Surface shape detection method of large curvature X-ray optical element based on near-field speckle

Abstract

The present invention discloses a method for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle. The method obtains image data of speckle pattern A, speckle pattern B and speckle pattern C respectively through different optical path layouts; performs DIC operation between speckle pattern A and speckle pattern B to obtain the wavefront distribution of the incident light; generates a reference image based on speckle pattern A, the wavefront of the incident light and the ideal model of the optical element to be measured by using optical simulation technology; performs DIC operation between the reference image and speckle pattern C to obtain the surface shape error of the optical element to be measured; synthesizes the ideal model of the optical element to be measured and the surface shape error to obtain the actual surface shape of the optical element to be measured. The present invention predicts the severe deformation of the speckle produced by the large curvature optical element based on the near-field speckle propagation theory and the ideal surface shape of the optical element, and then deducts this severe deformation to accurately measure the surface shape error. By synthesizing the ideal surface shape and the surface shape error, the actual surface shape of the large curvature X-ray optical element can be detected.

Description

Technical Field

[0001] The present invention relates to the technical field of optical element surface shape detection, and in particular to a large-curvature X-ray optical element surface shape detection method based on near-field speckle. Background Art

[0002] The foothold of existing near-field speckle wavefront detection technology is that the shape and size of the speckle pattern do not change during propagation. The reference image is obtained by directly taking pictures with the detector. While it is convenient and portable, it also limits the effective use range of the reference image. For example, in the detection of large-curvature optical components, the effective information of the directly measured reference image is obliterated and cannot be used. When the optical element to be measured is a thin lens or a plane mirror, the impact on the speckle pattern can be ignored. At this time, the speckle displacement caused by the surface shape error is the main phenomenon and can be used to detect the surface shape. When the surface curvature of the optical element to be measured is large (corresponding to a small surface curvature radius), the surface shape will cause the speckle pattern to change significantly, making it impossible to distinguish the required speckle displacement information. Therefore, a surface shape detection method for large-curvature X-ray optical elements based on near-field speckle is needed. Summary of the invention

[0003] The purpose of the present invention is to provide a method for detecting the surface shape of a large-curvature X-ray optical element based on near-field speckle.

[0004] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0005] The present invention includes separating the speckle displacement caused by the surface shape error, generating a reference image containing only the surface shape error information; synthesizing the ideal surface shape and the surface shape error to obtain a detection result, specifically including the following steps:

[0006] The image data of speckle pattern A, speckle pattern B and speckle pattern C are respectively obtained through different optical path layouts;

[0007] Perform DIC operation between speckle pattern A and speckle pattern B to obtain the wavefront distribution of the incident light;

[0008] Generate a reference image using optical simulation technology based on the speckle pattern A, the wavefront of the incident light and the ideal model of the optical element to be tested;

[0009] Performing DIC operation between the reference image and the speckle pattern C to obtain the surface error of the optical element to be measured;

[0010] The ideal model of the optical element to be measured and the surface shape error are synthesized to obtain the actual surface shape of the optical element to be measured.

[0011] Furthermore, the severe deformation of speckle produced by large curvature optical elements is predicted based on the near-field speckle propagation theory and the ideal surface shape of optical elements, the speckle displacement caused by the surface shape error is separated from it, and a reference image containing only the surface shape error information is generated; the surface shape error is directly detected; and the actual surface shape of large curvature X-ray optical elements is detected by synthesizing the ideal surface shape and the surface shape error.

[0012] Furthermore, the method for obtaining the image data of the speckle pattern A, the speckle pattern B and the speckle pattern C includes that the optical path is a synchrotron radiation monochromatic X-ray optical path, a speckle generator is arranged upstream of the optical path, and an image is collected through a detector, and the collected image is a speckle pattern;

[0013] The initial positions of the speckle generator and the detector are set to L1, and the collected image is the speckle pattern A;

[0014] The image collected after the detector moves away from the speckle generator by a distance △L along the optical path is a speckle pattern B;

[0015] When the element to be tested is added to the optical path, the collected image is a speckle pattern C, and the distance between the element to be tested and the detector is L2<△L;

[0016] Furthermore, the DIC technique divides the speckle image without sample information into grids, and then calculates the similarity between each sub-block and the corresponding sub-block at each position of the speckle image with sample information (i.e., the sample image). The most similar point is the position of the sub-block after the sample is added, and then the displacement of the sub-block is obtained. By combining the displacements of all sub-blocks, the refraction information of monochromatic X-rays passing through the sample can be obtained.

