A high-precision detection and error decoupling method for step grating splicing angle error

Abstract

The application discloses a high-precision detection and error decoupling method for a stepped grating splicing angle error. The application adopts an optical interference measurement technology, simultaneously performs stripe detection on a low diffraction order m1 and a high diffraction order m2 of a grating under a grating Littrow detection structure, records corresponding stripe images P1 and P2, performs phase recovery algorithm calculation on the images, jointly solves through calculation of wavefront coefficients, and obtains y-direction rotation error, x-direction rotation error and z-direction rotation error. The application solves the detection difficulty caused by low energy of the 0th order beam of the stepped grating, synchronously jointly calculates wave aberration coefficients through double-order interference stripes, and realizes accurate error decoupling and accurate analysis of the stepped grating splicing.

Description

Technical Field

[0001] This invention belongs to the field of grating splicing detection technology, specifically relating to a high-precision detection and error decoupling method for stepped grating splicing angle error. Background Technology

[0002] Large-size diffraction gratings are crucial optical components in fields such as astronomical spectroscopy and laser nuclear fusion. In astronomy, with the rapid development of astronomy and further exploration of the vast universe, larger telescope apertures (D>4m) and higher spectral resolutions (R>100,000) have become essential technological means for achieving space exploration. Currently, telescope apertures can be increased to 10m or even larger. The larger the telescope aperture, the larger the required echelle grating size for high-resolution spectrometers. Theoretically, high-resolution spectrometers with resolutions exceeding 100,000 require echelle gratings larger than 1m. Given the current limitations in manufacturing single meter-sized echelle gratings, the development of splicing technology has become key to realizing the fabrication of large-size astronomical gratings.

[0003] Currently, the main methods for grating splicing and inspection include the interference fringe method and the diffraction spot method. Among them, the POLARIS grating splicing method from Germany uses the spot method, while the OMEGA-EP grating from the United States and the Pico2000 pulse compression grating splicing from France use the interference fringe method, all achieving good results. The spot method analyzes errors by testing the changes in the energy of the light spot in the grating splicing area. However, the spot method is easily affected by system aberrations and environmental disturbances, making high-precision error quantification difficult. Interferometric detection technology is mature and can accurately calculate errors, making it a commonly used basic inspection method for grating splicing.

[0004] Six-dimensional errors exist during grating stitching. While the translation error parallel to the grating lines does not affect the stitching quality, the other five errors significantly impact the diffraction wavefront. Due to the coupling compensation effect among these errors, achieving precise stitching of large-size echelle gratings for astronomical applications requires decoupling and accurate calculation of these error couplings. Traditional interferometry methods, such as coplanar adjustment via the 0th order of the grating or in-plane rotation adjustment (or grating line adjustment) via diffraction orders, are unsuitable for echelle grating stitching because the 0th order beam is too weak to detect. The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) has published a method and system for stitching medium-sized echelle gratings (patent number: 202110930520.2), which uses shearing interferometry for grating stitching. However, the small field of view of the beam interference field and the system's complexity severely limit the widespread application of this method. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of angle coupling in large-size spliced ​​gratings, making it difficult to decouple and accurately detect angle errors. This is achieved by proposing a high-precision detection and error decoupling method for stepped grating splicing angle errors, enabling precise detection and adjustment of the spliced ​​grating angles. The angle adjustment error mainly includes ∆θ. x ∆θ y ∆θ z error.

[0006] To achieve the above objectives, the present invention adopts the following specific technical solution:

[0007] A high-precision detection and error decoupling method for stepped grating splicing angle error includes the following steps:

[0008] Step 1: Install reference grating G1 and reference grating G2 on the grating clamping mechanism and fix the orientation of the gratings.

[0009] Step 2: Adjust the attitude of the interferometer. Use one or two interferometers so that half of the parallel beam from the interferometer is incident on the reference grating G1. Adjust the incident angle of the parallel beam. Through the Littrow self-collimation structure of the grating, interference fringes of low diffraction order m1 and high diffraction order m2 can be obtained. The fringe orientation (density, tilt, etc.) of the interference fringes can be adjusted through the interferometer reference mirror. The reference grating G1 is fixed and the process ends.

[0010] Step 3: Place the adjustment grating G2 into the grating splicing structure and perform coarse adjustment on the adjustment grating G2 so that the other half of the parallel beam of the interferometer is incident on the adjustment grating G2. Through the Littrow self-collimation structure, interference fringes of the adjustment grating G2 at low diffraction order m1 and high diffraction order m2 can be observed in the interferometer. There are differences in the interference fringes formed by the adjustment grating G2 and the reference grating G1 in the two orders, indicating that there is an adjustment error in the splicing system.

