An intermediate image point-free off-axis three-mirror system alignment optical path and method

Abstract

The present application belongs to the field of precise optical machine adjustment, and relates to an off-axis three-mirror system adjustment optical path and method without intermediate image point. The adjustment optical path comprises an interferometer, a primary mirror, a secondary mirror, a third mirror, a computer holographic grating (CGH), a first flat crystal, a standard sphere and a light screen. The adjustment method requires that the primary mirror is first installed on the system frame, the positioning of the primary mirror and the third mirror is completed by cooperating with the CGH with the optical axis of the interferometer as the reference, the third mirror is then installed on the system frame, the relative position of the third mirror and the primary mirror is adjusted, the CGH is removed, the secondary mirror is installed on the multi-dimensional adjustment platform, the reference surface on the back of the secondary mirror is monitored by the interferometer, and the position of the secondary mirror in the X / Y / Z three-dimensional translation direction and the rotation around the Z axis are adjusted. After the system wavefront meets the design requirements, the secondary mirror is fixed, and the off-axis three-mirror system adjustment is completed. The off-axis three-mirror system adjustment method and the matching computer holographic grating (CGH) are provided, the technical problem of the off-axis reflection system adjustment with high freedom, long period and high difficulty without intermediate image point is solved, the adjustment efficiency is improved, and the adjustment quality is ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of precision optical machine adjustment, and relates to an off-axis three-mirror system adjustment optical path and method without intermediate image point. BACKGROUND

[0002] The off-axis reflective telescope system can realize large aperture, no obstruction, long focal length, and co-aperture, and has compact structure and image quality close to the diffraction limit. However, the off-axis reflective system has many degrees of freedom of mirror misalignment, is sensitive to position error, and is difficult to adjust. In order to reduce the adjustment difficulty, the primary mirror of some off-axis three-mirror systems adopts a parabolic surface, and the secondary mirror adopts a quadratic surface, so that the system adjustment reference can be established when the primary mirror is detected, and the primary and secondary mirrors can form a perfect image point, i.e. the intermediate image point in the system. Such a design ensures that only one of the three mirrors needs to be adjusted at the same time, thereby reducing the degrees of freedom of adjustment, but at the same time, the design freedom of the optical system is limited, and the performance index of the system is reduced.

[0003] If the off-axis three-mirror system does not require an intermediate image point, the design freedom of the optical system can be increased to achieve better performance index, but higher requirements are put forward for the adjustment accuracy. Therefore, it is urgent to propose an adjustment optical path and method to solve the above technical problems. SUMMARY

[0004] The purpose of the present application is to provide an off-axis three-mirror system adjustment optical path and method without intermediate image point, which ensures the adjustment feasibility of the off-axis three-mirror system without intermediate image point, and relaxes the design freedom of the optical system.

[0005] To achieve the above purpose, the present application provides a technical solution:

[0006] An off-axis three-mirror system adjustment optical path without intermediate image point comprises an interferometer, a primary mirror, a secondary mirror, a three-mirror, a computer generated hologram (CGH), a first flat crystal, a standard sphere, and a light screen.

[0007] The primary mirror and the three-mirror are both mounted on a system frame and placed on a multi-dimensional adjustment platform as a whole.

[0008] The secondary mirror is placed on a six-dimensional adjustment platform, and the primary and secondary mirror system has no intermediate image point.

[0009] The positioning of the primary mirror and the three-mirror is completed by the CGH in cooperation with the optical axis of the interferometer as a reference.

[0010] The first flat crystal is installed on the system frame to mark the system incident optical axis and complete the positioning of the primary mirror relative to the interferometer.

[0011] The light screen is used to receive the image point of the system during preliminary adjustment.

[0012] The standard sphere has its center at the theoretical image point of the system, measures the wavefront of the system, and is used for fine adjustment of the system.

[0013] The back surface of the secondary mirror is monitored by the interferometer, and the positions of the secondary mirror relative to the primary mirror and the tertiary mirror are adjusted to realize system assembly and adjustment.