[0017] Furthermore, the surface error data is interpolated before synthesis.

[0018] Furthermore, the speckle is generated in the X-ray optical path by a speckle generator, which modulates the wavefront of the incident light and imparts randomness to the wavefront in terms of its thickness or refractive index distribution, while the high-frequency random distribution of the wavefront remains unchanged during the propagation of the incident light.

[0019] Furthermore, the reference image and sample image are obtained by simulation and experiment respectively, and DIC operation is performed between the two to obtain the sub-block displacement distribution map. The refraction information of the monochromatic X-ray when passing through the sample is inferred in combination with the optical path layout, and reconstructed into the surface error of the sample.

[0020] The beneficial effects of the present invention are:

[0021] The present invention is a method and system for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle. Compared with the prior art, the present invention has the following technical effects:

[0022] The present invention predicts the severe deformation of speckle produced by a large curvature optical element based on the near-field speckle propagation theory and the ideal surface shape of the optical element, separates the speckle displacement caused by the surface shape error from it, and generates a reference image containing only the surface shape error information; directly detects the surface shape error; and realizes the detection of the actual surface shape of the large curvature X-ray optical element by synthesizing the ideal surface shape and the surface shape error.

[0023] The new method bypasses the limitation of "large curvature" by decomposing the ideal surface shape and surface shape error of large curvature optical elements, achieves the purpose of detecting the surface shape of large curvature X-ray optical elements, and establishes a near-field speckle wavefront detection method with a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of an experimental system for a method for detecting a surface shape of a large curvature X-ray optical element based on near-field speckle according to the present invention;

[0025] Figure 2 The present invention is a data processing flow chart of a method for detecting the surface shape of a large-curvature X-ray optical element based on near-field speckle. DETAILED DESCRIPTION

[0026] The present invention is further described below with specific examples. The illustrative examples and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0027] like Figure 1 and 2 As shown, the present invention provides a method for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle, comprising the following steps:

[0028] This method is divided into two parts: experiment and data processing. The main content of the experimental part is Figure 1 The optical path layout shown in the figure obtains speckle patterns A, B and C. The data processing flow is as follows Figure 2 As shown in the figure, the ideal surface shape of the input part refers to the ideal surface shape of the optical element to be measured, and the output part is the actual surface shape of the optical element to be measured. The specific experimental and data processing flow is as follows: establish an ideal model according to the design or nominal parameters of the optical element to be measured; Figure 1 The layouts 1, 2 and 3 shown in the experiment obtain speckle patterns A, B and C; a DIC (digital image cross correlation) operation is performed between speckle pattern A and speckle pattern B to obtain the wavefront distribution of the incident light; based on the speckle pattern A, the wavefront of the incident light and the ideal model of the optical element to be measured, a reference image is generated using optical simulation technology; a DIC operation is performed between the reference image and the speckle pattern C to obtain the surface error of the optical element to be measured; the ideal model of the optical element to be measured and the surface error are synthesized to obtain the actual surface shape of the optical element to be measured.

[0029] DIC calculation technology: DIC is to calculate the correlation between two digital images with or without the sample to be tested or before and after the sample to be tested is deformed to obtain sample information or its deformation information. Its basic principle is to grid the speckle image (i.e., reference image) without sample or before deformation, and then calculate the similarity of each sub-block with the corresponding sub-block at each position of the speckle image (i.e., sample image) with sample or after deformation. The most similar point is the position of the sub-block after adding the sample or after deformation, and then obtain the displacement of the sub-block. By combining the displacement of all sub-blocks and the optical path layout, the refraction information of monochromatic X-rays passing through the sample can be obtained. This solution will use the image processing module of OpenCV to achieve high-speed and accurate DIC calculation.

[0030] Optical simulation technology: Taking the experimentally acquired speckle image A, the incident wavefront (i.e., the propagation direction of each light ray in the light beam), and the model of the component to be measured (including the sample's refractive index, thickness distribution, and relative position in the light beam) as input, a reference image is generated by simulating the interaction between the light and the sample (this process is mainly described by the complex refractive index). The simulation of this solution is based on xrt (X Ray Tracer). xrt is a commonly used X-ray tracing software in the field of synchrotron radiation, and its main function is to simulate synchrotron radiation sources, beam lines, and their components.

