Reflection imaging device and method based on tilt angle spectrum

Abstract

The invention discloses a reflection imaging device and method based on a tilt angle spectrum, and relates to the field of diffraction propagation, the device comprises a laser device, a sample clamping device, a laser processing device, a probe and an image acquisition device, the laser device and the laser processing device are both arranged on one side of the probe, the sample clamping device obliquely fixes a to-be-detected sample on the other side of the probe, the image acquisition device is arranged at the same height of the surface of the to-be-detected sample, and the target surface of the image acquisition device is perpendicular to the optical axis of the laser; the position of the to-be-detected sample is adjusted through the sample clamping device, so that the included angle between the surface of the to-be-detected sample and the optical axis of the laser is a preset angle, and the laser is irradiated to the surface of the to-be-detected sample through the probe after being processed by the laser processing device and is reflected by the surface of the to-be-detected sample for diffraction propagation. The image acquisition device is used for acquiring diffraction images formed in the diffraction propagation process. The planar graph of the surface of the to-be-detected sample which cannot transmit light can be reconstructed.

Description

Technical Field

[0001] The present application relates to the field of diffraction propagation, and in particular to a reflective imaging device and method based on tilt angle spectrum. Background Art

[0002] As a type of computational imaging, stack imaging technology is widely known in the field of image phase recovery. After a coherent light beam (such as a laser) interacts with a sample to be tested, the propagated diffraction pattern is received and recorded by a detector. The sample to be tested and the probe are moved relative to each other to obtain a coherent diffraction pattern with a certain overlap rate. Finally, a reconstruction algorithm is used to reconstruct the amplitude and phase distribution information of the sample to be tested.

[0003] The stacking imaging technology is widely used due to its advantages such as no lens, expandable imaging range, and fast convergence speed. However, in industrial inspection, most of the samples to be tested cannot transmit light, so the transmission stacking imaging cannot be used. It is necessary to expand the stacking imaging technology to the reflection field. Summary of the invention

[0004] The purpose of the present application is to provide a reflective imaging device and method based on a tilt angle spectrum, which can reconstruct a plan view of the surface of a sample to be tested that is not transparent.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides a reflective imaging device based on a tilt angle spectrum, comprising: a laser, a sample holding device, a laser processing device, a probe, and an image acquisition device:

[0007] The laser and the laser processing device are both arranged on one side of the probe, the sample clamping device tilts and fixes the sample to be tested so that the sample to be tested is located on the other side of the probe, the image acquisition device is arranged at a height equal to the surface of the sample to be tested, and the target surface of the image acquisition device is perpendicular to the optical axis of the laser reflected by the surface of the sample to be tested, and the distance between the target surface and the center of the sample to be tested is a preset distance; wherein the optical axis of the laser processed by the laser processing device is collinear with the central axis of the probe;

[0008] The position of the sample to be tested is adjusted by the sample clamping device so that the angle between the surface of the sample to be tested and the optical axis of the laser is a preset angle. The laser is expanded and collimated by the laser processing device. The processed laser is irradiated to the surface of the sample to be tested through the probe, and diffracts and propagates after reflection from the surface of the sample to be tested. The image acquisition device is used to acquire the diffraction image formed during the diffraction propagation process.

[0009] Furthermore, the laser processing device comprises: a reflector group, an attenuation plate, a microscope objective lens, a spatial filter and a collimating convex lens;

[0010] The reflector group is arranged at the exit of the laser, and the attenuation plate, the microscope objective lens, the spatial filter and the collimating convex lens are arranged in sequence along the optical axis of the laser processed by the reflector group;

[0011] The laser light emitted by the laser is collimated by the reflector group, the collimated laser light is intensity-adjusted by the attenuation plate, and the intensity-adjusted laser light is sequentially expanded and collimated by the microscope objective, the spatial filter and the collimating convex lens.

[0012] Furthermore, the image acquisition device adopts a planar array detector.

[0013] Furthermore, the sample holding device comprises a three-dimensional movable platform and a base, and the three-dimensional movable platform is arranged on the base.

