A method and device for detecting relative error of curvature radius of a mosaic mirror

Abstract

The present application relates to the technical field of optical detection, in particular to a kind of splicing mirror curvature radius relative error detection method and device.The method and device principle are based on wavefront sensing technology, first according to the relative aperture of two mirrors to be measured, select the corresponding relative aperture of beam expander lens;Again, through the wavefront sensing system based on similar tyman green interferometer optical path structure with beam expander lens, the curvature radius relative error of two mirrors to be measured is detected, and the curvature radius relative error of two mirrors to be measured is obtained, the present application is combined with corresponding wavefront sensing algorithm, can realize non-contact, automation, the measurement of the relative difference of curvature radius between splicing mirror and mirror, make up the existing technology in the absence of curvature radius detection for splicing mirror, non-contact, decoupling piston error splicing mirror curvature radius relative error detection technical scheme.

Description

Technical Field

[0001] This invention relates to the field of optical inspection technology, and more specifically, to a method and apparatus for detecting the relative error of the curvature radius of a splicing mirror. Background Technology

[0002] As astronomical observations place increasing demands on telescope resolution and light-gathering capabilities, telescope apertures are gradually increasing, and the primary mirror structure is evolving from a traditional single structure to a modular structure. The consistency of the radius of curvature parameter in modular reflecting telescopes is a crucial issue affecting their imaging quality. For large-aperture modular optical systems, the reflecting mirrors form a relatively continuous reflecting surface after confocal and phase-coordinated reflection by the sub-mirrors. This requires a high degree of matching of the radii of curvature of the modular sub-mirrors to create a relatively continuous surface with consistent curvature. Typically, to achieve high-precision modularization, the radius of curvature error is required to be less than a few tens of micrometers.

[0003] Common methods for measuring the radius of curvature of large-aperture mirrors fall into two main categories: contact and non-contact methods.

[0004] The most commonly used contact-based optical curvature radius measurement method for large-aperture mirrors is the coordinate measuring machine (CMM) method, which has advantages such as high versatility and high measurement accuracy. However, contact measurement methods are prone to scratching and abrading the mirror surface. Furthermore, the accuracy and efficiency of the CMM method are affected by the shape of the mirror being measured, the measurement sampling scheme (for large-aperture modular optical systems, the number of sub-mirrors is large, resulting in low efficiency of CMM inspection; and there are limitations on the inspection aperture; if the sub-mirror has an unusual shape, such as a fan shape, the inner and outer rings are not consistent, which complicates the measurement scheme), and the measurement accuracy of the CMM itself. Its optimal measurement range is on the order of 500 mm, and it is not suitable for mirrors with larger apertures.

[0005] Non-contact optical radius of curvature measurement methods for large-aperture mirrors include spherical interferometry and laser differential confocal radius of curvature measurement. Spherical interferometry is affected by visual readings (cat's-eye image of the interferometer), and the maximum measured aperture is on the order of 200 mm. Laser differential confocal radius of curvature measurement has higher accuracy, but requires high confocal accuracy. Similarly, when there are many mirrors in a modular mirror, the focusing operation is more complicated and less efficient. Therefore, existing conventional radius of curvature measurement technologies cannot meet the goal of consistent radius of curvature detection for large-aperture modular mirrors.

[0006] For the relative detection of the curvature radius of spliced ​​mirrors, the technical literature: Lin Xudong, Chen Tao, Ming Ming, Wang Jianli, Chen Baogang, Dong Lei. Measurement of relative curvature radius of spherical spliced ​​mirrors [J] Optics and Precision Engineering, 2010, 18(1):75-82. A method for measuring the relative curvature radius of spherical sub-mirrors based on Shack-Hartmann sensor is proposed, but this method still needs to be combined with a contact-type high-precision sphere diameter meter to complete the measurement.

[0007] In summary, the limitations of the existing technology are as follows: (1) For the measurement of the radius of curvature between the spliced ​​mirrors, it is still necessary to use a contact-type high-precision sphere gauge to complete the measurement. Therefore, for the surface of the high-reflectivity film system, there is a risk of scratching the surface film system; (2) In addition, whether it is the laser differential confocal radius of curvature measurement method or the use of Shack-Hartmann sensors to confocalize the spliced ​​mirrors, the defocusing accuracy is on the order of hundreds of micrometers to tens of micrometers. It cannot detect and completely eliminate the translation between the sub-mirrors along the optical axis, that is, there is the so-called piston error during the co-phase stage of the spliced ​​mirrors. If the piston cannot be eliminated, when the relative radius of curvature deviation is measured with a sphere gauge, the sphere gauge reading is directly taken near the edge of the sub-mirror. The reading obtained is not the radius of curvature error, but the sum of the real relative radius of curvature error and the axial piston error between the sub-mirrors.

[0008]

[0009] Therefore, to accurately measure the relative radius of curvature error between the mirrors in a modular reflective mirror system, it is necessary to first perform mirror confocalization and phase synchronization. This process also eliminates larger piston errors in the sub-mirrors along the optical axis.

