A method and system for assembling a limited far point conjugate off-axis four-mirror optical system

Abstract

The application provides a precise assembling and adjusting method of a finite conjugate off-axis four-mirror optical system, which is suitable for solving the problems of the existing off-axis multi-mirror optical system assembling and adjusting method, such as difficult control of high-precision relative positions of multiple mirrors, easy generation of large aberration, and difficult calibration and correction of conjugate image points. The method first completes the assembling of the reference mirror of the off-axis multi-mirror optical system by the multi-sensing cooperative measurement and CGH common reference interference control of M2 and M4 mirrors, combines the measurement target ball to position and mark the coordinate position points of the optical system image points, uses the PSM to calibrate the ball center image position and record, and completes the precise positioning of the spherical mirror. According to the real-time detection of the wave aberration, the M3 mirror position is adjusted until the optical indicators completely meet the requirements, and the precise assembling and adjusting of the finite conjugate off-axis four-mirror optical system is completed. The method realizes the high-precision cooperative assembling and adjusting of the off-axis multi-mirror system, reduces the difficulty of assembling and integrating, and significantly improves the assembling and adjusting efficiency and the image quality control ability.

Description

Technical Field

[0001] This invention belongs to the field of optomechanical precision assembly and adjustment technology, and relates to an assembly and adjustment method and system for a finite distance object point conjugate off-axis four-reflector optical system. Background Technology

[0002] With the widespread application of high-resolution, high-precision imaging systems, off-axis four-mirror optical systems have gained significant attention in fields such as space remote sensing, high-end measurement, and astronomical observation due to their advantages, including no central obstruction, strong controllability of system aberrations, and compact structure. Especially in finite-distance conjugate imaging scenarios, these systems can balance a large field of view with high image quality, making them a core component of many high-end optical devices.

[0003] Off-axis four-mirror optical systems typically consist of multiple aspherical or freeform surface mirrors. The system has high requirements for the relative position and orientation of each mirror and low tolerance for assembly and adjustment errors.

[0004] Currently, the main assembly and adjustment methods for such complex systems include mirror-by-mirror adjustment, coaxial adjustment based on the principle of optical path refracting, and high-precision positioning methods using interferometers or laser trackers. However, in finite-distance conjugate structures, since the object image point is not located at an infinite distance outside the optical path, traditional adjustment methods cannot directly calibrate and correct the conjugate object image point of the off-axis four-reflector optical system, thus affecting the imaging quality and assembly and adjustment efficiency of the entire system.

[0005] Therefore, there is an urgent need to propose a high-precision and highly operable assembly and adjustment method suitable for finite-distance conjugate off-axis four-reflection systems. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a high-precision and highly operable assembly and adjustment method for a finite-distance conjugate off-axis four-mirror optical system, solving the challenges in precise control of the relative positions of optical elements and calibration and correction of conjugate object-image points. This method utilizes mechanical positioning technology, CGH common-reference interferometry detection technology, and the collaborative operation of multiple sensing measurement systems such as a laser tracker, PSM assembly and adjustment microscope, and theodolite to achieve high-precision collaborative assembly and adjustment of multiple mirrors, ultimately improving the system's assembly and adjustment efficiency and image quality control capabilities.

[0007] This invention is achieved through the following technical solution: A method for assembling and adjusting a finite-distance object-image point conjugate off-axis four-reflector optical system includes: Using the housing as the assembly reference, a spatial coordinate system for the housing is established, and the relative pose lock of the second reflector M2 and the fourth reflector M4 is completed based on the common reference detection optical path of CGH; wherein, the off-axis four-reflector optical system includes the housing and the first reflector M1, the second reflector M2, the third reflector M3 and the fourth reflector M4 arranged in sequence. In the spatial coordinate system of the box, the positions of the object point and image point of the off-axis four-reflector optical system are calibrated, and the spherical mirror and interferometer are positioned based on the position calibration to build the system wave aberration detection optical path; Based on the established wavefront aberration detection optical path, after completing the mechanical positioning of the first reflector M1 and the third reflector M3, the pose of the third reflector M3 is adjusted according to the real-time wavefront aberration detection results until the optical performance of the off-axis four-reflector optical system meets the standards.

[0008] Preferably, a laser tracker is used to measure the reference surface of the enclosure and establish a spatial coordinate system for the enclosure.

