Coaxial catadioptric infrared low-temperature optical system and adjustment test method thereof

Abstract

The invention discloses a coaxial refraction and reflection type infrared low-temperature optical system and an adjustment test method thereof. The optical system is composed of a main optical system, a main system supporting frame, a rear light path infrared lens group, an infrared lens group lens seat and a rear light path mounting bottom plate. In order to improve the assembling and adjusting precision and simplify the assembling and adjusting freedom degree, precision assembling and adjusting equipment such as an interferometer, a laser tracker, a centering instrument and a theodolite is adopted, a main optical system and a rear optical path infrared lens group serve as independent units to be assembled and adjusted, and then precision integration testing is conducted. In order to reduce the test period and cost of the low-temperature optical system, a test compensation lens is inserted into a low-temperature optical path, so that the low-temperature optical system can perform imaging test and image quality evaluation in a normal-temperature and normal-pressure environment. The method has the advantages of being simple in principle, high in precision, short in period and low in cost, and is suitable for adjustment testing of the coaxial refraction and reflection type infrared low-temperature optical system.

Description

Technical Field

[0001] The present invention relates to the field of infrared low-temperature optical system assembly, adjustment and testing, and in particular to a coaxial catadioptric infrared low-temperature optical system and an assembly, adjustment and testing method thereof. Background Art

[0002] With the development of infrared remote sensing technology, the detection sensitivity requirements for infrared optical systems are becoming increasingly higher. Cryogenic optical technology has become a primary means of reducing background noise and improving detection sensitivity in infrared optical systems. Due to the physical properties of thermal expansion and contraction, the relative positions of optical and mechanical components in cryogenic optical systems vary significantly compared to their normal temperature state, affecting the imaging quality of the optical system. To minimize this effect, cryogenic optical systems require higher assembly and adjustment precision.

[0003] Limited by the width of the crosshairs and mechanical positioning errors, the traditional method of controlling the relative position of optomechanical components by installing crosshairs in the center hole of the primary mirror and the rear optical path lens assembly can no longer meet the precision requirements of cryogenic optical systems. Furthermore, existing cryogenic vacuum environment simulators in China are complex and bulky, require long cooling times, and are expensive, making the assembly and testing of cryogenic optical systems difficult and costly. Summary of the Invention

[0004] The present invention is intended to provide a catadioptric low-temperature infrared optical system and an assembly, adjustment and testing method thereof to solve the problems raised in the above background technology.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A coaxial catadioptric infrared cryogenic optical system mainly consists of a main optical system and a rear optical path, which are connected by a carbon fiber truss structure.

[0007] The primary optical system comprises: a secondary mirror assembly 1, a main system support frame 2, a primary mirror assembly 3, a primary mirror assembly support structure 7, a secondary mirror assembly support structure 8 and a secondary mirror assembly fixing structure 9;

[0008] The rear optical path includes: a rear optical path first lens group 4, a rear optical path second lens group 5, and a rear optical path mounting base plate 6;

[0009] The primary mirror assembly support structure 7 is fixedly connected to one end of the main system support frame 2, the secondary mirror assembly support structure 8 is fixedly connected to the other end of the main system support frame 2 through the secondary mirror assembly fixing structure 9, the secondary mirror assembly 1 is mounted on the secondary mirror assembly support structure 8, the primary mirror assembly 3 is mounted on the primary mirror assembly support structure 7, the rear optical path mounting base plate 6 is arranged on the side of the primary mirror assembly support structure 7 away from the main system support frame 2, and the rear optical path first lens group 4 and the rear optical path second lens group 5 are sequentially arranged on the rear optical path mounting base plate 6.

[0010] A coaxial catadioptric infrared low-temperature optical system assembly and testing method, the assembly and testing method comprising:

[0011] S1. Main optical system adjustment: Use the optical path self-collimation method to adjust the main optical system. Stick a marker mirror A on the edge of the main system support frame to record the direction of the main system optical axis. After the adjustment is completed, perform thermal treatment on the main optical system.

[0012] S2. Adjustment of rear optical path lens assembly: Using the mounting datum surface in the lens holder as a reference, install the lens assembly into the lens holder in sequence. Use a two-way alignment instrument to test the tilt of the lens assembly, and use a micrometer to test the eccentricity of the lens assembly in the lens holder. Correct the tilt of the lens assembly by grinding the lens spacer or padding with copper sheet, and correct the eccentricity of the lens assembly by adjusting the coaxiality between the lens assembly and the mounting datum surface.