[0010] For the co-phase problem of mosaic mirrors, the consistency of the curvature radius of the mosaic mirrors in the fine co-phase stage is a key issue affecting the final image quality. The James Webb Telescope's technical solution for detecting the curvature radius error of sub-mirrors involves using the phase retrieval method to measure the relative curvature radius error between sub-mirrors during the fine co-phase stage (after coarse co-phase) and adjusting it using a curvature radius adjustment device. This adjustment reduces the curvature radius error from 0.15 mm to the 10 μm range. Summary of the Invention

[0011] This invention provides a method and apparatus for detecting the relative error of the curvature radius of a splicing mirror, thereby at least solving the technical problem that there is no existing non-contact, decoupled piston error-based technology for detecting the relative error of the curvature radius of a splicing mirror.

[0012] According to an embodiment of the present invention, a method for detecting the relative error of the curvature radius of a splicing mirror is provided. The principle is based on wavefront sensing technology and includes the following steps:

[0013] Select a beam expander lens with a corresponding relative aperture based on the relative apertures of the two mirrors under test;

[0014] A wavefront sensing system based on a similar optical path structure to a Thyman Green interferometer, coupled with a beam expander lens, is used to detect the relative error of the curvature radius of two mirrors under test, thereby obtaining the relative error of the curvature radius of the two mirrors under test.

[0015] Furthermore, a wavefront sensing system based on a similar optical path structure to a Thyman Green interferometer, coupled with a beam expander, is used to detect the relative error of the curvature radii of the two mirrors under test. The relative error of the curvature radii of the two mirrors under test is obtained as follows:

[0016] Sensor calibration: Insert the test optical path shield and cut out the calibration optical path shield. Use a laser light source and a white light source to calibrate the system's detector, respectively.

[0017] Coarse alignment of the test optical path: Cut out the test optical path light shield and cut in the calibration optical path light shield. Use a laser light source and a large field of view coarse confocal camera to align the stitching mirror. If there is no image point in the field of view, use the corresponding image point search algorithm to search for the image point of the test optical path. Then complete the image point recognition and automatic alignment of the test optical path.

[0018] Coarse confocal: After the image points of the two mirrors under test appear in the coarse confocal camera, the corresponding motion control mechanism is adjusted according to the corresponding algorithm to adjust the displacement along the optical axis to start coarse confocalization of the image points;

[0019] Precision confocal: The Shaker-Hartmann wavefront sensing system is used in conjunction with different working modes of the light shield to detect the tilt aberration and defocus aberration of the two mirrors under test, and the aberration is adjusted by the motion control mechanism.

[0020] Coarse co-phase: The axial relative error between the two mirrors under test is detected by a coarse co-phase error detection system in conjunction with a wavefront sensing method based on dispersive fringe images, and adjusted by a high-precision motion control mechanism.

[0021] Precise co-phase - relative error detection of radius of curvature: The relative defocusing aberration of the two mirrors under test is detected by a precise co-phase error detection system in conjunction with the corresponding phase difference method and phase recovery method, and the relative error of radius of curvature is output.

[0022] According to another embodiment of the present invention, a device for detecting the relative error of the curvature radius of a splicing mirror is provided, comprising: a relative error detection system for the curvature radius based on wavefront sensing technology, and a wavefront feedback motion control system; wherein:

[0023] First, two mirrors to be tested are installed on the wavefront feedback motion control system. The curvature radius relative error detection system selects a beam expander lens with the corresponding relative aperture according to the relative aperture of the two mirrors to be tested, and uses the beam expander lens to detect the relative error of the curvature radius of the two mirrors to be tested, thereby obtaining the relative error of the curvature radius of the two mirrors to be tested.

[0024] Furthermore, the device also includes a test optical path length adjustment frame that adjusts the test optical path length according to the different radii of curvature of the reflectors.

[0025] Furthermore, firstly, two mirrors under test are installed on the wavefront feedback motion control system. Then, based on the relative aperture of the mirrors under test, a beam expander with an appropriate F# number is selected for the curvature radius relative error detection system. Then, based on wavefront sensing technology, coarse confocalization, fine confocalization, coarse co-phase, and fine co-phase are performed on the two mirrors under test. After that, the curvature radius relative error detection is completed, and finally the curvature radius error is output.

[0026] Furthermore, the relative error detection system for radius of curvature includes: a coarse confocal error detection system, a fine confocal error detection system, a coarse co-phase error detection system, and a fine co-phase error detection system, which respectively perform coarse confocal, fine confocal, coarse co-phase, and fine co-phase detection on the two mirrors under test based on wavefront sensing technology.

[0027] Furthermore, the coarse confocal error detection system, the fine confocal error detection system, the coarse co-phase error detection system, and the fine co-phase error detection system are composed of detectors and corresponding motion control mechanisms to form a unit closed-loop detection and motion control, thereby realizing the unit function.

[0028] A storage medium storing a program file capable of implementing any of the above-mentioned methods for detecting the relative error of the curvature radius of spliced ​​mirrors.

[0029] A processor for running a program, wherein the program executes any of the above-mentioned methods for detecting the relative error of the curvature radius of a splicing mirror.

