Method and system for adjusting long cylinder type refraction and reflection zoom system

Abstract

The invention belongs to the related technical field of optical adjustment, and discloses an adjustment method and system for a long-cylinder type refraction and reflection zoom system. The method comprises the following steps: adjusting the optical axis of the autocollimator to be parallel to the optical axis of the plane interferometer; measuring the optical axis error of the plano-concave lens through the autocollimator, and adjusting the optical axes of the primary mirror assembly and the plano-concave lens assembly to be parallel to the optical axis of the autocollimator; an interference simulation model of a system composed of a primary mirror, a secondary mirror and a plano-concave lens is constructed, a misalignment amount is calculated by using a wavefront aberration Zernike expansion coefficient of the system, so that the optical axes of the secondary mirror assembly and the plano-concave lens assembly are adjusted to be coaxial with the optical axis of the primary mirror assembly, and the interval between the primary mirror assembly and the secondary mirror assembly and the interval between the secondary mirror assembly and the plano-concave lens assembly meet preset requirements. Therefore, the wavefront aberration of the system meets the requirement of a preset threshold value; and disassembling the plano-concave lens assembly and replacing the plano-concave lens assembly with the correction lens assembly so as to finish the installation and adjustment of the long cylinder type refraction and reflection zoom system. According to the invention, high-efficiency and high-precision adjustment of the long cylinder type refraction and reflection zoom system is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field related to optical adjustment, and more specifically, relates to an adjustment method and system for a long-tube catadioptric zoom system. Background Art

[0002] There are two basic types of optical systems composed of double mirrors (primary mirror and secondary mirror): Gregorian optical system and Cassegrain optical system. The focal length of Cassegrain optical system is usually larger. In the double mirror optical system, the primary mirror is used to increase the aperture of the optical system and increase the ability of the optical system to collect light energy. The secondary mirror is used to converge the compressed light beam and correct the aberration of the primary mirror. When designing a Cassegrain optical system, refractive elements are usually used near the focal plane to increase the field of view and correct off-axis aberrations and field curvature. How to efficiently and accurately control the eccentricity error, tilt error, and optical spacing error of the double mirrors and refractive elements is a difficult point in the assembly and adjustment of the system. Another difficulty is that the standard spherical interferometer cannot perform full-aperture testing of the wavefront aberration of the long-tube catadioptric zoom system.

[0003] CN201910881551.6 discloses a centering and adjustment method for a catadioptric common aperture system containing a relay mirror group. The invention uses a center deviation measuring instrument to first adjust the optical axis of the primary mirror and the relay mirror group, and then uses a spherical interferometer and a standard plane mirror to adjust the secondary mirror in the optical system. The invention has the advantage of high precision, but it uses a standard spherical interferometer for full-aperture wavefront aberration testing; CN201910881002.9 discloses a common aperture optical system adjustment method containing a secondary mirror focusing mechanism, and the optical system targeted by the invention is secondary mirror focusing; CN202211363678.7 discloses a precision assembly method for an off-axis two-mirror and lens combined optical system, and the optical system targeted by the invention is an off-axis reflection system; therefore, there is an urgent need for an adjustment method suitable for a long-tube catadioptric zoom system. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method and system for assembling and adjusting a long-tube catadioptric zoom system to solve the assembly and adjustment problem of the long-tube catadioptric zoom system.

[0005] To achieve the above object, according to one aspect of the present invention, a method for assembling and adjusting a long-tube catadioptric zoom system is provided, the method comprising the following steps:

[0006] A plane interferometer and an autocollimator are respectively arranged on both sides of the adjustment platform, and the optical axis of the autocollimator is made parallel to the optical axis of the plane interferometer;

[0007] Mounting a plano-concave lens assembly on the primary mirror assembly, and then mounting the primary mirror assembly with the plano-concave lens assembly mounted thereon on an adjustment platform, so that the optical axis of the plano-concave lens assembly is coaxial with the optical axis of the primary mirror assembly and is parallel to the optical axis of the autocollimator;

[0008] The secondary mirror assembly is connected to the primary mirror assembly, and the light emitted by the plane interferometer passes through the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly in sequence and then returns along the original path, thereby forming interference fringes in the plane interferometer, and the total misalignment of the secondary mirror assembly and the plano-concave lens assembly in each direction is calculated using the interference fringes, and the plano-concave lens assembly and the secondary mirror assembly are respectively adjusted according to the calculated total misalignment, so that the optical axes of the secondary mirror assembly and the primary mirror assembly are coaxial, and the intervals between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly meet preset requirements, thereby making the wavefront aberration of the optical system composed of the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly meet preset threshold requirements;

[0009] The plano-concave lens assembly is disassembled and replaced with a correction lens assembly, thereby completing the installation and adjustment of the long-tube catadioptric zoom system.

[0010] Further preferably, the total misalignment includes the misalignment of the secondary mirror assembly and the misalignment of the plano-concave lens assembly, the misalignment of the secondary mirror assembly includes the translation of the secondary mirror assembly along the X, Y and Z directions respectively, and the rotation of the secondary mirror assembly around the X and Y directions, and the misalignment of the plano-concave lens assembly is the translation of the plano-concave lens assembly along the Z direction.