[0011] Step 4: Record image p1 of the reference grating G1 and adjustment grating G2 fringes obtained by the interferometer at a low diffraction order diffraction angle α1, and record image p2 of the reference grating G1 and adjustment grating G2 fringes obtained by the interferometer at a high diffraction order diffraction angle α2. Perform phase retrieval on images p1 and p2. The error information contained therein has the following relationship:

[0012]

[0013] Where λ represents the wavelength, α represents the incident angle of the grating, and β represents the diffraction angle. This indicates a phase misalignment along the propagation direction. and The wavefront phase gradient is represented by d, the grating constant is represented by Δd, the grating period error is represented by m, and the diffraction order is represented by Δθ.y For rotation about the y-axis in the tilt direction, Δθ x For rotation about the x-axis in the tilt direction, Δθ z For rotation about the z-axis in the tilt direction, Δz is the longitudinal displacement error, and Δx is the lateral displacement error;

[0014] Step 5: Based on the relationship between the grating adjustment error and optical path difference in Step 4, wavefront fitting is performed using the wavefront information obtained through phase retrieval to obtain the coefficient parameters. The wavefront fitting terms include a constant term, x-axis tilt, and y-axis tilt, and the fitting formula is: L = aX + bY + c. In the low diffraction order m1, adjusting the attitude change of grating G2 relative to the reference grating G1, the error fitting formula can be expressed as: L1 = a1X + b1Y + c1. Similarly, in the high diffraction order m2, adjusting the attitude change of grating G2 relative to the reference grating G1, the error fitting formula can be expressed as: L2 = a2X + b2Y + c2.

[0015] Step 6: Based on the phase recovery, optical path difference, and coefficient relationship of images p1 and p2 in Step 5, obtain the y-axis rotation error Δθ. y x-axis rotation error Δθ x and z-axis rotation error Δθ z as follows:

[0016]

[0017]

[0018] Step 7: Adjust the reference grating G1 and the adjustment grating G2 according to the error values ​​in the three directions obtained in Step 6.

[0019] Furthermore, an interferometer is included. The interferometer is rotated to a first preset angle α1 to record the image p1 of the current reference grating and the adjusted grating fringes; the interferometer is rotated to a second preset angle α2 to record the image p2 of the rotated reference grating and the adjusted grating fringes.

[0020] Furthermore, it includes a first interferometer and a second interferometer. The angle between the first interferometer and the stitching mechanism is a first preset angle α1. The first interferometer records an image p1 of the reference grating and the adjustment grating fringes. The angle between the second interferometer and the stitching mechanism is a second preset angle α2. The second interferometer records an image p2 of the reference grating and the adjustment grating fringes.

[0021] Furthermore, the interferometer includes a light source, a collimating lens, a beam splitter, a grating clamping mechanism, a reference mirror, and a CCD. A reference grating G1 and an adjustment grating G2 are mounted on the grating clamping mechanism. The collimating lens adjusts the light beam generated by the light source into parallel light. The parallel light is split into a transmitted beam and a reflected beam by the beam splitter. The transmitted beam illuminates the grating clamping mechanism and returns along the original path. The reflected beam is reflected by the reference mirror and forms an interference image with the returned transmitted beam. The interference image is captured by the CCD.

[0022] Furthermore, the fringe structure in images p1 and p2 consists of two parts: one part is the interference between the diffracted beam of the reference grating G1 and the beam generated by the reference mirror, which can be used as a reference fringe; the other part is the interference between the diffracted beam of the adjustment grating and the beam generated by the reference mirror. The difference between the two types of fringes indicates error information.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This invention provides a high-precision detection and error decoupling method for the splicing angle error of stepped gratings. This method utilizes Michelson interferometry, where light emitted from a light source is split into two beams by a beam splitter, each propagating along a different optical path. One beam strikes the grating clamping mechanism, returns via the grating diffraction path, passes through the beam splitter, and enters the receiver. The other beam is reflected by a mirror before striking the receiving screen. When the two beams meet again, they interfere. Therefore, this invention determines the error magnitude by measuring the optical path difference corresponding to the interference fringes. By processing high- and low-diffraction-order interference fringes and performing error fitting and decoupling calculations, the error value is quantitatively analyzed, achieving precise adjustment of the grating angle error. This invention effectively solves the problem of accurate calculation of splicing grating angle errors, enabling high-speed and high-precision detection during stepped grating splicing. Attached Figure Description

[0025] Figure 1 This is one of the schematic diagrams of the method of the present invention;

[0026] Figure 2 This is the second schematic diagram of the method of the present invention;

[0027] Figure 3 This is a schematic diagram of the five degrees of freedom between adjacent gratings in a splicing grating assembly.