[0030] The method and apparatus for detecting the relative error of the curvature radius of a splicing mirror in this invention first selects a beam expander lens with a corresponding relative aperture based on the relative aperture of the two mirrors under test; then, a wavefront sensing system based on an optical path structure similar to a Thyman Green interferometer, coupled with the beam expander lens, is used to detect the relative error of the curvature radius of the two mirrors under test, thereby obtaining the relative error of the curvature radius of the two mirrors under test. This invention, combined with a corresponding algorithm, can realize non-contact, automated, and inter-mirror curvature radius relative measurement of splicing mirrors, making up for the lack of a non-contact, decoupled piston error splicing mirror curvature radius relative error detection technology in the prior art. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0032] Figure 1 This is a flowchart of the error detection process for the curvature radius mirror of the splicing mirror according to the present invention;

[0033] Figure 2 This is a flowchart illustrating the operation of the relative error detection system for the radius of curvature of this invention.

[0034] Figure 3 This is a functional control block diagram of the relative error detection system for the radius of curvature of the present invention;

[0035] Figure 4 This is a schematic diagram of the optical path of the radius of curvature detection device of the present invention.

[0036] Figure 5 This is a schematic diagram of the relative error detection system for curvature radius of the present invention used to detect the relative error of the curvature radius of the sub-mirrors in a primary mirror spliced ​​telescope system;

[0037] Figure 6 This diagram illustrates an arrangement of the dispersive Hartmann sensor, a key cophase element in the curvature radius relative error detection system of the present invention, used to detect the relative error of the curvature radius of a sub-mirror in a primary mirror spliced ​​telescope system. Detailed Implementation

[0038] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0039] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0040] Example 1

[0041] To address the shortcomings of existing technologies, such as contact-based detection and coupling of relative error detection results with piston error, this invention aims to propose a non-contact, piston-error-decoupled scheme for detecting the relative error of the pure radius of curvature between sub-mirrors in splicing mirrors. This invention also designs a non-contact, piston-error-decoupled method and apparatus for detecting the relative error of the radius of curvature of splicing mirrors.

[0042] For a spliced ​​mirror system, the focus is not on the tolerance of the actual optical reflective surface radius of curvature relative to the design value, but on the consistency of the error between the radius of curvature of each sub-mirror and the ideal design parameters. Therefore, the focus is not on accurately measuring the radius of curvature parameter, but on accurately measuring the relative radius of curvature error of each sub-mirror. That is, assuming there are N sub-mirrors to be processed, which will be combined into a spliced ​​mirror, or a composite aperture mirror. One sub-mirror has already been processed and serves as a reference with a known radius of curvature. The next step is to measure the relative radius of curvature error of the other N-1 sub-mirrors relative to the first sub-mirror to obtain the true value of the radius of curvature of all sub-mirrors.

[0043] This invention designs a scheme for detecting the relative error of the curvature radius of spliced ​​mirrors based on wavefront sensing technology. This scheme, combined with corresponding algorithms, can achieve non-contact, automated measurement of the relative curvature radius between spliced ​​mirrors. The basic content of this invention is described as follows:

[0044] The relative error detection device for the curvature radius of a mosaic mirror based on wavefront sensing technology is divided into four parts according to its modularity: a relative error detection system for the curvature radius based on wavefront sensing technology, or simply a wavefront detection system; a high-precision motion control platform with a large range of motion, called a wavefront feedback motion control system, or sample stage; two mosaic sub-mirrors whose curvature radius error is to be measured, called the mirror group under test; and a test optical path length adjustment frame that adjusts the test optical path length according to the different curvature radii of the mirrors.

[0045] The detection of curvature radius error in splicing mirrors is based on wavefront sensing technology and comprises four functional units: coarse confocal, fine confocal, coarse co-phase, and fine co-phase. The corresponding device is divided into four subsystems, each consisting of a detector and a corresponding motion control mechanism to achieve unit closed-loop detection and motion control, realizing the unit function. To minimize the interference of confocal and coarse co-phase errors in the relative curvature radius detection values, the first three functional units are used; therefore, the relative curvature radius error detection is completed in the fourth functional unit.

[0046] First, two mirrors (sub-mirrors) are installed on the sample stage. Then, based on the relative apertures of the mirrors under test, a beam expander with an appropriate F# number is selected for the curvature radius relative error detection system. Next, the most crucial step involves using wavefront sensing technology to perform coarse confocalization, fine confocalization, coarse co-phase detection, and fine co-phase detection on the two sub-mirrors. After this, the curvature radius relative error is detected, and finally, the curvature radius error is output. If the test involves the adjustment function of the curvature radius adjustment mechanism, closed-loop detection and adjustment can be achieved.

[0047] Since this method is used to detect the error of the horizontal curvature radius of the machining process, the detection range does not need to be very large. Usually, based on the existing machining level, the detection range is on the order of 0.15mm.

[0048] The present invention is as follows Figure 1 The process for detecting the relative error of the curvature radius of the splicing mirror is shown below:

[0049] Step 1: Install the sub-mirror of a spliced ​​reflector with the relative error of the radius of curvature to be tested on the sample stage, i.e., the high-precision motion control platform with a large range of motion.

[0050] Step 2: Select a beam expander with a suitable relative aperture based on the ratio of the radius of curvature to the aperture of the mirror under test.

[0051] Step 3: Run the relative error detection system for the curvature radius of the splicing mirror;

[0052] Step 4: Provide the relative error of the curvature radii of the two sub-mirrors;

[0053] The workflow of the relative error detection system for curvature radius is as follows: Figure 2 As shown, the description is as follows:

[0054] Step 1: Sensor Calibration

[0055] Cut into the test optical path shield and cut out the calibration optical path shield. Use a laser light source and a white light source to calibrate the system detector. During the calibration process, cut into different phase delay plates to generate general optical path phase delay, in preparation for subsequent detection of coarse co-phase error using template matching method.

