Microscopic imaging method and imaging system based on transmission-type relay projection screen

Abstract

The invention relates to the technical field of microscopic imaging, and provides a microscopic imaging method and system based on a transmission-type relay projection screen, and the method comprises the steps: S1, enabling a laser to emit a light beam to irradiate a sample, and enabling the diffraction light of the sample to be projected to the transmission-type relay projection screen; s2, shooting the transmission-type relay projection screen on the other side of the transmission-type relay projection screen, and recording a power spectrum image of the sample; wherein the laser, the sample and the shooting camera are on the same axis, and the axis is perpendicular to the transmission-type relay projection screen; and S3, reconstructing the power spectrum image of the sample to obtain a target reconstructed image. The scheme has the characteristics of coaxial arrangement, simple structure, easy integration, long working distance, large depth of field, wide field of view and high resolution, can effectively reduce perspective distortion, and is convenient to combine with other technologies. The system does not need scanning measurement or wavefront modulation, so that the cost, complexity and operation difficulty of the system are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microscopic imaging technology, in particular to a microscopic imaging method and imaging system based on a transmission type relay projection screen. BACKGROUND

[0002] Traditional optical microscopic technology has problems such as short working distance, small depth of field, and resolution limited by the numerical aperture of the objective lens. Lens-free optical computational microscopic imaging technology represented by coherent diffraction imaging (CDI) is proposed to overcome these challenges. In recent years, lens-free computational microscopic imaging technology and related algorithms have made significant progress in the field of precision imaging, such as Fresnel coherent diffraction imaging (FCDI), ptychographic imaging (PIE), Fourier ptychographic imaging (FPIE), coherent modulation imaging (CMI), and transport of intensity equation (TIE). These technologies expand the CDI technology to achieve the purposes of improving spatial resolution and increasing field of view. On the one hand, the above imaging technologies cannot simultaneously meet the imaging requirements of long working distance, large field of view, and high resolution. On the other hand, the above technologies usually require the use of high-precision motorized translation stages, spatial light modulators, and other devices for push scanning or light field modulation, which not only increases the complexity and cost of the system, but also limits the real-time performance and practicality of the system.

[0003] The existing reflective relay projection microscopic telescope (rPMT) technology can realize long working distance, large depth of field, wide field of view, and high resolution microscopic telescope imaging (see the applicant's published literature, Relay-projection microscopic telescopy. Light: Science & Applications 2025; 14: 117, and patent 202311867587.1 "Microscopic imaging method and microscopic imaging system"). The reflective rPMT (such as Figure 1 ) uses a diffuse reflection screen to obtain a high-frequency spatial power spectrum (SPS), and then reconstructs a high-resolution image through a proposed phase recovery reconstruction algorithm. However, the reflective architecture is arranged non-coaxially, which has relatively large imaging distortion, data registration difficulty, and difficulty in integrating with other imaging technologies (ptychographic imaging (PIE), transport of intensity equation (TIE), etc.).

[0004] Therefore, it is urgent to develop a microscopic imaging method and imaging system based on a transmission type relay projection screen, which has the characteristics of coaxial arrangement, simple structure, easy integration, long working distance, large depth of field, wide field of view, and high resolution, to solve the above technical problems.

[0005] The above information disclosed in the background section is only used to enhance the understanding of the background of the present application, and therefore it can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0006] The present application mainly aims at overcoming the problems of relatively large imaging distortion, difficult data registration and difficult integration with other imaging technologies in the existing microscopic imaging technology, and provides a microscopic imaging method and imaging system based on a transmission relay projection screen, which has the characteristics of coaxial arrangement, simple structure, easy integration, long working distance, large depth of field, wide field of view and high resolution, can effectively reduce the perspective distortion, and is convenient to combine with other technologies. The system does not need scanning measurement or wavefront modulation, thereby reducing the system cost, complexity and operation difficulty.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a microscopic imaging method based on a transmission relay projection screen, comprising the following steps: S1: a laser emits a light beam to irradiate on a sample, and the diffraction light of the sample is projected on a transmission relay projection screen; S2: the transmission relay projection screen is photographed on the other side of the transmission relay projection screen, and the power spectrum image of the sample is recorded; wherein the laser, the sample and the camera for photographing are on the same axis, and the axis is perpendicular to the transmission relay projection screen; S3: the power spectrum image of the sample is reconstructed to obtain a target reconstruction image.