[0014] A further technical solution of the present application is that each of the CGHs comprises:

[0015] An alignment area for realizing alignment of the CGH and the interferometer;

[0016] A primary mirror measurement ruling area and a tertiary mirror measurement ruling area for measuring the surface shapes of the primary mirror and the tertiary mirror, respectively;

[0017] A primary mirror alignment point and a tertiary mirror alignment point, the interferometer measurement light converges into two groups of positioning points after passing through the two groups of alignment points, and the two groups of positioning points are respectively coincident with the edges of the primary mirror and the tertiary mirror, and are used for preliminarily determining the positions of the mirror surfaces.

[0018] A further technical solution of the present application is that the secondary mirror and the six-dimensional adjustment table are fixed by a tooling, and there is a gap between the secondary mirror and the secondary mirror frame, which is used for adjusting the attitude of the secondary mirror and glue pouring fixation; the back surface of the secondary mirror is processed with a polished reference surface, the reference surface is perpendicular to the optical axis of the system, and the optical axis direction of the secondary mirror can be monitored through the reference surface.

[0019] A further technical solution of the present application is that the assembly and adjustment optical path further comprises a second flat crystal; the device for monitoring the back surface of the secondary mirror is a self-collimating instrument, and the second flat crystal is used for ensuring that the optical axis of the self-collimating instrument is parallel to the optical axis of the interferometer, and the angle of the self-collimating instrument is adjusted.

[0020] A further technical solution of the present application is that the primary mirror is an ellipsoidal surface, the secondary mirror is a hyperboloidal surface, and the tertiary mirror is a free-form surface, the curvature radii of the primary mirror and the tertiary mirror are close, and the included angle between the optical axes of the primary mirror and the tertiary mirror is not greater than 10°.

[0021] The present application provides another technical solution:

[0022] A method for assembling and adjusting an off-axis three-mirror system without intermediate image points, comprising the following method steps:

[0023] Step one: after the primary mirror is installed on the system frame, the primary mirror is placed on the multi-dimensional adjustment table as a whole, the interferometer is matched with the CGH lens, the position of the CGH is adjusted first to align with the interferometer, and then the position of the system frame and the primary mirror relative to the interferometer is confirmed by using the CGH;

[0024] Step two: the tertiary mirror is installed on the system frame, the position of the tertiary mirror is adjusted by using the CGH, and the positioning of the primary mirror and the tertiary mirror is completed;

[0025] Step three: remove the CGH, install the first flat crystal on the system frame, and install the interferometer parallel lens on the first flat crystal; adjust the position of the system frame to ensure that the main mirror optical axis is parallel to the interferometer optical axis, and the main mirror is covered by the interferometer parallel light; connect the secondary mirror to the six-dimensional adjustment table, move it into the optical system, use the device to monitor the back reference surface of the secondary mirror, and adjust the position of the secondary mirror in the X / Y / Z three-dimensional translation direction and the rotation around the Z axis; set up a standard spherical surface mirror at the system image point to measure the wavefront, and fix the secondary mirror after the wavefront meets the design requirements, to complete the installation and adjustment of the off-axis three-mirror system.

[0026] A further technical solution of the present application is that in step one, the process of confirming the relative position of the system frame and the main mirror is as follows: set up the CGH on the two-dimensional angle adjustment table in front of the interferometer, use the parallel lens of the interferometer, adjust the azimuth and pitch angle of the CGH, and align the CGH with the interferometer measurement light path; adjust the position of the system frame to make the convergence point of the interferometer measurement light through the main mirror alignment point on the CGH fall on the edge of the main mirror, to realize the coarse alignment of the main mirror with the interferometer; detect the surface shape of the main mirror and finely adjust the position of the system frame, to reduce the RMS value of the main mirror surface shape measurement data until it meets the design requirements, to determine that the main mirror is adjusted in place relative to the interferometer and the CGH, and fix the current position of the system frame.

[0027] A further technical solution of the present application is that in step two, the positioning process of the main mirror and the three mirrors is as follows: install the three mirrors on the system frame with screws, ensure the coarse alignment of the three mirrors with the interferometer by the machining precision of the system frame, and confirm that the three mirror positioning points of the CGH coincide with the edges of the three mirrors; detect the surface shape of the three mirrors and finely adjust the position of the three mirrors, to reduce the RMS value of the three mirror surface shape measurement data to meet the design requirements, and then fix the three mirrors to complete the positioning of the main mirror and the three mirrors.