[0013] S3. Mirror mount installation and adjustment: First, install the second lens group lens mount onto the rear optical path mounting base. Use the mounting reference surface within the second lens group lens mount as the mounting reference for the rear optical path lens group lens mount. The central axis of this reference surface is defined as the rear optical path optical axis. Attach a marker mirror B to the rear optical path mounting base to record the direction of the optical axis. Move the first lens group lens mount to adjust the spacing and coaxiality of the two lens mounts. Use a laser tracker to test the spacing and coaxiality of the two lens mounts. After installation, perform a thermal test on the rear optical path.

[0014] S4. Docking and adjustment of the main optical system and the rear optical path: The main optical system is fixed, and the position of the rear optical path mounting base is adjusted to ensure that the distance and eccentricity between the two are within the tolerance range. A laser tracker is used to test the distance and eccentricity between the main system and the rear optical path lens group, and adjustments are made by grinding shims. A theodolite is used to monitor the direction of the main system optical axis and the rear optical path optical axis to ensure that the two optical axes are in the same direction. After the docking is completed, the whole machine is heated.

[0015] S5. Test at normal temperature and pressure: Install a normal temperature test compensation lens in front of the second lens group in the rear optical path to compensate for the image quality of the optical system. Use an infrared target simulator to test the imaging quality of the optical system at normal temperature and pressure.

[0016] S6. Test in low-temperature vacuum environment: Remove the normal temperature test compensation lens, place the optical system in a low-temperature vacuum simulator, and use an infrared target simulator to test the imaging quality of the optical system; when defocusing occurs, the position of the detector focal plane can be fine-tuned through the focusing mechanism to optimize the low-temperature image quality of the optical system.

[0017] Preferably, the optical path self-collimation method described in step S1 is as follows:

[0018] A standard plane mirror is placed at the front end of the main system, and an interferometer is placed behind the main mirror. The theoretical positions of the interferometer focus and the main system focus coincide with each other. The converging light emitted by the interference is transformed into parallel light after being reflected by the main system. The parallel light is reflected by the standard plane mirror and converges again through the main system to enter the interferometer to form an interference pattern. The wavefront of the main system is evaluated by the interference pattern.

[0019] Preferably, the marking mirror A in step S1 is a cube having three vertical reflecting surfaces, and the normals of the three vertical surfaces are respectively parallel to the azimuth, pitch and rotation directions of the optical axis of the main optical system.

[0020] Preferably, in step S2, a mounting reference surface is machined in the lens holder to serve as a mounting reference for the lens assembly.

[0021] Preferably, the marking mirror B in step S3 is a cube with three vertical reflection surfaces, and the normals of the three vertical surfaces are parallel to the azimuth, pitch and rotation directions of the optical axis respectively.

[0022] Preferably, the step S4 specifically includes the following sub-steps:

[0023] S401: The main optical system is fixed, the position of the rear optical path mounting base is adjusted, and the distance and eccentricity between the main system and the rear optical path lens group are tested using a laser tracker. The distance and eccentricity are adjusted to the preset values ​​by grinding the shims.

[0024] S402, placing theodolite 1 in front of the main system, self-aligning the marker mirror A on the main system support frame, and then rotating it 180°;

[0025] S403, placing a standard plane mirror in front of the main system, adjusting the azimuth and elevation of the standard plane mirror to align the theodolite 1 with the standard plane mirror. At this time, the normal direction of the standard plane mirror is the direction of the optical axis of the main system;

[0026] S404, placing theodolite 2 on the side of the main optical system so that its optical axis is aligned with the standard plane mirror;

[0027] S405. Place theodolite 3 behind the marker mirror B on the rear optical path mounting base, adjust the azimuth and elevation of theodolite 3, and rotate the azimuth of theodolite 2 by α° to align it with theodolite 3.

[0028] S406. Rotate the azimuth of theodolite 3 by 180°-α° so that it is aimed at the marker mirror B. Finely adjust the azimuth and elevation of the rear optical path mounting base plate so that the optical axis of theodolite 3 is aligned with the marker mirror B. At this point, the optical axis direction of the main optical system is consistent with the optical axis direction of the rear optical path.