[0031] Synthesis method of actual surface shape: The final result of the test is the actual surface shape of the optical element to be tested, which is synthesized from the ideal surface shape and the surface shape error. Among them, the geometric dimensions of the ideal surface shape are consistent with the actual situation and can be used directly. However, due to the convergence and divergence effects of large curvature optical elements, the surface shape error data is often different from the actual geometric dimensions. Therefore, it needs to be interpolated before it can be superimposed with the ideal surface shape to synthesize the actual surface shape of the optical element to be tested. This solution will use the cubic spline interpolation method.

[0032] Implementation Case 1

[0033] Measure the surface shape of an X-ray focusing element CRL.

[0034] Experimental equipment and conditions:

[0035] Synchrotron radiation monochromatic X-ray source, photon energy 15keV

[0036] Speckle generator, used to generate speckle patterns on the X-ray beam path

[0037] The X-ray focusing element CRL to be tested has a rotating parabola with a vertex curvature radius of 10 microns. High-resolution detector for collecting speckle images with an effective pixel size of 300 nanometers.

[0038] Experimental steps:

[0039] In the absence of a component to be tested, a speckle pattern A is collected.

[0040] Move the detector along the optical path by a distance △L to collect the speckle pattern B.

[0041] The X-ray focusing element CRL to be tested is added into the optical path, and the speckle pattern C is collected.

[0042] Experimental data:

[0043] L1 = 1.5 meters (the distance between the speckle generator and the optical element to be measured)

[0044] L2 = 0.8 m (the distance between the optical element to be measured and the detector)

[0045] ΔL = 0.5 m (the distance the detector moves)

[0046] Data processing:

[0047] Perform DIC operation between speckle pattern A and speckle pattern B to obtain the wavefront distribution of the incident light; generate a reference image using optical simulation software xrt based on speckle pattern A, the wavefront of the incident light and the ideal model of the optical element to be tested; perform DIC operation between the reference image and speckle pattern C (using the peak-finding sub-pixel processing technology to increase the displacement resolution to one-tenth of the detector, i.e. 30 nanometers) to obtain the surface error of the optical element to be tested (corresponding to an angle resolution of approximately 37 nanoradians); synthesize the ideal model of the optical element to be tested and the surface error to obtain the actual surface shape of the optical element to be tested. Since the curvature of the optical element to be tested is large, it cannot be measured by traditional methods, but this method can measure its surface error and actual surface shape with high precision.

[0048] Implementation Case 2

[0049] Experimental equipment and conditions:

[0050] Synchrotron radiation monochromatic X-ray source, photon energy 15keV

[0051] Speckle generator, used to generate speckle patterns on the X-ray beam path

[0052] The X-ray lens to be tested is a rotating parabola with a vertex curvature radius of 50 microns. High-resolution detector for collecting speckle images with an effective pixel size of 650 nanometers.

[0053] Experimental steps:

[0054] Same as case 1.

[0055] Experimental data:

[0056] L1 = 1 meter (the distance between the speckle generator and the optical element to be measured)

[0057] L2 = 1.5 meters (the distance between the optical element to be measured and the detector)

[0058] ΔL = 2 meters (the distance the detector moves)

[0059] Data processing:

[0060] Perform DIC operation between speckle pattern A and speckle pattern B to obtain the wavefront distribution of the incident light; generate a reference image using optical simulation software xrt based on speckle pattern A, the wavefront of the incident light and the ideal model of the optical element to be tested; perform DIC operation between the reference image and speckle pattern C (using the peak-finding sub-pixel processing technology to increase the displacement resolution to one-tenth of the detector, i.e. 65 nanometers) to obtain the surface error of the optical element to be tested (corresponding to an angle resolution of approximately 43 nanoradians); synthesize the ideal model of the optical element to be tested and the surface error to obtain the actual surface shape of the optical element to be tested. Since the curvature of the optical element to be tested is large, it cannot be measured by traditional methods, but this method can measure its surface error and actual surface shape with high precision.

[0061] In these two implementation cases, by calculating the deflection angle and analyzing the distribution of surface errors, we can evaluate the performance of optical components and provide a basis for subsequent manufacturing or adjustment. These cases demonstrate the potential of near-field speckle technology in high-precision optical measurement, especially in the field of X-ray optical component inspection.

