Method for adjusting large-view-field off-axis three-mirror beam expanding optical system

Abstract

The invention discloses an adjusting method of a large-view-field off-axis three-mirror beam expanding optical system, and solves the problems that when the off-axis three-mirror beam expanding optical system is adjusted in an existing mode, the adjusting period is too long, and the adjusting precision is low, and by means of the concave off-axis paraboloid characteristics of an off-axis primary mirror and an off-axis three-mirror, the large-view-field off-axis three-mirror beam expanding optical system can be adjusted, and the large-view-field off-axis three-mirror beam expanding optical system can be adjusted. An interferometer and an auto-collimation plane mirror are used to carry out auto-collimation detection; the relative position relation of the off-axis primary mirror and the off-axis third mirror can be determined by using the focus; only a specific optical element needs to be adjusted when the system is adjusted every time, other optical elements do not need to be adjusted at the same time, and the adjustment uncertainty is greatly reduced; therefore, compared with the existing empirical method, the adjustment degree of freedom in the adjustment process is reduced by half, the controllability of the optical path adjustment process of the off-axis beam expanding optical system is realized, and the adjustment efficiency of the optical path of the optical system is improved.

Description

Technical Field

[0001] The invention relates to an assembling and adjusting method for an optical system, and in particular to an assembling and adjusting method for an off-axis three-reflection beam expanding optical system with a large viewing field. Background Art

[0002] With the widespread application and rapid development of optical technology, the spectral bands of optical systems have gradually developed from single visible light and infrared bands to multi-band combinations. Due to the limitations of transmission glass materials, it is necessary to design a common aperture reflective beam expansion optical system at the front end of the optical system (parallel light incident on the system, parallel light outgoing) to meet the system's multi-band requirements for visible light, short-wave infrared, medium-wave infrared, long-wave infrared, laser, etc., and then design a spectral splitting system at the back end of the total reflection common aperture to achieve imaging requirements for different spectral bands.

[0003] The total reflection off-axis three-reflection beam expansion optical system has no central obstruction, high energy utilization, easy stray light control, and can achieve a large field of view and a large relative aperture. It has now received widespread attention. However, its installation and adjustment is difficult and mainly relies on the experience of the installer. During the installation and adjustment of the off-axis three-reflection beam expansion optical system, the adjustment of each off-axis aspheric mirror mainly relies on experience. A single reflector needs to adjust 5 degrees of freedom, and at least 10 degrees of freedom need to be adjusted in the three-reflection beam expansion optical system. At the same time, there will be mutual coupling between the degrees of freedom. Therefore, when the existing method is used for adjustment, there is a great deal of blindness and randomness in the adjustment of each degree of freedom of the reflector, and its installation and adjustment cycle is too long and the installation and adjustment accuracy is low. Summary of the invention

[0004] The present invention aims to provide a method for adjusting an off-axis three-reflection beam expander optical system with a large field of view, so as to solve the technical problems of too long adjustment period and low adjustment accuracy when adjusting the off-axis three-reflection beam expander optical system in the existing method.

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

[0006] A method for assembling and adjusting a large-field off-axis three-mirror beam expander optical system, wherein the off-axis three-mirror beam expander optical system comprises an off-axis primary mirror, an off-axis secondary mirror, an off-axis third mirror and an aperture stop arranged in sequence along an optical path; the reflection surfaces of the off-axis primary mirror and the off-axis third mirror are concave off-axis paraboloids; the reflection surface of the off-axis secondary mirror is a convex aspheric surface;

[0007] The special thing about it is that it includes the following steps:

[0008] Step 1, establish the system optical axis;

[0009] Preset the coordinate system XYZ, set a linear guide rail parallel to the Z axis, set an interferometer with a standard lens on the linear guide rail, and determine the focal motion trajectory of the interferometer as the system optical axis;

[0010] Step 2: Installation of off-axis primary mirror;

[0011] A self-collimating plane mirror with a central hole is arranged on one side of the working end of the interferometer, so that the normal of the self-collimating plane mirror is parallel to the direction of the linear guide rail; an off-axis primary mirror is pre-installed on the side of the self-collimating plane mirror away from the interferometer, and the interferometer is translated so that the focal points of the interferometer and the off-axis primary mirror coincide and are located on the optical axis of the system; the off-axis primary mirror is adjusted based on the coordinate system XYZ so that the wavefront error accuracy of the primary mirror detected by the interferometer meets the requirements, and the installation of the off-axis primary mirror is completed;

