Microscopic imaging device and phase reconstruction method thereof

Abstract

The invention discloses a microscopic imaging device and a phase reconstruction method thereof, and relates to the field of digital holographic microscopic measurement. The method is used for solving the problems of positioning errors caused by multiple times of movement of an existing microscopic imaging device, complicated operation and low surface appearance reconstruction precision of a detected sample. The device comprises a first beam splitter prism which is located at the light emitting side of a light source module and is used for splitting a laser beam into reference light and object light; the object light splitting module is used for enabling the object light carrying the surface information of the sample to be detected to form four beams of diffracted light; the vortex reference module is used for converting the reference light into vortex reference light which is spirally distributed in phase and comprises four areas; the second beam splitting prism is used for combining the four diffracted light beams and the vortex reference light beams in the four areas, so that the four diffracted light beams and the vortex reference light beams in the four areas form interference fringes on an imaging target surface; and the image acquisition system is used for carrying out single-frame acquisition on the interference fringes to obtain a single-frame four-amplitude phase-shift hologram so as to realize real-time imaging measurement.

Description

Technical Field

[0001] The present invention relates to the field of digital holographic microscopic measurement, and more specifically to a microscopic imaging device and a phase reconstruction method thereof. Background Art

[0002] By combining phase shift technology with digital holographic microscopy, phase shift digital holographic microscopy can effectively solve the interference problem of zero-order and conjugate images during holographic reconstruction under the condition of coaxial recording, and obtain a holographic reconstruction image with higher resolution. At present, based on the different ways of generating phase shift, phase shift digital holography technology can be divided into two categories: time phase shift and space phase shift. Time phase shift refers to changing the phase of the reference light by mechanically moving the phase shifter in a time series, and then recording the corresponding hologram. It can only observe static samples or slowly changing processes, and the imaging accuracy is not high and the speed is slow; while the way to achieve spatial phase shift is to use multiple synchronized CCD cameras or divide the recording target surface of a CCD camera into multiple parts, so as to achieve the synchronous recording of multiple holograms with different phase shifts under one exposure, so as to observe the dynamic samples and their changing processes in real time. The digital holographic system combined with spatial phase shift technology needs to use a spectrometer to split the object light and the reference light, and then introduce the phase shift between the object light and the reference light through the phase shifter, and finally obtain holograms with different phase shift amounts.

[0003] At present, according to the number of imaging receiving devices, spatial phase-shift digital holography is divided into two methods: multi-camera recording and single-camera recording (pixel mask method). The multi-CCD recording method uses multiple independent and separate beam paths, each of which is synchronously exposed by a separate CCD, so as to record phase-shift interference patterns with different phase shift amounts. For example: In the paper entitled "Phase-shifting digital holographic microscopy by using amulti-camera setup" by Carlos T et al., in order to achieve a single shot and obtain the required phase-shift interference image, a multi-camera device was used. The device can simultaneously obtain the required phase-shift interference image by setting different output channels; the patent "Method for measuring optical phase using synchronous phase-shift interference method and realizing optical path" uses ordinary beam splitters and polarization beam splitters to perform six-way beam splitting on the incident light source, combined with polarization phase shift technology, and simultaneously records six phase-shift interference patterns, achieving efficient spatial separation and synchronous recording. The size of the interference pattern obtained by the multi-CCD recording method is consistent with the photosensitive area of ​​a single CCD, which can obtain a larger observation field of view, but the system structure is relatively complex, requiring precise synchronization control of the camera, and has extremely high requirements for the simultaneity of signal acquisition. The single-camera recording method is to cover the specially made micro-polarizer array on the recording target surface of the CCD so that each pixel can record a different phase shift. By resampling and combining the entire recorded interference pattern, multiple interference patterns with different phase shifts are formed. For example: In the paper "Dynamic Fizeau Interferometer Using Short Coherence Light Source", a pair of short coherence orthogonal polarized light beams were obtained by using a short coherence diode-pumped solid-state laser, and combined with a polarization camera, short coherence Fizeau-type spatial phase shift interference was realized.