[0009] Preferably, the relative pose locking of the second mirror M2 and the fourth mirror M4 is achieved using a common reference detection optical path based on CGH, including: The second reflector M2 is assembled into the housing, and an interferometric detection optical path based on CGH is built. The surface shape of the second reflector M2 is made to meet the requirements by adjusting the pose of CGH and interferometer. Keeping the CGH and interferometer poses unchanged, adjust the pose of the fourth mirror M4 so that its surface shape meets the requirements.

[0010] Preferably, during the adjustment of the pose of the fourth reflector M4, a theodolite is used to monitor the angular relationship between the reference plane of the fourth reflector M4 and the reference plane of the housing to ensure that it meets the theoretical requirements.

[0011] Preferably, the spherical mirror and interferometer are positioned by calibrating the object point and image point of the off-axis four-reflector optical system, and based on the position calibration, the spherical mirror and interferometer are positioned respectively, including: The object point and image point positions of the off-axis four-reflector optical system were calibrated in the spatial coordinate system of the box using a laser tracker. At the object point location, the spherical mirror is positioned by using the PSM microscope in conjunction with the target ball of the laser tracker, so that the center of the spherical mirror coincides with the object point location; At the image point location, the interferometer is positioned by self-collimating the interferometer with the target ball of the laser tracker, so that the focal point of the interferometer coincides with the image point location; The spherical mirror and the interferometer together form the optical path for system wavelet aberration detection.

[0012] Preferably, the spherical mirror for position calibration includes: The object point position of the off-axis four-reflector optical system was calibrated in the spatial coordinate system of the box using a laser tracker. Place the laser tracker target ball at the object point location, and auto-align the PSM microscope with the laser tracker target ball to make the focal point of the PSM microscope coincide with the center of the target ball; Remove the target ball, place the spherical mirror and adjust its position so that the light spot reflected by the spherical mirror is minimized in the PSM. At this time, the center of the spherical mirror coincides with the focal point of the PSM.

[0013] Preferably, the position calibration-based positioning interferometer includes: The object point and image point of the off-axis four-reflector optical system were calibrated in the spatial coordinate system of the box using a laser tracker. A laser tracker target ball is placed at the image point position. The interferometer is auto-aligned with the target ball, so that the interference fringes on the surface of the target ball are in a zero-fringe state. At this time, the focus of the interferometer coincides with the center of the target ball.

[0014] Preferably, during the positioning of the spherical mirror and the interferometer, a theodolite is used to monitor the angular relationship between the reference plane of the spherical mirror, the reference plane of the interferometer, and the reference plane of the housing.

[0015] Preferably, adjusting the pose of the third reflecting mirror M3 based on the real-time wavelet aberration detection results includes: The first reflector M1 and the third reflector M3 were assembled into the housing using a laser tracker to meet the mechanical position tolerances. The current system wavefront aberration is detected using the established system wavefront aberration detection optical path. Based on the detected wavefront aberration data, the pose of the third reflecting mirror M3 is adjusted until the system wavefront aberration meets the final optical specifications.