[0012] Step 3: Installation of three off-axis mirrors;

[0013] Pre-install the off-axis three mirrors on the side of the autocollimation plane mirror away from the interferometer, translate the interferometer so that the distance between the focus of the interferometer and the focus of the off-axis primary mirror meets the preset value, adjust the off-axis three mirrors based on the coordinate system XYZ so that the accuracy of the three-mirror wavefront error detected by the interferometer meets the requirements, and complete the installation of the off-axis three mirrors;

[0014] Step 4: Installation of off-axis secondary mirror;

[0015] Replace the standard lens of the interferometer with a plane lens, move the self-collimating plane mirror upward along the Y axis, and move the interferometer downward along the Y axis so that the parallel light beam emitted by it is incident on the off-axis three mirrors, pre-install the off-axis secondary mirror, and adjust the off-axis secondary mirror based on the coordinate system XYZ so that the detection result of the interferometer at this time, that is, the accuracy of the system wavefront error, meets the requirements;

[0016] Complete the installation and adjustment of the off-axis three-reflection beam expansion optical system.

[0017] Furthermore, step 1 specifically includes:

[0018] 1.1. Preset a straight line as the system optical axis, and establish the coordinate system XYZ with the preset system optical axis as the Z axis;

[0019] 1.2. Install an interferometer with a standard lens on the linear guide rail, adjust the linear guide rail so that its track is parallel to the Z axis, move the interferometer along the linear guide rail, and determine that the focal motion trajectory of the interferometer is the system optical axis.

[0020] Furthermore, step 1.2 is specifically as follows:

[0021] An interferometer with a standard lens is installed on the linear guide rail. The linear guide rail is adjusted using a theodolite to make its track parallel to the Z axis. The interferometer is moved along the linear guide rail, and the focal motion trajectory of the interferometer is determined to be the system optical axis.

[0022] Furthermore, step 2 specifically includes:

[0023] 2.1. A self-collimating plane mirror with a central hole is arranged on one side of the working end of the interferometer, and the focus of the interferometer can pass through the central hole. The normal of the self-collimating plane mirror is adjusted to be parallel to the track direction of the linear guide rail.

[0024] 2.2. Pre-install the off-axis primary mirror on the side of the autocollimator away from the interferometer. The off-axis primary mirror is located on the upper side of the system optical axis. The interferometer is translated along the linear guide rail, and the off-axis primary mirror is translated and adjusted along the Z-axis, X-axis, and Y-axis to make the focus of the interferometer coincide with the focus of the off-axis primary mirror.

[0025] 2.3. Adjust the off-axis primary mirror to rotate and tilt around the X-axis and Y-axis so that the outgoing light of the interferometer becomes parallel light after being reflected by the off-axis primary mirror and vertically enters the self-collimating plane mirror and returns along the original path;

[0026] 2.4. Obtain the interferometer's surface detection result for the off-axis primary mirror, that is, the wavefront error of the primary mirror; if the accuracy of the wavefront error of the primary mirror does not meet the requirements, return to step 2.3 until the accuracy of the wavefront error of the primary mirror meets the requirements; the installation of the off-axis primary mirror is completed.

[0027] Furthermore, step 2.1 is specifically as follows:

[0028] A self-collimating plane mirror with a central hole is arranged on one side of the working end of the interferometer, and the focus of the interferometer can pass through the central hole. The normal of the self-collimating plane mirror is adjusted to be parallel to the linear guide rail by using the theodolite.

[0029] Furthermore, step 3 specifically includes:

[0030] 3.1. Pre-install the off-axis three mirrors on the side of the autocollimation plane mirror away from the interferometer, and the off-axis three mirrors are located on the lower side of the optical axis of the system; translate the interferometer along the linear guide rail so that the distance between the focus of the interferometer and the focus of the off-axis primary mirror is a preset value, and then translate and adjust the off-axis three mirrors along the Z axis, X axis, and Y axis so that the focus of the interferometer coincides with the focus of the off-axis three mirrors;

[0031] 3.2. Adjust the rotation and tilt of the three off-axis mirrors around the X-axis and Y-axis so that the outgoing light of the interferometer becomes parallel light after being reflected by the three off-axis mirrors and vertically enters the self-collimating plane mirror and returns along the original path;

[0032] 3.3. Obtain the interferometer's surface detection results for the off-axis three mirrors, that is, the wavefront errors of the three mirrors; if the accuracy of the wavefront errors of the three mirrors does not meet the requirements, return to step 3.2 until the accuracy of the wavefront errors of the three mirrors meets the requirements; the installation of the off-axis three mirrors is completed.