[0029] S407, fix the rear optical path installation base plate and perform the whole machine hot-running.

[0030] Preferably, the compensation lens tested at room temperature in step S5 is a meniscus lens with a large curvature radius, which is installed at the front end of the second lens group in the rear optical path. The installation tolerance is loose and its position accuracy can be ensured by a mechanical positioning structure.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention provides a method for assembling and testing a coaxial catadioptric infrared low-temperature optical system. The method uses the main optical system and the rear optical path infrared lens group as independent optical path units for assembly and testing, thereby reducing the degree of freedom and difficulty in assembling a multi-component optical system and simplifying the assembly process. Precision assembly and adjustment equipment such as an interferometer, a centering instrument, a laser tracker, and a theodolite are used during the assembly and adjustment process, greatly improving the assembly and adjustment accuracy of the optical system and the temperature adaptability of the optical-mechanical system. By inserting a normal temperature test compensation mirror into the low-temperature optical path, the low-temperature optical system can undergo optical imaging testing and image quality evaluation under normal temperature and pressure, reducing the difficulty, cycle, and cost of testing the low-temperature optical system. The method has the advantages of simple principle, high precision, short cycle, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of a coaxial catadioptric infrared cryogenic optical system;

[0034] Figure 2 This is a flow chart for the assembly and testing of a coaxial catadioptric infrared cryogenic optical system;

[0035] Figure 3 This is a schematic diagram of the assembly and adjustment of the main optical system of a coaxial catadioptric infrared cryogenic optical system;

[0036] Figure 4 This is a cross-sectional view of the infrared lens assembly in the rear optical path of a coaxial catadioptric infrared cryogenic optical system;

[0037] Figure 5 This is a schematic diagram of the docking between the main system and the rear optical path of a coaxial catadioptric infrared cryogenic optical system.

[0038] The reference numerals in the drawings of the specification include:

[0039] 1. Secondary mirror assembly; 2. Main system support frame; 3. Primary mirror assembly; 4. First lens group of rear optical path; 5. Second lens group of rear optical path; 6. Rear optical path mounting base; 7. Primary mirror assembly support structure; 8. Secondary mirror assembly support structure; 9. Secondary mirror assembly fixing structure; 10. Standard plane mirror A; 11. Marking mirror A; 12. Interferometer; 13. PI adjustment frame; 41. Mirror mount of first lens group of rear optical path; 42. Mounting reference surface inside the mirror mount of first lens group; 43. Spacer of first lens group of rear optical path; 44. Infrared lens 1 assembly; 45. Infrared lens 2 assembly; 50. Normal temperature test compensation mirror assembly; 51. Mirror mount of second lens group of rear optical path; 52. Spacer of second lens group of rear optical path; 53. Mounting reference surface inside the mirror mount of second lens group; 54. Infrared lens 4 assembly; 55. Infrared lens 3 assembly; 56. Limiting structure of normal temperature test compensation mirror assembly; 14. Standard plane mirror B; 15. Marking mirror B. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments:

[0041] like Figure 1 As shown, a coaxial catadioptric infrared cryogenic optical system provided by an embodiment of the present invention mainly comprises a main optical system and a rear optical path, wherein the main optical system and the rear optical path are connected by a carbon fiber truss structure; wherein the main optical system is fixed to the front end of the carbon fiber truss structure via a main system support frame 2, and the rear optical path is fixed to the rear end of the carbon fiber truss structure via a rear optical path mounting base plate 6;

[0042] The primary optical system comprises: a secondary mirror assembly 1, a main system support frame 2, a primary mirror assembly 3, a primary mirror assembly support structure 7, a secondary mirror assembly support structure 8 and a secondary mirror assembly fixing structure 9;

[0043] The rear optical path includes: a rear optical path first lens group 4, a rear optical path second lens group 5, and a rear optical path mounting base plate 6;

[0044] The primary mirror assembly support structure 7 is fixedly connected to one end of the main system support frame 2, the secondary mirror assembly support structure 8 is fixedly connected to the other end of the main system support frame 2 through the secondary mirror assembly fixing structure 9, the secondary mirror assembly 1 is mounted on the secondary mirror assembly support structure 8, the primary mirror assembly 3 is mounted on the primary mirror assembly support structure 7, the rear optical path mounting base plate 6 is arranged on the side of the primary mirror assembly support structure 7 away from the main system support frame 2, and the rear optical path first lens group 4 and the rear optical path second lens group 5 are sequentially arranged on the rear optical path mounting base plate 6.