[0016] An assembly and adjustment system for a finite-distance conjugate off-axis four-reflector optical system, comprising: The laser tracker is used to measure the reference plane of the box to establish the box's spatial coordinate system, and to measure the positions of each mirror group, spherical mirror, and interferometer in the box's spatial coordinate system. The CGH and interferometer are used to build a common CGH reference interferometric detection optical path for mounting and adjusting the second reflector M2 and the fourth reflector M4. The PSM microscope is used in conjunction with a laser tracker to precisely position the spherical mirror as the target sphere, ensuring that the center of the spherical mirror coincides with the position of the object point in the system. The interferometer is also used for self-collimation with the target ball of the laser tracker, positioning itself so that the focus of the interferometer coincides with the position of the system image point, and for system wave aberration detection; At least two theodolites are used to monitor the angular relationship between the reference plane of the second reflecting mirror M2, the fourth reflecting mirror M4, the spherical mirror, and the interferometer and the reference plane of the box. The off-axis four-mirror optical system includes a housing and a first mirror M1, a second mirror M2, a third mirror M3, and a fourth mirror M4 arranged sequentially.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention provides a method for assembling and adjusting a conjugate off-axis four-mirror optical system with a finite distance object-image point. It proposes using a laser tracker to establish a spatial coordinate system for the housing and measuring the relative positional relationship between the reference planes of mirrors M2 and M4 and the housing. An M2 mirror detection optical path is constructed, and the surface shape of mirror M2 is measured to determine the positions of the interferometer and CGH. The detection optical path measures the surface shape of mirror M4 and adjusts the pose of mirror M4. The pose adjustments of mirrors M2 and M4 are completed, while a theodolite monitors the angular relationship between the reference planes of mirrors M2 and M4 and the reference plane of the housing. The laser tracker is used to calibrate the positions of the system's object and image points. The laser tracker target sphere determines the interferometer position, and the PSM determines the pose of the spherical mirror. A wavelet aberration detection optical path for the system is then constructed. A laser tracker measures the positional relationship between the M1 and M3 reference planes and the housing reference plane. The system wavefront aberration detection optical path detects the system wavefront aberration, and the pose of mirror M3 is adjusted until the assembly requirements are met. This assembly and adjustment method addresses the challenges of existing off-axis multi-mirror optical system assembly and adjustment methods, such as difficulty in controlling the high-precision relative pose of multiple mirrors, the generation of large aberrations, and the calibration and correction of conjugate object points. This method first uses multi-sensor collaborative measurement and CGH common-reference interferometry to adjust mirrors M2 and M4 to complete the assembly of the reference mirrors for the off-axis multi-mirror optical system. A measurement target sphere is used to mark the coordinates of the object points in the optical system. A microscopic system (PSM) is used to calibrate and record the position of the sphere's center image, completing the precise positioning of the spherical mirror. The pose of mirror M3 is adjusted based on the real-time detected wavefront aberration until the optical parameters fully meet the requirements, thus completing the precision assembly and adjustment of the finite-distance conjugate off-axis four-mirror optical system. The method of this invention enables high-precision collaborative assembly and adjustment of off-axis multi-mirror systems, reduces the difficulty of assembly and integration, and significantly improves assembly and adjustment efficiency and image quality control capabilities. It can not only meet the system's requirements for high-precision relative positional relationships of multiple mirrors, but also efficiently achieve accurate calibration and correction of finite-distance conjugate object points, thereby improving the overall assembly and adjustment efficiency and final optical performance of the system. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the assembly of the M2 and M4 lens groups of the present invention.

[0020] Figure 2 This is a schematic diagram A of the assembly of the spherical mirror for precise positioning according to the present invention.

[0021] Figure 3 This is Schematic diagram B of the assembly for precisely positioning the spherical mirror according to the present invention.

[0022] Figure 4 This is a schematic diagram illustrating the interferometer pose adjustment for the present invention.

[0023] Figure 5 This is an assembly diagram of the optical path setup for debugging the optical system of the present invention. Detailed Implementation

[0024] 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, not all, of the embodiments of the present invention. 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. Therefore, the following detailed description of the embodiments of the present 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 present invention without inventive effort are within the scope of protection of the present invention.

[0025] A method for assembling and adjusting a finite-distance conjugate off-axis four-mirror optical system is disclosed. The off-axis four-mirror optical system includes a housing and four mirrors M1, M2, M3, and M4 arranged sequentially along the optical path. Each mirror is an aspherical or freeform surface. The object point and image point of the system are located at a finite distance, forming a finite-distance conjugate imaging relationship. This method is applicable to optical systems containing four mirrors M1, M2, M3, and M4. Precise assembly and adjustment of the optical system are achieved by constructing detection optical paths using a CGH (Conductivity, Hearing, and Gear), an interferometer, and spherical mirrors. The positional relationship between mirrors M2 and M4 and the housing is determined through common reference assembly and adjustment. A laser tracker is used to establish the spatial coordinate system of the housing, calibrating the positions of the object and image points in the global coordinate system. A theodolite and a PSM microscope are used to determine the relative positional relationship between the interferometer, spherical mirrors, and the housing, and the poses of mirrors M1 and M3 are adjusted.

[0026] Using the housing as the assembly reference, a laser tracker is used to measure the housing's reference surfaces to establish a housing spatial coordinate system. This system is used to determine the positions of each lens group and the system's object / image points within the housing spatial coordinate system during system assembly and adjustment. It also determines the relative positional relationships between the interferometer, spherical mirror, and housing during assembly. Based on the theoretical model, the theoretical positions of all lens group reference surfaces within the housing spatial coordinate system are obtained. The laser tracker measures the positions of each assembled lens group's reference surfaces in the actual assembly pose and compares them with the theoretical positions. The poses of the lens groups are adjusted until the deviations of all reference surfaces from their theoretical positions are within the assembly tolerance range. The system's object / image points are precisely calibrated within the housing spatial coordinate system, and the positions of the spherical mirror, interferometer, and housing are accurately located, ensuring precise assembly in subsequent processes.

