An off-axis four-mirror optical adjustment system and method with coaxial entrance and exit pupils.

Abstract

This invention relates to the field of optical system assembly and adjustment technology, specifically to an off-axis four-mirror optical adjustment system and method with coaxial entrance and exit pupils. By placing a laser interferometer and a standard plane mirror at the incident and exit optical paths of the off-axis four-mirror optical system with coaxial entrance and exit pupils, respectively, a detection beam is emitted by the laser interferometer. After transmission through the optical system, the beam is self-reflected by the standard plane mirror and returns to the laser interferometer along the original optical path, forming interference. This achieves precise detection and adjustment of the attitude of each lens in the off-axis four-mirror optical system. By organically integrating the detection optical path with the optical system's own optical path, a quantifiable and real-time feedback wavefront aberration adjustment platform is provided for off-axis four-mirror optical systems containing freeform surfaces. This effectively solves the technical problems of numerous degrees of freedom and difficulty in decoupling the coupling between degrees of freedom in the traditional serial assembly and adjustment mode, significantly improving assembly and adjustment efficiency and accuracy.

Description

Technical Field

[0001] This invention relates to the field of optical system assembly and adjustment technology, specifically to an off-axis four-reflector optical adjustment system and method with coaxial entrance and exit pupils. Background Technology

[0002] The spectrum of gravitational waves is a function of frequency and time. When detecting gravitational waves in space, it is necessary to achieve the transmission and reception of laser signals at a distance of more than one million kilometers. The main technical challenges are twofold: first, strong stability in space, and second, the ability to detect spatial distance changes at the picometer level. The commonly used method is to use three sets of telescope optical systems in an equilateral triangle for inter-satellite laser interferometry to achieve interferometric measurements with picometer-level accuracy. This places extremely high demands on the various performance indicators of the telescope optical systems.

[0003] An off-axis four-mirror optical system with coaxial entrance and exit pupils is one implementation of this type of afocal telescope optical system. It mainly consists of an off-axis concave parabolic mirror (M1), an off-axis convex hyperboloid mirror (M2), a freeform surface mirror (M3), and a freeform surface mirror (M4). The image plane formed by the RC system composed of mirrors M1 and M2 is not perfect. During the assembly and adjustment of this type of optical system, due to its complex structure and the presence of freeform surface elements, the traditional cascade assembly and adjustment mode results in numerous degrees of freedom variables. The coupling between these degrees of freedom is difficult to decouple, making it hard to simultaneously meet the design specifications for wave aberrations in each field of view. This severely restricts the realization of system performance and assembly and adjustment efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide an off-axis four-mirror optical adjustment system and method with coaxial entrance and exit pupils, thereby solving the technical problem of low assembly and adjustment efficiency in off-axis four-mirror optical systems with coaxial entrance and exit pupils.

[0005] The solution of the present invention to the above-mentioned technical problems is as follows: An off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils includes adjustment devices set at the incident and exit positions of the off-axis four-mirror optical system with coaxial entrance and exit pupils. The debugging device includes a laser interferometer and a standard plane mirror. The laser interferometer is used to emit a test beam, and the standard plane mirror is used to self-collimate and reflect the test beam after it has been transmitted through the off-axis four-reflector optical system with coaxial entrance and exit pupils, and to make the reflected beam return to the laser interferometer along the original optical path to form interference.

[0006] Further defining the off-axis four-mirror optical system with coaxial entrance and exit pupils, the system includes mirrors M1, M2, M3, and M4 arranged sequentially along the optical path. Mirror M1 is an off-axis concave paraboloid, and mirror M2 is an off-axis convex hyperboloid. Mirrors M1 and M2 form an RC system. The incident beam is converged by the RC system to form a primary image plane, and then collimated and contracted by mirrors M3 and M4 before exiting. The exit beam is coaxial with the incident beam.

[0007] Furthermore, the primary image plane is an imperfect image.

[0008] Further specified, the incident beam aperture is φ300mm, and the outgoing beam diameter is 5mm.

[0009] Furthermore, both the M3 and M4 mirrors are fringe Zernike polynomial freeform surfaces, and both the M3 and M4 mirrors have C4 and C5 coefficients to compensate for field curvature and astigmatism of the first-order image plane of the RC system.

[0010] Further specifying, the debugging device includes a small-aperture laser interferometer and a large-aperture standard plane mirror. The small-aperture laser interferometer is located at the exit position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M4 mirror. The large-aperture standard plane mirror is located at the incident position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M1 mirror.