[0056] Step 2: Coarse alignment test of the optical path

[0057] Cut out the test optical path light shield and cut in the calibration optical path light shield. Use a laser light source and a large field of view coarse confocal camera to align the stitching mirror. If there is no image point in the field of view, use the corresponding image point search algorithm to search for the image point of the test optical path. Then complete the image point recognition and automatic alignment of the test optical path.

[0058] Step 3: Coarse Confocal

[0059] After the image points of the two mirrors appear in the coarse confocal camera, the corresponding motion control mechanism is adjusted according to the corresponding algorithm to start the coarse confocalization of the image points, thereby eliminating large tilt aberrations and large defocus aberrations.

[0060] Step 4: Fine confocalization

[0061] The small tilt aberration and small defocus aberration of the two mirrors are detected by using a fine confocal Shaker-Hartmann wavefront sensing system in conjunction with different working modes of the light shield, and adjusted by a motion control mechanism.

[0062] Step 5: Rough Cophase

[0063] The axial relative error between the two mirrors is detected by a coarse co-phase error detection system combined with a wavefront sensing method based on dispersive fringe images, and adjusted by a high-precision motion control mechanism.

[0064] Step 6: Precise Cophase - Relative Error Detection of Radius of Curvature

[0065] A fine co-phase error detection system is used in conjunction with corresponding phase difference and phase recovery methods to detect the relative defocus aberration of the two mirrors as the output of the relative error of the radius of curvature.

[0066] The functional control block diagram of the present invention is as follows: Figure 3 As shown, the description is as follows:

[0067] An industrial control computer serves as the central control unit, controlling light source switching, optical path switching (including switching the working mode of the light-shielding plate and switching the phase delayer used for reference optical path calibration), data acquisition and processing of various sensors, high-precision motion mechanism movement, and large-range motion mechanism movement. A laser light source is used as the working light source for the coarse and fine confocal and fine cophase sensors, while a broadband white light source is used as the working light source for the coarse cophase sensor. The industrial control computer controls the filter wheel in the coarse cophase sensor to detect different curvature radius error ranges at different wavelengths. The industrial control computer controls the defocusing movement of the detector in the fine cophase sensor to obtain images with different defocus amounts required by the algorithm. The large-range motion mechanism executes the motion parameters output by the coarse and fine two-stage confocal systems, and the high-precision motion mechanism executes the motion parameters output by the coarse and fine cophase systems. Finally, the relative error of the curvature radius of the two mirrors is output through the fine cophase sensor.

[0068] The working principle of the relative error detection system for radius of curvature is as follows: Figure 4 The principle optical path diagram of the radius of curvature detection device is shown. The system, with a modular structure, is divided into the overall wavefront detection system, the mirror group under test, the wavefront feedback motion control system, and the test optical path length adjustment system; among which... Figure 4 The marking is shown as:

[0069] 1. The first light source, the laser light source, is used to emit narrow-band light waves for quick installation and alignment of the lens group under test;

[0070] 2. Second light source, a broadband light source with tunable bandwidth, whose function is to emit broadband light waves;

[0071] 3. Pinhole filter, point light source incident;

[0072] 4. Achromatic collimating lens, which collimates the spherical wave emitted by a point light source into a plane wave for emission;

[0073] 5. A semi-transparent and semi-reflective beam splitter 1 is used to reflect part of the incident light and transmit the other part out.

[0074] 6. Beam blocking plate 1, used to switch the working mode of the reference (calibration) optical path, has four working modes: full blockage with no light transmission, left half of the optical path blocked with right half of the optical path open, right half of the optical path blocked with left half of the optical path open, and no blockage with full light transmission.

[0075] 7. Reference mirror, used as a reference mirror for back-end unit calibration;

[0076] 8. Beam shield 2 is used to switch the working mode of the test optical path. It has four working modes: full blockage with no light passing through, left half of the optical path blocked and right half of the optical path open, right half of the optical path blocked and left half of the optical path open, and no blockage with full light passing through. Working modes 2 and 3 are required when the fine confocal sensor is working.

[0077] 9. Beam expander group: converts the collimated beam into a spherical wave output. For mirrors under test with different radii of curvature, beam expander groups with different relative apertures are selected in order to maximize the illumination of the full aperture of the mirror group under test and obtain more return light.

[0078] 10. Phase delay wheel, used to generate half of the optical path phase delay. The delay phase is divided into multiple levels, which can be set according to the reference optical path calibration requirements.

[0079] 11. First aperture mask, used to standardize the entrance pupil of beams from mirrors of different shapes and apertures;

[0080] 12. A semi-transparent and semi-reflective beam splitter 2 reflects part of the beam to the fine co-phase detection unit and transmits part of the beam to the coarse confocal detection unit;

[0081] 13. Achromatic imaging lens group 1, used for imaging of the coarse confocal detection unit;

[0082] 14. Large target area detector 1, used to receive coarse confocal images;

[0083] 15. A semi-transparent and semi-reflective beam splitter 2 reflects part of the beam to the fine confocal detection unit and transmits part to other detection units;

[0084] 16. Achromatic beam shrinking lens group 1, which reduces the collimated beam by a certain ratio to concentrate light energy;

[0085] 17. Shack-Hartmann sensor, used in the wavefront confocal detection unit for fine confocal detection;

[0086] 18. A semi-transparent and semi-reflective beam splitter 3 is used to send half of the beam returned from the reference or test optical path into other detection units and half into the coarse co-phase detection unit.