[0014] In a second aspect, the present application provides a reflection imaging method based on tilt angle spectrum, comprising:

[0015] The above-mentioned reflective imaging device based on the tilt angle spectrum is used to collect multiple diffraction images of the sample to be tested at different positions; the diffraction images at adjacent positions overlap in a preset ratio;

[0016] Using a stacking reproduction algorithm, a tilt angle spectrum algorithm and the diffraction information of the diffraction image, the complex amplitude distribution function of the surface of the sample to be tested at different positions is updated and calculated to obtain an updated complex amplitude distribution function of the surface of the sample to be tested;

[0017] De-noising the updated complex amplitude distribution function of the surface of the sample to be tested by using a total variation denoising algorithm to obtain a de-noised complex amplitude distribution function of the surface of the sample to be tested;

[0018] The denoised complex amplitude distribution function of the surface of the sample to be tested at all positions is reconstructed to obtain a reconstructed plane image of the surface of the sample to be tested.

[0019] Further, the diffraction information includes the position coordinates of the diffraction image and the diffraction light intensity distribution;

[0020] Using the stacking reproduction algorithm, the tilt angle spectrum algorithm and the diffraction information of the diffraction image, the complex amplitude distribution function of the surface of the sample to be tested at different positions is updated and calculated to obtain an updated complex amplitude distribution function of the surface of the sample to be tested, including:

[0021] Setting initial values ​​of the complex amplitude distribution function of the surface of the sample to be tested and the complex amplitude distribution function of the probe to obtain an initial complex amplitude distribution function of the surface of the sample to be tested and an initial complex amplitude distribution function of the probe;

[0022] Determine a first exit field on the surface of the sample to be tested according to an initial complex amplitude distribution function of the surface of the sample to be tested and an initial complex amplitude distribution function of the probe;

[0023] The first exit field propagates a preset distance to the target surface of the image acquisition device through the tilt angle spectrum diffraction, and obtains the target surface complex amplitude distribution function; wherein the preset distance is the distance from the center of the sample to be measured to the target surface, and the tilt angle spectrum diffraction propagation adopts the tilt angle spectrum algorithm;

[0024] Updating the target surface complex amplitude distribution function according to the target surface complex amplitude distribution function and the diffraction light intensity distribution;

[0025] Performing an inverse transformation of the updated target surface complex amplitude distribution function using a tilt angle spectrum algorithm to obtain a second output field on the surface of the sample to be tested;

[0026] The complex amplitude distribution function of the surface of the sample to be measured is updated according to the second output field of the surface of the sample to be measured.

[0027] Furthermore, the updated target surface complex amplitude distribution function expression is:

[0028]

[0029] Among them, φ′ j (u) is the target surface complex amplitude distribution function after the jth position is updated, I s(j) (u) is the diffraction intensity distribution of the target surface at the jth position, i is an imaginary number, is the phase of the target surface at the jth position after the tilt angle spectrum algorithm, r is the spatial domain coordinate, and u is the frequency domain coordinate.

[0030] Furthermore, the updated expression of the complex amplitude distribution function of the surface of the sample to be tested is:

[0031]

[0032] Among them, O′ j (r) is the complex amplitude distribution function of the surface of the sample to be tested after the jth position is updated, YesP j The conjugate complex number of (·), O j (r) is the initial complex amplitude distribution function of the sample surface at the jth position, P j (r) is the initial complex amplitude distribution function of the probe at the jth position, ψ j (r) is the first outgoing field of the sample surface to be tested at the jth position, ψ′ j (r) is the second outgoing field of the j-th position of the sample surface to be tested, r is the position coordinate of the initial position of the sample surface to be tested, R s(j) (r) is the position coordinate of the jth position on the surface of the sample to be tested.

[0033] Furthermore, the tilt angle spectrum algorithm is an algorithm obtained by performing tilt angle spectrum correction on Fresnel diffraction.