[0011] Further specifying, the debugging device includes a large-aperture laser interferometer and a small-sized standard plane mirror. The large-aperture laser interferometer is located at the incident position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M1 mirror. The small-sized standard plane mirror is located at the exit position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M4 mirror.

[0012] A method for adjusting an off-axis four-lens reflex optical system with coaxial entrance and exit pupils, based on the aforementioned off-axis four-lens reflex optical system with coaxial entrance and exit pupils, includes the following steps: S1. Use the autocollimating theodolite and the large-aperture standard plane mirror for autocollimation to determine the optical axis pointing reference for the optical system assembly and adjustment; S2. Use a small-aperture laser interferometer to emit a spherical wave to the M1 mirror, so that the focal point of the spherical wave coincides with the original focal point (1) of the M1 mirror. The spherical wave is reflected by the M1 mirror and becomes a plane wave. It returns through the self-reflection path of the large-aperture standard plane mirror and enters the optical channel of the small-aperture laser interferometer to interfere with the reference light of the small-aperture laser interferometer to form interference fringes. Adjust the attitude of the M1 mirror according to the interference fringes of the small-aperture laser interferometer until the aberration of each field of view meets the requirements, and then fix the M1 mirror. The position of the original focal point (1) of the M1 mirror is used as the origin of the installation coordinate. S3. The relative spacing between mirrors M3 and M4 and their relative angle with mirror M1 are controlled by the limiting fixture. The exit pupil height is controlled by the equal-height circular hole fixture so that it is consistent with the entrance pupil height, thereby achieving coaxiality of the entrance and exit pupils and fixing mirrors M3 and M4. S4. Use a small-aperture laser interferometer to measure wavelet aberrations and adjust the attitude of the M2 mirror in real time until the wavelet aberrations of each field of view meet the requirements. Then fix the M2 mirror to complete the assembly and adjustment.

[0013] A method for adjusting an off-axis four-lens reflex optical system with coaxial entrance and exit pupils, based on the aforementioned off-axis four-lens reflex optical system with coaxial entrance and exit pupils, includes the following steps: S1. Use the autocollimating theodolite and the large-aperture standard plane mirror for autocollimation to determine the optical axis pointing reference for the optical system assembly and adjustment; S2. Use a large-aperture laser interferometer to emit a spherical wave to the M1 mirror, so that the spherical wave passes through the M1 mirror, M2 mirror, M3 mirror and M4 mirror in sequence to shrink into a small-aperture parallel beam, and after self-collimation by a small-size standard plane mirror, it returns along the original path and enters the optical channel of the large-aperture laser interferometer to interfere with the reference light of the large-aperture laser interferometer to form interference fringes. Adjust the attitude of the M1 mirror according to the interference fringes of the large-aperture laser interferometer until the aberration of each field of view meets the requirements, and then fix the M1 mirror, and use the original focal point (1) position of the M1 mirror as the origin of the installation coordinates. S3. The relative spacing between mirrors M3 and M4 and their relative angle with mirror M1 are controlled by the limiting fixture. The exit pupil height is controlled by the equal-height circular hole fixture so that it is consistent with the entrance pupil height, thereby achieving coaxiality of the entrance and exit pupils and fixing mirrors M3 and M4. S4. Use a small-aperture laser interferometer to measure wavelet aberrations and adjust the attitude of the M2 mirror in real time until the wavelet aberrations of each field of view meet the requirements. Then fix the M2 mirror to complete the assembly and adjustment.

[0014] An off-axis four-mirror telescope for space laser interferometry is assembled and adjusted using the above-mentioned off-axis four-mirror optical system with coaxial entrance and exit pupils.

[0015] The beneficial effects of this invention are as follows: 1. This invention achieves precise detection and adjustment of the attitude of each lens in an off-axis four-mirror optical system with coaxial entrance and exit pupils by placing a laser interferometer and a standard plane mirror at the entrance and exit optical paths respectively. The laser interferometer emits a detection beam, which is transmitted through the optical system and then reflected by the standard plane mirror and returns to the laser interferometer along the original optical path to form interference. By organically integrating the detection optical path with the optical system's own optical path, this invention provides a quantifiable and real-time feedback adjustment platform for off-axis four-mirror optical systems containing freeform surfaces. This effectively solves the technical problems of multiple degrees of freedom and difficulty in decoupling the coupling between degrees of freedom in the traditional serial adjustment mode, and significantly improves the adjustment efficiency and accuracy.