[0045] like Figure 2 As shown, a coaxial catadioptric infrared low-temperature optical system assembly and testing method according to an embodiment of the present invention includes the following steps:

[0046] S1. Adjustment of the main optical system. The specific implementation method is as follows:

[0047] Build as Figure 3 In the self-collimating optical path shown, a standard plane mirror A10 is placed at the front end of the main system. The normal direction of the standard plane mirror A10 is consistent with the optical axis direction of the main mirror. The optical axis direction of the main mirror can be marked in the main mirror surface detection optical path; an interferometer 12 is placed behind the main mirror assembly 3, so that the focus of the interferometer 12 is at the theoretical position of the focus of the main system;

[0048] Install the secondary mirror assembly 1 on the PI adjustment frame 13. Use the PI adjustment frame 13 to adjust the position and angle of the secondary mirror assembly 1 so that the main system wavefront collected by the interferometer 12 reaches the preset value. The secondary mirror assembly 1 is first fixed to the secondary mirror assembly support structure 8, and then fixed to the main system support frame 2 through the secondary mirror assembly fixing structure 9. Remove the assembly PI adjustment frame 13 to complete the main optical system installation and adjustment. Affix a marker mirror A11 to the edge of the main system support frame 2 to record the main system optical axis direction and perform thermal testing on the main system.

[0049] S2, rear optical path lens assembly adjustment. The rear optical path lens assembly cross section is as follows Figure 4 As shown, it includes two parts: the first lens group of the rear optical path and the second lens group of the rear optical path.

[0050] The specific implementation method for adjusting the first lens assembly of the rear optical path is as follows: first, place the first lens group lens holder 41 on the installation and adjustment platform of the two-way alignment instrument, and install the infrared lens 1 assembly 44 with the installation reference surface 42 in the lens holder as the reference and fix it; then, rotate the first lens group lens holder 41 180 degrees and reset the optical axis, and then sequentially place the first lens group spacer 43 and the infrared lens 2 assembly 45 into the first lens group lens holder 41, adjust the eccentricity and tilt of the infrared lens 2 assembly 45 to the preset values, and then fix it;

[0051] The specific implementation method of the adjustment of the second lens assembly of the rear optical path is as follows: first, place the second lens group lens holder 51 on the adjustment platform of the two-way alignment instrument, and install and fix the infrared lens 4 assembly 54 based on the installation reference surface 53 in the lens holder; then place the second lens group spacer 52 and the infrared lens 3 assembly 55 into the second lens group lens holder 51 in turn, test and adjust the eccentricity and tilt of the infrared lens 3 assembly 55, and fix it after meeting the preset values; the room temperature test compensation mirror assembly 50 is installed to the front end of the second lens group lens holder 51 of the rear optical path through the mechanical limit structure 56.

[0052] S3. Install and adjust the infrared lens assembly mount. Use the mounting datum surface 53 of the second lens assembly mount as the mounting datum. The central axis of this datum surface is defined as the optical axis of the rear optical path. Affix a marker mirror B15 to the rear optical path mounting base to record the direction of this optical axis. Move the first lens assembly mount 41 to adjust the relative position of the two mounts. Use a laser tracker to test the spacing and coaxiality between the two mounts. After installation, perform a thermal test on the rear optical path.

[0053] S4, the main optical system and the rear optical path docking and adjustment. The main optical system and the rear optical path docking and adjustment method is as follows Figure 5 As shown, the specific implementation sub-steps are as follows:

[0054] Step S4 specifically includes the following sub-steps:

[0055] S401, fix the main system, adjust the position of the rear optical path mounting base 6, use a laser tracker to test the distance and eccentricity between the main system and the first lens group 4 of the rear optical path, and make adjustments by grinding the shims.