[0034] Furthermore, the expression of the total variation denoising algorithm is:

[0035]

[0036] Among them, || || E represents the norm, E takes the value of 1 or 2, represents gradient difference, h is the image after denoising and optimization, g is the image corresponding to the updated complex amplitude distribution function of the surface of the sample to be tested, is the regularization term, is the prior term, and σ is the parameter that balances the regularization term and the prior term.

[0037] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0038] The present application provides a reflective imaging device and method based on tilt angle spectrum, wherein a sample to be tested that is not light-transmitting is tilted and fixed by a sample clamping device, so that the surface of the sample to be tested and the optical axis of the laser form a preset angle, and the laser is diffracted and propagated to an image acquisition device after being reflected by the surface of the sample to be tested. The image acquisition device acquires multiple diffraction images of the sample to be tested at different positions, and on this basis, the surface of the sample to be tested is reconstructed using the diffraction image to obtain a reconstructed plane map of the surface of the sample to be tested, thereby realizing reconstruction of the surface of the sample to be tested that is not light-transmitting. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 This is a schematic diagram of a top view of a reflective imaging device based on a tilt angle spectrum in one embodiment of the present application;

[0041] Figure 2 A schematic diagram of a flow chart of a reflective imaging method based on tilt angle spectrum provided in one embodiment of the present application;

[0042] Figure 3 A relationship diagram of scanning positions in a Fermat spiral scanning method provided in an embodiment of the present application;

[0043] Figure 4 A schematic diagram of the tilt angle spectrum provided in one embodiment of the present application;

[0044] Figure 5 A schematic diagram of the reflective propagation principle provided in one embodiment of the present application. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0046] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0047] The embodiment of the present application provides a reflective imaging device based on a tilt angle spectrum, such as Figure 1 As shown, it includes: a laser 11, a sample holding device ( Figure 1 ), a laser processing device 13, a probe 14 and an image acquisition device 15.

[0048] The laser 11 and the laser processing device 13 are both arranged on one side of the probe 14. In this embodiment, the laser 11 is a red light helium-neon laser with a wavelength of 632 nm, and the probe 14 is an obstacle with a circular hole.

[0049] The laser processing device 13 includes a reflector group 31, an attenuation plate 32, a microscope objective lens 33, a spatial filter 34 and a collimating convex lens 35. The reflector group 31 includes a first reflector M1 and a second reflector M2, both of which are arranged at the exit of the laser 11; the attenuation plate 32, the microscope objective lens 33, the spatial filter 34 and the collimating convex lens 35 are arranged in sequence along the optical axis of the laser processed by the reflector group 31.

[0050] The laser light emitted by the laser 11 is collimated by the first reflector M1 and the second reflector M2. The collimated laser light is subjected to light intensity adjustment by the attenuation plate 32. The laser light after light intensity adjustment is subjected to beam expansion and collimation by the microscope objective 33, the spatial filter 34 and the collimating convex lens 35 in sequence.

[0051] The sample holding device fixes the sample 12 to be tested at an angle, and makes the sample 12 to be tested be located at the other side of the probe 14. The sample holding device comprises a three-dimensional moving platform and a base, and the three-dimensional moving platform is arranged on the base.

[0052] In this embodiment, the sample 12 to be tested is mounted on a three-dimensional translation stage of model GCM-1641M which can move along the x and y directions; the base model is a GCM-1108M rotating stage, and the position of the sample 12 to be tested is adjusted along the x and y directions of the three-dimensional translation stage so that the angle between the surface of the sample to be tested and the laser optical axis is a preset angle, and the angle value of the preset angle is read by the base. The sample 12 to be tested uses the Edmund 1951USAF resolution test target plate, negative film.

[0053] The optical axis of the laser processed by the laser processing device is collinear with the central axis of the probe 14 . The laser after beam expansion and collimation is irradiated to the surface of the sample to be measured through the probe 14 . The laser is diffracted and propagated after reflection from the surface of the sample to be measured, and then propagates to the target surface of the image acquisition device 15 .