[0027] After mechanical assembly of mirror M2, a common reference assembly optical path based on CGH and interferometer is established to measure the surface shape of mirror M2. By adjusting CGH and interferometer as a whole, the surface shape data of mirror M2 meets the requirements. A laser tracker is used to measure the position of the reference plane of mirror M2 in global coordinates to determine its relative positional relationship with the housing, ensuring it meets mechanical assembly tolerances. A common reference interferometric detection optical path based on CGH (calculated hologram generation) is established. By detecting that the surface shape data of mirror M2 meets the assembly tolerances, the relative positional relationship between the interferometer, CGH, and housing is determined. While maintaining the stable relative positional relationship between CGH, interferometer, housing, and mirror M2, the pose of mirror M4 is precisely adjusted so that the surface shape data of both M2 and M4 meet the assembly requirements. The M2 and M4 mirrors are assembled using a common reference based on CGH, ensuring that the final surface shape data of M2 and M4 meet the assembly requirements.

[0028] After completing the assembly and adjustment of mirrors M2 and M4, the conjugate object point of the system in the box space coordinate system is calibrated using a laser tracker. The position of the system object point in the box space coordinate system is then measured and calibrated using the laser tracker. The interferometer and the laser tracker target ball are auto-aligned to determine the position of the interferometer, specifically as follows: Place the laser tracker target sphere at the conjugate point, and autoalign the PSM microscope with the laser tracker target sphere, aligning the PSM focal point with the center point of the target sphere. Remove the target mount, and place and adjust the position of the spherical mirror so that the PSM light reflected back from the spherical mirror appears as a clear spot with the smallest diameter in the software. Simultaneously, use at least two theodolites to monitor the angular relationship between the spherical mirror and the reference plane of the box to ensure that the requirements are met. The conjugate image points of the system image points in the box space coordinate system are measured and calibrated using a laser tracker. A laser tracker target sphere is placed at the conjugate image point, and the interferometer is autocollimated with the target sphere so that the interferometer focus coincides with the center of the target sphere. At least two theodolites are used to measure and monitor the angular relationship between the interferometer reference plane and the box reference plane to ensure it meets theoretical requirements. The system detection optical path is then complete.

[0029] After the system detection optical path is built, a laser tracker is used to measure the positions of the reference planes of mirrors M1 and M3 in the space coordinate system of the housing, determining their relative positional relationship with the housing to ensure it meets assembly requirements. The system wavefront aberration is detected using the system detection optical path, and the pose of mirror M3 is adjusted to ensure that the final system wavefront aberration meets assembly requirements.

[0030] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 Combination Figures 1 to 4 This embodiment is described in detail. The purpose of this embodiment is to use the above-described finite-far conjugate off-axis four-reflection system for precise assembly and adjustment.

[0032] like Figure 1 The diagram shows the assembly schematic of off-axis quad-reflector mirrors M2 and M4. Reference planes B, C, and D are the reference planes of the housing's spatial coordinate system, and all assembly and adjustment positions originate from these three reference planes. A laser tracker is used to measure the housing's reference planes, establishing the housing's spatial coordinate system. Within this coordinate system, the actual positions of the reference planes of mirrors M2 and M4 are measured, and the position of mirror M2 is adjusted until the assembly tolerances are met. A common reference detection optical path based on the CGH is constructed, the surface shape of mirror M2 is measured, and the poses of the CGH and interferometer are adjusted to ensure the surface shape of mirror M2 meets the assembly requirements. Keeping the CGH and interferometer stationary, the surface shape of mirror M4 is measured, and the pose of mirror M4 is adjusted to meet the assembly requirements. Throughout this process, at least two theodolites are used to monitor the angular relationship between the housing's reference planes and the optical side surface of mirror M4, completing the assembly of mirrors M2 and M4.

[0033] like Figure 2 , Figure 3 As shown, a laser tracker was used to calibrate the position of the system's object point in the spatial coordinate system of the housing. A target sphere for the laser tracker was placed at the object point. The PSM (Precision Stress-Free Microscope) microscope was autocollimated with the target sphere until the focal point of the PSM microscope coincided with the center of the target sphere. The target sphere was then removed. A spherical mirror was placed in the light-emitting direction of the PSM. By adjusting the pose of the spherical mirror, the laser reflected by the mirror was made to produce a minimum spot size on the PSM software, coinciding with the laser spot reflected by the target sphere; that is, the center of the spherical mirror coincided with the focal point of the PSM. Simultaneously, a theodolite was used to monitor the angular relationship between the optical back of the spherical mirror and the housing's reference plane, ensuring that the angular relationship between the spherical mirror and the housing was close to the theoretical value, meaning that the relative positional relationship between the spherical mirror and the housing met the assembly tolerances.