[0056] S402, placing theodolite 1 in front of the main system, first self-aligning the marker mirror A11 on the main system support frame, and then rotating 180°;

[0057] S403, placing a standard plane mirror 14 in front of the main system, adjusting the azimuth and elevation of the standard plane mirror 14 to align the theodolite 1 with the standard plane mirror 14;

[0058] S404, placing the theodolite 2 on the side of the main optical system, aligning its optical axis with the standard plane mirror 14, and then turning the theodolite 2 180°;

[0059] S405, placing theodolite 3 behind the rear optical path optical axis marker mirror B15, adjusting the azimuth and elevation of theodolite 3 so that theodolite 2 can be self-aligned with theodolite 3 after being rotated α° in azimuth;

[0060] S406. Rotate the azimuth of theodolite 3 by 180°-α° so that it is aimed at the rear optical path optical axis marker mirror B15. Finely adjust the azimuth and elevation of the rear optical path mounting base plate 6 so that the optical axis of theodolite 3 is aligned with the optical axis of the marker mirror B15. At this point, the optical axis direction of the main optical system is aligned with the optical axis direction of the rear optical path.

[0061] S407, fixing the rear optical path installation base plate 6, and performing a whole machine hot run;

[0062] S5. Test at room temperature and pressure: Install a room temperature test compensation mirror 50 in front of the second lens group in the rear optical path to compensate for the image quality of the optical system, and use an infrared target simulator to test the imaging quality of the optical system at room temperature and pressure.

[0063] S6. Test in a cryogenic vacuum environment. Remove the room-temperature test compensating mirror 50 and place the optical system in a cryogenic vacuum simulator. Use an infrared target simulator to test the optical system's imaging quality. If defocus is present, fine-tune the detector's focal plane using the focusing mechanism to optimize the optical system's low-temperature image quality.

[0064] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A coaxial catadioptric infrared cryogenic optical system, characterized by: The coaxial catadioptric infrared cryogenic optical system consists of a main optical system and a rear optical path, and the main optical system and the rear optical path are connected by a carbon fiber truss structure; The primary optical system comprises: a secondary mirror assembly 1, a main system support frame 2, a primary mirror assembly 3, a primary mirror assembly support structure 7, a secondary mirror assembly support structure 8 and a secondary mirror assembly fixing structure 9; The rear optical path includes: a rear optical path first lens group 4, a rear optical path second lens group 5, and a rear optical path mounting base plate 6; The primary mirror assembly support structure 7 is fixedly connected to one end of the main system support frame 2, the secondary mirror assembly support structure 8 is fixedly connected to the other end of the main system support frame 2 through the secondary mirror assembly fixing structure 9, the secondary mirror assembly 1 is mounted on the secondary mirror assembly support structure 8, the primary mirror assembly 3 is mounted on the primary mirror assembly support structure 7, the rear optical path mounting base plate 6 is arranged on the side of the primary mirror assembly support structure 7 away from the main system support frame 2, and the rear optical path first lens group 4 and the rear optical path second lens group 5 are sequentially arranged on the rear optical path mounting base plate 6.

2. A method for assembling and testing a coaxial catadioptric infrared cryogenic optical system according to claim 1, characterized in that: The installation and adjustment test method comprises: S1. Main optical system adjustment: Use the optical path self-collimation method to adjust the main optical system. Stick a marker mirror A on the edge of the main system support frame to record the direction of the main system optical axis. After the adjustment is completed, perform thermal treatment on the main optical system. S2. Adjustment of rear optical path lens assembly: Using the mounting datum surface in the lens holder as a reference, install the lens assembly into the lens holder in sequence. Use a two-way alignment instrument to test the tilt of the lens assembly, and use a micrometer to test the eccentricity of the lens assembly in the lens holder. Correct the tilt of the lens assembly by grinding the lens spacer or padding with copper sheet, and correct the eccentricity of the lens assembly by adjusting the coaxiality between the lens assembly and the mounting datum surface. S3. Mirror mount installation and adjustment: First, install the second lens group lens mount onto the rear optical path mounting base. Use the mounting reference surface within the second lens group lens mount as the mounting reference for the rear optical path lens group lens mount. The central axis of this reference surface is defined as the rear optical path optical axis. Attach a marker mirror B to the rear optical path mounting base to record the direction of the optical axis. Move the first lens group lens mount to adjust the spacing and coaxiality of the two lens mounts. Use a laser tracker to test the spacing and coaxiality of the two lens mounts. After installation, perform a thermal test on the rear optical path. S4. Docking and adjustment of the main optical system and the rear optical path: The main optical system is fixed, and the position of the rear optical path mounting base is adjusted to ensure that the distance and eccentricity between the two are within the tolerance range. A laser tracker is used to test the distance and eccentricity between the main system and the rear optical path lens group, and adjustments are made by grinding shims. A theodolite is used to monitor the direction of the main system optical axis and the rear optical path optical axis to ensure that the two optical axes are in the same direction. After the docking is completed, the whole machine is heated. S5. Test at normal temperature and pressure: Install a normal temperature test compensation lens in front of the second lens group in the rear optical path to compensate for the image quality of the optical system. Use an infrared target simulator to test the imaging quality of the optical system at normal temperature and pressure. S6. Test in low-temperature vacuum environment: Remove the normal temperature test compensation lens, place the optical system in a low-temperature vacuum simulator, and use an infrared target simulator to test the imaging quality of the optical system; when defocusing occurs, the position of the detector focal plane can be fine-tuned through the focusing mechanism to optimize the low-temperature image quality of the optical system.