[0028] Figure 4 This is an optional form of the present invention.

[0029] Figure 5 This is a schematic diagram of an interference image at one interference level according to the present invention.

[0030] The markings in the diagram are: 1. Light source; 2. Collimating lens; 3. Beam splitter; 4. Reference mirror; 5. CCD; 6. Grating clamping mechanism; 7. Reference grating G1; 8. Adjustment grating G2. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings.

[0032] Example 1

[0033] This embodiment provides a high-precision detection and error decoupling method for stepped grating splicing angle errors, which is based on, as follows: Figure 1-2 The system shown includes a light source 1, a collimating lens 2, a beam splitter 3, a reference mirror 4, a CCD 5, and a grating clamping mechanism 6. A splicing grating, including a reference grating G17 and an adjustment grating G2 8, can be mounted on the grating clamping mechanism 6. The light source 1, collimating lens 2, beam splitter 3, reference mirror 4, and CCD 5 constitute an interferometer. In this embodiment, the light source 1 is preferably a helium-neon laser with a wavelength of 632.8 nm.

[0034] Collimating lens 2 adjusts the beam generated by light source 1 into parallel light, which is then split into a transmitted beam and a reflected beam by beam splitter 3. The transmitted beam enters grating clamping mechanism 6 and returns along its original path, while the reflected beam, reflected by reference mirror, forms an interference image with the returning transmitted beam. This interference image is captured by CCD 5. By analyzing the interference image, the angular error can be obtained.

[0035] The present invention provides a high-precision detection and decoupling method for stepped grating splicing angle error, comprising the following steps:

[0036] Rotate the turntable to a low diffraction order diffraction angle α1, such as Figure 1 Record the image p1 of the two grating fringes of the image acquisition unit; rotate the turntable to a high diffraction order diffraction angle α2, as shown. Figure 2 The image p2 of the rotated fringes is recorded. In this embodiment, the low-order diffraction angle α1 is preferably a low-order Littrow angle, such as -5th order, and the high-order diffraction angle α2 is preferably a high-order Littrow angle, such as -90th order. The Littrow angle refers to the angle at which the incident light and the diffracted light are in a self-collimated state, i.e., the incident angle and the exit angle are equal. A schematic diagram of the interference image at its interference order is shown below. Figure 5 As shown.

[0037] Phase retrieval is performed on images p1 and p2, and the error information contained therein has the following relationship:

[0038]

[0039] Where λ represents the wavelength, α represents the incident angle of the grating, and β represents the diffraction angle. This indicates a phase misalignment along the propagation direction. and The phase gradient of the wavefront is represented by d, the grating constant (i.e., the distance between two grating lines) is represented by Δd, the grating groove spacing error is represented by m, and the diffraction order is represented by m, which is an integer. The coordinate axes x, y, and z are defined as follows: Figure 3 As shown, Δθ y For rotation about the y-axis in the tilt direction, Δθ x For the rotation about the x-axis and Δθ z The rotation is tilted about the z-axis, where Δz is the longitudinal displacement error and Δx is the lateral displacement error.

[0040] The fringe structure in images p1 and p2 consists of two parts. One part is the interference between the diffracted beam of the reference grating G1 and the beam generated by the reference mirror, which can be used as a reference fringe. The other part is the interference between the diffracted beam of the adjustment grating and the beam generated by the reference mirror. The difference between the two types of fringes shows error information.

[0041] In the Littrow configuration, the incident angle equals the diffraction angle, α=β. Based on Equations 1 and 2, the optical path difference ΔL between the reference grating G1 and the adjustment grating G2 with alignment error can be expressed by the following formula:

[0042]

[0043]

[0044] m is the diffraction order, x i and y i It refers to the detector grating pixels in the detected grating region. Theoretically, Δθ y Errors will cause the fringes to tilt, Δθ x and Δθ z Errors will alter the spatial period of the fringes, and errors in Δx and Δz will cause a fringes mismatch between the reference grating and the adjustment grating G2, thus resulting in Δθ in the y-direction. x and Δθ z Error coupling exists, requiring decoupling calculations. This invention only applies to Δθ. y , Δθ x and Δθ z Adjustments will be made.