[0004] Compared with the time phase shifting technology, the spatial phase shifting technology can collect multiple phase-shifted holograms at the same time, solving the problems of slow imaging speed and inability to achieve real-time online imaging. However, the spatial phase shifting technology also has some limitations. For example, the multi-CCD recording method requires that the exposure of all cameras must be precisely synchronized, and has strict requirements on the simultaneity of acquisition; the single-camera recording method relies on the polarization phase shifting scheme, which is easily affected by the deviation of the azimuth angle and delay amount of the polarization optical element. In addition, in the phase reconstruction process, a fixed-step phase shift algorithm is usually used, which reduces the flexibility of the system. Summary of the invention

[0005] The embodiment of the present invention provides a microscopic imaging device and a phase reconstruction method thereof, which are used to solve the problems of positioning error caused by multiple movements of the device in the existing microscopic imaging, complex operation and low reconstruction accuracy of the surface morphology of the measured sample.

[0006] An embodiment of the present invention provides a microscopic imaging device, comprising:

[0007] A first beam splitter prism, which is located at the light output side of the light source module and is used to split the laser beam into a reference beam and an object beam;

[0008] An object light splitting module, which is used to make the object light carrying the surface information of the sample to be measured form four beams of diffracted light;

[0009] A vortex reference module, which is used to convert the reference light into a vortex reference light having a spiral phase distribution and including four regions;

[0010] a second beam splitter prism, which is used to combine the four diffracted lights and the vortex reference lights of four regions, so that the four diffracted lights and the vortex reference lights of four regions form interference fringes on an imaging target surface;

[0011] The image acquisition system is used to perform single-frame acquisition of the interference fringes to obtain four phase-shifted holograms in a single frame, thereby realizing real-time imaging measurement.

[0012] Preferably, the objective light splitting module comprises a second microscope objective lens, an aperture and a two-dimensional grating splitting system;

[0013] The second microscope objective lens is used to make the object light carrying the surface information of the sample to be measured form parallel light;

[0014] An aperture, which is used to limit the beam aperture angle of the parallel object light carrying the surface information of the sample to be measured;

[0015] A two-dimensional grating spectroscopic system is used to diffract parallel object light carrying surface information of a sample to be measured to obtain four beams of diffracted light.

[0016] 3. The device according to claim 1, wherein the vortex reference module comprises a spiral phase plate and a first microscope objective lens;

[0017] The spiral phase plate is used to modulate the reference light to form a vortex reference light with a spirally distributed phase and including four regions;

[0018] The first microscope objective lens is used to make the vortex reference lights in four areas form parallel lights.

[0019] An embodiment of the present invention provides a phase reconstruction method, including:

[0020] Based on a microscopic imaging device, four single-frame phase-shift holograms of the sample to be tested and an intensity map of a vortex reference light are obtained, the intensity map of the vortex reference light is binarized, and the intensity minimum point in the obtained vortex light intensity map is determined as the coordinate of the vortex phase singular point, and according to the coordinates of each pixel point in the four phase-shift holograms and the coordinates of the vortex phase singular point, the angle of each pixel point in each sub-phase-shift hologram relative to the vortex phase singular point is determined;

[0021] When the phase shift value of each pixel point in the first sub-phase-shift hologram is zero, the phase shift value of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram is determined in sequence according to the geometric relationship between the four phase-shift holograms;

[0022] When the phase shift value of each pixel in the four phase-shift holograms does not change with the change of pixels, the least squares error between the actual light intensity and the theoretical light intensity of each pixel is determined according to the least squares theory, and the phase corresponding to each pixel is obtained according to the least squares error. The phase of the sample to be tested is reconstructed according to the phase corresponding to each pixel.

[0023] Preferably, the angle of each pixel point in each sub-phase shift hologram relative to the vortex phase singular point is expressed by the following formula:

[0024]

[0025] Among them, o(x0,y0) represents the coordinates of the vortex phase singularity, p m (x m,n ,y m,n ) represents the coordinates of each pixel in the hologram, θ m,n represents the angle of the nth pixel in the mth sub-phase shift hologram relative to the vortex phase singularity, y m,n represents the coordinate of the nth pixel in the mth sub-phase shift hologram on the y-axis, xm ,n represents the coordinate of the nth pixel point in the mth sub-phase shift hologram on the x-axis, y0 represents the coordinate of the vortex phase singularity on the y-axis, x0 represents the coordinate of the vortex phase singularity on the x-axis, m=1,2,3,4, n=1,2,....N, N represents a positive integer.