[0008] According to an example embodiment of the present application, in step S1, the laser emits a light beam to irradiate on a sample includes: the laser emits laser light, which is irradiated on the sample after passing through a beam expander and a converging lens.

[0009] According to an example embodiment of the present application, in step S2, the distance between the sample and the transmission relay screen in the optical axis direction is kept unchanged, the sample is moved to adjust the sample, and the power spectrum images of multiple samples are recorded. In step S4, the power spectrum images of multiple samples are reconstructed to obtain multiple target reconstruction images, which are spliced into one target reconstruction image.

[0010] According to an example embodiment of the present application, in step S3, the power spectrum image of the sample is reconstructed to obtain a target reconstruction image, which includes: The power spectrum image of the sample and the required parameters for reconstruction are reconstructed by using a phase recovery reconstruction algorithm to obtain a target reconstruction image; The required parameters include the wavelength of the laser, the distance between the sample and the transmission relay projection screen, and the sampling interval of the transmission relay projection screen.

[0011] According to an example embodiment of the present application, the phase recovery reconstruction algorithm includes pre-processing and triple-loop processing.

[0012] According to an example embodiment of the present application, the pre-processing includes: Calculating the object plane sampling interval; Computing the plane wave factor of a plane wave; A support domain matrix is established.

[0013] According to an example embodiment of the present application, the performing the triple loop processing comprises: Performing an outer loop, the outer loop updating the support domain; The outer loop performs a middle loop once per step increment; The middle loop updates the modulus of the Fourier spectrum; The middle loop performs an inner loop once per step decrement; The inner loop comprises: a fast Fourier transform operation, replacing the Fourier modulus, an inverse fast Fourier transform operation, and a plane wave support domain constraint.

[0014] As a second aspect of the present application, the present application provides a microscopic imaging system based on a transmission relay projection screen, comprising: a laser, a camera, a transmission relay projection screen, and an image reconstruction module; The laser is used to emit a light beam to irradiate onto a sample, and diffracted light of the sample is projected onto the transmission relay projection screen; The camera is used to shoot the transmission relay projection screen on the other side of the transmission relay projection screen, and record a power spectrum image of the sample; wherein the laser, the sample, and the shooting camera are on the same axis, and the axis is perpendicular to the transmission relay projection screen; The image reconstruction module is used to reconstruct the power spectrum image of the sample to obtain a target reconstructed image.

[0015] According to an example embodiment of the present application, the transmission relay projection screen adopts a light-transmissive diffuse reflection material.

[0016] According to an example embodiment of the present application, the transmission relay projection screen adopts a standard printing paper, a Teflon film, or a sulfuric acid paper.

[0017] According to an example embodiment of the present application, the distance between the sample and the transmission relay projection screen is 10 cm to 10 m.

[0018] According to an example embodiment of the present application, the distance between the camera and the transmission relay projection screen is 10 cm to 10 m.

[0019] The present application has the following advantages: The present application has the following advantages: Based on the premise of coaxial imaging system, the large working distance (meter level), large depth of field, large field of view, high spatial resolution of the calculation microscopic imaging is realized. The system is essentially based on the transmission relay projection of the calculation phase imaging system, which can effectively reduce the perspective distortion and facilitate the combination with other technologies. The system does not need to scan measurement or wavefront modulation, thereby reducing the system cost, complexity and operation difficulty.

