the optimization function of the optical design software until the system wave aberration obtained by the software is consistent with the system wave aberration actually measured and obtained, so that the curvature radius of the to-be-detected mirror is obtained.

Description

Technical Field

[0001] This invention relates to the technical field of optical interferometry instruments, and more particularly to a method for measuring radius of curvature, and a system for measuring radius of curvature. Background Technology

[0002] Spherical optical elements have wide applications in advanced optical systems such as photolithography, astronomical optics, and inertial confinement fusion. The radius of curvature determines the modulation effect of light by a spherical mirror and is one of the most important parameters of a spherical optical element. Therefore, high-precision measurement of the radius of curvature is of great significance in the manufacturing of spherical optical elements.

[0003] Interferometry is the most widely used method for measuring radius of curvature. Interferometry first determines the cat's-eye position and confocal position using an interferogram, then moves the mirror under test between these two positions, obtaining the radius of curvature by measuring the distance the mirror moves. Moving the mirror typically requires a precision linear guide, and the guide length must be greater than the radius of curvature. When the radius of curvature of the mirror is large, the linear guide will also be long, making it difficult to guarantee its straightness, and the longer guide significantly increases testing costs. Therefore, the guide length severely limits the range of radius of curvature measurement using interferometry. Furthermore, moving the mirror a long distance greatly increases testing time, reduces testing efficiency, and makes the test results susceptible to environmental factors such as temperature and air disturbances. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a method for measuring the radius of curvature, which can achieve high-precision detection of the radius of curvature using a shorter guide rail, greatly increasing the measurement range of the interferometric method and reducing the testing cost.

[0005] The technical solution of this invention is: this method for measuring the radius of curvature includes the following steps:

[0006] (1) Set up the detection optical path, measure the aperture of the mirror to be tested, and move the mirror to be tested to the confocal position;

[0007] (2) Move the mirror under test along the optical axis, obtain the axial displacement distance in the displacement measurement interferometer, and obtain the defocused wavefront in the phase measurement interferometer;

[0008] (3) Perform Zernike fitting on the defocus wavefront to obtain the defocus coefficient;

[0009] (4) Accurately model the test optical path in the optical design software, take the defocus coefficient in the system wave aberration as the optimization target of the system, take the radius of curvature of the mirror under test as the optimization variable, and use the optimization function of the optical design software to optimize until the system wave aberration obtained by the software is consistent with the system wave aberration obtained by actual measurement, and obtain the radius of curvature of the mirror under test.

[0010] This invention calculates the radius of curvature by utilizing the relationship between the radius of curvature, the defocused wavefront, and the axial movement distance. Compared with the traditional interferometry method, it significantly reduces the dependence on the guide rail length, increases the measurement range, shortens the test time, and improves the test efficiency. Therefore, it can achieve high-precision detection of the radius of curvature using a shorter guide rail, greatly increasing the measurement range of the interferometry method and reducing the test cost.

[0011] A radius of curvature measurement system is also provided, which includes: a wavefront measurement interferometer (1), a spherical mirror to be measured (2), a displacement measurement interferometer (3), a linear guide rail (4), a measurement module, a fitting module, and a system wavefront aberration optimization module;

[0012] The measurement module is configured to measure the aperture of the mirror under test;

[0013] The fitting module is configured to perform Zernike fitting on the measured systematic wave aberrations to obtain the defocus coefficient of the systematic wave aberrations;

[0014] The systematic wave aberration optimization module is configured in the optical design software to use the defocus coefficient of the systematic wave aberration as the optimization target of the system and the radius of curvature of the mirror under test as the optimization variable. The optimization function of the optical design software is used to optimize until the systematic wave aberration obtained by the software is consistent with the systematic wave aberration obtained by actual measurement. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the hardware structure of the radius of curvature measurement system according to the present invention.

[0016] Figure 2 The defocused wavefront is obtained by a wavefront measurement interferometer.

[0017] Figure 3 This is a flowchart of the radius of curvature measurement method according to the present invention. Detailed Implementation

[0018] like Figure 3 As shown, this method for measuring the radius of curvature includes the following steps:

[0019] (1) Set up the detection optical path, measure the aperture of the mirror to be tested, and move the mirror to be tested to the confocal position;

[0020] (2) Move the mirror under test along the optical axis, obtain the axial displacement distance in the displacement measurement interferometer, and obtain the defocused wavefront in the phase measurement interferometer;

[0021] (3) Perform Zernike fitting on the defocus wavefront to obtain the defocus coefficient;

[0022] (4) Accurately model the test optical path in the optical design software, take the defocus coefficient in the system wave aberration as the optimization target of the system, take the radius of curvature of the mirror under test as the optimization variable, and use the optimization function of the optical design software to optimize until the system wave aberration obtained by the software is consistent with the system wave aberration obtained by actual measurement, and obtain the radius of curvature of the mirror under test.