[0026] Preferably, the phase shift values ​​of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram are as follows:

[0027]

[0028] Among them, δ 2,nrepresents the phase shift value of the nth pixel in the second sub-phase shift hologram, δ 3,n represents the phase shift value of the nth pixel in the third sub-phase shift hologram, δ 4,n represents the phase shift value of the nth pixel in the fourth sub-phase shift hologram, θ 1,n represents the angle of the nth pixel of the first sub-phase-shifted hologram relative to the vortex phase singularity, θ 2,n represents the angle of the nth pixel of the second sub-phase-shifted hologram relative to the vortex phase singularity, θ 3,n represents the angle of the nth pixel of the third sub-phase-shifted hologram relative to the vortex phase singularity, θ 4,n Represents the angle of the nth pixel of the fourth sub-phase-shifted hologram relative to the vortex phase singularity.

[0029] Preferably, the least square error between the actual light intensity of each pixel and the theoretical light intensity is determined by the following formula:

[0030]

[0031] Among them, L(x,y) represents the least square error between the actual light intensity and the theoretical light intensity of each pixel. represents the actual light intensity of four phase-shifted holograms in a single frame, I m,n (x, y) represents the theoretical light intensity of a single-frame four-phase-shifted hologram, I m,n (x,y)=A+B cos[δ m,n (x,y)]+C sin[δ m,n (x, y)], A represents the background light intensity of the hologram, A=I m,0 (x, y), B represents the product of the modulation degree of the hologram and the phase cosine, C represents the product of the modulation degree of the hologram and the sine of the phase, cos[δ m,n (x, y)] represents the phase shift cosine value of all measurement frames m at the nth pixel; sin[δ m,n (x,y)] represents the sine value of the phase shift of all measurement frames m at the nth pixel, ΔI m (x,y) represents the modulation degree of the hologram; Represents the phase cosine value of the nth pixel; Indicates the phase sine value of the nth pixel.

[0032] Preferably, the phase corresponding to each pixel is determined by the following formula:

[0033]

[0034] in, Indicates the phase corresponding to each pixel, {Xn}=[ABC] T =[H n ] -1 [K n ],{X n} represents a set of linear equations, H n represents a linear system of equations containing sine and cosine terms of phase shift values, K n represents a vector containing the actual light intensity of four phase-shifted holograms in a single frame; represents the sum of the phase shift cosine values ​​of all measurement frames m at the nth pixel point, represents the sum of the squared cosine values ​​of the phase shift of all measurement frames m at the nth pixel point, represents the sum of the products of the sine and cosine values ​​of the phase shift of all measurement frames m at the nth pixel point, represents the sum of the phase shift sine values ​​of all measurement frames m at the nth pixel point, represents the sum of the squared sine values ​​of the phase shift of all measurement frames m at the nth pixel point, It means summing the light intensity values ​​of all measurement frames m at the nth pixel point. It is the sum of the total light intensity of the nth pixel and the cosine value of the phase shift. It is the sum of the total light intensity of the nth pixel and the sine value of the phase shift.

[0035] An embodiment of the present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes any one of the above-mentioned phase reconstruction methods.

[0036] An embodiment of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes any one of the above-mentioned phase reconstruction methods.

[0037] The embodiment of the present invention provides a microscopic imaging device and a phase reconstruction method thereof, the device comprising: a first beam splitter prism, which is located at the light output side of a light source module and is used to split a laser beam into a reference beam and an object beam; an object beam splitter module, which is used to make the object beam carrying the surface information of a sample to be measured form four diffracted beams; a vortex reference module, which is used to convert the reference light into a vortex reference light having a spiral phase distribution and including four regions; a second beam splitter prism, which is used to combine the four diffracted lights and the vortex reference lights of the four regions, so that the four diffracted lights and the vortex reference lights of the four regions form interference fringes on an imaging target surface; and an image acquisition system, which is used to perform single-frame acquisition of the interference fringes to obtain a single-frame four-frame phase-shifted hologram, thereby realizing real-time imaging measurement. The vortex reference module in the device uses a vortex phase plate to modulate the vortex reference light, and uses the special spiral phase distribution of the vortex light to obtain a vortex reference light with a vortex distribution in phase and including four regions. The vortex reference light with a vortex distribution in phase and including four regions interferes with the four diffracted lights from the object light splitting module, and four phase-shifted holograms of the object to be measured are obtained through single-frame imaging, which effectively avoids the positioning error caused by multiple movements of the phase shifter and the singularity problem of the vortex light. The device has the advantages of simple operation and real-time imaging measurement, and can be widely used in fields such as surface morphology detection of micro-optical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 A schematic diagram of the module structure of a microscopic imaging device provided by an embodiment of the present invention;