[0020] Based on the selection of appropriate relay screen material, the high signal-to-background ratio (SBR, signal intensity divided by background intensity), high spatial resolution imaging is realized. The contrast test shows that the material selection of the transmission relay projection screen S is sulfuric acid paper, ordinary printing paper, Teflon film, and the imaging effect of sulfuric acid paper is better than ordinary printing paper and Teflon film. BRIEF DESCRIPTION OF DRAWINGS

[0021] The above and other objects, features and advantages of the present application will become more apparent from the following detailed description of example embodiments thereof, when taken in conjunction with the accompanying drawings. The drawings described below are only some embodiments of the present application, and other drawings can be obtained according to these drawings without creative labor for those skilled in the art.

[0022] Figure 1 The structure diagram of the microscopic imaging system in the background art is schematically shown.

[0023] Figure 2 The structure diagram of the microscopic imaging system based on the transmission relay projection screen of the first specific embodiment is schematically shown.

[0024] Figure 3 The step diagram of the microscopic imaging method based on the transmission relay projection screen is schematically shown.

[0025] Figure 4 The sampling interval calibration diagram is schematically shown.

[0026] Figure 5 The flowchart of the sample image reconstruction is schematically shown.

[0027] Figure 6 The structure diagram of the microscopic imaging system based on the transmission relay projection screen of the third specific embodiment is schematically shown.

[0028] Figure 7 The structure diagram of the microscopic imaging system based on the transmission relay projection screen of the fourth specific embodiment is schematically shown. DETAILED DESCRIPTION

[0029] Example embodiments now will be described more fully hereinafter with reference to the accompanying drawings; however, the example embodiments can be implemented in any number of ways. Rather, the present disclosure should be understood to include any number of implementations within the scope of the present disclosure, which will become apparent to those skilled in the art from the following description.

[0030] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the application. One skilled in the relevant art will recognize, however, that the

[0031] The block diagrams in the drawings show only the functionality of the embodiments and do not imply any particular physical or architectural arrangement of the devices, systems, or methods. No inference should be drawn regarding the implementational aspects of the embodiments as shown and described herein. Further, having described a few embodiments, many variations and modifications will become apparent to those skilled in the art. Any feature, structure, material, or combination thereof can be

[0032] The flow diagrams depicted herein are examples of sequences of operations that can be performed, for example, by a computing device. The depicted examples are not meant to limit the scope of the application. One or more of the operations shown can be repeated, omitted, or performed in a different order. Further, examples of the flow diagrams can be implemented by hardware, software, firmware, or a combination thereof. In the context of software, the operations represent computer-executable instructions stored on one or more computer-readable media that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions include routines, subroutines, programs, functions, methods, procedures, modules, software, and / or code segments that perform particular tasks or implement particular abstract data types. Computer-executable instructions can be stored and / or transported within any computer-readable media for use by or in connection with an instruction execution system, apparatus, or device.

[0033] It should be understood that although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0034] Those skilled in the art will understand that the figures are merely illustrative of example embodiments and that they should not be taken as limiting the scope of the present application.

[0035] According to a first specific embodiment of the present application, a microscopic imaging system based on a transmissive relay projection screen is provided, as shown in Figure 2As shown, it comprises: a laser L, a beam expander BE, a converging lens CL, a camera C, a transmissive relay screen S and an image reconstruction module (not shown in the figure).

[0036] Figure 2 The camera C of the transmissive rPMT is located on the other side of the transmissive relay screen S and takes pictures in a coaxial manner, with almost 0 perspective distortion.

[0037] rPMT (relay projection microscopy and telescopic) is a new optical imaging technology developed by the National University of Defense Technology. Through a unique square-law relay projection mechanism and a non-line-of-sight light collection strategy, it realizes the fusion of microscopy and telescopic functions, and breaks through the balance problem among spatial resolution, imaging distance and depth of field in traditional optical imaging. The technical advantage of rPMT is that it can realize micron-level high-resolution dynamic video imaging in the range of centimeters to hundreds of meters with simple equipment, and the resolution capability and depth of field range are both improved by tens of times. It does not require fluorescent reagents, avoiding complex processes such as wavefront modulation and synthetic aperture, and has better practicality and real-time performance. Application fields: This technology can be applied to biomedical research (such as in vivo imaging), semiconductor manufacturing and remote diagnosis, and provides a new solution for ultra-long working distance, ultra-large depth of field microscopy and remote micro-scale target detection.