[0034] like Figure 2 , Figure 4 , Figure 5 As shown, a laser tracker target sphere is placed at the image point location on the system housing, and an interferometer is placed at the corresponding location. The interferometer is auto-aligned with the target sphere; that is, the interference fringes on the target sphere surface show zero fringes on the interferometer software, and the positional relationship between the interferometer and the housing meets the theoretical requirements. Simultaneously, at least two theodolites are set up to mutually monitor the angular relationship between the housing reference plane and the interferometer reference plane, ensuring it meets the theoretical requirements. The optical path for wavelet aberration detection in the system is then complete.

[0035] like Figure 5 As shown, after the system wave aberration detection optical path is built, a laser tracker is used to measure the positions of the reference planes of mirrors M1 and M3 in the space coordinate system of the housing, so that their positional relationship with the housing is close to the theoretical one. The system wave aberration is detected using the system wave aberration detection optical path, and the pose of mirror M3 is adjusted according to the detected wave box aberration data until the assembly tolerance is met, thus completing the assembly and adjustment of the finite distance object point conjugate off-axis four-reflector optical system.

[0036] Example 2 Based on Embodiment 1, this embodiment provides a precision assembly and adjustment method and system for a finite-distance conjugate off-axis four-mirror optical system. The off-axis four-mirror optical system includes a housing and a first mirror M1, a second mirror M2, a third mirror M3, and a fourth mirror M4 arranged sequentially along the optical path. Each mirror is an aspherical or freeform surface. The system object point and image point are located at a finite distance, forming a finite-distance conjugate imaging relationship.

[0037] The assembly and adjustment system used in this embodiment includes: The laser tracker is used to measure the reference plane of the box to establish the box's spatial coordinate system, and to measure the positions of each mirror group, spherical mirror, and interferometer in the box's spatial coordinate system. The CGH and interferometer are used to build a common CGH reference interferometric detection optical path for mounting and adjusting the second reflector M2 and the fourth reflector M4. The PSM microscope is used in conjunction with a laser tracker to precisely position the spherical mirror as the target sphere, ensuring that the center of the spherical mirror coincides with the position of the object point in the system. The interferometer is also used for self-collimation with the target ball of the laser tracker, positioning itself so that the focus of the interferometer coincides with the position of the system image point, and for system wave aberration detection; At least two theodolites are used to monitor the angular relationship between the reference plane of the second reflecting mirror M2, the fourth reflecting mirror M4, the spherical mirror, and the interferometer and the reference plane of the box. The laser tracker, CGH, interferometer, PSM microscope, and theodolite work together to achieve a precise assembly and adjustment method for a finite-distance conjugate off-axis four-reflector optical system.

[0038] Among them, laser trackers (such as the Leica AT960) are used for high-precision three-dimensional coordinate measurement; Computationally generate a hologram (CGH) device to produce the reference wavefront required for aspherical detection; Interferometers (such as the ZYGO interferometer) are used for surface shape detection and wavelet aberration detection. PSM microscopes (point diffraction microscopes or point sensing microscopes) are used to precisely locate the center of a spherical mirror. At least two theodolites (e.g., Leica TM6100A) are used to monitor the angular relationship between the reference plane of each component and the reference plane of the box. The laser tracker target sphere (Spherically Mounted Retroreflector, SMR) serves as a physical reference point for position calibration. A spherical mirror is used as a reflective reference for the position of a system object point.

[0039] S1. Establish the spatial coordinate system of the box. like Figure 1 As shown, the housing has three precision-machined reference surfaces B, C, and D, which serve as the references for global measurements. First, a laser tracker is used to measure these three reference surfaces respectively, and a spatial coordinate system O-XYZ for the housing is established through fitting calculations. The origin and axis of this coordinate system are strictly consistent with the theoretical coordinate system in the optical design model, serving as a unified reference for the subsequent assembly, adjustment, and positioning of all lens groups and measuring equipment.

[0040] Common reference adjustment for S2, M2 and M4 lenses Initial mechanical assembly and optical path setup for testing S21 and M2 mirrors The M2 mirror is initially fixed to the housing using a flexible mounting structure. A laser tracker is used to measure the three preset reference surfaces (or reference holes) on the M2 mirror, and their actual positions are compared with those in the theoretical model. By adjusting the shims or fine-motion mechanisms, the mechanical position of the M2 mirror is made to meet the preset tolerances (e.g., translational deviation ≤ 0.05 mm, angular deviation ≤ 30″).