[0054] The image acquisition device 15 is arranged at the same height as the sample to be tested, and the target surface of the image acquisition device 15 is perpendicular to the optical axis of the laser after being reflected by the surface of the sample to be tested, and the distance between the target surface and the center of the sample to be tested 12 is a preset distance. In this embodiment, the preset distance is 60 mm. The image acquisition device 15 is used to collect the diffraction image formed in the diffraction propagation process.

[0055] Specifically, the image acquisition device 15 uses a planar array detector, model a2A4504-18umPRO, with an actual array size of 1500×1500 pixels, and each pixel size is 2.74um.

[0056] In actual use, the sample clamping device is adjusted so that the angle between the surface of the sample 12 to be tested and the optical axis of the laser is a preset angle. The laser emitted by the red helium-neon laser passes through the first reflector M1 and the second reflector M2. The light path is collimated by adjusting the up, down, left, and right knobs of the first reflector M1 and the second reflector M2. An attenuation plate 32 is placed behind the collimated laser to adjust the light intensity of the laser to ensure that the image received by the image acquisition device 5 is not overexposed. The laser after adjusting the light intensity is expanded and collimated by the microscope objective 33, the spatial filter 34 and the collimating convex lens 35 to ensure that the laser beam is uniformly amplified. The collimated and expanded laser is irradiated onto the tilted sample 12 to be tested for reflection. The laser reflected from the surface of the sample 12 to be tested is diffracted and propagated, and the diffracted laser is irradiated onto the image acquisition device 15 and received by the target surface of the image acquisition device 15.

[0057] In an exemplary embodiment, Figure 2 As shown, the reflection imaging method based on the tilt angle spectrum includes steps 101 to 104:

[0058] Step 101 : using the above-mentioned reflection imaging device based on the tilt angle spectrum to collect multiple diffraction images of the sample to be tested at different positions; the diffraction images at adjacent positions overlap in a preset ratio.

[0059] Move the probe or the sample to be tested and scan 50 positions using the Fermat spiral scanning method, such as Figure 3 As shown, 50 diffraction images are collected, and the diffraction information of the diffraction images includes the position coordinates of the diffraction images and the diffraction light intensity distribution, and the diffraction images at adjacent positions overlap in a preset ratio, and the overlap rate is above 70%.

[0060] Step 102 , using a stacking reproduction algorithm, a tilt angle spectrum algorithm and the diffraction information of the diffraction image, the complex amplitude distribution function of the surface of the sample to be tested at different positions is updated and calculated to obtain an updated complex amplitude distribution function of the surface of the sample to be tested.

[0061] This embodiment takes the diffraction image at the j-th position as an example to illustrate the process of updating the complex amplitude distribution function of the surface of the sample to be tested, which specifically includes steps 1021 to 1026:

[0062] Step 1021 , setting initial values ​​of the complex amplitude distribution function of the surface of the sample to be tested and the complex amplitude distribution function of the probe to obtain initial complex amplitude distribution function of the surface of the sample to be tested and initial complex amplitude distribution function of the probe.

[0063] Step 1022: determine a first output field on the surface of the sample to be tested according to the initial complex amplitude distribution function of the surface of the sample to be tested and the initial complex amplitude distribution function of the probe.

[0064] The expression of the first outgoing field on the surface of the sample to be tested at the jth position is:

[0065] ψ j (r) = O j (r)*P j (r s(j) (r));

[0066] Among them, ψ j (r) is the first outgoing field of the sample surface to be tested at the jth position, O j (r) is the initial complex amplitude distribution function of the sample surface at the jth position, P j (r) is the initial complex amplitude distribution function of the probe at the jth position, r is the position coordinate of the initial position on the surface of the sample to be tested, R s(j) (r) is the position coordinate of the jth position on the surface of the sample to be tested.

[0067] Step 1023, the first output field propagates a preset distance through tilt angle spectrum diffraction to the target surface of the image acquisition device to obtain a target surface complex amplitude distribution function; wherein the preset distance is the distance from the center of the sample to be measured to the target surface, and the tilt angle spectrum diffraction propagation adopts a tilt angle spectrum algorithm.