[0040] Figure 2 A schematic diagram of the specific structure of a microscopic imaging device provided by an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a phase reconstruction method provided by an embodiment of the present invention;

[0042] Figure 4 A schematic diagram of a vortex reference beam provided by an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of calculating each pixel point in a phase-shift hologram provided by an embodiment of the present invention;

[0044] Among them, there are light source module ~10, objective light spectroscopic module ~20, vortex reference module ~30, image acquisition system ~40, He-Ne laser ~101, beam expander collimator ~102, first spectroscopic prism ~501, element to be measured ~201, second microscope objective lens ~202, second plane reflector ~203, aperture ~204, two-dimensional grating spectroscopic system ~205, first plane reflector ~301, spiral phase plate ~302, first microscope objective lens ~303, second spectroscopic prism ~502, imaging tube lens ~401, CMOS ~402, computer ~403. DETAILED DESCRIPTION

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

[0046] Figure 1 A schematic diagram of the module structure of a microscopic imaging device provided by an embodiment of the present invention; Figure 2 A schematic diagram of a specific structure of a microscopic imaging device provided by an embodiment of the present invention; Figure 1 and Figure 2 , a microscopic imaging device provided by an embodiment of the present invention is described in detail, such as Figure 1 As shown, the microscopic imaging device provided by the embodiment of the present invention mainly includes: a light source module 10, a first beam splitting prism 501, an object light splitting module 20, a vortex reference module 30, a second beam splitting module 502 and an image acquisition system 40.

[0047] Specifically, the light source module is used to provide a laser light source. In an embodiment of the present invention, the light source module 10 includes a He-Ne laser 101 and a beam expander collimator 102, wherein the He-Ne laser is connected to the beam expander collimator, the beam expander collimator is composed of a microscope objective lens and a lens, and the beam expander collimator is arranged at a position close to the He-Ne laser. In the light source module, the light beam emitted by the He-Ne laser is adjusted to a suitable spot size through the microscope objective lens and the lens.

[0048] Furthermore, the first beam splitter prism is arranged opposite to the light source module and located at the light output side of the light source module. The first beam splitter prism is used to split the laser beam from the light source module into object light and reference light.

[0049] Furthermore, an object light splitting module is located at the object light exiting side, and a sample to be tested 201 is also arranged between the object light exiting side and the object light splitting module. After the object light from the first beam splitting prism passes through the sample to be tested, it enters the object light splitting module after carrying the surface information of the sample to be tested. The object light splitting module splits the incoming object light carrying the surface information of the sample to be tested, so that it forms four diffracted lights.

[0050] Furthermore, the vortex reference module located at the light-emitting side of the reference light is used to convert the reference light from the first beam splitter prism into a vortex reference light having a spiral phase distribution and including four regions.

[0051] The second spectroscopic prism is located on the light output side of the object light spectroscopic module and the reference light spectroscopic module, and is used to combine the four diffracted light beams from the object light spectroscopic module and the vortex reference light beam including four regions from the reference light spectroscopic module, so that the combined four diffracted light beams and the vortex reference light beam including four regions form interference fringes on the imaging target surface.

[0052] In an embodiment of the present invention, the image acquisition system is located on the light-emitting side of the second beam splitter prism, and the combined four-beam diffracted light and the vortex reference light including four regions can form an interference pattern on the imaging target surface of the image acquisition system. The image acquisition system performs single-frame acquisition of the above-mentioned interference fringes to obtain a single-frame four-frame phase-shifted hologram, thereby realizing real-time imaging measurement.

[0053] In the microscopic imaging device provided by an embodiment of the present invention, a vortex reference module utilizes a vortex phase plate to modulate vortex reference light, and utilizes the special spiral phase distribution of vortex light to obtain vortex reference light with a vortex distribution in phase and including four regions. The vortex reference light with a vortex distribution in phase and including four regions interferes with four beams of diffracted light from the object light splitting module, and four phase-shifted holograms of the object to be measured are obtained through single-frame imaging, which effectively avoids positioning errors caused by multiple movements of the phase shifter and the singularity problem of the vortex light. The device has the advantages of simple operation and the ability to realize real-time imaging measurement, and can be widely used in fields such as surface morphology detection of micro-optical elements.