[0087] 19. Filters, select different bands to match the corresponding radius of curvature to be measured range;

[0088] 20. Achromatic beam shrinking lens group 2, which shrinks the collimated beam according to a certain ratio to concentrate light energy;

[0089] 21. Second aperture stop mask, used to standardize the entrance pupil shape of the two-beam interference;

[0090] 22. Dispersive elements, including but not limited to gratings, prisms, and prism grids, may be selected as dispersive elements to ensure that the center wavelength of visible light is emitted without deviation.

[0091] 23. Achromatic imaging lens group 2, used for imaging the dispersive fringe sensor in the coarse co-phase detection unit;

[0092] 24. Large target area detector 2, including but not limited to CMOS and CCD detectors, for receiving coarse co-phase images;

[0093] 25. Achromatic imaging lens group 3, used for imaging the fine cophase detection unit;

[0094] 26. Small target surface detectors, including but not limited to CMOS and CCD detectors, are used to receive fine co-phase images;

[0095] 27. The wavefront detection system of the entire relative error detection device of curvature radius includes a light source, a switching element, and four sensing systems. The system is made into a closed box, and the switching device is controlled by an electric mechanism to perform the switching motion.

[0096] 28. A spherical reflecting mirror with a known radius of curvature;

[0097] 29. A spherical reflecting mirror with radius of curvature to be measured;

[0098] 30. A high-precision, wide-range motion mechanism serves as both a mirror mounting platform and a motion feedback unit for the wavefront detection system.

[0099] 31. Six-degree-of-freedom electric displacement platform;

[0100] 32. Piezoelectric ceramic actuator;

[0101] 33. Test optical path length adjustment frame, used to adjust the length of the test optical path for different radii of curvature of the mirror under test.

[0102] The system is functionally divided into four parts: collimation optical path, reference optical path, test optical path, and wavefront sensing optical path. The system structure is modeled after the optical path of a Thyman-Green interferometer. The collimation optical path converts the spherical wave from the point source into a plane wave for emission. The reference optical path calibrates the wavefront sensing optical path using aberration-free plane waves. The test optical path emits spherical waves to illuminate the two spliced ​​mirrors. The wavefront sensing optical path is used for wavefront sensing and confocal / phase co-positioning of the two spliced ​​mirrors (including relative error detection of curvature radius), comprising four parts: coarse confocal, fine confocal, coarse co-phase, and fine co-phase. In this system, the coarse confocal optical path is equipped with corresponding image point search, edge detection, and centroid algorithms to form a coarse confocal detection system; the fine confocal optical path is equipped with a Shaker-Hartmann sensor to form a fine confocal detection system; the coarse co-phase optical path is equipped with a co-phase error detection method based on dispersive fringe images to form a coarse co-phase detection system; and the fine co-phase optical path is equipped with phase difference and phase recovery methods to form a fine co-phase detection system. After the first three subsystems complete the detection and adjustment (i.e., elimination) of confocal error and piston error, this step performs the detection of the relative error of the curvature radius of the clean splicing mirror.

[0103] The system's working principle is described as follows:

[0104] A first light source 1, a laser light source, is used for rapid installation and alignment of the mirror assembly under test (two spliced ​​reflectors). A second light source 2, a bandwidth-tunable broadband light source, is used as the test light source and the working light source for the wavefront sensing optical path. The two light sources are switched by a switching device, and both pass through a pinhole filter 3 as point light sources entering the optical system. After passing through an achromatic collimator 4, the spherical waves emitted by the point light sources are collimated into plane waves for exit. After passing through a semi-transparent and semi-reflective beam splitter 5, a portion of the incident light is reflected to the reference optical path, and then enters the wavefront sensing optical path through a reference reflector 7. A beam shield 6 is used to cut in and out of the reference optical path in the system. When the reference optical path is needed to work, the shield is cut out in the optical path; when the reference optical path is not needed to work, the shield is cut in the optical path. The phase delayer 10 works in the reference optical path, and the phase delayer does not work when switching to the test optical path. The function of the reference optical path, including the phase delayer 10, is to calibrate the four wavefront sensors.

[0105] The semi-transparent and semi-reflective beam splitter 5 transmits the other half of the collimated beam out of the system. After passing through the beam expander group 9, the collimated beam is converted into a spherical wave for emission. For mirrors under test with different radii of curvature, the beam expander group 9 with different relative apertures can be selected to maximize the full aperture illumination of the mirror group under test and obtain more return light. The beam shield 8 is used to cut in and out of the test optical path. When the test optical path needs to work, the shield is cut out in the optical path; when the test optical path does not need to work, the shield is cut in the optical path. After passing through the beam expander group 9, the beam is reflected back to the system by the spherical reflector 28 with a known radius of curvature and the spherical reflector 29 with a radius of curvature to be measured. The reflectors 28 and 29 are mounted on the high-precision large-range motion mechanism reflector mounting platform 30. Among them, 31 is a large-range six-degree-of-freedom electric displacement platform and 32 is a high-precision piezoelectric ceramic actuator. The test optical path length of the reflectors with different radii of curvature is adjusted by adjusting the test optical path length adjustment frame.