[0068] The expression of the complex amplitude distribution function of the target surface at the jth position is:

[0069]

[0070] Among them, φ j ( u ) is the target surface complex amplitude distribution function at the jth position, Tilt is the tilt angle spectrum algorithm, A j ( u is the amplitude of the target surface at the jth position, is the phase of the target surface at the jth position, and i is an imaginary number.

[0071] In an exemplary embodiment, the tilt angle spectrum algorithm is an algorithm obtained by performing tilt angle spectrum correction on Fresnel diffraction.

[0072] The expression for Fresnel diffraction is:

[0073]

[0074] Among them, U(x,y) is the complex amplitude distribution function of the reflective sample plane, U(x 0 ,y 0 ) is the complex amplitude distribution function of the target surface, z is the distance from the reflective sample plane to the target surface, λ is the wavelength of the laser, and F{·} is the Fourier transform.

[0075] The source plane complex amplitude U(x,y) is Fourier transformed, the wave field is decomposed into plane waves, and the spectrum G is calculated ( ξ,η ) , where the source plane is the reflective sample surface, x and y are spatial coordinates, and ξ and η are frequency domain coordinates.

[0076]

[0077] In the Fourier domain, the Fourier frequency of the source plane is converted to the Fourier frequency of the tilted plane using a rotation matrix, so that the reflective sample surface is at a preset angle to the optical axis of the laser to obtain a tilted reflective sample surface, which is the tilted plane. Zero filling in the frequency domain is performed before the conversion. Specifically, the spectrum of the source plane is placed in the center of a larger matrix, increasing the frequency domain size of the image. This reduces the loss of frequency components after the rotation operation, and the spectrum information is better preserved. During rotation, more high-frequency components remain in the effective area, preventing the image from darkening due to the loss of high-frequency components. The part of the frequency domain zero filling will not interfere with the frequency components of the source plane image.

[0078] Figure 4 As shown, the angle between the tilted plane and the source plane is θ, d is the diffraction distance, that is, the distance from the center of the tilted plane to the target surface, through the rotation matrix T -1 , the Fourier frequency of the source plane ( ξ,η ) Transition to inclined plane

[0079] The expression of the rotation matrix is:

[0080]

[0081] Among them, a 1 、a 2 、a 3 、a 4 、a 5 、a 6 、a 7 、a 8 and a 9 is a parameter about the angle θ.

[0082] Relate the Fourier frequencies in the source coordinates to the Fourier frequencies in the reference coordinates (the coordinates where the tilt plane is located) as follows:

[0083]

[0084] in, is the spatial frequency in the z direction.

[0085] The spectral relationship between the source coordinate system and the reference coordinate system is established by the following formula:

[0086]

[0087] Among them, α and β are calculated according to the rotation matrix.

[0088] For example, the rotation matrix T for an angle θ along the y-axis is -1 The expression is:

[0089]

[0090] Then, α=(a 1 , a 2 , a 3 ), β=(a 4 , a 5 , a 6 ), a 7 、a 8 and a 9 Both are 0.

[0091] The above method is used for interpolation processing. In spectrum transformation, due to the uneven spectrum points caused by nonlinear transformation, the spectrum needs to be Interpolation is performed to ensure that the Fast Fourier Transform (FFT) can accurately calculate the complex amplitude distribution function. Specifically, the interpolation process is to set the source plane grid and the inclined plane grid, and use the bicubic interpolation method for interpolation. The interpolation setting should be based on the actual propagation situation, and a scale factor cos(θ) should be multiplied on the actual pixel size.

[0092] Finally, an inverse Fourier transform is performed to transform the light field from the frequency domain back to the spatial domain.

[0093] In an exemplary embodiment, Figure 5 As shown, the laser is reflected by the sample to be tested that is not transparent, and the reflected laser is diffracted and propagated to the target surface of the image acquisition device 15. In the process of reflection propagation, the incident field is transformed into an elliptical spot after being diffracted and transmitted to the sample to be tested by the probe 14. After the elliptical spot irradiates the surface of the sample to be tested, the exit field is still an elliptical spot. However, the target surface of the image acquisition device 15 is perpendicular to the optical axis of the reflected light, so the exit field is projected again after being diffracted and transmitted to the target surface of the image acquisition device 15, and the diffraction surface is changed from an elliptical spot back to a circular spot.