[0016] 2. This invention provides two debugging methods. One method places a small-aperture laser interferometer at the output end and a large-aperture standard plane mirror at the input end, utilizing the beam-shrinking characteristic to complete the wavefront aberration detection of the large-aperture beam using the small-aperture interferometer. The other method places a large-aperture laser interferometer at the input end and a small-sized standard plane mirror at the output end, utilizing the beam-expanding characteristic for detection. Both debugging methods can be flexibly selected according to actual test conditions. Both methods can provide real-time feedback of the system wavefront aberration through interference fringes. Combined with the insensitivity characteristics of the M3 and M4 mirrors, only the attitude of the M2 mirror needs to be precisely adjusted to ensure that the wavefront aberration of each field of view meets the index requirements. The assembly and adjustment process is simple and efficient, and is especially suitable for the assembly and adjustment of a high-precision off-axis four-mirror optical system for space gravitational wave detection. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the off-axis four-mirror optical system with coaxial entrance and exit pupils according to the present invention; Figure 2 This is a schematic diagram of the off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram illustrating the self-collimation of the theodolite and the standard plane mirror in this invention. Figure 4 This is a schematic diagram of the off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils in Embodiment 3 of the present invention.

[0018] In the diagram, 1. M1 mirror; 1-1. Origin focal point; 2. M2 mirror; 3. M3 mirror; 4. M4 mirror; 5. First image plane of the R / C system; 6. Coaxial circular hole fixture; 7. Large-aperture standard plane mirror; 7-1. Small-aperture standard plane mirror; 8. Small-aperture laser interferometer; 8-1. Large-aperture laser interferometer; 9. Autocollimating theodolite. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0021] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0022] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0023] The present invention provides an off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils, including adjustment devices disposed at the incident position and the exit position of the off-axis four-mirror optical system with coaxial entrance and exit pupils; The debugging device includes a laser interferometer and a standard plane mirror. The laser interferometer is used to emit a test beam, and the standard plane mirror is used to self-collimate and reflect the test beam after it has been transmitted through the off-axis four-reflector optical system with coaxial entrance and exit pupils, and to make the reflected beam return to the laser interferometer along the original optical path to form interference.

[0024] refer to Figure 1 The off-axis four-mirror optical system with coaxial entrance and exit pupils includes mirrors M11, M22, M33, and M44 arranged sequentially along the optical path. Mirror M11 is an off-axis concave paraboloid with a unique origin focal point 1-1; mirror M22 is an off-axis convex hyperboloid; mirrors M33 and M44 are both fringe Zernike polynomial freeform surfaces with no radius of curvature and only two terms, C4 and C5, to compensate for aberrations such as field curvature and astigmatism.

[0025] A parallel incident beam with an aperture of φ300mm passes through an RC system consisting of mirror M1 and mirror M2 to form a primary image plane 5, which is an imperfect image. The beam then passes through mirror M3 and mirror M4 to form a collimated and constricted parallel beam, making the outgoing beam coaxial with the incident beam. The diameter of the outgoing parallel beam is 5mm, and the magnification is 60 times.

[0026] Mirrors M3 and M4 are determined to be insensitive components based on optical system sensitivity analysis. Their impact on the overall wavefront aberration of the system is much smaller than that of mirrors M1 and M2. Therefore, mirrors M3 and M4 can be fixed first during the assembly and adjustment process. The system wavefront aberration can be calibrated simply by adjusting the attitude of mirror M2, thereby achieving effective decoupling of the assembly and adjustment degrees of freedom.

[0027] Example 1 refer to Figure 2The off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils provided in this embodiment includes an adjustment device comprising a small-aperture laser interferometer 8 and a large-aperture standard plane mirror 7. The small-aperture laser interferometer 8 is located at the exit position of the off-axis four-mirror optical system with coaxial entrance and exit pupils and faces the M4 mirror 4, while the large-aperture standard plane mirror 7 is located at the incident position of the off-axis four-mirror optical system with coaxial entrance and exit pupils and faces the M1 mirror 1.

[0028] The aperture of the small-aperture laser interferometer 8 is matched with the aperture of the system's output beam, and the aperture of the large-aperture standard plane mirror 7 is matched with the aperture of the system's incident beam, to ensure that the detection beam can completely cover the effective aperture of the optical system.