[0054] For example, in the microscopic imaging device provided by the embodiment of the present invention, the objective light splitting module includes a second microscope objective lens 202 , an aperture 204 and a two-dimensional grating splitting system 205 .

[0055] Among them, the second microscope objective lens can make the object light carrying the surface information of the sample to be measured form parallel light, that is, form parallel object light carrying the surface information of the sample to be measured; the aperture located on the light exit side of the second microscope is used to limit the beam aperture angle of the parallel object light carrying the surface information of the sample to be measured, and the two-dimensional grating spectroscopic system is located on the light exit side of the aperture, and the two-dimensional grating spectroscopic system is used to diffract the parallel object light with limited beam aperture angle, thereby forming four beams of diffracted light.

[0056] In an embodiment of the present invention, a two-dimensional grating spectroscopic system includes a two-dimensional grating, a positive lens and a pinhole aperture. The two-dimensional grating is used to disperse the parallel object light that limits the aperture angle of the light beam into multiple diffraction orders, each of which carries the surface information of the sample to be measured; the positive lens is located on the light-exiting side of the two-dimensional grating and is used to focus the four diffracted lights to ensure that the focused four diffracted lights have consistent light intensity and coherence in the subsequent interference process; the pinhole aperture is located on the light-exiting side of the positive lens and is used to limit the diameter of the four diffracted lights after focusing to prevent interference from stray light.

[0057] It should be noted that, in actual applications, the object light splitting module also includes a second plane reflector 203, wherein the second plane reflector is arranged between the second microscope objective lens and the aperture, and is used to reflect the parallel object light carrying the surface information of the sample to be measured from the second microscope objective lens, so that the reflected parallel object light carrying the surface information of the sample to be measured enters the aperture.

[0058] For example, in the microscopic imaging device provided by the embodiment of the present invention, the vortex reference module includes a spiral phase plate 302 and a first microscopic objective lens 303;

[0059] Among them, the spiral phase plate is used to modulate the reference light to form a vortex reference light with a spiral phase distribution and including four regions; the spiral phase plate can introduce high-precision phase shift, thereby effectively avoiding the phase shift error introduced by multiple movements of the phase shifter; the first microscope objective lens is used to make the vortex reference light in the four regions form parallel light, and the parallel light beam can form a clear image after passing through the first microscope objective lens while maintaining the phase information of the parallel light.

[0060] It should be noted that in practical applications, the vortex reference module also includes a first plane mirror 301, wherein the first plane mirror is arranged between the spiral phase plate and the first beam splitter prism, and is used to reflect the reference light from the first beam splitter prism so that the reflected reference light enters the spiral phase plate.

[0061] The microscopic imaging device provided by the embodiment of the present invention has an image acquisition module including an imaging tube lens 401 , a CMOS 402 and a computer 403 .

[0062] In order to more clearly introduce the microscopic imaging device provided by the embodiment of the present invention, the following describes the processing process of the single-frame four-phase-shifted hologram acquired by the microscopic imaging device, that is, the phase reconstruction method. Figure 3 A flow chart of a phase reconstruction method provided by an embodiment of the present invention is shown in FIG. Figure 3 As shown, the method comprises the following steps:

[0063] Step 101, obtaining four single-frame phase-shift holograms of the sample to be tested and an intensity map of a vortex reference light based on a microscopic imaging device, binarizing the intensity map of the vortex reference light, determining the intensity minimum point in the obtained vortex light intensity map as the coordinate of the vortex phase singular point, and determining the angle of each pixel point in each sub-phase-shift hologram relative to the vortex phase singular point according to the coordinates of each pixel point in the four phase-shift holograms and the coordinates of the vortex phase singular point;

[0064] Step 102, when the phase shift value of each pixel point in the first sub-phase-shift hologram is zero, the phase shift value of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram is determined in sequence according to the geometric relationship between the four phase-shift holograms;

[0065] Step 103, when the phase shift value of each pixel in the four phase-shift holograms does not change with the change of the pixel, the least squares error between the actual light intensity and the theoretical light intensity of each pixel is determined according to the least squares theory, the phase corresponding to each pixel is obtained according to the least squares error, and the phase of the sample to be tested is reconstructed according to the phase corresponding to each pixel.