[0028] A further technical solution of the present application is that in step three, the process of using the interferometer to monitor the secondary mirror is as follows: connect the secondary mirror to the multi-dimensional adjustment table, move it into the optical system, use the light screen to monitor the system image point, and coarsely adjust the position of the secondary mirror to make the image point on the light screen roundest; remove the light screen and set up a standard spherical surface mirror at the system imaging point; use the interferometer to monitor the back reference surface of the secondary mirror, adjust the position of the secondary mirror in the X / Y / Z three-dimensional translation direction and the rotation direction around the Z axis relative to the main mirror and the three mirrors, iteratively adjust the positions of the secondary mirror and the standard spherical surface mirror, to make the system wavefront minimum and ensure the design optical indicators; fix the secondary mirror to complete the installation and adjustment of the off-axis reflective system.

[0029] Further technical solutions of the present application are: in the step three, the process of monitoring the secondary mirror by using the autocollimator is: the interferometer covers the main mirror aperture, and the system frame position is fixed; the system image point is connected by using the light screen, the secondary mirror position is coarsely adjusted, and the image point on the light screen is the roundest; the autocollimator is arranged in front of the interferometer, and is aligned with the secondary mirror installation position; the second flat crystal is arranged in front of the interferometer, and is adjusted to be aligned with the interferometer, the interferometer measurement light path reference is transferred, the autocollimator is adjusted to be aligned with the second flat crystal; the second flat crystal is removed, and the autocollimator position is fixed; the light screen is removed, the standard spherical mirror is arranged at the system convergence point, and the system wavefront is measured by using the interferometer; the back of the secondary mirror is monitored by using the autocollimator, the azimuth and pitch angle are ensured to be unchanged, the position of the secondary mirror in the X / Y / Z three-dimensional translation direction and the angle of the secondary mirror in the roll rotation direction around the Z axis are adjusted, the standard spherical mirror position is adjusted to compensate, the system wavefront is minimized, and the designed optical index is ensured; the secondary mirror and the system frame are filled with glue to be fixed, and the system assembly and adjustment are completed.

[0030] Beneficial effects:

[0031] Compared with the prior art, the present application has the beneficial effects that:

[0032] (1) The application discloses a kind of off-axis three-mirror system assembly and adjustment light path and method without intermediate image point, and light path includes interferometer, main mirror, secondary mirror, three mirrors, computer holographic grating CGH and first flat crystal, standard ball, light screen;A piece of CGH is used to complete the surface shape measurement and positioning of main mirror and three mirrors, and the assembly and adjustment efficiency is improved.

[0033] (2) The application discloses a kind of off-axis three-mirror system assembly and adjustment light path and method without intermediate image point, by installing main mirror on system frame, confirming the position of system frame and main mirror relative to interferometer by using CGH as reference, then installing three mirrors on system frame, adjusting three mirrors to ensure the relative position of three mirrors and main mirror, finally installing secondary mirror, monitoring the back reference surface of secondary mirror by using interferometer or other alignment equipment, adjusting the position of secondary mirror in X / Y / Z three-dimensional translation direction and the angle of secondary mirror in rotation direction around Z axis, to ensure the assembly and adjustment quality.

[0034] (3) The application discloses a kind of off-axis three-mirror system assembly and adjustment light path and method without intermediate image point, laser interferometer is used, or autocollimator is used to monitor the back reference surface of secondary mirror, the position of standard spherical mirror is adjusted to compensate, to minimize the system wavefront, and ensure the designed optical index, to improve the assembly and adjustment precision. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is the light path diagram of the off-axis three-mirror system assembly and adjustment light path without intermediate image point of the present application;

[0036] Figure 2 It is the CGH schematic diagram of the off-axis three-mirror system assembly and adjustment light path without intermediate image point of the present application;

[0037] Figure 3The figure is a detection schematic diagram of the main mirror of the optical path of the intermediate image point-free off-axis three-mirror system of the present application;

[0038] Figure 4 The figure is a three-mirror assembling and adjusting schematic diagram of the optical path of the intermediate image point-free off-axis three-mirror system of the present application;

[0039] Figure 5 The figure is a secondary mirror assembling and adjusting schematic diagram of the optical path of the intermediate image point-free off-axis three-mirror system of the present application.