[0029] Example 2 Based on the off-axis four-lens optical adjustment system with coaxial entrance and exit pupils provided in Embodiment 1, this embodiment provides an off-axis four-lens optical adjustment method with coaxial entrance and exit pupils, including the following steps: S1. Use the autocollimating theodolite 9 and the large-aperture standard plane mirror 7 to autocollimate and determine the optical axis pointing reference for the optical system assembly and adjustment; S2. A spherical wave is emitted to mirror M1 using a small-aperture laser interferometer 8, so that the focal point of the spherical wave coincides with the original focal point 1-1 of mirror M1. The spherical wave is reflected by mirror M1 and becomes a plane wave, which returns via the collimated reflection path of the large-aperture standard plane mirror 7. It enters the optical channel of the small-aperture laser interferometer 8 and interferes with the reference light of the small-aperture laser interferometer 8 to form interference fringes. The attitude of mirror M1 is adjusted according to the interference fringes of the small-aperture laser interferometer 8 until the wave aberrations of each field of view meet the requirements. Then mirror M1 is fixed, and the position of the original focal point 1-1 of mirror M1 is used as the origin of the adjustment coordinates. S3. The relative spacing between M3 mirror 3 and M4 mirror 4 and the relative angle with M1 mirror 1 are controlled by the limiting fixture. The exit pupil height is controlled by the equal height circular hole fixture 6 so that it is consistent with the entrance pupil height, thereby realizing coaxiality of the entrance and exit pupils and fixing M3 mirror 3 and M4 mirror 4. S4. Use a small-aperture laser interferometer 8 to measure wavelet aberrations and adjust the attitude of mirror 2 in real time until the wavelet aberrations of each field of view meet the requirements. Then fix mirror 2 to complete the assembly and adjustment.

[0030] For further explanation, please refer to Figure 3 Step S1 is as follows: Place the autocollimating theodolite 9 horizontally on the ground and adjust the attitude of the large-aperture standard plane mirror 7 so that the autocollimating theodolite 9 and the large-aperture standard plane mirror 7 are completely aligned. Use the large-aperture standard plane mirror 7 as the optical axis pointing reference for the optical system assembly. The optical axis of the autocollimating theodolite 9 coincides with the normal of the large-aperture standard plane mirror 7, ensuring that the position and attitude of each lens during subsequent assembly are referenced to this optical axis, thereby guaranteeing the coaxiality of the system's entrance and exit pupils.

[0031] In step S2, by precisely aligning the spherical wave focus with the original focus 1-1, the assembly and adjustment accuracy of mirror M1 can be guaranteed to reach the diffraction limit level.

[0032] The center hole axis of the equal-height circular hole fixture 6 is collinear with the optical axis pointing reference established in step S1 to ensure that the exit pupil center and the entrance pupil center are located on the same axis.

[0033] In step S4, the parallel beam emitted by the small-aperture laser interferometer 8 is expanded into a large-aperture parallel beam by mirrors M4, M3, M2, and M1 in sequence. After self-reflection by the large-aperture standard plane mirror 7, it returns along the same path and enters the small-aperture laser interferometer 8 to interfere with the reference light, forming interference fringes for real-time monitoring of wavefront aberration. Since mirrors M3 and M4 have been fixed in step S3 and are not sensitive to system wavefront aberration, adjusting only mirror M2 is sufficient to achieve simultaneous convergence of wavefront aberrations in each field of view, fundamentally solving the problem of multi-degree-of-freedom coupling in traditional series assembly.

[0034] Example 3 refer to Figure 4 Unlike Embodiment 2, the off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils provided in this embodiment includes a large-aperture laser interferometer 8-1 and a small-size standard plane mirror 7-1. The large-aperture laser interferometer 8-1 is located at the incident position of the off-axis four-mirror optical system with coaxial entrance and exit pupils and faces the M1 mirror 1. The small-size standard plane mirror 7-1 is located at the exit position of the off-axis four-mirror optical system with coaxial entrance and exit pupils and faces the M4 mirror 4.

[0035] The aperture of the large-aperture laser interferometer 8-1 matches the aperture of the system's incident beam, allowing it to directly emit a large-aperture parallel detection beam to cover the entire incident aperture of the system. The aperture of the small-sized standard plane mirror 7-1 only needs to match the diameter of the system's output beam. It is small in size and easy to install and adjust. It is suitable for testing conditions with a large-aperture laser interferometer and can directly perform full-aperture detection of the system with a large-aperture parallel beam.