[0045] Furthermore, the result can be derived by rearranging the fitting formula L=aX+bY+c:

[0046]

[0047] Furthermore, by analyzing the phase retrieval, optical path difference, and coefficient relationships between images p1 and p2, the y-axis rotation error Δθ is obtained. y x-axis rotation error Δθ x and z-axis rotation error Δθ z as follows:

[0048]

[0049]

[0050] The actuator controls the rotational error Δθ in the y-direction. y x-axis rotation error Δθ x and z-axis rotation error Δθ z Adjustments will be made.

[0051] Example 2

[0052] The detection principle of this embodiment of a high-precision detection and error decoupling method for stepped grating splicing angle error is basically the same as that of Embodiment 1. This method is based on, for example, Figure 4 The system shown comprises two sets of interferometers, namely a first interferometer and a second interferometer. Each set of interferometers includes a light source 1, a collimating lens 2, a beam splitter 3, a reference mirror 4, and a CCD 5. A plane mirror or a splicing grating can be mounted on the grating clamping mechanism 6. The splicing grating includes a reference grating G17 and an adjustment grating G28.

[0053] The first interferometer and the grating clamping mechanism form a low-diffraction order diffraction angle α1, and the second interferometer and the grating clamping mechanism form a high-diffraction order diffraction angle α2. In this embodiment, the low-diffraction order diffraction angle α1 is preferably a -5th order Littrow angle, and the high-diffraction order diffraction angle α2 is preferably a -90th order Littrow angle. At the low-diffraction order diffraction angle α1, the image p1 of the two grating fringes of the CCD of the first interferometer is recorded; at the high-diffraction order diffraction angle α2, the image p2 of the two grating fringes of the CCD of the second interferometer is recorded.

[0054] Based on images p1 and p2, perform the steps described in Example 1.

[0055] The method of this invention employs optical interferometry to simultaneously detect fringes of both the low diffraction order m1 and the high diffraction order m2 of the grating within a Littrow detection structure. The corresponding fringe images P1 and P2 are recorded, and a phase retrieval algorithm is used to calculate the images. By jointly solving for the wavefront coefficients, the y-axis rotation error, x-axis rotation error, and z-axis rotation error are obtained. This invention overcomes the detection challenge caused by the low energy of the 0th-order beam in a grating. By simultaneously and jointly calculating the wavefront aberration coefficients of the two-order interference fringes, precise error decoupling and accurate analysis of grating splicing are achieved.

[0056] In summary, this invention provides a high-precision detection and error decoupling method for the splicing angle error of a stepped grating. This method utilizes Michelson interferometry, where light emitted from the light source is split into two beams by a beam splitter, each propagating along a different optical path. One beam strikes the grating clamping mechanism, returns via the original diffraction path, passes through the beam splitter, and enters the receiver. The other beam is reflected by a mirror before striking the receiving screen. When the two beams meet again, interference occurs. Therefore, this invention determines the error magnitude by measuring the optical path difference corresponding to the interference fringes, quantitatively calculates the error value, and then calibrates the error to achieve strict adjustment of the grating angle error. This method employs optical interferometry, simultaneously detecting fringes of both the low diffraction order m1 and the high diffraction order m2 of the grating under a Littrow detection structure, and recording the corresponding fringe images P1 and P2. A phase retrieval algorithm is used to calculate the images, and the wavefront coefficients are calculated jointly to obtain the y-axis rotation error, x-axis rotation error, and z-axis rotation error. This invention overcomes the detection challenge caused by the low energy of the zero-order beam in a grating. By simultaneously calculating the wavefront aberration coefficient using two-order interference fringes, it achieves precise error decoupling and analysis in grating splicing. Addressing the challenge of zero-order detection in spliced ​​gratings, this invention obtains error information by simultaneously calculating the interference fringes of two diffraction orders. This method boasts high calculation accuracy and ease of use. Through precise processing of the interference fringes, it extracts the magnitude of the corresponding grating adjustment error, providing crucial technical support for rapid and effective angle adjustment during splicing. Furthermore, it is significant for real-time detection during and after the use of the spliced ​​grating, as well as for the accurate calculation and evaluation of wavefront errors.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-precision detection and error decoupling method for the splicing angle error of stepped gratings, characterized in that, Includes the following steps: Step 1: Install the reference grating G1 and adjust the grating G2 on the grating clamping mechanism, and fix the orientation of the grating; Step 2: Adjust the attitude of the interferometer. Use one or two interferometers so that half of the parallel beam emitted from the interferometer is incident on the reference grating G1. Adjust the incident angle of the parallel beam. Obtain the interference fringes of the reference grating G1 with low diffraction order m1 and high diffraction order m2 through the Littrow self-collimation structure of the grating. Fix the reference grating G1 to end. Step 3: Place the adjustment grating G2 into the grating splicing structure and perform coarse adjustment on the adjustment grating G2 so that the other half of the parallel beam emitted from the interferometer is incident on the adjustment grating G2. Obtain the interference fringes of the adjustment grating G2 for low diffraction order m1 and high diffraction order m2 through the Littrow self-collimation structure. There is a difference between the interference fringes formed by the adjustment grating G2 and the reference grating G1 in the two orders, indicating that there is an adjustment error in the splicing system. Step 4: Record the image p1 of the reference grating G1 and the adjustment grating G2 fringes obtained by the interferometer at a low diffraction order diffraction angle α1, and record the image p2 of the reference grating G1 and the adjustment grating G2 fringes obtained by the interferometer at a high diffraction order diffraction angle α2. Perform phase recovery on images p1 and p2. Step 5: Based on the relationship between the grating adjustment error and the optical path difference in Step 4, perform wavefront fitting using the wavefront information obtained through phase recovery to obtain the coefficient parameters; Step 6: Based on the phase recovery, optical path difference, and coefficient relationship of images p1 and p2 in Step 5, obtain the y-axis rotation error Δθ. y x-axis rotation error Δθ x and z-axis rotation error Δθ z ; Step 7: Adjust the reference grating G1 and the adjustment grating G2 according to the error values ​​in the three directions obtained in Step 6.