[0011] Further preferably, the calculation of the offset is performed according to the following steps:

[0012] Construct an optical interference simulation model according to the optical parameters of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly;

[0013] Misalignment D for plano-concave lens assembly H Assign values ​​and input them into the optical interference simulation model to obtain different D H The defocus Z4 of the optical system composed of the corresponding primary mirror assembly, secondary mirror assembly and plano-concave lens assembly is thus fitted with Z4 and D H The curvilinear relationship between the two;

[0014] Constructing a relationship between the wavefront aberration Zernike expansion coefficient Z of the interference fringes and the total misalignment X, assigning a value to the total misalignment X and inputting it into the optical interference simulation model to obtain a corresponding Zernike expansion coefficient, thereby determining the relationship between the total misalignment X and the Zernike expansion coefficient Z;

[0015] Obtain the measured defocus Z4 and Zernike expansion coefficient Z, and use the Z4 and D HThe curve relationship between the two and the relationship between the total misalignment X and the Zernike expansion coefficient Z are used to calculate the actual misalignment D H And the total offset X.

[0016] Further preferably, the total imbalance X is calculated according to the following formula:

[0017] Z=AX

[0018] Z=[Z5 Z6 Z7 Z8 Z9] T

[0019]

[0020] X=[T x T y T z R x R y D H ] T

[0021] Among them, Z5, Z6, Z7, Z8 and Z9 are respectively the first-order astigmatism of the X axis, the first-order astigmatism of the Y axis, the first-order coma of the X axis, the first-order coma of the Y axis and the first-order spherical aberration of the optical system composed of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly. Tx, Ty, Tz, Rx and Ry are respectively the translation of the secondary mirror along the X, Y and Z directions and the rotation around the X and Y directions. D H is the misalignment of the plano-concave lens assembly.

[0022] Further preferably, the misalignment D of the plano-concave lens assembly is H Calculate according to the following formula:

[0023] D H =-1.438·Z4 2 +27.56·Z4

[0024] Among them, Z4 is the defocus of the optical system composed of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly.

[0025] Further preferably, before the plano-concave lens assembly is disassembled and replaced with a correction lens assembly, the actual required thickness of the trimming pad of the correction lens assembly is calculated, and the calculation formula of the thickness is as follows:

[0026] JZJZXQD_L=JZJZXQD_L(theoretical)-△JZJZ_H+△R-△H_PATJZ-△PATJXQD_L

[0027] Among them, JZJZXQD_L is the actual required thickness of the trimming pad in the correction mirror assembly, JZJZXQD_L(theoretical) is the theoretical thickness of the trimming pad in the correction mirror assembly, △JZJZ_H is the distance error from the concave vertex of the lens in the correction mirror assembly to the mounting end face of the correction mirror group, △R is the curvature radius error of the plano-concave lens, △H_PATJZ is the distance error from the concave vertex of the plano-concave lens to the end face of the plano-concave lens barrel, and △PATJXQD_L is the thickness error of the trimming pad in the plano-concave lens assembly.

[0028] Further preferably, before installing the plano-concave lens assembly on the primary mirror assembly, the following steps are performed:

[0029] Adjusting the optical axis of the primary mirror in the primary mirror assembly to be coaxial with the central axis of the primary mirror barrel and perpendicular to the end surface of the primary mirror barrel;

[0030] The optical axis of the plano-concave lens in the plano-concave lens assembly is adjusted to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end surface of the plano-concave lens barrel.

[0031] Further preferably, the method for adjusting the optical axis of the main mirror in the main mirror assembly to be coaxial with the central axis of the main lens barrel and perpendicular to the end face of the main lens barrel is: aligning and connecting the central hole and the back side of the main mirror with the main lens barrel.

[0032] Further preferably, the method for adjusting the optical axis of the plano-concave lens in the plano-concave lens assembly to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end face of the plano-concave lens barrel is: taking the optical axis of the plano-concave lens as a reference, centering and edge-turning the outer cylindrical surface and the end face of the plano-concave lens barrel, so that the central axis of the outer cylindrical surface is coaxial with the optical axis of the plano-concave lens, and the end face of the plano-concave lens barrel is perpendicular to the optical axis of the plano-concave lens.

[0033] According to another aspect of the present invention, a system for adjusting using the long-tube catadioptric zoom adjustment method described above is provided, the system comprising: a plane interferometer, an autocollimator, an adjustment stage, a primary mirror assembly, a secondary mirror assembly, a plano-concave lens assembly and a correction mirror assembly, wherein:

[0034] The plane interferometer and the autocollimator are arranged on both sides of the adjustment platform, and the primary mirror assembly, the secondary mirror assembly, the plano-concave lens assembly and the correction mirror assembly are all arranged on the adjustment platform;

[0035] The plano-concave lens assembly is arranged on the primary mirror assembly and is used to adjust the optical axes of the primary mirror assembly, the secondary mirror assembly and the correction mirror assembly and the optical intervals therebetween;

[0036] The secondary mirror assembly is arranged between the plano-concave lens assembly and the plane interferometer and is connected to the primary mirror assembly;

[0037] The correction lens assembly is used to replace the plano-concave lens assembly after the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly are assembled and adjusted.