[0033] Furthermore, step 4 specifically includes:

[0034] 4.1. Replace the standard lens of the interferometer with a plane lens, so that the parallel light emitted by it is parallel to the optical axis of the system. Move the interferometer downward along the Y axis so that the parallel light beam emitted by it is incident on the off-axis three mirrors.

[0035] 4.2. Pre-install the off-axis secondary mirror on the side of the autocollimator away from the interferometer, and move the autocollimator upward along the Y axis so that the autocollimator is located on the upper side of the system optical axis;

[0036] 4.3. Adjust the off-axis secondary mirror to translate along the Z axis, X axis, and Y axis, and rotate and tilt around the X axis and Y axis, so that the outgoing light of the interferometer is reflected by the off-axis three mirrors, the off-axis secondary mirror, and the off-axis primary mirror in sequence, and then becomes parallel light and vertically incident on the self-collimating plane mirror and returns along the original path, forming the system self-collimation detection result;

[0037] 4.4. Obtain the system self-alignment detection result of the interferometer, that is, the system wavefront error. If the accuracy of the system wavefront error does not meet the requirement, return to step 4.3 until the accuracy of the system wavefront error detected by the interferometer meets the requirement;

[0038] Complete the installation and adjustment of the off-axis three-reflection beam expansion optical system.

[0039] Furthermore, the linear guide is a digital display linear guide.

[0040] Beneficial effects of the present invention:

[0041] The method for assembling and adjusting a large-field off-axis three-reflection beam expanding optical system provided by the present invention utilizes the concave off-axis parabolic characteristics of an off-axis primary mirror and an off-axis three-mirror, and uses an interferometer and a self-aligning plane mirror to perform self-alignment detection on them; the relative position relationship between the off-axis primary mirror and the off-axis three-mirror can be determined by using their focal points; each time the system is adjusted, only a specific optical element (five degrees of freedom) needs to be adjusted, and other optical elements (five degrees of freedom) do not need to be adjusted at the same time, thereby greatly reducing adjustment uncertainty; it can be seen that compared with the existing empirical method, the adjustment method of the present invention reduces the adjustment degrees of freedom in the adjustment process by half, thereby realizing the controllability of the optical path adjustment process of the off-axis beam expanding optical system, and improving the adjustment efficiency of the optical path of the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the structure of a large-field off-axis three-reflection beam expansion optical system;

[0043] Figure 2 It is a structural schematic diagram corresponding to step 2 of a method for assembling and adjusting a large-field off-axis three-reflection beam expanding optical system of the present invention;

[0044] Figure 3 It is a structural schematic diagram corresponding to step 3 of a method for assembling and adjusting a large-field off-axis three-reflection beam expanding optical system of the present invention;

[0045] Figure 4 It is a structural schematic diagram corresponding to step 4 of a method for assembling and adjusting a large-field off-axis three-reflection beam expanding optical system of the present invention.

[0046] Figure Number:

[0047] 1-off-axis primary mirror, 2-off-axis secondary mirror, 3-off-axis tertiary mirror, 4-aperture stop, 5-interferometer, 6-linear guide, 7-self-collimating plane mirror. DETAILED DESCRIPTION

[0048] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] The embodiment of the present invention provides a method for assembling and adjusting a large-field off-axis three-mirror beam expander optical system. The method utilizes the characteristics of parallel light incident and parallel light output in the off-axis three-mirror beam expander optical system, and combines the design result that the off-axis primary mirror and the off-axis three mirrors in the system are concave off-axis paraboloids. The relative positions of the off-axis primary mirror and the off-axis three mirrors can be accurately determined by the principle of self-collimation. When assembling and adjusting the off-axis three-mirror optical beam expander system, the number of optical elements that need to be adjusted simultaneously is reduced to only one optical element. The controllability of the optical path adjustment process of the off-axis optical system is achieved, and work efficiency can be improved.