[0106] The beam returning to the test optical path system is shaped by the first aperture mask 11 to standardize the entrance pupil of the beams from the test mirrors of different shapes and apertures before entering the wavefront sensing optical path. First, it passes through the semi-transparent and semi-reflective beam splitter 12, which reflects part of the beam to the coarse confocal detection unit and transmits part to the subsequent detection unit. The beam reflected to the coarse confocal detection unit passes through the large field-of-view achromatic imaging lens group 13 and is imaged on the coarse confocal detector 14.

[0107] The beam transmitted to the subsequent detection unit then passes through a semi-transparent and semi-reflective beam splitter 15, reflecting part of the beam to the fine confocal detection unit and transmitting part to the subsequent detection unit. The fine confocal detection unit is equipped with an achromatic beam shrinker group 16, which shrinks the collimated beam according to a certain ratio to concentrate the light energy, and a Shack-Hartmann sensor 17 is placed at the exit pupil position for wavefront fine confocal detection of the lens group under test.

[0108] The beam transmitted to the subsequent detection unit passes again through a semi-transparent, semi-reflective beam splitter 18, with half reflected into the coarse co-phase detection unit and the other half transmitted into the subsequent detection unit. The beam reflected into the coarse co-phase detection unit passes through a broadband filter 19, which is a group of filters with different bandwidths controlled by a rotating wheel. The rotating wheel switches between different operating bands to match the corresponding radius of curvature error measurement range. It then passes through an achromatic beam shrinker group 20, which shrinks the collimated beam according to a certain ratio to concentrate the light energy. A second aperture stop mask 21 is placed at the exit pupil position to standardize the entrance pupil shape of the double-beam interference and enhance the diffraction effect. After passing through the aperture... The beam from the radial aperture mask continues to pass through the dispersive element 22 to disperse the diffraction spots of different working wavelengths. The dispersive element includes, but is not limited to, gratings, prisms, and prism grids. In order to ensure that the center wavelength of visible light is emitted without deviation, a prism grid can be selected as the dispersive element. Then, an achromatic imaging mirror group 23 is added for imaging the dispersive fringe sensor in the coarse cophase detection unit. Then, it passes through a large target detector 24, including but not limited to CMOS and CCD detectors, to receive the coarse cophase image. The elements 21-24 in the coarse cophase detection unit are called dispersive fringe sensors.

[0109] The beam entering the subsequent detection unit passes through the achromatic imaging lens group 25 and the detector 26 (including but not limited to CMOS and CCD detectors) to form a fine co-phase detection unit. The detector 26 can move back and forth in focus to form in-focus and out-of-focus images required by the algorithm. After the first three beam splitting paths have completed the corresponding co-focus and coarse co-phase detection and adjustment, this step is used to detect the curvature radius error of the stitching mirror.

[0110] Compared with the prior art, the advantages of the present invention are as follows:

[0111] This invention designs a method and device for detecting the relative error of the curvature radius of spliced ​​mirrors based on a wavefront sensing system. Combined with corresponding algorithms, this invention can achieve accurate measurement of the curvature radius error between spliced ​​mirrors in a non-contact, automated manner.

[0112] Implementing the embodiments of the present invention has the following three beneficial effects:

[0113] (i) Improved testing efficiency: When testing a large number of mirrors with the same radius of curvature design value, it is only necessary to test the radius of curvature error of one sub-mirror. Then, by using the technical solution given by the example device in this method to test the relative radius of curvature error, the true value of the radius of curvature of all the sub-mirrors to be tested can be obtained.

[0114] (ii) Non-contact measurement: Because the present invention is combined with the corresponding algorithm, the curvature radius error can be detected as a wavefront aberration. The design of the present invention does not require the use of a direct contact detection device, such as a sphere diameter meter, to complete the detection of the relative error of the curvature radius of the two mirrors.

[0115] (III) High confocal accuracy: In fact, this invention is based on a curvature radius detection device after co-phase detection, which has higher accuracy than detection based on fine confocal methods. The detection results do not have systematic errors and can completely eliminate piston errors. Existing technologies detect curvature radius errors of splicing mirrors but fail to eliminate coarse co-phase errors between the splicing mirrors, i.e., piston errors along the optical axis. This results in the piston error along the optical axis being present in the curvature radius error reading of the junction edge of the two splicing mirrors by the spherical diameter meter. This is calibrated by wavefront sensing, which is achieved in the coarse co-phase detection stage and can be eliminated with the help of a corresponding motion platform. Therefore, it can be regarded as a systematic error.

[0116] The modified design, alternative solutions and other uses of this invention are as follows:

[0117] (a) This invention can also be used for error detection of the curvature radius adjustment device:

[0118] This invention can not only measure the curvature radius error between pre-fabricated and assembled sub-mirrors, but also detect curvature inconsistencies among multiple mirrors with the same curvature. Furthermore, with corresponding algorithms, it can also perform closed-loop detection and verification of the adjustment function and accuracy of the mirror curvature radius adjustment mechanism. Closed-loop motion control is achieved through a large-range motion control platform and high-precision piezoelectric ceramic actuators, achieving curvature radius detection accuracy on the order of tens of nanometers.