3. The method for assembling and testing a coaxial catadioptric infrared low-temperature optical system according to claim 1, characterized in that: The optical path self-collimation method described in step S1 is as follows: A standard plane mirror is placed at the front end of the main system, and an interferometer is placed behind the main mirror. The theoretical positions of the interferometer focus and the main system focus coincide with each other. The converging light emitted by the interference is transformed into parallel light after being reflected by the main system. The parallel light is reflected by the standard plane mirror and converges again through the main system to enter the interferometer to form an interference pattern. The wavefront of the main system is evaluated by the interference pattern.

4. The method for assembling and testing a coaxial catadioptric infrared low-temperature optical system according to claim 1, characterized in that: The marking mirror A described in step S1 is a cube with three vertical reflection surfaces, and the normals of the three vertical surfaces are parallel to the azimuth, pitch and rotation directions of the optical axis of the main optical system respectively.

5. The method for assembling and testing a coaxial catadioptric infrared low-temperature optical system according to claim 1, characterized in that: In step S2, a mounting reference surface is machined in the lens holder to serve as a mounting reference for the lens assembly.

6. The method for assembling and testing a coaxial catadioptric infrared low-temperature optical system according to claim 1, characterized in that: In step S3, the marking mirror B is a cube with three vertical reflection surfaces, and the normals of the three vertical surfaces are parallel to the azimuth, pitch and rotation directions of the optical axis respectively.

7. The method for assembling and testing a coaxial catadioptric infrared low-temperature optical system according to claim 1, characterized in that: The step S4 specifically includes the following sub-steps: S401: The main optical system is fixed, the position of the rear optical path mounting base is adjusted, and the distance and eccentricity between the main system and the rear optical path lens group are tested using a laser tracker. The distance and eccentricity are adjusted to the preset values ​​by grinding the shims. S402, placing theodolite 1 in front of the main system, self-aligning the marker mirror A on the main system support frame, and then rotating it 180°; S403, placing a standard plane mirror in front of the main system, adjusting the azimuth and elevation of the standard plane mirror to align the theodolite 1 with the standard plane mirror. At this time, the normal direction of the standard plane mirror is the direction of the optical axis of the main system; S404, placing theodolite 2 on the side of the main optical system so that its optical axis is aligned with the standard plane mirror; S405. Place theodolite 3 behind the marker mirror B on the rear optical path mounting base, adjust the azimuth and elevation of theodolite 3, and rotate the azimuth of theodolite 2 by α° to align it with theodolite 3. S406. Rotate the azimuth of theodolite 3 by 180°-α° so that it is aimed at the marker mirror B. Finely adjust the azimuth and elevation of the rear optical path mounting base plate so that the optical axis of theodolite 3 is aligned with the marker mirror B. At this point, the optical axis direction of the main optical system is consistent with the optical axis direction of the rear optical path. S407, fix the rear optical path installation base plate and perform the whole machine hot-running.

8. The method for assembling and testing a coaxial catadioptric infrared low-temperature optical system according to claim 1, characterized in that: The compensation lens tested at room temperature in step S5 is a meniscus lens with a large curvature radius. The lens is installed at the front end of the second lens group in the rear optical path. The installation tolerance is loose and its position accuracy can be ensured by a mechanical positioning structure.

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