[0040] Explanation of reference signs:

[0041] Main mirror 1, secondary mirror 2, three-mirror 3, first flat crystal 11, second flat crystal 12, standard sphere 4, light screen 5;

[0042] Main mirror measurement line area 1A, main mirror alignment point 1P, alignment area B, three-mirror measurement line area 3C, three-mirror alignment point 3P. DETAILED DESCRIPTION

[0043] The present application will be further described in conjunction with specific embodiments, but does not constitute any limitation to the present application.

[0044] Example 1

[0045] An intermediate image point-free off-axis three-mirror system assembling and adjusting optical path, comprising an interferometer, a main mirror 1, a secondary mirror 2, a three-mirror 3, a computer holographic grating CGH, a first flat crystal 11, a standard sphere 4 and a light screen 5;

[0046] The main mirror 1 and the three-mirror 3 can be measured and positioned by a CGH. The main mirror 1 is a non-parabolic surface, and both the main mirror 1 and the three-mirror 3 are installed on a system frame and placed on a multi-dimensional adjusting table as a whole;

[0047] The secondary mirror 2 is placed on a six-dimensional adjusting table, and the main mirror and the secondary mirror system have no intermediate image point;

[0048] The positioning of the main mirror 1 and the three-mirror 3 is completed by the interferometer optical axis and the CGH;

[0049] The first flat crystal 11 is installed on the system frame, marks the system incident optical axis, and completes the positioning of the main mirror 1 relative to the interferometer with the CGH;

[0050] The light screen 5 is used to connect the system image point during preliminary assembling and adjusting;

[0051] The standard sphere 4 has its center at the system theoretical image point, measures the system wavefront, and is used for system fine adjustment;

[0052] The back of the secondary mirror 2 is monitored by the interferometer, the position of the secondary mirror 2 relative to the main mirror 1 and the three-mirror 3 is adjusted, and the system assembling and adjusting is realized.

[0053] CGH is used to confirm the position of the system frame and the primary mirror 1 and the secondary mirror 2 relative to the interferometer, and the CGH structure is shown in Figure 2 , which includes an alignment area B for realizing the alignment of the CGH and the interferometer, a primary mirror measurement scale area 1A and a three-mirror measurement scale area 3C for measuring the primary mirror 1 and the three-mirror 3 respectively, and a primary mirror alignment point 1P and a three-mirror alignment point 3P, through which the measurement light of the interferometer converges into two sets of positioning points, which are respectively coincident with the edges of the primary mirror 1 and the three-mirror 3, for determining the positions of the mirror surfaces.

[0054] The primary mirror 1 and the secondary mirror 2 are installed on the system frame, and the CGH is used to confirm the position of the system frame and the primary mirror 1 and the secondary mirror 2 relative to the interferometer. The secondary mirror 2 is installed on a multi-dimensional adjustment platform, and the secondary mirror 2 is monitored by the interferometer. The position of the secondary mirror 2 in the three-dimensional translation direction relative to the primary mirror 1 and the three-mirror 3 is adjusted. After the test conditions are met, the system is completed.

[0055] The primary mirror 1 is an ellipsoidal surface, the secondary mirror 2 is a hyperboloidal surface, and the three-mirror 3 is a free-form surface. The system optical path diagram is shown in Figure 1 . The curvature radii of the primary mirror 1 and the three-mirror 3 are close, and the included angle between the optical axes of the primary mirror and the three-mirror is not greater than 10°. The standard sphere 4 can be a standard spherical mirror.

[0056] The back surface of the secondary mirror 2 is processed with a polished reference surface, which is perpendicular to the system optical axis and can monitor the pointing direction of the optical axis of the secondary mirror 2. The secondary mirror 2 and the multi-dimensional adjustment platform are fixed by a tooling. There is a gap between the secondary mirror 2 and the secondary mirror 2 frame for adjusting the attitude of the secondary mirror 2 and pouring glue for fixing.