[0119] (ii) With slight modifications and the addition of some plane mirrors and rotating mechanisms, this invention can detect the relative error of the curvature radius of each sub-mirror in a primary mirror splicing telescope system;

[0120] like Figure 5 The diagram illustrates a system for detecting the relative error of the radius of curvature of sub-mirrors in a primary mirror-mounted telescope system. Figure 5 The annotations in the attached figures are explained as follows:

[0121] 1. The wavefront detection system of the entire relative error detection device for the radius of curvature includes a light source, a switching element, and four sensing systems, which is equivalent to... Figure 4 27 in the middle;

[0122] 2. Beam expander group: For primary mirror splicing telescope systems with different relative apertures, beam expander groups with different relative apertures are selected. This is to maximize the illumination of the tested mirror group across the entire aperture and obtain more reflected light, which is equivalent to... Figure 4 9 in the middle;

[0123] 3. Optical path folding mirror of the telescope system;

[0124] 4. The three mirrors of the primary mirror splicing telescope system;

[0125] 5. Secondary mirror of the telescope system;

[0126] 6. For the spliced ​​primary mirror of the telescope system, the radius of curvature of each sub-mirror must be consistent. The relative error of the relative radius of curvature between the sub-mirrors needs to be detected by device 1 in conjunction with appropriate device 2.

[0127] 7. A wide-range, high-precision six-degree-of-freedom motion control mechanism for each sub-mirror;

[0128] 8. A plane mirror with tilt angle adjustment capability, used to return the plane light wave emitted from the radius of curvature detection device and exiting the telescope system along its original path;

[0129] 9. The plane mirror rotation mechanism is used to rotate and align the splicing areas of different sub-apertures.

[0130] Figure 5 The specific principle is described as follows:

[0131] Laser and broadband light sources are emitted from the wavefront detection system 1 of the entire curvature radius relative error detection device, pass through the beam expander group 2, and are incident on the optical path folding mirror 3 of the telescope system. They then pass through the three mirrors 4 and secondary mirrors 5 of the telescope system, and are reflected onto the telescope primary mirror 6, which is composed of numerous sub-mirrors. Each sub-mirror of the primary mirror is controlled by a large-range, high-precision six-degree-of-freedom motion control system 7. The reflected light from the primary mirror continues to propagate forward to the plane mirror 8 and returns along the original path. The plane mirror can cover the splicing area of ​​the three sub-mirrors. There is also a plane mirror rotation mechanism, which can cover different projection areas of the primary mirror by rotating the plane reflective environment. The unequal-arm rotating plane mirror completes the detection of the curvature radius error of the inner and outer three layers of sub-mirrors in one revolution. A reasonable curvature radius relative error detection link between sub-mirrors is established to measure the curvature radius relative error of all sub-mirrors.

[0132] To further improve the detection efficiency of the relative curvature radius error detection device, some components can be replaced. For example, the dispersive fringe sensor in the coarse co-phase error detection system can be replaced with a dispersive Hartmann sensor. The working principle remains the same; the only difference is that the two-aperture mask is replaced with a multi-aperture mask arranged in the selected area of ​​the diffractor aperture, along with an array of micro-elements in the corresponding dispersion directions. For example... Figure 6 The image shows an example of the arrangement of a dispersive Hartmann sensor in a three-sub-mirror spliced ​​telescope. Figure 6 The annotations in the attached figures are explained as follows:

[0133] 1-3, the first, second, and third spliced ​​mirrors;

[0134] 4-6. Selection area for confocal and fine co-phase aperture of the first, second, and third splicing mirrors;

[0135] 7-9. The aperture diffraction selection regions between the three sub-mirrors, where the rectangular gray-scale gradient from light to dark represents the dispersion direction of the dispersive element.

[0136] Example 2

[0137] A storage medium storing a program file capable of implementing any of the above-mentioned methods for detecting the relative error of the curvature radius of spliced ​​mirrors.

[0138] Example 3

[0139] A processor for running a program, wherein the program executes any of the above-mentioned methods for detecting the relative error of the curvature radius of a splicing mirror.

[0140] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0141] In the above embodiments of the present invention, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0142] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. The system embodiments described above are merely illustrative; for example, the division of units can be a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection of units or modules may be electrical or other forms.

[0143] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0144] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0145] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0146] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for detecting the relative error of the curvature radius of a spliced ​​mirror, based on wavefront sensing technology, characterized in that... Includes the following steps: Select a beam expander lens with a corresponding relative aperture based on the relative apertures of the two mirrors under test; A wavefront sensing system, constructed with reference to the optical path structure of a Thyman Green interferometer, is used in conjunction with a beam expander to detect the relative error of the curvature radius of two mirrors under test, thereby obtaining the relative error of the curvature radius of the two mirrors under test. The wavefront sensing system is structured with reference to the optical path of a Thyman Green interferometer, and is divided into four parts: a collimating optical path, a reference optical path, a test optical path, and a wavefront sensing optical path. The collimating optical path is used to convert the spherical wave from the point source into a plane wave for emission. The reference optical path is used to calibrate the wavefront sensing optical path with an aberration-free plane wave. The test optical path is used to emit a spherical wave to illuminate the two mirrors under test. The wavefront sensing optical path is used to perform wavefront sensing confocal and phase-coordinated operation and relative error detection of curvature radius on the two mirrors under test. The wavefront sensing confocal and cophase operation and the relative error detection of the radius of curvature include four steps in sequence: coarse confocal, fine confocal, coarse cophase, and fine cophase-relative error detection of the radius of curvature. After the confocal error and piston error of the two mirrors under test are detected and adjusted in the first three steps, the relative error of the radius of curvature of the two mirrors under test is obtained by detecting the fine cophase step.