[0038] The laser L is used to emit a light beam which is sequentially irradiated to the sample O through the beam expander BE and the converging lens CL, and the diffracted light of the sample O is projected to the transmissive relay screen S.

[0039] The camera C is used to take pictures of the transmissive relay screen S on the other side of the transmissive relay screen S, and record the power spectrum image of the sample O; wherein the laser L, the beam expander BE, the converging lens CL, the sample O and the camera C for taking pictures are on the same axis, and the axis is perpendicular to the transmissive relay screen S. The focal length of the converging lens CL is shorter than the distance between the converging lens CL and the sample O. The camera C is a fixed-focus lens. The material of the relay screen is paper or curtain, which can be made into large size at a low cost, such as tens of centimeters or even several meters. The size of the camera or lens is limited by the manufacturing industry and cost, and the size of the camera plane array is in the order of centimeters at present, while the diameter of the lens aperture is generally less than 10 cm, and the cost is high above this size. The ratio of the size of the relay screen to the size of the camera plane array (or the lens aperture) is the number of times of the improvement of the cut-off frequency and the resolution. The size of the transmissive relay screen S is much larger than the size of the detector plane array or the lens aperture. Therefore, the cut-off frequency and the spatial bandwidth of the sample power spectrum collected by the transmissive relay screen S are significantly increased, and the spatial resolution of the microscopic imaging is improved by 1 to 3 orders of magnitude.

[0040] According to the perspective imaging model (principle of similar ratio), assuming the focal length of the fixed-focus lens is f, the width of the detector plane array of the camera C is , then under the condition of paraxial approximation, the size of the camera imaging field of view is about , assuming the distance between the camera lens and the relay screen Z is , and then the camera field of view can cover the power spectrum pattern with a width of about , and if the camera array is directly used for lensless imaging collection, the width of the collected power spectrum pattern is only .

[0041] The cut-off frequency of the power spectrum is defined as , where is the actual size of the power spectrum, and Z is the distance between the object and the power spectrum observation surface (the distance between the object and the camera if the camera directly images, and the distance between the object and the relay screen if the relay projection images). In this cut-off frequency formula, the size of the power spectrum is the lens diameter or the camera array size, which obtains the cut-off frequency of the traditional imaging technology, and is replaced by the size of the relay screen, which obtains the cut-off frequency of the present technology. The spatial bandwidth is equal to twice the cut-off frequency, and the diffraction limit resolution (the limit resolution of the imaging system) is equal to the reciprocal of the cut-off frequency.

[0042] Therefore, the cut-off frequency of the power spectrum collected by the transmissive relay projection is , and the cut-off frequency of the power spectrum collected by the camera array directly is , and the cut-off frequency of the power spectrum collected by the relay projection is increased by times, and since the diffraction limit resolution is equal to the reciprocal of the cut-off frequency, the spatial resolution is theoretically increased by times.

[0043] For example, in the experiment, , f = 50 mm, and the cut-off frequency is increased by times, that is, the spatial resolution is theoretically increased by 20 times. Since the diffraction limit resolution is equal to the reciprocal of the cut-off frequency, the increase of the cut-off frequency by 20 times will result in the spatial resolution being 1 / 20. However, the spatial resolution is better with a smaller value, so here the performance index of the spatial resolution is also increased by 20 times. Further increasing the distance between the camera lens and the relay screen to , or using a lens with a smaller focal length, can further increase the multiple, for example, when the distance is increased to 5 m, or the focal length of the lens is reduced to 10 mm, the cut-off frequency is increased by times, and it is necessary to ensure that the size of the relay screen (paper or curtain) is large enough, that is, the size is greater than .

[0044] The image reconstruction module is configured to reconstruct the power spectrum image of the sample O to obtain a target reconstruction image.

[0045] The transmission relay projection screen is made of light-transmissive diffuse reflection material, preferably standard printing paper, Teflon film or sulfuric acid paper. In effect, sulfuric acid paper is better than ordinary printing paper, and ordinary printing paper is better than Teflon film.