[0057] Embodiment 2

[0058] A no-intermediate-image-point off-axis three-mirror system adjustment optical path is provided. The same parts as in embodiment 1 are not described again. The different features from embodiment 1 are that a self-collimator is used as a device for monitoring the secondary mirror instead of an interferometer, and the adjustment optical path further includes a second flat crystal 12, which ensures that the optical axis of the self-collimator is parallel to the optical axis of the interferometer, and is used for adjusting the position and orientation of the self-collimator.

[0059] Embodiment 3

[0060] A no-intermediate-image-point off-axis three-mirror system adjustment method is provided, and the steps are as follows:

[0061] 1) First, install the primary mirror 1 on the system frame. The position of the primary mirror 1 and the system frame does not need to be adjusted, but the primary mirror 1 can be detected by the CGH to determine whether the surface profile index affects the system optical performance;

[0062] 2) A CGH is erected in front of the interferometer. The relative position of the CGH and the interferometer is determined by the alignment area of the CGH, which is used as a subsequent adjustment reference;

[0063] 3) Install the system frame (integrated with the primary mirror 1) on the multi-dimensional adjustment platform, use the primary mirror 1 positioning point to coarsely adjust the relative position of the primary mirror 1 and the CGH, and then use the primary mirror measurement scale area 1A to finely adjust the position of the primary mirror 1;

[0064] 4) Use the three-mirror 3 positioning point to coarsely adjust the relative position of the three-mirror 3 and the CGH, and then use the three-mirror measurement scale area 3C to finely adjust the position of the three-mirror 3, and then fix the three-mirror 3;

[0065] 5) Remove the CGH, connect the secondary mirror 2 to the multi-dimensional adjustment platform, move it into the optical system, use the light screen 5 to connect the system image point, coarsely adjust the position of the secondary mirror 2, and make the image point on the light screen 5 the most round;

[0066] 6) Remove the light screen 5, and set up the standard ball 4 at the system imaging point;

[0067] 7) Use the interferometer or other equipment to monitor the back of the secondary mirror 2, adjust the position of the secondary mirror 2 in the X / Y / Z three-dimensional translation direction relative to the primary mirror 1 and the three-mirror 3, iteratively adjust the position of the secondary mirror 2 and the standard ball 4, so that the system wavefront is minimized, and the designed optical indicators are ensured;

[0068] 8) Fix the secondary mirror 2, and complete the optical path adjustment of the off-axis reflective system.

[0069] Example 4

[0070] The embodiment is a kind of off-axis three-mirror system without intermediate image point adjustment method, and the adjustment method is as follows:

[0071] 1) As shown in Figure 2 , it is a schematic diagram of the CGH for the system adjustment, the CGH is set up on the two-dimensional angle adjustment platform in front of the laser interferometer, the parallel lens is used for the laser interferometer, and the azimuth and pitch angle of the CGH is adjusted to align the area with the collimation of the measurement optical path of the laser interferometer;

[0072] 2) Install the primary mirror 1 on the system frame with screws, and fix the system frame on the five-dimensional adjustment platform, and set up in front of the interferometer;

[0073] 3) Adjust the pose of the system frame, so that the convergence point of the interferometer measurement light through the primary mirror 1 alignment point on the CGH falls on the edge of the primary mirror 1, to realize the coarse alignment of the primary mirror 1 and the interferometer;

[0074] 4) As shown in Figure 3 , detect the surface shape of the primary mirror 1 and finely adjust the pose of the system frame, so that the RMS value of the primary mirror 1 surface shape measurement data is reduced until it meets the design requirements, at this time the primary mirror 1 can be determined to be adjusted in place relative to the interferometer and the CGH, and the current system frame pose is fixed;

[0075] 5) install the third mirror 3 on the system frame by screw, the system frame precision ensures the coarse alignment of the third mirror 3 and the interferometer, and confirms that the third mirror 3 positioning point of the CGH coincides with the edge of the third mirror 3;