[0041] Subsequently, an interferometric detection optical path based on a CGH was constructed in front of the M2 mirror: the CGH was mounted on a precision adjustment frame, and the interferometer was placed behind the CGH. The poses of the CGH and the interferometer were adjusted so that the spherical wave emitted from the interferometer, after being transformed by the CGH, was incident perpendicularly onto the surface of the M2 mirror. The returning light interfered with the reference light, and clear interference fringes were observed in the interferometer software. The surface shape of the M2 mirror was measured using the interferometer, and the poses of the CGH and the interferometer were fine-tuned until the root mean square (RMS) value of the measured surface shape of the M2 mirror was better than λ / 40 (λ=632.8 nm). At the same time, the spatial positions of the CGH and the interferometer were recorded, and their invariance was ensured throughout the subsequent process.

[0042] Precision assembly and adjustment of S22 and M4 mirrors Keeping the CGH and interferometer positions fixed, initially install the M4 mirror on the housing. Use a laser tracker to measure the reference surface of the M4 mirror, ensuring its mechanical position meets tolerance requirements. Then, measure the surface shape of the M4 mirror using the same CGH interferometric optical path (at this point, the M2 mirror has been installed and adjusted, but its presence in the optical path does not affect the detection of the M4 mirror, as the CGH design focuses the detection light only on the M4 mirror). Based on the surface shape data displayed by the interferometer, adjust the pose of the M4 mirror (including tilt, eccentricity, and spacing) until its surface shape RMS value is also better than λ / 40. During the adjustment process, simultaneously use two theodolites to aim at the housing reference surface B and the optical side (or back reference surface) of the M4 mirror, respectively, monitoring the angular deviation between them in real time to ensure the M4 mirror's pose is consistent with the theoretical design and to avoid introducing additional tilt errors. At this point, the common reference installation and adjustment of the M2 and M4 mirrors is complete.

[0043] S3. Calibration of system object points and image points and positioning of reference devices S31, Object point position calibration and spherical mirror positioning (see...) Figure 2 , Figure 3 ) Based on the optical design model, the theoretical coordinates of the system object point in the box coordinate system are determined. The location of this point is then marked in the space near the box using a laser tracker, and a laser tracker target sphere (SMR) is placed at this location.

[0044] Adjust the position of the PSM microscope so that its emitted beam is aligned with the center of the target sphere. By observing the spot image in the PSM software, fine-tune the PSM to minimize and sharpen the reflected spot. At this point, the focus of the PSM precisely coincides with the center of the target sphere. Record the current spatial position of the PSM.

[0045] Remove the target ball and install the spherical mirror in the light output direction of the PSM. Observe the PSM software again and adjust the position and orientation of the spherical mirror so that the light spot reflected back to the PSM by the spherical mirror is also minimized and sharpest, and the position of this light spot coincides with the position of the light spot reflected by the target ball. At this time, the center of the spherical mirror coincides with the focal point of the PSM, that is, it coincides with the position of the system object point. During the adjustment process, use two theodolites to monitor the angular relationship between the back reference plane of the spherical mirror and the reference plane of the box, ensuring that the tilt angle of the spherical mirror meets the theoretical requirements (deviation ≤ 10″).

[0046] S32, Image point position calibration and interferometer positioning (see...) Figure 2 , Figure 4 ) Similarly, the theoretical coordinates of the system image point are determined in the box coordinate system, and the laser tracker target sphere is placed at this point. The interferometer (the same interferometer used for subsequent system wave aberration detection) is moved to the vicinity of the image point, and its pose is adjusted so that its emitted beam is aligned with the target sphere. The interference fringes formed by reflection from the target sphere surface are observed in the interferometer software, and the position of the interferometer is finely adjusted until the fringes become zero-friction (i.e., uniform brightness across the entire field with no interference fringes). At this point, the focus of the interferometer precisely coincides with the center of the target sphere, that is, it coincides with the position of the system image point.

[0047] During the adjustment process, two theodolites were used simultaneously to monitor the angular relationship between the interferometer reference plane and the box reference plane to ensure that its attitude met the theoretical requirements (deviation ≤ 10″). At this point, the two reference points at both ends of the system wave aberration detection optical path—the spherical mirror at the object point and the interferometer at the image point—were precisely positioned.