[0046] The distance Z between the sample O and the transmission relay projection screen S is OS 10 cm to 10 m. The distance Z between the camera C and the transmission relay projection screen S is CS 10 cm to 10 m, Compared with traditional microscopes or computational imaging techniques, the present solution can significantly improve the working distance, from millimeter or centimeter order to meter level.

[0047] According to a second specific embodiment of the present application, a microscopic imaging method based on a transmission relay projection screen is provided, which uses the microscopic imaging system based on the transmission relay projection screen of the first specific embodiment.

[0048] As shown in Figure 3 , the microscopic imaging method comprises the following steps: S1: the laser emits a light beam to irradiate the sample, and the diffraction light of the sample is projected onto the transmission relay projection screen.

[0049] The laser emits a light beam to irradiate the sample, which includes: the laser emits laser light, which is irradiated onto the sample after passing through the beam expander and the converging lens.

[0050] S2: photographing the transmission relay projection screen on the other side of the transmission relay projection screen to record the power spectrum image of the sample; wherein the laser L, the sample O and the camera C for photographing are on the same axis, and the axis is perpendicular to the transmission relay projection screen S.

[0051] The distance between the sample and the transmission relay screen in the optical axis direction is kept unchanged, and the sample is adjusted by moving the sample using the two-dimensional motorized translation stage, and the power spectrum images of multiple samples, i.e. a sequence of power spectrum images, are recorded.

[0052] Taking the direction of the optical axis as the z-axis, the plane where the xy-axis is perpendicular to the z-axis, and the two-dimensional motorized platform moves on the xy-axis, the image stitching is performed, and the image of the larger object surface field after stitching is obtained.

[0053] S3: reconstructing the power spectrum image of the sample to obtain a target reconstruction image.

[0054] Reconstructing the power spectrum image of the sample to obtain a target reconstruction image comprises: The power spectrum image of the sample and the parameters required for reconstruction are reconstructed using a phase retrieval reconstruction algorithm to obtain the target reconstructed image; the phase retrieval reconstruction algorithm includes the phase modulation nonlinear constraint ping-pong algorithm.

[0055] Required parameters include the laser wavelength λ, the distance Z between the sample O and the transmission relay projection screen S. OS The sampling interval Δx of the transmission-type relay projection screen. The laser wavelength λ can be measured using the laser instruction manual or a spectrometer. The distance Z between sample O and the transmission-type relay projection screen S. OS The working distance, Z, can be measured using a meter stick or laser rangefinder. Due to the high robustness of this solution, the distance Z... OS Measurement errors on the order of millimeters are acceptable, as they have little impact on the method of this invention. The measurement process for the sampling interval Δx of the transmissive relay projection screen is as follows: A card is placed facing the camera C and attached to the center of the transmissive relay projection screen S. Under natural light or fluorescent lighting, the camera C images the card to obtain calibration image I. C (like Figure 4 Then select two feature points from the card, such as... Figure 4 Points a and b are given in the diagram. The actual distance l between points a and b is measured using a ruler. ab Then, in calibration diagram I C Read the pixel coordinates of points a and b respectively. and The sampling interval Δx on the relay screen can then be obtained: It should be noted that the above calibration only needs to be performed on the system once. If only the sample is changed but the system configuration is not altered, repeated calibration is not required.

[0056] like Figure 5 As shown, after calibration and power spectrum acquisition, the single-frame power spectrum image and the parameters required for reconstruction (including laser wavelength λ, working distance Z) are then used. OS By inputting a specific phase recovery and reconstruction algorithm with the diffraction power spectrum image dimension N and the sampling interval Δx of the transmission relay projection screen, the target reconstructed image can be obtained.

[0057] The specific methods of phase retrieval and reconstruction algorithms include: The input data is: Diffraction power spectrum image I, with dimensions N×N; Laser wavelength, working distance, sampling interval; A random real matrix g0 with dimensions N×N; The length l of the object obj and width w obj A rough estimate or measurement is sufficient, as the support domain (the support domain is the approximate area occupied by the object) will gradually increase later.