[0036] Example 4 Based on the off-axis four-lens optical adjustment system with coaxial entrance and exit pupils provided in Embodiment 3, this embodiment provides an off-axis four-lens optical adjustment method with coaxial entrance and exit pupils, including the following steps: S1. Use the autocollimating theodolite 9 and the large-aperture standard plane mirror 7 to autocollimate and determine the optical axis pointing reference for the optical system assembly and adjustment; S2. A spherical wave is emitted to mirror M1 using a large-aperture laser interferometer 8-1. The spherical wave passes sequentially through mirrors M1, M2, M3, and M4, where it is reduced to a small-aperture parallel beam. After self-collimation by a small-sized standard plane mirror 7-1, the beam returns along the same path and enters the optical channel of the large-aperture laser interferometer 8-1. It interferes with the reference light of the large-aperture laser interferometer 8-1, forming interference fringes. The attitude of mirror M1 is adjusted according to the interference fringes of the large-aperture laser interferometer 8-1 until the aberrations of each field of view meet the requirements. Then, mirror M1 is fixed, and the position of the original focal point 1-1 of mirror M1 is used as the origin of the adjustment coordinates. S3. The relative spacing between M3 mirror 3 and M4 mirror 4 and the relative angle with M1 mirror 1 are controlled by the limiting fixture. The exit pupil height is controlled by the equal height circular hole fixture 6 so that it is consistent with the entrance pupil height, thereby realizing coaxiality of the entrance and exit pupils and fixing M3 mirror 3 and M4 mirror 4. S4. Use a small-aperture laser interferometer 8 to measure wavelet aberrations and adjust the attitude of mirror 2 in real time until the wavelet aberrations of each field of view meet the requirements. Then fix mirror 2 to complete the assembly and adjustment.

[0037] To further explain, the large-aperture standard plane mirror 7 used in step S1 is only used to establish the optical axis reference, and can be removed after the optical axis reference is established.

[0038] In step S4, the parallel beam emitted by the large-aperture laser interferometer 8-1 is sequentially reduced into a small-aperture parallel beam by mirrors M1, M2, M3, and M4, and then returns along the same path after self-collimation by the small-sized standard plane mirror 7-1, forming interference fringes for real-time monitoring of wave aberrations. Based on this, the attitude of mirror M2 is adjusted so that the wave aberrations of each field of view converge to the design specifications simultaneously.

[0039] Example 5 This embodiment also provides an off-axis four-mirror telescope for space laser interferometry, which is assembled and adjusted using the off-axis four-mirror optical system with coaxial entrance and exit pupils provided in Embodiment 2 or Embodiment 4.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0041] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils, characterized in that, Including adjustment devices for the incident and exit positions of an off-axis four-reflector optical system with coaxial entrance and exit pupils; The debugging device includes a laser interferometer and a standard plane mirror. The laser interferometer is used to emit a test beam, and the standard plane mirror is used to self-collimate and reflect the test beam after it has been transmitted through the off-axis four-reflector optical system with coaxial entrance and exit pupils, and to make the reflected beam return to the laser interferometer along the original optical path to form interference.

2. The off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils according to claim 1, characterized in that, The off-axis four-mirror optical system with coaxial entrance and exit pupils includes mirrors M1 (1), M2 (2), M3 (3), and M4 (4) arranged sequentially along the optical path. Mirror M1 (1) is an off-axis concave paraboloid, and mirror M2 (2) is an off-axis convex hyperboloid. Mirrors M1 (1) and M2 (2) constitute an RC system. The incident beam is converged by the RC system to form a primary image plane (5), and then collimated and constricted by mirrors M3 (3) and M4 (4) before exiting. The exit beam is coaxial with the incident beam.

3. The off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils according to claim 2, characterized in that, The first image plane (5) is an imperfect image.

4. The off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils according to claim 2, characterized in that, The incident beam aperture is φ300mm, and the outgoing beam diameter is 5mm.

5. The off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils according to claim 2, characterized in that, Both the M3 mirror (3) and the M4 mirror (4) are fringe Zernike polynomial freeform surfaces. The M3 mirror (3) and the M4 mirror (4) have C4 and C5 coefficients to compensate for the field curvature and astigmatism of the first-order image plane of the RC system.

6. The off-axis four-reflector optical adjustment system with coaxial entrance and exit pupils according to any one of claims 2 to 4, characterized in that, The debugging device includes a small-aperture laser interferometer (8) and a large-aperture standard plane mirror (7). The small-aperture laser interferometer (8) is located at the exit position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M4 mirror (4). The large-aperture standard plane mirror (7) is located at the incident position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M1 mirror (1).