[0048] Assembly and system optimization of S4, M1 and M3 mirrors (see [link to documentation]). Figure 5 ) Initial mechanical assembly of S41, M1 and M3 mirrors The reference surfaces of mirrors M1 and M3 were measured using a laser tracker, and they were initially installed on the housing. The mechanical positions were adjusted to meet the preset tolerances (translational deviation ≤ 0.1 mm, angular deviation ≤ 1′) by adjusting the shims. At this time, the optical path of the system was not yet closed, and the precise pose of M1 and M3 needed to be guided and adjusted by subsequent wavelet aberration detection.

[0049] S42. System Waveform Aberration Detection Optical Path Setup After confirming the fixed positions of the spherical mirror at the object point and the interferometer at the image point, the entire optical system (M1, M2, M3, M4) is in the optical path. The detection light emitted from the interferometer is reflected by M4, M3, M2, and M1, then reflected back along the same path by the spherical mirror at the object point, and returns to the interferometer through the system again, forming a self-collimated detection optical path. The full-field wave aberration of the system can then be observed in the interferometer software.

[0050] S43. M3 Mirror Optimization Adjustment Based on Waveform Aberration The initial measurement of the system wavelet aberration is usually large (RMS may > λ / 10). Based on the wavelet aberration distribution map displayed by the interferometer (such as Zernike coefficients), the main aberration components (such as astigmatism, coma, spherical aberration, etc.) are analyzed to determine the degrees of freedom that need adjustment. Then, the pose (tilt, eccentricity, spacing) of the M3 mirror is fine-tuned, and the wavelet aberration is remeasured after each adjustment until the wavelet aberration RMS value is better than λ / 20 (or meets the design specifications). Since the assembly and adjustment error of the M1 mirror can be compensated for later, in this embodiment, the M1 mirror is only used for mechanical positioning, and the image quality correction is mainly carried out by the M3 mirror, because the M3 mirror is located in the middle of the optical path and is most sensitive to aberration adjustment. During the adjustment process, the reference plane of the M3 mirror can be repeatedly measured using a laser tracker to ensure that its position is still within a controllable range.

[0051] S44, Final Inspection Once the system wavefront aberrations meet the specifications, tighten all the screws securing the mirror groups, and then re-measure the final pose of each mirror group and reference device using a laser tracker and theodolite, recording and archiving the results. At this point, the precision assembly and adjustment of the finite-distance conjugate off-axis four-mirror optical system is complete.

[0052] It should be noted that this embodiment is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For example, a multi-wavelength interferometer can also be used in the CGH detection optical path to improve measurement accuracy; the number of theodolites can be increased to three depending on the site conditions to achieve three-dimensional spatial angle monitoring; the measurement target ball of the laser tracker can also be replaced with other types of cooperative targets. Any equivalent transformations, modifications or combinations based on the technical solutions described in the claims of this invention fall within the scope of protection of this invention.

[0053] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for assembling and adjusting a finite-distance object-image point conjugate off-axis four-reflector optical system, characterized in that, include: Using the housing as the assembly reference, a spatial coordinate system for the housing is established, and the relative pose lock of the second reflector M2 and the fourth reflector M4 is completed based on the common reference detection optical path of CGH; wherein, the off-axis four-reflector optical system includes the housing and the first reflector M1, the second reflector M2, the third reflector M3 and the fourth reflector M4 arranged in sequence. In the spatial coordinate system of the box, the positions of the object point and image point of the off-axis four-reflector optical system are calibrated, and the spherical mirror and interferometer are positioned based on the position calibration to build the system wave aberration detection optical path; Based on the established wavefront aberration detection optical path, after completing the mechanical positioning of the first reflector M1 and the third reflector M3, the pose of the third reflector M3 is adjusted according to the real-time wavefront aberration detection results until the optical performance of the off-axis four-reflector optical system meets the standards.

2. The assembly and adjustment method of a finite-distance object point conjugate off-axis four-reflector optical system according to claim 1, characterized in that, A laser tracker is used to measure the reference surface of the enclosure and establish the spatial coordinate system of the enclosure.

3. The assembly and adjustment method of a finite-distance object point conjugate off-axis four-reflector optical system according to claim 1, characterized in that, The relative pose locking between the second mirror M2 and the fourth mirror M4 is achieved using a common reference detection optical path based on CGH, including: The second reflector M2 is assembled into the housing, and an interferometric detection optical path based on CGH is built. The surface shape of the second reflector M2 is made to meet the requirements by adjusting the pose of CGH and interferometer. Keeping the CGH and interferometer poses unchanged, adjust the pose of the fourth mirror M4 so that its surface shape meets the requirements.