2. The high-precision detection and error decoupling method for stepped grating splicing angle error according to claim 1, characterized in that, In step 2, the fringe orientation of the interference fringes is adjusted using the interferometer reference mirror.

3. The high-precision detection and error decoupling method for stepped grating splicing angle error according to claim 1, characterized in that, The error information included in the phase recovery in step 4 has the following relationship: ； Where λ represents the wavelength, α represents the incident angle of the grating, and β represents the diffraction angle. This indicates a phase misalignment along the propagation direction. and The phase gradient of the wavefront is represented by d, the grating constant is represented by Δd, the grating groove spacing error is represented by m, and the diffraction order is represented by Δθ. y For rotation about the y-axis in the tilt direction, Δθ x For rotation about the x-axis in the tilt direction, Δθ z The rotation is tilted around the z-axis, where Δz is the longitudinal displacement error and Δx is the lateral displacement error.

4. The high-precision detection and error decoupling method for stepped grating splicing angle error according to claim 1, characterized in that, In step 5, the wavefront fitting term includes a constant term, x-axis tilt, and y-axis tilt, and the fitting formula is: L=aX+bY+c; In the low diffraction order m1, the attitude change of grating G2 relative to the reference grating G1 is adjusted, and its error fitting formula is expressed as: L1=a1X+b1Y+c1. Similarly, in the high diffraction order m2, the attitude change of grating G2 relative to the reference grating G1 is adjusted, and its error fitting formula can be expressed as: L2=a2X+b2Y+c2.

5. The high-precision detection and error decoupling method for stepped grating splicing angle error according to claim 1, characterized in that, In step 6, the y-axis rotation error Δθ y x-axis rotation error Δθ x and z-axis rotation error Δθ z as follows: ； 。 6. A high-precision detection and error decoupling method for stepped grating splicing angle error according to any one of claims 1 to 5, characterized in that, The interferometer includes a light source, a collimating lens, a beam splitter, a grating clamping mechanism, a reference mirror, and a CCD. The grating clamping mechanism is equipped with a reference grating G1 and an adjustment grating G2. The collimating lens adjusts the light beam generated by the light source into parallel light. The parallel light is split into a transmitted beam and a reflected beam by the beam splitter. The transmitted beam illuminates the grating clamping mechanism and returns along the original path. The reflected beam is reflected by the reference mirror and forms an interference image with the returned transmitted beam. The interference image is captured by the CCD.

7. The high-precision detection and error decoupling method for stepped grating splicing angle error according to claim 6, characterized in that, The light source is a helium-neon laser with a wavelength of 632.8nm.

8. The high-precision detection and error decoupling method for stepped grating splicing angle error according to claim 1, characterized in that, The low-order diffraction angle α1 is a Littrow angle of -5th order; the high-order diffraction angle α2 is a Littrow angle of -90th order.

9. The high-precision detection and error decoupling method for stepped grating splicing angle error according to claim 1, characterized in that, The fringe patterns in images p1 and p2 consist of two parts: one part is the interference pattern between the diffracted beam of the reference grating G1 and the beam generated by the reference mirror, and the other part is the interference pattern between the diffracted beam of the adjustment grating G2 and the beam generated by the reference mirror. The difference in the fringe patterns between the two modes indicates the misalignment error.

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