[0066] Before step 101, the microscopic imaging device is first put into working state, specifically including: the laser beam emitted by the He-Ne laser passes through the microscope objective lens and lens in the beam expansion and collimation system in turn to obtain a suitable spot size, the laser beam enters the first beam splitter prism and is divided into object light and reference light, wherein the object light carries the surface information of the sample to be tested after passing through the sample to be tested, passes through the second microscope objective lens and the plane reflector, and after passing through the aperture, reaches the beam splitter system composed of a two-dimensional grating, a positive lens and a pinhole aperture, and then generates four diffracted lights; after passing through the plane reflector, the reference light is incident on the spiral phase plate (SpiralPhase Plate, also called vortex phase plate) and converted into a vortex beam, and the vortex beam is divided into four areas, such as Figure 4 As shown in (b), the four diffracted lights reach the second beam splitter prism through the first microscope objective lens; the four diffracted lights are matched and combined with the vortex reference lights including the four regions and then pass through the tube lens to form stable interference on the imaging target surface of the CMOS camera, thereby realizing the acquisition of a single digital hologram.

[0067] In step 101, a single-frame four-frame phase-shift hologram of the sample to be tested and an intensity map of the vortex reference light are obtained based on a microscopic imaging device. When the microscopic imaging device works normally, a single-frame four-frame phase-shift hologram can be obtained, such as Figure 4 As shown in (c), when the microscope imaging device is working normally, the light path diagram of the obstruction light can be used to collect the intensity diagram of the vortex reference light.

[0068] like Figure 4According to this characteristic, as shown in (a), it can be determined that the four diffracted lights carrying the surface information of the sample to be tested are coherently interfered with the vortex reference light respectively, and the interference light intensity distribution can be expressed as follows:

[0069]

[0070] Among them, I0(x,y) represents the background light intensity of the interference pattern; ΔI(x,y) represents the modulation degree of the interference pattern; ΔI(x,y) is the phase of the sample to be tested.

[0071] Furthermore, the intensity map of the collected vortex reference light is grayed and binarized, and the minimum intensity value in the obtained vortex light intensity map is determined as the coordinate of the vortex phase singularity. In an embodiment of the present invention, the coordinate of the vortex phase singularity is determined to be o(x0, y0).

[0072] Furthermore, according to the coordinates of each pixel point in the four phase-shift holograms and the coordinates of the vortex phase singular point, the angle of each pixel point in each sub-phase-shift hologram relative to the vortex phase singular point is determined. Among them, the coordinates of each pixel point in the four phase-shift holograms can be expressed as p m (x m,n ,y m,n ), where m is the ordinal number of the four holograms, m=1,2,3,4; n is the ordinal number of the pixels in the four holograms, n=1,2,....N, and N is a positive integer.

[0073] Furthermore, the angle of each pixel point in each sub-phase shift hologram relative to the vortex phase singularity can be determined by the following formula:

[0074]

[0075] Among them, o(x0,y0) represents the coordinates of the vortex phase singularity, p m (x m,n ,y m,n ) represents the coordinates of each pixel in the hologram, θ m,n represents the angle of the nth pixel in the mth sub-phase shift hologram relative to the vortex phase singularity, y m,n represents the coordinate of the nth pixel in the mth sub-phase shift hologram on the y-axis, x m,n represents the coordinate of the nth pixel point in the mth sub-phase shift hologram on the x-axis, y0 represents the coordinate of the vortex phase singularity on the y-axis, x0 represents the coordinate of the vortex phase singularity on the x-axis, m=1,2,3,4, n=1,2,....N, N represents a positive integer.

[0076] In step 102, the four phase-shift holograms are named as the first sub-phase-shift hologram, the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram. In the embodiment of the present invention, when the corresponding values ​​of each pixel point in the first sub-phase-shift hologram are set to zero, the geometric relationship between the four corresponding holograms can be calculated, such as Figure 5 As shown, the phase shift values ​​of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram are determined in sequence.

[0077] Specifically, let the corresponding value δ of each pixel point in the first sub-phase shift hologram be 1,n If the phase shift value of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram is 0, the phase shift value of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram can be determined by the following formula:

[0078]

[0079] Among them, δ 2,n represents the phase shift value of the nth pixel in the second sub-phase shift hologram, δ 3,n represents the phase shift value of the nth pixel in the third sub-phase shift hologram, δ 4,n represents the phase shift value of the nth pixel in the fourth sub-phase shift hologram, θ 1,n represents the angle of the nth pixel of the first sub-phase-shifted hologram relative to the vortex phase singularity, θ 2,n represents the angle of the nth pixel of the second sub-phase-shifted hologram relative to the vortex phase singularity, θ 3,n represents the angle of the nth pixel of the third sub-phase-shifted hologram relative to the vortex phase singularity, θ 4,n Represents the angle of the nth pixel of the fourth sub-phase-shifted hologram relative to the vortex phase singularity.