[0094] Step 1024, updating the target surface complex amplitude distribution function according to the target surface complex amplitude distribution function and the diffraction light intensity distribution.

[0095] The expression of the complex amplitude distribution function of the updated target surface is:

[0096]

[0097] Among them, φ′ j (u) is the updated target surface complex amplitude distribution function at the jth position, I s(j) (u) is the diffraction light intensity distribution at the jth position.

[0098] Step 1025, performing an inverse transformation of the updated target surface complex amplitude distribution function using a tilt angle spectrum algorithm to obtain a second output field on the surface of the sample to be tested.

[0099] ψ′ j (r)=Tilt'{φ′ j (u)};

[0100] Among them, ψ′ j (r) is the second output field of the surface of the sample to be tested at the jth position, and Tilt' is the inverse propagation function of the tilt angle spectrum algorithm.

[0101] Step 1026: update the complex amplitude distribution function of the surface of the sample to be tested according to the second output field of the surface of the sample to be tested.

[0102] The expressions of the updated complex amplitude distribution function of the sample surface to be tested and the updated complex amplitude distribution function of the probe are respectively:

[0103]

[0104] Among them, O′ j (r) is the complex amplitude distribution function of the surface of the sample to be tested after the jth position is updated, P′ j (r) is the updated probe complex amplitude distribution function at the jth position, YesP j The complex conjugate of (·), Yes j The complex conjugate of (·).

[0105] Step 103 , denoising the updated complex amplitude distribution function of the surface of the sample to be tested by using a total variation denoising algorithm to obtain a denoised complex amplitude distribution function of the surface of the sample to be tested.

[0106] The expression of the total variation denoising algorithm is:

[0107]

[0108] Among them, || || E represents the norm, E takes the value of 1 or 2, represents gradient difference, h is the image after denoising and optimization, g is the image corresponding to the updated complex amplitude distribution function of the surface of the sample to be tested, is the regularization term, is the prior term, and σ is the parameter that balances the regularization term and the prior term.

[0109] Step 104 , reconstructing the denoised complex amplitude distribution functions of the surface of the sample to be tested at all positions to obtain a reconstructed plane image of the surface of the sample to be tested.

[0110] The iterative process is described by taking the jth position as an example. After the above steps 102-103, the denoised complex amplitude distribution function of the surface of the sample to be tested at the jth position is obtained, and the initial complex amplitude distribution function of the surface of the sample to be tested at the jth position is updated and denoised to obtain the reconstructed complex amplitude distribution function of the surface of the sample to be tested at the jth position. Since the diffraction images of adjacent positions overlap, the complex amplitude distribution function of the surface of the sample to be tested at the jth position and the overlapping part of the j+1th position is the reconstructed complex amplitude distribution function of the surface of the sample to be tested at the jth position. Therefore, the initial complex amplitude distribution function of the surface of the sample to be tested at the j+1th position is updated and denoised to obtain the reconstructed complex amplitude distribution function of the surface of the sample to be tested at the jth position. Part of the initial complex amplitude distribution function of the sample surface is the complex amplitude distribution function of the sample surface to be tested reconstructed at the j-th position, and the complex amplitude distribution function of the sample surface to be tested at the j+1-th position is continued to be updated, and the above steps 102-103 are executed to traverse all positions to obtain the complex amplitude distribution function of the sample surface to be tested after updating and denoising at all positions, and obtain the reconstructed plane image of the sample surface to be tested, complete one iteration, and execute a preset number of iterations. When the autocorrelation coefficient between the reconstructed plane image of the sample surface to be tested and the collected plane image of the sample surface to be tested exceeds a preset value, the iteration is terminated.