[0058] Preprocessing of data data: Let ; Calculate the sampling interval of the object surface , ; 3、Calculate the object surface spherical wave factor , where p and q are integers and satisfy ; 4、Establish the support domain matrix , and assign initial values: , that is, a matrix with N×N dimensions and all elements are 0 . The support domain is the approximate range occupied by the object on the object surface. A tight support domain is used to achieve rapid convergence, and then the support domain is gradually increased to achieve fine reconstruction. Because the estimated object size and the support domain may be too small at the beginning, resulting in low reconstruction accuracy.

[0059] Three-loop processing is performed, and the middle loop is performed once for each increment of the outer loop step, and the inner loop is performed once for each decrement of the middle loop step: Outer loop: For α from 1 to 1.2 with a step of 0.1, update the support domain each time the step is incremented, , that is, the elements in the sub-window (sub-region) with a central height of pixels and a width of pixels are assigned a value of 1; the values of elements outside the sub-window with a value of 1 are all 0.

[0060] Middle loop: For γ from 1.2 to 1 with a step of 0.1, let , where M is the modulus of the Fourier spectrum.

[0061] Inner loop: For j from 0 to 30 with a step of 1, perform: 1、Forward transmission: , where FFT is the fast Fourier transform operation; 2、Replace the Fourier modulus: ; 3、Inverse transmission: ; IFFT is the fast inverse Fourier transform operation 4、Object surface support domain constraint: .

[0062] After completing the three-loop processing, the sample reconstruction image g can be output by the algorithm.

[0063] Compared with the reconstruction method of non-negative constraint, the non-negative constraint is only applicable to real number target (transmittance is a real number). The present solution cancels the non-negative constraint and replaces it with a support domain constraint, so that the transmittance is not required to be a real number, and the transmittance can also be a complex number. The real number target is, for example, a mask plate, a usaf1951 resolution target, a thickness less than one wavelength, generally below the thickness of 100 nm. The complex target has a thickness greater than one wavelength, such as a biological tissue.

[0064] If the power spectrum image is a power spectrum image of a plurality of samples, the plurality of target reconstruction images obtained by reconstructing the power spectrum images of the plurality of samples are spliced into one target reconstruction image.

[0065] According to the third specific embodiment of the present application, a microscopic imaging method based on a transmission relay projection screen is provided, which is basically the same as the method of the second specific embodiment, and the difference is that, as shown in Figure 6 The corresponding microscopic imaging system based on the transmission relay projection screen also does not have the converging lens CL.

[0066] According to the fourth specific embodiment of the present application, a microscopic imaging method based on a transmission relay projection screen is provided, which is basically the same as the method of the second specific embodiment, and the difference is that, as shown in Figure 7 The converging lens CL is defocus converging illumination, and the focal length of the converging lens CL of the corresponding microscopic imaging system based on the transmission relay projection screen is longer than the distance between the converging lens CL and the sample O.

[0067] Although the second, third and fourth specific embodiments can realize coaxial imaging and reconstruction, there are differences in imaging signal-to-noise ratio and field of view size (size of laser illumination area).

[0068] The second specific embodiment is divergent spherical wave illumination, which causes the diffracted light to be more divergent, the power spectrum image energy to be more dispersed, and the power spectrum image to be less likely to be overexposed, thereby reducing the requirement for the dynamic range of the camera. The third specific embodiment is plane wave illumination, and the distance between the sample and the light source is not limited, so that the light path is more flexible, but the central part of the power spectrum image is stronger and is easy to overexpose. The fourth specific embodiment is convergent spherical wave illumination, which shortens the distance between the sample and the converging lens compared with the divergent spherical wave illumination, but further increases the distance between the sample and the screen, i.e. increases the working distance, and the imaging becomes inverted image. It can be seen that the three specific embodiments have their own characteristics.

[0069] The present solution realizes microscopic imaging with micrometer-level resolution in the case of millimeter-level working distance range with a coaxial imaging system.