[0038] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0039] 1. The present invention adopts a plane interferometer to obtain interference fringes, calculates the misalignment of the secondary mirror assembly and the plano-concave lens assembly and uses the misalignment to adjust the posture of the secondary mirror assembly and the plano-concave lens assembly, thereby making the optical axis of the secondary mirror assembly and the plano-concave lens assembly coaxial with the optical axis of the primary mirror assembly, and the intervals between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly meet preset requirements, thereby making the wavefront aberration of the optical system meet preset threshold requirements, and realizing full-aperture testing of the wavefront aberration of the long-tube optical system, and the method has high assembly and adjustment accuracy and efficiency.

[0040] 2. In the process of installation and adjustment, the present invention uses a plano-concave lens assembly to adjust the optical axes of the primary mirror, the secondary mirror and the correction mirror group, the interval between the primary mirror and the secondary mirror, and between the secondary mirror and the correction mirror group, and uses a plane interferometer, a primary mirror, a secondary mirror, and a plano-concave lens to form an interference measurement system, establish an optical interference simulation model, and construct the misalignment value D in the simulation model. H The relationship between X and the Zernike first-order aberration coefficients Z4 and Z is used to calculate the misalignment. This method guides the secondary mirror adjustment with high efficiency and high precision.

[0041] 3. The present invention combines the distance error between the adopted plano-concave lens assembly and the end face of the main lens barrel to construct a calculation formula for the actual thickness required for the trimming pad of the correction lens group. The thickness of the trimming pad obtained by using the calculation formula is accurate, and the error after installation is small, which effectively controls the optical spacing error between the double reflector and the refractive assembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a cross-sectional schematic diagram of a catadioptric zoom system constructed according to a preferred embodiment of the present invention;

[0043] Figure 2 It is a structural schematic diagram of a catadioptric zoom system assembly and adjustment system constructed according to a preferred embodiment of the present invention;

[0044] Figure 3 It is a schematic diagram of position tolerances of the primary mirror reference surface, the reflection surface, and the outer cylindrical surface constructed according to the preferred embodiment of the present invention;

[0045] Figure 4 Schematic diagram of position tolerance of the main lens barrel reference surface and the mounting surface constructed according to the preferred embodiment of the present invention, wherein (a) is a left view and (b) is a front view;

[0046] Figure 5is a schematic diagram of a correction lens assembly constructed according to a preferred embodiment of the present invention and its dimensions to be measured;

[0047] Figure 6 It is a structural schematic diagram of the primary mirror installation and gluing method constructed according to the preferred embodiment of the present invention;

[0048] Figure 7 is a schematic structural diagram of a plano-concave lens constructed according to a preferred embodiment of the present invention;

[0049] Figure 8 It is a structural schematic diagram of the centering and edge turning of a plano-concave lens assembly constructed according to a preferred embodiment of the present invention;

[0050] Fig. 9 1 is a schematic structural diagram of a trimming pad of a correction lens assembly constructed according to a preferred embodiment of the present invention, wherein (a) is a front view and (b) is a right view;

[0051] Fig.10 1 is a schematic structural diagram of a plano-concave lens assembly trimming pad constructed according to a preferred embodiment of the present invention, wherein (a) is a front view and (b) is a right view;

[0052] Fig.11 is the relationship between the misalignment of the secondary mirror along the X direction and the change of the Zernike expansion coefficient constructed according to the preferred embodiment of the present invention, wherein (a) is the translation of the secondary mirror along the X axis and the change of the 7 Zernike coefficients, (b) is the translation of the secondary mirror along the X axis and the change of the 2 Zernike coefficients, (c) is the rotation of the secondary mirror around the X axis and the change of the 7 Zernike coefficients, and (d) is the rotation of the secondary mirror around the X axis and the change of the 2 Zernike coefficients;

[0053] Fig.12 : is the relationship between the misalignment of the secondary mirror along the Y direction and the change of the Zernike expansion coefficient constructed according to the preferred embodiment of the present invention, (a) is the translation of the secondary mirror along the Y axis and the change of the 7 Zernike coefficients, (b) is the translation of the secondary mirror along the Y axis and the change of the 2 Zernike coefficients, (c) is the rotation of the secondary mirror around the Y axis and the change of the 7 Zernike coefficients, (d) is the rotation of the secondary mirror around the Y axis and the change of the 2 Zernike coefficients;

[0054] Fig.13 is the relationship between the misalignment of the secondary mirror along the Z direction and the change of the Zernike expansion coefficient constructed according to the preferred embodiment of the present invention, wherein (a) is the translation of the secondary mirror along the Z axis and the change of the 7 Zernike coefficients, (b) is the translation of the secondary mirror along the Z axis and the change of the 2 Zernike coefficients, (c) is the rotation of the secondary mirror around the Z axis and the change of the 7 Zernike coefficients, and (d) is the rotation of the secondary mirror around the Z axis and the change of the 2 Zernike coefficients;

[0055] Fig.14 : It is the relationship between the misalignment amount and the change of Zernike expansion coefficient of the plano-concave lens constructed according to the preferred embodiment of the present invention, wherein (a) is the translation of the plano-concave lens along the Z axis and the change of 7 Zernike coefficients, and (b) is the translation of the plano-concave lens along the Z axis and the change of 2 Zernike coefficients.