7. The off-axis four-mirror optical adjustment system with coaxial entrance and exit pupils according to any one of claims 2 to 4, characterized in that, The debugging device includes a large-aperture laser interferometer (8-1) and a small-size standard plane mirror (7-1). The large-aperture laser interferometer (8-1) is located at the incident position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M1 mirror (1). The small-size standard plane mirror (7-1) is located at the exit position of the off-axis four-reflector optical system with coaxial entrance and exit pupils and faces the M4 mirror (4).

8. A method for adjusting an off-axis four-reflector optical system with coaxial entrance and exit pupils, characterized in that, The off-axis four-reflector optical adjustment system with coaxial entrance and exit pupils as described in claim 6 includes the following steps: S1. Using the autocollimating theodolite (9) and the large-aperture standard plane mirror (7) for autocollimation, determine the optical axis pointing reference of the optical system assembly and adjustment; S2. Use the small-aperture laser interferometer (8) to send a spherical wave to the M1 mirror (1), so that the focal point of the spherical wave coincides with the original focal point (1-1) of the M1 mirror (1). The spherical wave is reflected by the M1 mirror (1) and becomes a plane wave. It returns through the quasi-reflection path of the large-aperture standard plane mirror (7) and enters the optical channel of the small-aperture laser interferometer (8) to interfere with the reference light of the small-aperture laser interferometer (8) to form interference fringes. Adjust the attitude of the M1 mirror (1) according to the interference fringes of the small-aperture laser interferometer (8) until the wave aberration of each field of view meets the requirements, and then fix the M1 mirror (1). The position of the original focal point (1-1) of the M1 mirror (1) is used as the origin of the adjustment coordinate. S3. The relative spacing between M3 mirror (3) and M4 mirror (4) and the relative angle with M1 mirror (1) are controlled by the limiting fixture. The exit pupil height is controlled by the equal height circular hole fixture (6) so that it is consistent with the entrance pupil height, thereby realizing coaxiality of the entrance and exit pupils and fixing M3 mirror (3) and M4 mirror (4). S4. Measure the wave aberration using a small-aperture laser interferometer (8), adjust the attitude of the M2 mirror (2) in real time until the wave aberration of each field of view meets the index requirements, then fix the M2 mirror (2) to complete the assembly and adjustment.

9. A method for adjusting an off-axis four-mirror optical system with coaxial entrance and exit pupils, characterized in that, The off-axis four-reflector optical adjustment system with coaxial entrance and exit pupils as described in claim 7 includes the following steps: S1. Using the autocollimating theodolite (9) and the large-aperture standard plane mirror (7) for autocollimation, determine the optical axis pointing reference of the optical system assembly and adjustment; S2. Use a large-aperture laser interferometer (8-1) to emit a spherical wave to mirror M1 (1), so that the spherical wave passes through mirror M1 (1), mirror M2 (2), mirror M3 (3) and mirror M4 (4) in sequence to be reduced into a small-aperture parallel beam. After self-reflection by a small-size standard plane mirror (7-1), it returns along the original path and enters the optical channel of the large-aperture laser interferometer (8-1) to interfere with the reference light of the large-aperture laser interferometer (8-1) to form interference fringes. Adjust the attitude of mirror M1 (1) according to the interference fringes of the large-aperture laser interferometer (8-1) until the aberration of each field of view meets the requirements, and then fix mirror M1 (1). Use the position of the original focal point (1-1) of mirror M1 (1) as the origin of the adjustment coordinate. S3. The relative spacing between M3 mirror (3) and M4 mirror (4) and the relative angle with M1 mirror (1) are controlled by the limiting fixture. The exit pupil height is controlled by the equal height circular hole fixture (6) so that it is consistent with the entrance pupil height, thereby realizing coaxiality of the entrance and exit pupils and fixing M3 mirror (3) and M4 mirror (4). S4. Measure the wave aberration using a small-aperture laser interferometer (8), adjust the attitude of the M2 mirror (2) in real time until the wave aberration of each field of view meets the index requirements, then fix the M2 mirror (2) to complete the assembly and adjustment.

10. An off-axis four-reflector telescope for space laser interferometry, characterized in that, The system is assembled and adjusted using the off-axis four-reflector optical system with coaxial entrance and exit pupils as described in claim 8 or 9.

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