[0062] The existing near-field speckle wavefront detection technology is limited by the assumption that the near-field speckle does not deform, and can only detect the surface shape of small-curvature lenses and reflectors. The present invention can detect the surface shape of large-curvature X-ray optical elements. The foothold of the existing near-field speckle wavefront detection technology is that the shape and size of the speckle pattern do not change during the propagation process. When the optical element to be measured is a thin lens and a plane mirror, the influence of the surface shape on the speckle pattern can be ignored. At this time, the speckle displacement caused by the surface shape error is the main phenomenon and can be used to detect the surface shape. When the surface curvature of the optical element to be measured is large (corresponding to a small surface curvature radius), the surface shape will cause the speckle pattern to change significantly, making it impossible to distinguish the required speckle displacement information. This method takes the speckle deformation into consideration, predicts it, and then extracts the speckle displacement information to achieve the detection of large-curvature optical elements.

[0063] The traditional surface shape detection technology first measures the surface shape of the optical element, then subtracts the ideal surface shape to obtain the surface shape error. This method directly measures the surface shape error, and then obtains the surface shape data by adding the error data to the ideal surface shape. This is because the ideal surface shape is accurately known, so its influence can be accurately predicted and deducted in advance. In addition, when the traditional method integrates the directly measured angle into the surface shape data, the error will accumulate along the integration direction. This method avoids this influence by deducting the surface shape in advance.

[0064] Traditional near-field speckle detection technology directly measures the reference image, while this method indirectly obtains the reference image through measurement and calculation. The traditional method obtains the reference image by directly taking pictures with the detector. While it is convenient and portable, it also limits the effective use range of the reference image. For example, in the above-mentioned large-curvature optical component detection, the effective information of the directly measured reference image is annihilated and cannot be used. This method measures data such as the wavefront of the incident light, and can accurately predict and eliminate interference information through calculation, thereby obtaining a more "pure" and "generalized" reference image. This method separates the effective displacement information of the reference image, has a wider effective range, and broadens the application scope of near-field speckle detection technology.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle, characterized in that: By separating the speckle displacement caused by the surface error, a reference image containing only the surface error information is generated; and the ideal surface shape and the surface error are synthesized to obtain the detection result, which specifically includes the following steps: Acquire image data of speckle pattern A, speckle pattern B, and speckle pattern C; Perform DIC operation between speckle pattern A and speckle pattern B to obtain the wavefront distribution of the incident light; Based on the speckle pattern A, the wavefront of the incident light and the ideal surface shape of the optical element to be measured, a reference image is generated using optical simulation technology; Performing DIC operation between the reference image and the speckle pattern C to obtain the surface error of the optical element to be measured; The ideal model of the optical element to be measured and the surface shape error are synthesized to obtain the actual surface shape of the optical element to be measured; The method for obtaining the image data of the speckle pattern A, the speckle pattern B and the speckle pattern C includes: the optical path is a synchrotron radiation monochromatic X-ray optical path, a speckle generator is arranged upstream of the optical path, and an image is collected through a detector, and the collected image is a speckle pattern; The initial positions of the speckle generator and the detector are set to L1, and the collected image is the speckle pattern A; The image collected after the detector moves away from the speckle generator by a distance △L along the optical path is a speckle pattern B; When the element to be tested is added to the optical path, the collected image is a speckle pattern C, and the distance between the element to be tested and the detector is L2<△L; DIC divides the speckle image without sample information into grids, and then calculates the similarity between each sub-block and the corresponding sub-block at each position of the speckle image with sample information. The most similar point is the position of the sub-block after the sample is added, and then the displacement of the sub-block is obtained.

2. According to claim 1, a method for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle, characterized in that: The severe deformation of speckle produced by large curvature optical elements is predicted based on the near-field speckle propagation theory and the ideal surface shape of optical elements. The speckle displacement caused by surface shape errors is separated from it to generate a reference image containing only surface shape error information. The surface shape errors are directly detected. The actual surface shape of large curvature X-ray optical elements is detected by synthesizing the ideal surface shape and the surface shape error.

3. According to claim 1, a method for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle, characterized in that: The surface error data is interpolated before synthesis.

4. According to claim 1, a method for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle, characterized in that: Speckle is generated in the X-ray optical path by a speckle generator, which modulates the wavefront of the incident light and imparts randomness to the wavefront, either in terms of thickness or refractive index distribution. Meanwhile, the high-frequency random distribution of the wavefront remains unchanged during the propagation of the incident light.

5. According to claim 1, a method for detecting the surface shape of a large curvature X-ray optical element based on near-field speckle, characterized in that: The reference image and sample image are obtained by simulation and experiment respectively, and DIC operation is performed between the two to obtain the sub-block displacement distribution map. The refraction information of monochromatic X-rays when passing through the sample is inferred in combination with the optical path layout, and reconstructed into the surface error of the sample.

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