[0076] 6) as shown in the figure, detect the third mirror 3 surface type and fine-tune the third mirror 3 position, ensure that the third mirror 3 surface type measurement data RMS value is reduced to meet the design requirements, then fix the third mirror 3, complete the positioning of the primary mirror 1 and the third mirror 3; Figure 4

[0077] 7) remove the CGH, paste the first flat crystal 11 on the system frame reference surface, adjust the system frame pose to make the first flat crystal 11 collimate with the interferometer measurement light path, and the interferometer covers the primary mirror 1 aperture, fix the system frame pose; when the CGH used is matched with the parallel light lens of the interferometer, the positioning and alignment of the primary mirror 1 and the third mirror 3 are completed, and the first flat crystal 11 can also not be set;

[0078] 8) connect the secondary mirror 2 to the multi-dimensional adjustment table, move into the optical system, and use the light screen 5 to image at the system convergence point, coarsely adjust the secondary mirror 2 position to make the light screen 5 image point roundest;

[0079] 9) set up a autocollimator in front of the interferometer to align the secondary mirror 2 installation position;

[0080] 10) set up the second flat crystal 12 in front of the interferometer and adjust its alignment with the interferometer, shift the interferometer measurement light path reference, and adjust the autocollimator to align the second flat crystal 12;

[0081] 11) remove the second flat crystal 12 and fix the autocollimator angle;

[0082] 12) remove the light screen 5, set up a standard ball 4 at the system convergence point, and measure the system wavefront by the interferometer;

[0083] 13) monitor the secondary mirror 2 back surface by the autocollimator, ensure that its azimuth and pitch angle are unchanged, adjust the secondary mirror 2 position in X / Y / Z three-dimensional translation direction and the angle of rotation around Z axis, and adjust the standard ball 4 position at the same time to compensate, so that the system wavefront is minimized and the design optical index is ensured;

[0084] 14) fill glue between the secondary mirror 2 and the system frame to fix, complete the system installation and adjustment.

[0085] Through the installation and adjustment optical path and method of the application, the technical problem of multiple free adjustment degrees in the installation and adjustment process of the off-axis three-mirror system, which cannot be adjusted by a single mirror, is solved, the installation and adjustment quality is ensured, and the installation and adjustment efficiency is improved.

[0086] ​Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that changes, modifications, substitutions and variations can be made by those skilled in the art without departing from the spirit and scope of the present application.

Claims

1. A method for assembling and adjusting the optical path of an off-axis three-mirror system without intermediate image points, characterized in that: The method includes the following steps: Step 1: After mounting the primary mirror on the system frame, place the system frame on the multi-dimensional adjustment stage, and set up the CGH on the two-dimensional angle adjustment stage in front of the interferometer. First, adjust the CGH pose to align it with the interferometer, and then use the CGH to confirm the position of the system frame and the primary mirror relative to the interferometer. Step 2: Install the three lenses on the system frame, and use CGH to adjust the position of the three lenses to complete the positioning of the primary lens and the three lenses; Step 3: Remove the CGH, install the first optical flat on the system frame, and align the interferometer's parallel light lens with the first optical flat; adjust the system frame orientation to ensure that the primary mirror's optical axis is parallel to the interferometer's optical axis, and that the primary mirror is covered by the interferometer's parallel light; connect the secondary mirror to the six-dimensional adjustment stage, move it into the optical system, use equipment to monitor the reference plane on the back of the secondary mirror, and adjust the secondary mirror's position in the X / Y / Z three-dimensional translation directions and its rotation around the Z-axis; set up a screen to coarsely adjust the secondary mirror's position so that the convergence point is the most circular; set up a standard spherical mirror at the convergence point to measure the system wavefront, and fix the secondary mirror after the wavefront meets the design requirements, completing the off-axis three-mirror system assembly and adjustment; The primary mirror is an ellipsoid, the secondary mirror is a hyperboloid, and the third mirror is a freeform surface, with the angle between the optical axes of the primary mirror and the third mirror not exceeding 10°; The CGH includes: an alignment area for aligning the CGH with the interferometer; a primary mirror measurement scribe line area and a three-mirror measurement scribe line area for measuring the primary mirror and the three-mirror surface types, respectively; a primary mirror alignment point and a three-mirror alignment point, wherein the interferometer measurement light converges into two sets of positioning points after passing through the two sets of alignment points, and the two sets of positioning points coincide with the edges of the primary mirror and the three-mirror surface, respectively, for initially determining the mirror position.