[0056] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0057] Main mirror assembly: 1-main mirror, 2-main mirror barrel, 3-main mirror barrel bracket, 5-main mirror pressure ring, 4-system adjustment fixture;

[0058] Secondary mirror assembly: 6-secondary mirror bracket, 7-secondary mirror bracket pressure ring, 8-secondary mirror seat, 9-secondary mirror trimming pad, 10-secondary mirror;

[0059] Correction mirror assembly: 11-correction mirror group, 12-correction mirror group pressure ring, 13-correction mirror group trimming pad;

[0060] Plano-concave lens assembly: 16-plano-concave lens, 17-plano-concave lens barrel, 18-plano-concave lens pressure ring, 19-plano-concave lens group trimming pad;

[0061] 14-zoom group, 15-focusing group, 20-adjustment stage, 21-plane interferometer, 22-autocollimator, 23-correction lens group lens 1, 24-ultra-precision air-floating turntable. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0063] like Figure 1As shown, a long-tube catadioptric zoom system is composed of a primary mirror assembly, a secondary mirror assembly, a correction mirror assembly, a zoom group 14, a focusing group 15, etc., wherein the primary mirror assembly includes a primary mirror 1, a primary mirror pressure ring 5, a primary lens barrel 2, a primary lens barrel bracket 3 and a system mounting fixture 4, the secondary mirror assembly includes a secondary mirror 10, a secondary mirror bracket 6, a secondary mirror bracket pressure ring 7, a secondary mirror seat 8 and a secondary mirror trimming pad 9, and the correction mirror assembly includes a correction lens group 11, a correction lens group pressure ring 12 and a correction lens group trimming pad 13. In one embodiment of the present invention, the Cassegrain optical system composed of the primary mirror 1 and the secondary mirror 10 has an aperture of 200 mm and an F number of 2.5, the distance from the focus of the Cassegrain optical system to the rear end face of the primary lens barrel 2 is 204 mm, and the maximum diameter of the inner hole of the primary lens barrel 2 is Φ45 mm.

[0064] The plano-concave lens assembly comprises a plano-concave lens 16 , a plano-concave lens barrel 17 , a plano-concave lens pressing ring 18 and a plano-concave lens group trimming pad 19 .

[0065] The primary mirror 1 and the secondary mirror 10 are reflectors, and the correction lens group 11, the zoom group 14, and the focus group 15 are refractive elements. The zoom group 14 and the focus group 15 are respectively used for zooming and focusing of the optical system. The primary mirror 1 is fixed to the outer circle and end face of the main lens barrel 2 through the center hole and the back glue connection, and the primary mirror pressure ring 5 is installed to the main lens barrel 2 through a threaded connection to protect the primary mirror 1. The main lens barrel 2 is installed on the main lens barrel bracket 3 through screws and cylindrical pins, and the main lens barrel bracket 3 is installed on the system adjustment fixture 4 through a screw connection. The secondary mirror 10 is fixed to the secondary mirror seat 8 through the back glue connection, and the secondary mirror trimming pad 9 is installed between the secondary mirror seat 8 and the secondary mirror bracket 6, and connected by screws. The secondary mirror bracket 6 and the main lens barrel 2 are matched with a small gap shaft hole and end face installation. The secondary mirror bracket pressure ring 7 is threadedly connected to the main lens barrel 2 to press and fix the secondary mirror bracket 6 to the main lens barrel 2. The correction lens group 11 and the main lens barrel 2 are matched with a small gap shaft hole and end surface mounted. The correction lens group trimming pad 13 is installed between the correction lens group 11 and the main lens barrel 2. The correction lens group pressure ring 12 is threadedly connected to the main lens barrel 2, and the correction lens group 11 and the correction lens group trimming pad 13 are pressed and fixed to the main lens barrel 2. The main lens barrel bracket 3 is installed on the system adjustment fixture 4 by screw connection. The zoom group 14 and the focus group 15 are matched with the main lens barrel 2 with a small gap shaft hole.

[0066] The following is an introduction to the installation and adjustment method of the long-tube catadioptric zoom system. The specific steps are as follows:

[0067] S1: A plane interferometer and an autocollimator are respectively arranged on both sides of the adjustment platform, and the pitch angle and yaw angle of the autocollimator 22 are adjusted so that the optical axes of the autocollimator and the plane interferometer are parallel. The postures of the plane interferometer 21 and the autocollimator 22 are kept unchanged.

[0068] S2 adjusts the optical axes of the primary mirror assembly and the plano-concave lens assembly to be coaxial, and adjusts the optical axes of the primary mirror assembly and the plano-concave lens assembly to be parallel to the optical axis of the autocollimator. Specifically, it includes the following steps:

[0069] (1) The optical axis of the main mirror in the main mirror assembly is adjusted to be coaxial with the central axis of the main mirror barrel and perpendicular to the end face of the main mirror barrel.