[0070] The present scheme is further developed on the basis of the existing technology of the reflective rPMT to obtain a coaxial transmissive rPMT system. As shown in Figure 2 The present scheme uses a coherent plane wave (generated by laser beam expansion collimation) or a spherical wave (generated by a plane wave passing through a converging lens and using defocusing illumination) to irradiate the object; the diffraction light of the object is projected to a relay screen and occurs diffuse scattering; a camera is placed on the other side of the screen and focused on the screen surface to collect the diffuse transmitted light, thereby recording the SPS (spatial power spectrum) pattern, and through phase recovery reconstruction, remote, large field of view, and high resolution computational microscopy imaging is achieved. It is worth noting that in the transmissive screen-based rPMT system, the light source, relay screen, and camera are coaxially aligned, and compared with the non-coaxial reflective screen-based rPMT system, the perspective distortion is smaller, and this structure is more suitable for specific application scenarios and combined with other technologies.

[0071] The reason why the existing technology adopts the reflective type is that it is limited by the projection curtain material. For example, the current curtain material is generally difficult for light to penetrate, which on the one hand causes non-coaxial imaging and perspective distortion, and on the other hand causes interference between the camera and the sample. For example, the camera blocks the diffraction light of the sample, or the sample and its support block the camera's field of view. In the present scheme, the relay projection imaging technology realizes coaxial measurement for the first time, solving the two shortcomings of the reflective type. The difficulties encountered in the process are: one is the selection of materials. If the material has too high or too thick absorption rate, the light cannot penetrate, resulting in that the image cannot be collected from the other side (the signal-to-noise ratio of the image collected by the camera is too low); the other is that glass cannot be selected as the material (if glass is used as the curtain, the projection image on the curtain cannot be seen from the sample side, because the human eye is focused on the point on the surface of the curtain, and the glass curtain has no light scattering / diffusion). Therefore, the material selection of the transmissive relay projection screen S is particularly important.

[0072] Coaxiality is achieved through a transmissive optical path. Coaxiality results in small image distortion, which is more suitable for application scenarios that require strict distortion requirements such as industrial detection and measurement. The reflective optical path Figure 1 is non-coaxial and has image distortion (similar to the trapezoidal distortion correction function of a projector, because the projector, the reflective curtain, and the viewer's eye are non-coaxial, if the projector projects obliquely without correction, a square will be projected into a trapezoid).

[0073] The coaxial advantage is that the target object can now be pushed / scanned to increase the field of view, such as originally single-frame imaging with a limited field of view. The target can now be translated in a direction perpendicular to the optical axis (black dashed line, z-axis) (translation along the x and y axes), moved once per acquisition, and finally reconstructed and stitched into a large field of view target image. The original reflective optical path does not work well in this way because the image is distorted, and the stitching effect is poor. For example, the object is originally a seamless nine-square grid composed of nine squares. If there is no distortion, the 9 measured object images are 9 identical squares, which can be easily registered and stitched to form the original seamless nine-square grid. However, with distortion, each distorted image may be a trapezoid, and it is not possible to stitch a seamless nine-square grid. This coaxial transmissive rPMT system can increase the imaging field of view through push-broom imaging.

[0074] In summary, the present scheme has the characteristics of coaxial arrangement, simple structure, easy integration, long working distance, large depth of field, wide field of view, and high resolution, can effectively reduce perspective distortion, and is convenient for combination with other technologies. The system does not require scanning measurement or wavefront modulation, thereby reducing system cost, complexity and operation difficulty, specifically: Based on the coaxial imaging system, a large working distance (meter level), large depth of field, large field of view, and high spatial resolution are achieved. The system is essentially a transmissive relay projection-based computational phase imaging system, which can effectively reduce perspective distortion and facilitate combination with other technologies. The system does not require scanning measurement or wavefront modulation, thereby reducing system cost, complexity and operation difficulty.