[0050] like Figure 1 As shown, the off-axis three-reflection beam expanding optical system of the method comprises an off-axis primary mirror 1, an off-axis secondary mirror 2, an off-axis third mirror 3 and an aperture stop 4 which are sequentially arranged along the optical path direction; the reflecting surfaces of the off-axis primary mirror 1 and the off-axis third mirror 3 are concave off-axis paraboloids (K is -1); the reflecting surface of the off-axis secondary mirror 2 is a convex aspheric surface (K is -30.989); the off-axis primary mirror 1, the off-axis secondary mirror 2 and the off-axis third mirror 3 are all aspheric mirrors. In the present embodiment, the radii of the off-axis primary mirror 1, the off-axis secondary mirror 2 and the off-axis third mirror 3 are 678.91 mm, 263.61 mm and 483.3 mm respectively. The distance from the vertex of the off-axis primary mirror to the vertex of the off-axis secondary mirror is 299mm, the distance from the vertex of the off-axis secondary mirror 2 to the vertex of the off-axis three-mirror 3 is 300mm, and the distance from the off-axis three-mirror 3 to the aperture stop 4 is 465mm; the center of the incident parallel light is translated upward by 100mm along the Y axis relative to the system optical axis, and the center of the outgoing parallel light is translated downward by 50mm along the Y axis relative to the system optical axis. During the self-alignment detection, the interferometer focus positions of the off-axis primary mirror 1 and the off-axis three-mirror 3 are 98.805mm apart in the Z axis direction.

[0051] The installation steps of this method are as follows:

[0052] Step 1, establish the system optical axis;

[0053] A coordinate system XYZ is preset, and a linear guide rail 6 is set parallel to its Z axis. The linear guide rail 6 is a digital linear guide rail, and its movement amount is readable; an interferometer 5 with a standard lens is installed on the linear guide rail 6, and the focal motion trajectory of the interferometer 5 is determined to be the system optical axis; specifically, the following steps are included:

[0054] 1.1. A straight line is preset as the system optical axis, and a coordinate system XYZ is established with the preset system optical axis as the Z axis, where the X axis and the Y axis are perpendicular to the Z axis; an interferometer 5 with a standard lens is installed on the linear guide rail 6, and the linear guide rail 6 is adjusted by a theodolite so that its track is parallel to the Z axis, and the interferometer 5 is moved along the linear guide rail 6, and the focal motion trajectory of the interferometer 5 is determined to be the system optical axis.

[0055] Step 2: Installation of off-axis primary mirror 1;

[0056] like Figure 2 As shown, a self-collimating plane mirror 7 with a central hole is arranged on one side of the working end of the interferometer 5, so that the normal of the self-collimating plane mirror 7 is parallel to the linear guide 6; an off-axis primary mirror 1 is pre-installed on the side of the self-collimating plane mirror 7 away from the interferometer 5, and the interferometer 5 is translated so that the focal points of the interferometer 5 and the off-axis primary mirror 1 coincide and are located on the optical axis of the system, and the off-axis primary mirror 1 is adjusted based on the coordinate system XYZ so that the accuracy of the primary mirror wavefront error detected by the interferometer 5 meets the requirements, and the installation of the off-axis primary mirror 1 is completed; specifically, it includes:

[0057] 2.1. A self-collimating plane mirror 7 with a central hole is arranged on one side of the working end of the interferometer 5, and the focus of the interferometer 5 can pass through the central hole. The normal of the self-collimating plane mirror 7 is adjusted to be parallel to the linear guide rail 6 by using a theodolite.

[0058] 2.2. Pre-install the off-axis primary mirror 1 on the side of the autocollimator 7 away from the interferometer 5. The off-axis primary mirror 1 is located on the upper side of the system optical axis. The interferometer 5 is translated along the linear guide 6, and the off-axis primary mirror 1 is translated and adjusted along the Z-axis, X-axis, and Y-axis to make the focus of the interferometer 5 coincide with the focus of the off-axis primary mirror 1.

[0059] 2.3. Adjust the off-axis primary mirror 1 to rotate and tilt around the X-axis and Y-axis, so that the outgoing light of the interferometer 5 becomes parallel light after being reflected by the off-axis primary mirror 1, vertically incident on the self-collimating plane mirror 7 and returns along the original path.