[0070] In one embodiment of the present invention, Figure 3 , Figure 4 , Figure 6 As shown, the main mirror tube 2 is installed on the ultra-precision air-floating turntable 24, and the reference plane C and the reference plane D are adjusted so that the reference plane C of the main mirror tube 2 coincides with the rotation axis of the ultra-precision air-floating turntable 24, and the reference plane D coincides with the rotation axis of the ultra-precision air-floating turntable 24 and is vertical, and then the main mirror 1 is installed on the main mirror tube 2, and the eccentricity of the main mirror 1 is adjusted so that the radial runout of the outer cylindrical surface of the main mirror 1 meets the requirements, and then the center hole of the main mirror 1 is glued to the outer cylindrical surface of the main mirror tube 2, and the back of the main mirror 1 is glued to the end face of the main mirror tube 2. The glue injection hole on the back of the main mirror tube 2 is 3×Φ2, the glue storage tank is 3×Φ14, and the depth is 0.2mm, and the glue injection hole of the center hole is 6×Φ2.

[0071] (2) The optical axis of the plano-concave lens in the plano-concave lens assembly is adjusted to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end surface of the plano-concave lens barrel.

[0072] In one embodiment of the present invention, a plano-concave lens 16 is designed, and the central thickness and curvature radius of the plano-concave lens 16 are measured. The plano-concave lens 16 is installed in a plano-concave lens barrel 17, and the plano-concave lens pressure ring 18 is used to fix the plano-concave lens 16. An interferometer is used to detect the surface shape accuracy of the plano-concave lens 16 to ensure that the surface shape accuracy of the plano-concave lens 16 before and after fixing remains unchanged. Silicon rubber is used to glue the plano-concave lens 16 to the plano-concave lens barrel 17. An ultra-precision centering lathe and a natural diamond turning tool are used to center and edge the outer cylindrical surface M and the end surface N of the plano-concave lens barrel 17, control the eccentricity error between the outer cylindrical surface M of the plano-concave lens barrel 17 and the optical axis of the plano-concave lens 16, and the verticality error between the end surface N and the optical axis of the plano-concave lens 16, and measure the distance H_PATJZ from the concave vertex of the plano-concave lens 16 to the end surface N of the plano-concave lens barrel 17.

[0073] (3) installing the plano-concave lens assembly on the primary mirror assembly so that the optical axis of the primary mirror assembly and the optical axis of the plano-concave lens assembly are coaxial;

[0074] (4) Figure 2 As shown in the figure, the assembled primary mirror assembly and the plano-concave lens assembly are fixed on the adjustment platform 20, and the Figure 2Place it between the plane interferometer 21 and the autocollimator 22. Use the autocollimator to measure the angular error between the optical axis of the plano-concave lens and the optical axis of the autocollimator, and use the adjustment stage to adjust the optical axes of the primary mirror assembly and the plano-concave lens assembly to be parallel to the optical axis of the autocollimator.

[0075] S3 connects the secondary mirror assembly to the primary mirror assembly, and the light emitted by the plane interferometer passes through the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly in sequence and then returns to the original path. In this way, the plane interferometer 21, the primary mirror 1, the secondary mirror 10, and the plano-concave lens 16 spherical surface form a normal-incidence interference measurement system. In this way, the interference fringes and the Zernike expansion coefficients of the system wavefront aberration are formed in the plane interferometer, and the Zernike coefficients are used to calculate the misalignment of the secondary mirror assembly and the plano-concave lens assembly in various directions. According to the calculated misalignment, the plano-concave lens assembly and the secondary mirror assembly are respectively adjusted, so that the optical axes of the secondary mirror assembly and the plano-concave lens assembly are coaxial with the reference, and the intervals between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly meet the preset requirements, thereby making the wavefront aberration of the system meet the preset threshold requirements.

[0076] In one embodiment of the present invention, the misalignment includes 6 rigid body displacements of the secondary mirror 10 and 6 rigid body displacements of the plano-concave lens 16, a total of 12 errors. The Fringe Zernike expansion coefficients of the first-order aberration of the system are shown in Table 1. Since the outer cylindrical surface M and the end surface N of the plano-concave lens assembly have been centered and edged based on the optical axis of the plano-concave lens 16, after the plano-concave lens assembly is installed on the reference plane C and the reference plane D of the main lens barrel 2, the translation errors of the plano-concave lens 16 along the X-axis and the Y-axis and the rotation errors around the X-axis and the Y-axis have been eliminated. Since the spherical surface is a rotationally symmetric surface, its rotation around the Z-axis will not change the wavefront aberration of the interference measurement system. Therefore, in the interference measurement system of the present invention, the misalignment can be simplified to the 7 errors shown in Table 2.