[0111] The formula for calculating the autocorrelation coefficient is:

[0112]

[0113] Among them, I(x,y) and J(x,y) are the pixel values ​​of image I and image J at position (x,y), respectively. and is the average pixel value of image I and image J. Image I is the diffraction image corresponding to the complex amplitude distribution function of the reconstructed complex amplitude distribution function of the surface of the sample to be tested after propagation of the tilt angle spectrum. Image J is the diffraction image collected by the image acquisition device.

[0114] This application has the following advantages:

[0115] 1. The reflective imaging method based on the tilt angle spectrum in the present application can be applied in reflective imaging, and can be applied to situations such as defect detection of samples to be tested that are not light-transmitting, to reconstruct the surface of the samples to be tested that are not light-transmitting, thus solving the problem that traditional stacked imaging cannot be applied to samples to be tested that are not light-transmitting.

[0116] 2. This application adopts the propagation model of the tilt angle spectrum algorithm and uses a better interpolation method, and performs spectrum zero filling, so that the entire restored and reconstructed image is clear to the naked eye, without image defocusing caused by the tilt of the sample to be tested, and can achieve precise focusing diffraction imaging to obtain high-quality real-focus images.

[0117] 3. Since the surface of the sample to be tested is not parallel to the target surface of the image acquisition device, the size of the diffraction image received by the target surface of the image acquisition device will be compressed in the tilt direction, and the traditional diffraction model cannot be effectively corrected. The tilt angle spectrum algorithm can restore the diffraction image of the surface of the sample to be tested to the correct size during the frequency domain interpolation process. The complex amplitude information conforms to the actual situation of the surface of the sample to be tested, thereby achieving high-precision complex amplitude imaging.

[0118] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A reflective imaging device based on tilt angle spectrum, characterized in that: The reflective imaging device based on the tilt angle spectrum includes: a laser, a sample holding device, a laser processing device, a probe and an image acquisition device; The laser and the laser processing device are both arranged on one side of the probe, the sample clamping device tilts and fixes the sample to be tested so that the sample to be tested is located on the other side of the probe, the image acquisition device is arranged at the same height as the surface of the sample to be tested, and the target surface of the image acquisition device is perpendicular to the optical axis of the laser reflected by the surface of the sample to be tested, and the distance between the target surface and the center of the sample to be tested is a preset distance; wherein the optical axis of the laser processed by the laser processing device is collinear with the central axis of the probe; The position of the sample to be tested is adjusted by the sample clamping device so that the angle between the surface of the sample to be tested and the optical axis of the laser is a preset angle. The laser is expanded and collimated by the laser processing device. The processed laser is irradiated to the surface of the sample to be tested through the probe, and diffracts and propagates after reflection from the surface of the sample to be tested. The image acquisition device is used to acquire the diffraction image formed during the diffraction propagation process.

2. The reflective imaging device based on tilt angle spectrum according to claim 1, characterized in that: The laser processing device comprises: a reflector group, an attenuation plate, a microscope objective lens, a spatial filter and a collimating convex lens; The reflector group is arranged at the exit of the laser, and the attenuation plate, the microscope objective lens, the spatial filter and the collimating convex lens are arranged in sequence along the optical axis of the laser processed by the reflector group; The laser light emitted by the laser is collimated by the reflector group, the collimated laser light is intensity-adjusted by the attenuation plate, and the intensity-adjusted laser light is sequentially expanded and collimated by the microscope objective, the spatial filter and the collimating convex lens.

3. The reflective imaging device based on tilt angle spectrum according to claim 1, characterized in that: The image acquisition device adopts a planar array detector.

4. The reflective imaging device based on tilt angle spectrum according to claim 1, characterized in that: The sample clamping device comprises a three-dimensional moving platform and a base, and the three-dimensional moving platform is arranged on the base.