[0060] 2.4. Obtain the surface detection result of the interferometer 5 on the off-axis primary mirror 1, that is, the RMS wavefront error of the primary mirror; if the accuracy of the RMS wavefront error of the primary mirror does not meet the requirements, return to step 2.3 until the accuracy of the RMS wavefront error of the primary mirror meets the requirements, that is, the accuracy of the RMS wavefront error of the primary mirror is less than 0.025λ (λ=632.8nm is the wavelength of the interferometer 5); the installation of the off-axis primary mirror 1 is completed.

[0061] Step 3, installation of off-axis three mirrors 3;

[0062] like Figure 3 As shown, pre-install the off-axis three-mirror 3 on the side of the self-collimating plane mirror 7 away from the interferometer 5, translate the interferometer 5 so that the focus distance between the interferometer 5 and the focus of the off-axis primary mirror 1 meets the preset value, adjust the off-axis three-mirror 3 based on the coordinate system XYZ so that the accuracy of the three-mirror wavefront error detected by the interferometer 5 meets the requirements, and complete the installation of the off-axis three-mirror 3; specifically including:

[0063] 3.1. Pre-install the off-axis three-mirror 3 on the side of the autocollimation plane mirror 7 away from the interferometer 5, and the off-axis three-mirror 3 is located on the lower side of the system optical axis; translate the interferometer 5 along the linear guide 6 so that the distance between the focus of the interferometer 5 and the focus of the off-axis primary mirror 1 is 98.805 mm, and then translate and adjust the off-axis three-mirror 3 along the Z-axis, X-axis, and Y-axis so that the focus of the interferometer 5 coincides with the focus of the off-axis three-mirror 3.

[0064] 3.2. Adjust the rotation and tilt of the off-axis three-mirror 3 around the X-axis and the Y-axis so that the outgoing light of the interferometer 5 becomes parallel light after being reflected by the off-axis three-mirror 3 and vertically enters the self-collimating plane mirror 7 and returns along the original path.

[0065] 3.3. Obtain the surface detection result of the off-axis three-mirror 3 by the interferometer 5, that is, the wavefront error of the three-mirror; if the accuracy of the wavefront error of the three-mirror does not meet the requirements, return to step 3.2 until the accuracy of the wavefront error of the three-mirror meets the requirements, that is, the accuracy of the wavefront error of the three-mirror is less than 0.025λ; at this time, the relative position relationship adjustment of the system off-axis main mirror 1 and the off-axis three mirror 3 is completed.

[0066] Step 4: Installation of off-axis secondary mirror 2;

[0067] like Figure 4 As shown, the standard lens of the interferometer 5 is replaced with a plane lens, the self-collimating plane mirror 7 is moved upward along the Y axis, and the interferometer 5 is moved downward along the Y axis so that the parallel light beam emitted by it is incident on the off-axis three-mirror 3, the off-axis secondary mirror 2 is pre-installed, and the off-axis secondary mirror 2 is adjusted based on the coordinate system XYZ so that the detection result of the interferometer 5 at this time, that is, the accuracy of the system wavefront error meets the requirements; specifically including:

[0068] 4.1. Replace the standard lens of interferometer 5 with a plane lens, so that the parallel light emitted by it is parallel to the system optical axis. Translate interferometer 5 downward along the Y axis by 50 mm so that the parallel light beam emitted by it is incident on the off-axis three-mirror 3;

[0069] 4.2. Pre-install the off-axis secondary mirror 2 on the side of the auto-collimation plane mirror 7 away from the interferometer 5, and move the auto-collimation plane mirror 7 upward along the Y axis so that the auto-collimation plane mirror 7 is located on the upper side of the system optical axis;

[0070] 4.3. Adjust the off-axis secondary mirror 2 to translate along the Z axis, X axis, and Y axis, and to rotate and tilt around the X axis and Y axis, so that the outgoing light of the interferometer 5 is reflected by the off-axis three mirrors 3, the off-axis secondary mirror 2, and the off-axis primary mirror 1 in sequence, and then becomes parallel light and vertically incident on the self-collimating plane mirror 7 and returns along the original path, thereby forming the system self-collimation detection result;

[0071] 4.4. Obtain the system self-alignment detection result of the interferometer 5, that is, the system wavefront error. If the accuracy of the system wavefront error does not meet the requirement, return to step 4.3 until the accuracy of the system wavefront error detected by the interferometer 5 meets the requirement, that is, the accuracy of the system wavefront error is less than 0.08λ;

[0072] The installation and adjustment of the off-axis three-reflection beam expansion optical system is completed.