2. The method for detecting the relative error of the curvature radius of spliced ​​mirrors according to claim 1, characterized in that, The wavefront sensing system, constructed using a reference optical path structure of a Thyman-Green interferometer, and in conjunction with a beam expander lens, detects the relative error of the curvature radii of two mirrors under test, thereby obtaining the relative error of the curvature radii of the two mirrors under test. Specifically, the system includes the following steps: Sensor calibration: Insert the test optical path shield and cut out the calibration optical path shield. Use a laser light source and a white light source to calibrate the system's detector, respectively. Coarse alignment of the test optical path: Cut out the test optical path light shield and cut in the calibration optical path light shield. Use a laser light source and a large field of view coarse confocal camera to align the stitching mirror. If there is no image point in the field of view, use the corresponding image point search algorithm to search for the image point of the test optical path. Then complete the image point recognition and automatic alignment of the test optical path. Coarse confocal: After the image points of the two mirrors under test appear in the coarse confocal camera, the displacement of the corresponding motion control mechanism along the optical axis is adjusted according to the centroid algorithm to perform coarse confocal imaging. Precision confocalization: using Shaker The Hartmann sensor-based fine confocal detection system, in conjunction with different working modes of the light-shielding plate, detects the tilt aberration and defocus aberration of the two mirrors under test, and adjusts and corrects them through a motion control mechanism. Coarse co-phase: A coarse co-phase detection system based on a co-phase error detection method using dispersive fringe images is used to detect the axial piston error of the two mirrors under test, and the error is adjusted and corrected by a high-precision motion control mechanism. Precise Co-phase - Relative Error Detection of Radius of Curvature: Based on the phase difference method and the phase retrieval method, the precise co-phase detection system detects the relative defocus aberration of two mirrors under test and outputs it as the relative error of radius of curvature.

3. A device for detecting the relative error of the curvature radius of a spliced ​​mirror, characterized in that, include: A curvature radius relative error detection system and a wavefront feedback motion control system based on wavefront sensing technology were constructed, referencing the optical path structure of a Thyman Green interferometer; wherein: The relative error detection system for the radius of curvature is structured with reference to the optical path of a Thyman Green interferometer, and is divided into four parts: a collimating optical path, a reference optical path, a test optical path, and a wavefront sensing optical path. The collimating optical path is used to convert the spherical wave from the point source into a plane wave for emission. The reference optical path is used to calibrate the wavefront sensing optical path with an aberration-free plane wave. The test optical path is used to emit a spherical wave to illuminate the two mirrors under test. The wavefront sensing optical path includes a coarse confocal error detection system, a fine confocal error detection system, a coarse co-phase error detection system, and a fine co-phase error detection system, which are used to perform coarse confocal, fine confocal, coarse co-phase, and fine co-phase operations on the two mirrors under test, respectively. The wavefront feedback motion control system is used to mount two mirrors under test and adjust the pose of the two mirrors under test according to the detection results of the relative error detection system of the radius of curvature. The curvature radius relative error detection system is used to select a beam expander lens with a corresponding relative aperture based on the relative aperture of the two mirrors under test, and to detect the two mirrors under test in conjunction with the beam expander lens. After the coarse confocal, fine confocal, and coarse cophase operations are completed to detect and adjust the confocal error and piston error of the two mirrors under test, the relative error of the curvature radius of the two mirrors under test is detected by the fine cophase error detection system.

4. The splicing mirror curvature radius relative error detection device according to claim 3, characterized in that, The device also includes a test optical path length adjustment frame for adjusting the test optical path length according to different radii of curvature of the reflectors.

5. The splicing mirror curvature radius relative error detection device according to claim 3, characterized in that, First, two mirrors to be tested are installed on the wavefront feedback motion control system. Then, based on the relative aperture of the mirrors to be tested, a beam expander with an appropriate F# number is selected for the relative error detection system of the radius of curvature. Then, based on wavefront sensing technology, coarse confocalization, fine confocalization, coarse co-phase, and fine co-phase are performed on the two mirrors to be tested. After that, the relative error detection of the radius of curvature is completed, and finally the radius of curvature error is output.

6. The splicing mirror curvature radius relative error detection device according to claim 5, characterized in that, The relative error detection system for the radius of curvature includes: a coarse confocal error detection system, a fine confocal error detection system, a coarse co-phase error detection system, and a fine co-phase error detection system, which respectively perform coarse confocal, fine confocal, coarse co-phase, and fine co-phase detection on the two mirrors under test based on wavefront sensing technology.

7. The splicing mirror curvature radius relative error detection device according to claim 6, characterized in that, The coarse confocal error detection system, fine confocal error detection system, coarse co-phase error detection system, and fine co-phase error detection system are composed of detectors and corresponding motion control mechanisms to achieve unit closed-loop detection and motion control, realizing unit functions.

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