5. A reflection imaging method based on tilt angle spectrum, characterized in that: The reflectance imaging method based on the tilt angle spectrum comprises: The reflective imaging device based on the tilt angle spectrum of claim 1 is used to collect multiple diffraction images of the sample to be tested at different positions; the diffraction images at adjacent positions overlap in a preset ratio; Using a stacking reproduction algorithm, a tilt angle spectrum algorithm and the diffraction information of the diffraction image, the complex amplitude distribution function of the surface of the sample to be tested at different positions is updated and calculated to obtain an updated complex amplitude distribution function of the surface of the sample to be tested; De-noising the updated complex amplitude distribution function of the surface of the sample to be tested by using a total variation denoising algorithm to obtain a de-noised complex amplitude distribution function of the surface of the sample to be tested; The denoised complex amplitude distribution function of the surface of the sample to be tested at all positions is reconstructed to obtain a reconstructed plane image of the surface of the sample to be tested.

6. The reflective imaging method based on tilt angle spectrum according to claim 5, characterized in that: The diffraction information includes the position coordinates of the diffraction image and the diffraction light intensity distribution; Using the stacking reproduction algorithm, the tilt angle spectrum algorithm and the diffraction information of the diffraction image, the complex amplitude distribution function of the surface of the sample to be tested at different positions is updated and calculated to obtain an updated complex amplitude distribution function of the surface of the sample to be tested, including: Setting initial values ​​of the complex amplitude distribution function of the surface of the sample to be tested and the complex amplitude distribution function of the probe to obtain an initial complex amplitude distribution function of the surface of the sample to be tested and an initial complex amplitude distribution function of the probe; Determine a first exit field on the surface of the sample to be tested according to an initial complex amplitude distribution function of the surface of the sample to be tested and an initial complex amplitude distribution function of the probe; The first exit field propagates a preset distance to the target surface of the image acquisition device through the tilt angle spectrum diffraction, and obtains the target surface complex amplitude distribution function; wherein the preset distance is the distance from the center of the sample to be measured to the target surface, and the tilt angle spectrum diffraction propagation adopts the tilt angle spectrum algorithm; Updating the target surface complex amplitude distribution function according to the target surface complex amplitude distribution function and the diffraction light intensity distribution; Performing an inverse transformation of the updated target surface complex amplitude distribution function using a tilt angle spectrum algorithm to obtain a second output field on the surface of the sample to be tested; The complex amplitude distribution function of the surface of the sample to be measured is updated according to the second output field of the surface of the sample to be measured.

7. The reflective imaging method based on tilt angle spectrum according to claim 6, characterized in that: The updated target surface complex amplitude distribution function expression is: Among them, φ′ j (u) is the target surface complex amplitude distribution function after the jth position is updated, I s(j) (u) is the diffraction intensity distribution of the target surface at the jth position, i is an imaginary number, is the phase of the target surface at the jth position after the tilt angle spectrum algorithm.

8. The reflective imaging method based on tilt angle spectrum according to claim 5, characterized in that: The updated expression of the complex amplitude distribution function of the surface of the sample to be tested is: Among them, O′ j (r) is the complex amplitude distribution function of the surface of the sample to be tested after the jth position is updated, YesP j The conjugate complex number of (·), O j (r) is the initial complex amplitude distribution function of the sample surface at the jth position, P j (r) is the initial complex amplitude distribution function of the probe at the jth position, ψ j (r) is the first outgoing field on the surface of the sample to be tested at the jth position, ψ′ j (r) is the second outgoing field of the j-th position of the sample surface to be tested, r is the position coordinate of the initial position of the sample surface to be tested, R s(j) (r) is the position coordinate of the jth position on the surface of the sample to be tested.

9. The reflective imaging method based on tilt angle spectrum according to claim 5, characterized in that: The tilt angle spectrum algorithm is an algorithm obtained by performing tilt angle spectrum correction on Fresnel diffraction.

10. The reflective imaging method based on tilt angle spectrum according to claim 5, characterized in that: The expression of the total variation denoising algorithm is: in, || ||E represents the norm, E takes the value of 1 or 2, represents gradient difference, h is the image after denoising and optimization, g is the image corresponding to the updated complex amplitude distribution function of the surface of the sample to be tested, is the regularization term, is the prior term, and σ is the parameter that balances the regularization term and the prior term.

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