4. The assembly and adjustment method of a finite-distance object point conjugate off-axis four-reflector optical system according to claim 3, characterized in that, During the adjustment of the pose of the fourth reflector M4, a theodolite was used to monitor the angular relationship between the reference plane of the fourth reflector M4 and the reference plane of the housing to ensure that it meets the theoretical requirements.

5. The assembly and adjustment method of a finite-distance object point conjugate off-axis four-reflector optical system according to claim 1, characterized in that, By calibrating the positions of the object point and image point of the off-axis four-reflector optical system, the spherical mirror and interferometer are positioned based on the calibration, including: The object point and image point positions of the off-axis four-reflector optical system were calibrated in the spatial coordinate system of the box using a laser tracker. At the object point location, the spherical mirror is positioned by using the PSM microscope in conjunction with the target ball of the laser tracker, so that the center of the spherical mirror coincides with the object point location; At the image point location, the interferometer is positioned by self-collimating the interferometer with the target ball of the laser tracker, so that the focal point of the interferometer coincides with the image point location; The spherical mirror and the interferometer together form the optical path for system wavelet aberration detection.

6. The assembly and adjustment method of a finite-distance object point conjugate off-axis four-reflector optical system according to claim 5, characterized in that, Position-calibrated spherical mirrors include: The object point position of the off-axis four-reflector optical system was calibrated in the spatial coordinate system of the box using a laser tracker. Place the laser tracker target ball at the object point location, and auto-align the PSM microscope with the laser tracker target ball to make the focal point of the PSM microscope coincide with the center of the target ball; Remove the target ball, place the spherical mirror and adjust its position so that the light spot reflected by the spherical mirror is minimized in the PSM. At this time, the center of the spherical mirror coincides with the focal point of the PSM.

7. The assembly and adjustment method of a finite-distance object point conjugate off-axis four-reflector optical system according to claim 5, characterized in that, Position calibration-based positioning interferometers include: The object point and image point of the off-axis four-reflector optical system were calibrated in the spatial coordinate system of the box using a laser tracker. A laser tracker target ball is placed at the image point position. The interferometer is auto-aligned with the target ball, so that the interference fringes on the surface of the target ball are in a zero-fringe state. At this time, the focus of the interferometer coincides with the center of the target ball.

8. The assembly and adjustment method of a finite-distance object-image point conjugate off-axis four-reflector optical system according to claim 5, characterized in that, During the positioning of the spherical mirror and the interferometer, a theodolite is used to monitor the angular relationship between the reference plane of the spherical mirror, the reference plane of the interferometer, and the reference plane of the housing.

9. The assembly and adjustment method of a finite-distance object-image point conjugate off-axis four-reflector optical system according to claim 1, characterized in that, The adjustment of the pose of the third reflecting mirror M3 based on the real-time wavefront aberration detection results includes: The first reflector M1 and the third reflector M3 were assembled into the housing using a laser tracker to meet the mechanical position tolerances. The current system wavefront aberration is detected using the established system wavefront aberration detection optical path. Based on the detected wavefront aberration data, the pose of the third reflecting mirror M3 is adjusted until the system wavefront aberration meets the final optical specifications.

10. An assembly and adjustment system for a finite-distance conjugate off-axis four-reflector optical system, characterized in that, include: The laser tracker is used to measure the reference plane of the box to establish the box's spatial coordinate system, and to measure the positions of each mirror group, spherical mirror, and interferometer in the box's spatial coordinate system. The CGH and interferometer are used to build a common CGH reference interferometric detection optical path for mounting and adjusting the second reflector M2 and the fourth reflector M4. The PSM microscope is used in conjunction with a laser tracker to precisely position the spherical mirror as the target sphere, ensuring that the center of the spherical mirror coincides with the position of the object point in the system. The interferometer is also used for self-collimation with the target ball of the laser tracker, positioning itself so that the focus of the interferometer coincides with the position of the system image point, and for system wave aberration detection; At least two theodolites are used to monitor the angular relationship between the reference plane of the second reflecting mirror M2, the fourth reflecting mirror M4, the spherical mirror, and the interferometer and the reference plane of the box. The off-axis four-mirror optical system includes a housing and a first mirror M1, a second mirror M2, a third mirror M3, and a fourth mirror M4 arranged sequentially.

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