[0073] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for assembling and adjusting a large-field off-axis three-mirror beam expander optical system, the off-axis three-mirror beam expander optical system comprising an off-axis primary mirror (1), an off-axis secondary mirror (2), an off-axis third mirror (3) and an aperture stop (4) arranged in sequence along an optical path; the reflection surfaces of the off-axis primary mirror (1) and the off-axis third mirror (3) are concave off-axis paraboloids; the reflection surface of the off-axis secondary mirror (2) is a convex aspheric surface; It is characterized in that The following steps are involved: Step 1, establish the system optical axis; A coordinate system XYZ is preset, a linear guide rail (6) parallel to the Z axis is provided, an interferometer (5) with a standard lens is installed on the linear guide rail (6), and the focal motion trajectory of the interferometer (5) is determined as the system optical axis; Step 2, installation of the off-axis primary mirror (1); A self-collimating plane mirror (7) with a central hole is arranged on one side of the active end of the interferometer (5), so that the normal of the self-collimating plane mirror (7) is parallel to the direction of the linear guide rail (6); an off-axis primary mirror (1) is pre-installed on the side of the self-collimating plane mirror (7) away from the interferometer (5), the interferometer (5) is translated so that the focal points of the interferometer (5) and the off-axis primary mirror (1) coincide and are located on the optical axis of the system, and the off-axis primary mirror (1) is adjusted based on the coordinate system XYZ so that the accuracy of the primary mirror wavefront error detected by the interferometer (5) meets the requirements, thereby completing the installation of the off-axis primary mirror (1); Step 3, installation of off-axis three mirrors (3); Pre-installing the off-axis three mirrors (3) on the side of the self-collimating plane mirror (7) away from the interferometer (5), translating the interferometer (5) so that the distance between the focus of the interferometer (5) and the focus of the off-axis primary mirror (1) meets a preset value, adjusting the off-axis three mirrors (3) based on the coordinate system XYZ so that the accuracy of the three-mirror wavefront error detected by the interferometer (5) meets the requirements, and completing the installation of the off-axis three mirrors (3); Step 4: Installation of the off-axis secondary mirror (2); The standard lens of the interferometer (5) is replaced with a plane lens, the self-collimating plane mirror (7) is moved upward along the Y axis, and the interferometer (5) is moved downward along the Y axis so that the parallel light beam emitted by the interferometer (5) is incident on the off-axis three mirrors (3), the off-axis secondary mirror (2) is pre-installed, and the off-axis secondary mirror (2) is adjusted based on the coordinate system XYZ so that the detection result of the interferometer (5) at this time, that is, the accuracy of the system wavefront error meets the requirements; Complete the installation and adjustment of the off-axis three-reflection beam expansion optical system.

2. The method for assembling and adjusting a large-field off-axis three-mirror beam expansion optical system according to claim 1, characterized in that: Step 1 specifically includes: 1.

1. Preset a straight line as the system optical axis, and establish the coordinate system XYZ with the preset system optical axis as the Z axis; 1.

2. An interferometer (5) with a standard lens is installed on a linear guide rail (6), and the linear guide rail (6) is adjusted so that its track is parallel to the Z axis. The interferometer (5) is moved along the linear guide rail (6), and the focal motion trajectory of the interferometer (5) is determined to be the system optical axis.

3. The method for assembling and adjusting a large-field off-axis three-mirror beam expansion optical system according to claim 2, characterized in that: Step 1.2 is as follows: An interferometer (5) with a standard lens is installed on a linear guide rail (6), the linear guide rail (6) is adjusted using a theodolite so that its track is parallel to the Z axis, the interferometer (5) is moved along the linear guide rail (6), and the focal motion trajectory of the interferometer (5) is determined to be the system optical axis.

4. The method for assembling and adjusting a large-field-of-view off-axis three-mirror beam expansion optical system according to claim 1, 2 or 3, characterized in that: Step 2 specifically includes: 2.

1. A self-collimating plane mirror (7) with a central hole is arranged on one side of the working end of the interferometer (5), and the focus of the interferometer (5) can pass through the central hole, and the normal of the self-collimating plane mirror (7) is adjusted to be parallel to the track direction of the linear guide rail (6); 2.