[0075] Based on selecting appropriate relay screen materials, high signal-to-background ratio (SBR, signal intensity divided by background intensity) and high spatial resolution imaging are achieved. Comparative tests show that the material selection of the transmissive relay projection screen S can be sulfuric acid paper, ordinary printing paper, and Teflon film. The imaging effect of sulfuric acid paper is better than that of ordinary printing paper, and the imaging effect of ordinary printing paper is better than that of Teflon film.

[0076] The above specifically illustrates and describes the exemplary embodiments of the present application. It should be understood that the present application is not limited to the detailed structure, arrangement or implementation method described herein; on the contrary, the present application is intended to cover various modifications and equivalent arrangements within the spirit and scope of the appended claims.

Claims

1. A microscopic imaging method based on a transmissive relay projection screen, characterized in that, Includes the following steps: S1: The laser beam shines onto the sample, and the diffracted light from the sample is projected onto the transmission relay projection screen. S2: Take a picture of the transmissive relay projection screen from the other side and record the power spectrum image of the sample; wherein, the laser, the sample, and the camera are on the same axis, which is perpendicular to the transmissive relay projection screen. S3: Reconstruct the target image by reconstructing the power spectrum image of the sample.

2. The microscopic imaging method based on a transmissive relay projection screen according to claim 1, characterized in that, In step S1, the laser beam illuminating the sample includes: the laser emits a laser beam, which then passes through a beam expander and a converging lens before illuminating the sample.

3. The microscopic imaging method based on a transmissive relay projection screen according to claim 1, characterized in that, In step S2, the distance between the sample and the transmission relay screen in the optical axis direction is kept constant, the sample is moved and adjusted, and the power spectrum images of multiple samples are recorded. Step S4 also includes stitching together multiple target reconstruction images obtained from the power spectrum images of multiple samples into a single target reconstruction image.

4. The microscopic imaging method based on a transmissive relay projection screen according to claim 1, characterized in that, In step S3, reconstructing the power spectrum image of the sample to obtain the target reconstructed image includes: The power spectrum image of the sample and the parameters required for reconstruction are reconstructed using a phase retrieval reconstruction algorithm to obtain the target reconstructed image; The required parameters include the laser wavelength, the distance between the sample and the transmissive relay projection screen, and the sampling interval of the transmissive relay projection screen.

5. The microscopic imaging method based on a transmissive relay projection screen according to claim 4, characterized in that, The phase recovery and reconstruction algorithm includes preprocessing and triple loop processing.

6. The microscopic imaging method based on a transmissive relay projection screen according to claim 5, characterized in that, The preprocessing includes: Calculate the surface sampling interval; Calculate the spherical wave factor of the object surface; Establish the support domain matrix.

7. The microscopic imaging method based on a transmissive relay projection screen according to claim 6, characterized in that, The triple loop processing includes: Perform an outer loop, which updates the supporting domains. Each time the outer loop increments the step size, a middle loop is executed. The modulus of the Fourier spectrum is updated in the middle loop; The inner loop executes one iteration for each step decrease in the middle loop. The inner loop includes: Fast Fourier Transform operation, replacement Fourier modulus, inverse Fast Fourier Transform operation, and surface support domain constraint.

8. A microscopic imaging system based on a transmissive relay projection screen, characterized in that, include: Laser, camera, transmissive relay projection screen and image reconstruction module; The laser is used to emit a beam of light that shines onto the sample, and the diffracted light from the sample is projected onto a transmission relay projection screen. The camera is used to photograph the transmissive relay projection screen from the other side of the screen and record the power spectrum image of the sample; wherein the laser, the sample, and the camera are on the same axis, which is perpendicular to the transmissive relay projection screen. The image reconstruction module is used to reconstruct the power spectrum image of the sample to obtain the target reconstructed image.

9. The microscopic imaging system based on a transmissive relay projection screen according to claim 8, characterized in that, The transmissive relay projection screen uses a light-transmitting diffuse reflection material.

10. The microscopic imaging system based on a transmissive relay projection screen according to claim 9, characterized in that, The transmissive relay projection screen uses standard printing paper, Teflon film, or sulfuric acid paper.

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