[0023] This invention calculates the radius of curvature by utilizing the relationship between the radius of curvature, the defocused wavefront, and the axial movement distance. Compared with the traditional interferometry method, it significantly reduces the dependence on the guide rail length, increases the measurement range, shortens the test time, and improves the test efficiency. Therefore, it can achieve high-precision detection of the radius of curvature using a shorter guide rail, greatly increasing the measurement range of the interferometry method and reducing the test cost.

[0024] Preferably, in step (4), the optical design software is Zemax.

[0025] like Figure 1 As shown, a radius of curvature measurement system is also provided, which includes: a wavefront measurement interferometer 1, a spherical mirror under test 2, a displacement measurement interferometer 3, a linear guide rail 4, a measurement module, a fitting module, and a system wavefront aberration optimization module;

[0026] The measurement module is configured to measure the aperture of the mirror under test;

[0027] The fitting module is configured to perform Zernike fitting on the measured systematic wave aberrations to obtain the defocus coefficient of the systematic wave aberrations;

[0028] The systematic wave aberration optimization module is configured in the optical design software to use the defocus coefficient of the systematic wave aberration as the optimization target of the system and the radius of curvature of the mirror under test as the optimization variable. The optimization function of the optical design software is used to optimize until the systematic wave aberration obtained by the software is consistent with the systematic wave aberration obtained by actual measurement.

[0029] Preferably, the central outgoing beam of the wavefront measurement interferometer is the principal optical axis, and the moving direction of the linear guide rail is parallel to the working direction of the displacement measurement interferometer and the principal optical axis. The plane mirror under test is moved by the load of the linear guide rail, and the moving distance is monitored by the displacement measurement interferometer. The diverging beam is emitted from the wavefront measurement interferometer, reflected by the spherical mirror under test, and returns to the wavefront measurement interferometer. The defocused wavefront is obtained in the phase measurement interferometer.

[0030] The following describes a specific embodiment of the present invention in detail.

[0031] The spherical mirror to be tested in this embodiment has an aperture of 23.62 mm. The mirror to be tested was adjusted to a confocal position, and the optical design software used was Zemax.

[0032] Step 1: Set up the detection optical path, measure the aperture of the mirror under test, and move the mirror under test to the confocal position;

[0033] Step 2: Move the mirror under test along the optical axis. Obtain the axial displacement distance of 1.4936 mm using a displacement measurement interferometer. Obtain the defocused wavefront using a phase measurement interferometer. Figure 2 As shown;

[0034] Step 3: Perform Zernike fitting on the defocused wavefront to obtain the defocus coefficient as 9.0890λ;

[0035] Step 4: Accurately model the test optical path in the optical design software, take the defocus coefficient in the system wave aberration as the optimization target of the system, and take the radius of curvature of the mirror under test as the optimization variable. Use the optimization function of the optical design software to optimize until the system wave aberration obtained by the software is consistent with the system wave aberration obtained by actual measurement. Then the radius of curvature of the mirror under test is 101.6870mm.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for measuring radius of curvature, characterized in that: It includes the following steps: (1) Set up the detection optical path, measure the aperture of the mirror to be tested, and move the mirror to be tested to the confocal position; (2) Move the mirror under test along the optical axis, obtain the axial displacement distance in the displacement measurement interferometer, and obtain the defocused wavefront in the phase measurement interferometer; (3) Perform Zernike fitting on the defocus wavefront to obtain the defocus coefficient; (4) Accurately model the test optical path in the optical design software, take the defocus coefficient in the system wave aberration as the optimization target of the system, take the radius of curvature of the mirror under test as the optimization variable, and use the optimization function of the optical design software to optimize until the system wave aberration obtained by the software is consistent with the system wave aberration obtained by actual measurement, and obtain the radius of curvature of the mirror under test.

2. A radius of curvature measurement system, which performs the radius of curvature measurement method according to claim 1, characterized in that: It includes: Wavefront measurement interferometer (1), mirror under test (2), displacement measurement interferometer (3), linear guide rail (4), measurement module, fitting module, system wavefront aberration optimization module; The measurement module is configured to measure the aperture of the mirror under test. The fitting module is configured to perform Zernike fitting on the measured systematic wave aberrations to obtain the defocus coefficient of the systematic wave aberrations; The systematic wave aberration optimization module is configured in the optical design software to use the defocus coefficient of the systematic wave aberration as the optimization target of the system and the radius of curvature of the mirror under test as the optimization variable. The optimization function of the optical design software is used to optimize until the systematic wave aberration obtained by the software is consistent with the systematic wave aberration obtained by actual measurement.

3. The radius of curvature measurement system according to claim 2, characterized in that: The central outgoing beam of the wavefront measurement interferometer is the principal optical axis, and the direction of movement of the linear guide rail is parallel to the working direction of the displacement measurement interferometer. The mirror under test is moved by the load of the linear guide rail, and the moving distance is monitored by the displacement measurement interferometer. The diverging beam is emitted from the wavefront measurement interferometer, reflected by the mirror under test, and returns to the wavefront measurement interferometer. The defocused wavefront is obtained in the phase measurement interferometer.

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