2. Pre-install an off-axis primary mirror (1) on the side of the autocollimation plane mirror (7) away from the interferometer (5), the off-axis primary mirror (1) being located on the upper side of the system optical axis, the interferometer (5) being translated along the linear guide rail (6), and the off-axis primary mirror (1) being translated and adjusted along the Z axis, X axis, and Y axis, so that the focus of the interferometer (5) coincides with the focus of the off-axis primary mirror (1); 2.

3. Adjust the rotation and tilt of the off-axis primary mirror (1) around the X-axis and the Y-axis so that the outgoing light of the interferometer (5) is reflected by the off-axis primary mirror (1) and becomes parallel light, which is vertically incident on the self-collimating plane mirror (7) and returns along the original path; 2.

4. Obtain the surface detection result of the off-axis primary mirror (1) by the interferometer (5), that is, the wavefront error of the primary mirror; if the accuracy of the wavefront error of the primary mirror does not meet the requirements, return to step 2.3 until the accuracy of the wavefront error of the primary mirror meets the requirements; the installation of the off-axis primary mirror (1) is completed.

5. The method for assembling and adjusting a large-field-of-view off-axis three-mirror beam expansion optical system according to claim 4, characterized in that: Step 2.1 is as follows: A self-collimating plane mirror (7) with a central hole is arranged on one side of the active end of the interferometer (5), and the focus of the interferometer (5) can pass through the central hole. The normal of the self-collimating plane mirror (7) is adjusted to be parallel to the linear guide rail (6) by using a theodolite.

6. The method for assembling and adjusting the large-field off-axis three-mirror beam expansion optical system according to claim 5, characterized in that: Step 3 specifically includes: 3.

1. Pre-installing an off-axis three-mirror (3) on the side of the autocollimation plane mirror (7) away from the interferometer (5), wherein the off-axis three-mirror (3) is located on the lower side of the optical axis of the system; translating the interferometer (5) along the linear guide rail (6) so that the distance between the focus of the interferometer (5) and the focus of the off-axis primary mirror (1) is a preset value, and then translating and adjusting the off-axis three-mirror (3) along the Z axis, X axis, and Y axis so that the focus of the interferometer (5) coincides with the focus of the off-axis three-mirror (3); 3.

2. Adjust the rotation and tilt of the off-axis three mirrors (3) around the X-axis and Y-axis so that the outgoing light of the interferometer (5) is transformed into parallel light after being reflected by the off-axis three mirrors (3), vertically incident on the self-collimating plane mirror (7) and returns along the original path; 3.

3. Obtain the surface detection result of the off-axis three mirrors (3) by the interferometer (5), that is, the wavefront error of the three mirrors; if the accuracy of the wavefront error of the three mirrors does not meet the requirements, return to step 3.2 until the accuracy of the wavefront error of the three mirrors meets the requirements; the installation of the off-axis three mirrors (3) is completed.

7. The method for assembling and adjusting a large-field off-axis three-mirror beam expansion optical system according to claim 6, characterized in that: Step 4 specifically includes: 4.

1. Replace the standard lens of the interferometer (5) with a plane lens, so that the parallel light emitted by it is parallel to the optical axis of the system. The interferometer (5) is translated downward along the Y axis so that the parallel light beam emitted by it is incident on the off-axis three mirrors (3); 4.

2. Pre-install the off-axis secondary mirror (2) on the side of the autocollimator (7) away from the interferometer (5), and move the autocollimator (7) upward along the Y axis so that the autocollimator (7) is located on the upper side of the system optical axis; 4.

3. Adjust the off-axis secondary mirror (2) to translate along the Z axis, X axis, and Y axis, and to rotate and tilt around the X axis and Y axis, so that the outgoing light of the interferometer (5) is reflected by the off-axis three mirrors (3), the off-axis secondary mirror (2), and the off-axis primary mirror (1) in sequence, and then becomes parallel light, vertically incident on the self-collimating plane mirror (7) and returns along the original path, thereby forming a system self-collimation detection result; 4.

4. Obtain the system self-alignment detection result of the interferometer (5), that is, the system wavefront error. If the accuracy of the system wavefront error does not meet the requirement, return to step 4.3 until the accuracy of the system wavefront error detected by the interferometer (5) meets the requirement; Complete the installation and adjustment of the off-axis three-reflection beam expansion optical system.

8. The method for assembling and adjusting a large-field-of-view off-axis three-mirror beam expansion optical system according to claim 7, characterized in that: The linear guide rail (6) is a digital display linear guide rail.

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