[0077] Table 1 Fringe Zernike first-order aberration polynomial expansion coefficients

[0078]

[0079]

[0080] Table 2 Misalignment of the interferometric measurement system composed of primary mirror 1, secondary mirror 10, and plano-concave lens 16 spherical surface

[0081]

[0082] According to the optical parameters of the interferometric measurement system of the present invention shown in Table 3, an optical model of the interferometric measurement system is established in the ZEMAX software, and MATLAB and ZEMAX software are used to interact, and the 7 misalignments of the secondary mirror 10 and the plano-concave lens 16 are respectively assigned with equally spaced errors, and multiple groups of Fringe Zernike coefficients are extracted, and the difference is made with the initial Fringe Zernike coefficients when the system has no misalignment to obtain the Fringe Zernike coefficient change. Then, the damped least squares method is used to fit the Zernike coefficient change and the corresponding misalignment, and the 7 misalignments of the secondary mirror 10 and the plano-concave lens 16 and the change of the Zernike expansion coefficient are obtained as shown in the attached figure. Figures 11 to 14 As shown by Fig.11 From (a) and (b), we can see that the translation of the secondary mirror along the X-axis has the greatest impact on Z2, Z5, and Z7. Fig.11 From (c) and (d), we can see that the rotation of the secondary mirror around the X axis has the greatest impact on Z3 and Z8. Fig.12 From (a) and (b), we can see that the translation of the secondary mirror along the Y axis has the greatest impact on Z3 and Z8. Fig.12 From (c) and (d), we can see that the rotation of the secondary mirror around the Y axis has the greatest impact on Z2 and Z7. Fig.13 From (a) and (b), we can see that the translation of the secondary mirror along the Z axis has the greatest impact on Z1, Z4 and Z9. Fig.13 From (c) and (d), we can see that the rotation of the secondary mirror around the Z axis has very little effect on the Zernike coefficient. Fig.14 From (a) and (b), it can be seen that the translation of the plano-concave lens along the Z axis has the greatest impact on Z1, Z4 and Z9.

[0083] Because the change in the wavefront aberration Zernike expansion coefficient of the interference measurement system of the present invention caused by the rotation of the secondary mirror 10 around the Z axis is negligible, the misalignment of the secondary mirror 10 and the plano-concave lens 16 can be further simplified to the six errors in Table 4.

[0084] Table 3 Optical parameters of the interferometric measurement system composed of primary mirror 1, secondary mirror 10, and plano-concave lens 16 spherical surface

[0085]

[0086] The Z-direction translation misalignment of the plano-concave lens 16 is assigned an error with equal spacing, and the change in the Zernike coefficient Z4 is extracted. The change is plotted as discrete points with the corresponding misalignment error, and the discrete points are curve-fitted using the least squares method to obtain D H The relationship with Z4 is shown in formula (1).

[0087] D H =-1.438·Z4 2 +27.56·Z4 (1)

[0088] In the formula, Z4 is in λ (λ=6.33×10-4mm), D H The unit is mm.

[0089] Taylor's theorem shows that if the function f(x) is 0 has an nth-order derivative at x. 0 In a neighborhood near , for any x in the neighborhood, the value of the function in the neighborhood can be approximated by formula (2):

[0090]

[0091] The main purpose of system adjustment is to eliminate the first-order aberration. In the interferometer measurement system, Z1, Z2, and Z3 are system errors, which can be removed by the interferometer software. In the interferometer measurement system of the present invention, the defocus Z4 can be compensated by the Z-direction translation of the spherical surface of the plano-concave lens 16. Assuming that there is a first-order linear relationship between the change in the Fringe Zernike first-order aberration coefficient and the misalignment, the change in the Fringe Zernike first-order aberration polynomial coefficient Zi can be expanded according to formula (2) as follows:

[0092]

[0093] Where, X = (Tx, Ty, Tz, Rx, Ry, D H ), Zi=(Z5, Z6, Z7, Z8, Z9), Zi unit is λ(λ=6.33×10 -4 mm), X is in mm.

[0094] By writing formula (3) in matrix form, we can get formula (4):

[0095] Z=AX (4)

[0096] In the formula,

[0097] According to the above method, the matrix A of formula (4) in the interferometric measurement system of the present invention is obtained as shown in Table 4. The unit of the Zernike expansion coefficient is λ (λ = 6.33 × 10 -4 The unit of misalignment is mm.

[0098] According to formula (4), using the damped least squares method, the relationship between the misalignment and the change Zi of the Fringe Zernike first-order aberration polynomial coefficient can be obtained as shown in formula (5):

[0099] X=(A T A+p 2 I) -1 A T Z (5)

[0100] Where p is the damping factor, whose absolute value is greater than or equal to 1; I is the unit matrix.

[0101] Table 4 Conversion matrix A of the Fringe Zernike expansion coefficient change and misalignment of the interferometric measurement system of the present invention

[0102]

[0103] After building the above-mentioned interferometric measurement system and establishing the mathematical model of the above-mentioned misalignment and the change of the Fringe Zernike first-order aberration coefficient, all misalignments are calculated according to the above-mentioned formula, and the plano-concave lens assembly and the secondary mirror assembly are adjusted according to the calculated misalignment, so that the system assembly can be completed efficiently and with high precision.

[0104] In one embodiment of the present invention, the steps of adjusting the plano-concave lens assembly and the secondary mirror assembly according to the calculated misalignment are as follows:

[0105] Keep the plane interferometer 21, the autocollimator 22, and the plano-concave lens 16 unchanged, and roughly adjust the secondary mirror 10 to make the image point where the plane interferometer 21 light beam is reflected and converged by the primary mirror 1, the secondary mirror 10, and the plano-concave lens 16 coincide with the center of the plane interferometer 21 detector. Then check the corresponding values ​​of the defocus (Z4), the first-order astigmatism (Z5) of the X axis, the first-order astigmatism (Z6) of the Y axis, the first-order coma (Z7) of the X axis, the first-order coma (Z8) of the Y axis, and the first-order spherical aberration (Z9) in the Zernike aberration. According to formula (2), replace the plano-concave lens group trimming pad 19 with different thicknesses to make -0.02λ≤Z4≤0.02λ.