2. The method for assembling and adjusting the optical path of an off-axis three-mirror system without intermediate image points according to claim 1, characterized in that: The secondary mirror is fixed to the six-dimensional adjustment platform using tooling. There is a gap between the secondary mirror and the secondary mirror frame, which is used to adjust the posture of the secondary mirror and fix it with glue. The back of the secondary mirror is machined with a polished reference surface, which is perpendicular to the optical axis of the system and can be used to monitor the direction of the optical axis of the secondary mirror.

3. The method for assembling and adjusting the optical path of an off-axis three-mirror system without intermediate image points according to claim 1, characterized in that: The optical path also includes a second flat crystal; the device on the back of the monitoring secondary mirror is an autocollimator, and the second flat crystal is used to ensure that the optical axis of the autocollimator is parallel to the optical axis of the interferometer and to adjust the angle of the autocollimator.

4. The method for assembling and adjusting the optical path of an off-axis three-mirror system without intermediate image points according to claim 1, characterized in that: Step one includes: setting up the CGH on a two-dimensional angle adjustment stage in front of the interferometer; using a lens that matches the CGH on the interferometer; adjusting the azimuth and pitch angles of the CGH to align the CGH alignment area with the interferometer's measurement optical path; adjusting the system frame pose so that the convergence point of the interferometer's measurement light passing through the primary mirror alignment point on the CGH falls on the edge of the primary mirror, achieving coarse alignment between the primary mirror and the interferometer; detecting the primary mirror surface shape and fine-tuning the system frame pose to reduce the RMS value of the primary mirror surface shape measurement data until it meets the design requirements, confirming that the primary mirror is properly adjusted relative to the interferometer and CGH, and fixing the current system frame pose.

5. The method for assembling and adjusting the optical path of an off-axis three-mirror system without intermediate image points according to claim 1, characterized in that: In step two, the positioning process of the primary mirror and the three mirrors is as follows: the three mirrors are installed on the system frame with screws, and the machining accuracy of the system frame ensures that the three mirrors are roughly aligned with the interferometer. At the same time, it is confirmed that the positioning points of the three mirrors of the CGH coincide with the edges of the three mirrors. The surface shape of the three mirrors is detected and the position of the three mirrors is finely adjusted. After ensuring that the RMS value of the surface shape measurement data of the three mirrors is reduced to meet the design requirements, the three mirrors are fixed to complete the positioning of the primary mirror and the three mirrors.

6. The method for assembling and adjusting the optical path of an off-axis three-mirror system without intermediate image points according to claim 1, characterized in that: In step three, the process of monitoring the secondary mirror using equipment is as follows: the equipment is an autocollimator; the interferometer covers the aperture of the primary mirror to fix the system frame pose; the screen is used to connect to the convergence point to coarsely adjust the position of the secondary mirror so that the image point on the screen is the most circular; the autocollimator is set up in front of the interferometer and aligned with the installation position of the secondary mirror; a second flat crystal is set up in front of the interferometer and adjusted to be aligned with the interferometer; the interferometer's measurement optical path reference is transferred; and the autocollimator is adjusted to be aligned with the second flat crystal. Remove the second flat crystal and fix the autocollimator's position; remove the screen and set up a standard spherical mirror at the system convergence point, then use an interferometer to measure the system wavefront; monitor the back of the secondary mirror with the autocollimator to ensure its azimuth and pitch angles remain unchanged, adjust the secondary mirror's position in the X / Y / Z three-dimensional translation directions and its tumble rotation angle around the Z-axis, and simultaneously adjust the standard spherical mirror's position compensation to minimize the system wavefront while ensuring the designed optical specifications; fix the secondary mirror to the system frame with glue, completing the system assembly and adjustment.

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