[0106] Keep the plane interferometer 21, the autocollimator 22, and the plano-concave lens 16 unchanged, and fine-tune the X-axis and Y-axis translation and tilt of the secondary mirror 10 according to formula (4), Table 4 and formula (5) to make -0.05λ≤Z7≤0.05λ, -0.05λ≤Z8≤0.05λ, -0.05λ≤Z5≤0.05λ, and -0.05λ≤Z6≤0.05λ, so that the image point of the plane interferometer 21 light beam reflected by the primary mirror 1, the secondary mirror 10, and the plano-concave lens 16 coincides with the center of the detector; according to formula (4), Table 4 and formula (5), adjust the Z-axis translation of the secondary mirror 10 to make -0.03λ≤Z9≤0.03λ; according to formula (1), replace the plano-concave lens group trimming pad 19 with different thicknesses to make -0.02λ≤Z4≤0.02λ. Repeat this step to minimize Z4, Z5, Z6, Z7, Z8, and Z9, and make the system wavefront aberration RMS ≤ 0.05λ.

[0107] S4 removes the plano-concave lens assembly and replaces it with a correction lens assembly to complete the installation of the long-tube catadioptric zoom system.

[0108] In one embodiment of the present invention, Figure 5 , Figure 7 , Figure 8 , Fig. 9 , Fig.10 As shown, according to the thickness error △PATJXQD_L (measured thickness-theoretical thickness) of the plano-concave lens group trimming pad 19, the curvature radius error △R (measured curvature radius-theoretical curvature radius) of the plano-concave lens 16, the distance error △H_PATJZ (measured distance-theoretical distance) from the concave vertex of the plano-concave lens 16 to the end surface N of the plano-concave lens barrel 17, and the distance error △JZJZ_H (measured distance-theoretical distance) from the concave vertex of the correction lens group lens 1 23 to the installation end surface K of the correction lens group 11, the thickness JZJZXQD_L of the correction lens group trimming pad 13 is calculated according to formula (6). Then the correction lens group trimming pad 13, the correction lens group 11, the correction lens group pressure ring 12, the zoom group 14, and the focus group 15 are installed to the main lens barrel 2. At this point, the installation and adjustment of the primary mirror 1, the secondary mirror 10, the correction mirror group 11, the zoom group 14, and the focusing group 15 have been completed, and the wavefront aberration of the Cassegrain optical system has been controlled efficiently and accurately, and the eccentricity error, tilt error, and optical spacing error of the double reflecting mirrors and the refractive element have been controlled.

[0109] JZJZXQD_L= JZJZXQD_L(theoretical)-△JZJZ_H+△R-△H_PATJZ-△PATJXQD_L (6)

[0110] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for assembling and adjusting a long-tube catadioptric zoom system, characterized in that: The method comprises the following steps: A plane interferometer and an autocollimator are respectively arranged on both sides of the adjustment platform, and the optical axis of the autocollimator is made parallel to the optical axis of the plane interferometer; Mounting a plano-concave lens assembly on the primary mirror assembly, and then mounting the primary mirror assembly with the plano-concave lens assembly mounted thereon on an adjustment platform, so that the optical axis of the plano-concave lens assembly is coaxial with the optical axis of the primary mirror assembly and is parallel to the optical axis of the autocollimator; The secondary mirror assembly is connected to the primary mirror assembly, and the light emitted by the plane interferometer passes through the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly in sequence and then returns along the original path, thereby forming interference fringes in the plane interferometer, and the total misalignment of the secondary mirror assembly and the plano-concave lens assembly in each direction is calculated using the interference fringes, and the plano-concave lens assembly and the secondary mirror assembly are respectively adjusted according to the calculated total misalignment, so that the optical axes of the secondary mirror assembly and the primary mirror assembly are coaxial, and the intervals between the primary mirror assembly and the secondary mirror assembly, and between the secondary mirror assembly and the plano-concave lens assembly meet preset requirements, thereby making the wavefront aberration of the optical system composed of the primary mirror assembly, the secondary mirror assembly, and the plano-concave lens assembly meet preset threshold requirements; The plano-concave lens assembly is disassembled and replaced with a correction lens assembly, thereby completing the installation and adjustment of the long-tube catadioptric zoom system.

2. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 1, characterized in that: The total misalignment includes the misalignment of the secondary mirror assembly and the misalignment of the plano-concave lens assembly. The misalignment of the secondary mirror assembly includes the translation of the secondary mirror assembly along the X, Y and Z directions respectively, and the rotation of the secondary mirror assembly around the X and Y directions. The misalignment of the plano-concave lens assembly is the translation of the plano-concave lens assembly along the Z direction.

3. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 2, characterized in that: The calculation of the offset is performed according to the following steps: Construct an optical interference simulation model according to the optical parameters of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly; Misalignment D for plano-concave lens assembly H Assign values ​​and input them into the optical interference simulation model to obtain different D H The defocus Z4 of the optical system composed of the corresponding primary mirror assembly, secondary mirror assembly and plano-concave lens assembly is thus fitted with Z4 and D H The curvilinear relationship between the two; Constructing a relationship between the wavefront aberration Zernike expansion coefficient Z of the interference fringes and the total misalignment X, assigning a value to the total misalignment X and inputting it into the optical interference simulation model to obtain a corresponding Zernike expansion coefficient, thereby determining the relationship between the total misalignment X and the Zernike expansion coefficient Z; Obtain the measured defocus Z4 and Zernike expansion coefficient Z, and use the Z4 and D H The curve relationship between the two and the relationship between the total misalignment X and the Zernike expansion coefficient Z are used to calculate the actual misalignment D H And the total offset X.

4. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 3, characterized in that: The total offset X is calculated according to the following formula: Z=AX Z=[Z5 Z6 Z7 Z8 Z9] T X=[T x T y T z R x R y D H ] T Among them, Z5, Z6, Z7, Z8 and Z9 are respectively the first-order astigmatism of the X axis, the first-order astigmatism of the Y axis, the first-order coma of the X axis, the first-order coma of the Y axis and the first-order spherical aberration of the optical system composed of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly. Tx, Ty, Tz, Rx and Ry are respectively the translation of the secondary mirror along the X, Y and Z directions and the rotation around the X and Y directions. D H is the misalignment of the plano-concave lens assembly.

5. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 3 or 4, characterized in that: The misalignment D of the plano-concave lens assembly H Calculate according to the following formula: D H =-1.438 Z4 2 +27.56 Z4 Among them, Z4 is the defocus of the optical system composed of the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly.

6. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 1 or 2, characterized in that: Before disassembling the plano-concave lens assembly and replacing it with a correction lens assembly, first calculate the actual required thickness of the trimming pad of the correction lens assembly. The calculation formula for the thickness is as follows: JZJZXQD_L=JZJZXQD_L(theoretical)-△JZJZ_H+△R-△H_PATJZ-△PATJXQD_L Among them, JZJZXQD_L is the actual required thickness of the trimming pad in the correction mirror assembly, JZJZXQD_L(theoretical) is the theoretical thickness of the trimming pad in the correction mirror assembly, △JZJZ_H is the distance error from the concave vertex of the lens in the correction mirror assembly to the mounting end face of the correction mirror group, △R is the curvature radius error of the plano-concave lens, △H_PATJZ is the distance error from the concave vertex of the plano-concave lens to the end face of the plano-concave lens barrel, and △PATJXQD_L is the thickness error of the trimming pad in the plano-concave lens assembly.

7. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 1, characterized in that: Before installing the plano-concave lens assembly on the primary mirror assembly, perform the following steps: Adjusting the optical axis of the primary mirror in the primary mirror assembly to be coaxial with the central axis of the primary mirror barrel and perpendicular to the end surface of the primary mirror barrel; The optical axis of the plano-concave lens in the plano-concave lens assembly is adjusted to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end surface of the plano-concave lens barrel.

8. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 7, characterized in that: The method for adjusting the optical axis of the main mirror in the main mirror assembly to be coaxial with the central axis of the main lens barrel and perpendicular to the end face of the main lens barrel is: aligning and connecting the central hole and the back of the main mirror with the main lens barrel.

9. A method for assembling and adjusting a long-tube catadioptric zoom system as claimed in claim 7 or 8, characterized in that: The method for adjusting the optical axis of the plano-concave lens in the plano-concave lens assembly to be coaxial with the central axis of the plano-concave lens barrel and perpendicular to the end face of the plano-concave lens barrel is: taking the optical axis of the plano-concave lens as a reference, centering and edge-turning the outer cylindrical surface and the end face of the plano-concave lens barrel so that the central axis of the outer cylindrical surface is coaxial with the optical axis of the plano-concave lens, and the end face of the plano-concave lens barrel is perpendicular to the optical axis of the plano-concave lens.

10. A system for adjusting using the long-tube catadioptric zoom adjustment method according to any one of claims 1 to 9, characterized in that: The system comprises: a plane interferometer, an autocollimator, an adjustment stage, a primary mirror assembly, a secondary mirror assembly, a plano-concave lens assembly and a correction mirror assembly, wherein: The plane interferometer and the autocollimator are arranged on both sides of the adjustment platform, and the primary mirror assembly, the secondary mirror assembly, the plano-concave lens assembly and the correction mirror assembly are all arranged on the adjustment platform; The plano-concave lens assembly is arranged on the primary mirror assembly and is used to adjust the optical axes of the primary mirror assembly, the secondary mirror assembly and the correction mirror assembly and the optical intervals therebetween; The secondary mirror assembly is arranged between the plano-concave lens assembly and the plane interferometer and is connected to the primary mirror assembly; The correction lens assembly is used to replace the plano-concave lens assembly after the primary mirror assembly, the secondary mirror assembly and the plano-concave lens assembly are assembled and adjusted.

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