[0080] In step 103, according to the phase shift value of each sub-phase-shift hologram obtained in the above steps, the least square method can be performed on each pixel of the four phase-shift holograms, and then the phase distribution of each pixel can be calculated.

[0081] Specifically, when the phase shift value of each pixel in the four phase-shift holograms does not change with the change of the pixel, that is, the background light intensity and modulation degree of each pixel in the phase-shift hologram are consistent and do not change with the change of the pixel, formula (1) can be rewritten as follows:

[0082]

[0083] Furthermore, if the following variables exist in the formula, formula (4) can be further rewritten as:

[0084] I m,n=A+B cos[δ m,n (x,y)]+C sin[δ m,n (x,y)] (5)

[0085] The variables include: A = I m,0 (x,y),

[0086] Furthermore, A represents the background light intensity of the hologram, B represents the product of the modulation degree of the hologram and the phase cosine, and C represents the product of the modulation degree of the hologram and the phase sine; cos[δ m,n (x, y)] represents the phase shift cosine value of all measurement frames m at the nth pixel; sin[δ m,n (x,y)] represents the sine value of the phase shift of all measurement frames m at the nth pixel, ΔI m (x,y) represents the modulation degree of the hologram (the degree of change in the light intensity in the hologram); Represents the phase cosine value of the nth pixel; Indicates the phase sine value of the nth pixel.

[0087] Furthermore, according to the least squares theory, if the actual light intensity is That is, the actual light intensity of a single-frame four-phase-shifted hologram is Then the least squares error between the actual light intensity and the theoretical light intensity can be expressed by the following formula:

[0088]

[0089] Among them, L(x,y) represents the least square error between the actual light intensity and the theoretical light intensity of each pixel. represents the actual light intensity of four phase-shifted holograms in a single frame, I m,n (x,y) represents the theoretical light intensity of four phase-shifted holograms in a single frame.

[0090] In practical applications, when When , L(x,y) has a minimum value, and the linear equation system is:

[0091] {X n}=[H n ] -1 [K n ] (7)

[0092] It should be noted that formula (6) defines the least square error between the actual light intensity of a pixel and the theoretical light intensity. When the partial derivative of L(x, y) with respect to A, B, and C is zero, L(x, u) reaches its minimum value. n}=[H n ] -1[K n ] can be used to find the optimal solution of A, B, and C. Formula (7) can also be written as:

[0093] {X n}=[ABC] T (8)

[0094] in,

[0095]

[0096] Among them, {X n} represents a set of linear equations, including A, B and C; H n represents a linear system of equations containing sine and cosine terms of phase shift values, K n A vector representing the actual light intensity of four phase-shifted holograms in a single frame. represents the sum of the cosine values ​​of the phase shift of all measurement frames m at the nth pixel, and represents the sum of the cosine components of the phase shift change; represents the sum of the squares of the cosine values ​​of the phase shift of all measurement frames m at the nth pixel, representing the sum of the squares of the cosine components of the phase shift change; represents the sum of the products of the sine and cosine values ​​of the phase shift of all measurement frames m at the nth pixel, representing the cross term of the sine and cosine components of the phase shift change; represents the sum of the sinusoidal values ​​of the phase shift of all measurement frames m at the nth pixel, representing the sum of the sinusoidal components of the phase shift change; It represents the sum of the squares of the sine values ​​of the phase shift of all measurement frames m for the nth pixel, and represents the sum of the squares of the sinusoidal components of the phase shift change. is the sum of the light intensity values ​​of all measurement frames m at the nth pixel, representing the total light intensity at the nth pixel; It is the sum of the total light intensity of the nth pixel and the product of the cosine value of the phase shift, which represents the part of the light intensity that changes with the cosine component of the phase shift; It is the sum of the total light intensity of the nth pixel and the product of the sine value of the phase shift, representing the part of the light intensity that changes with the sinusoidal component of the phase shift.

[0097] After obtaining the unknown quantities A, B and C according to the above formula, the phase corresponding to each pixel can be determined by the following formula:

[0098]

[0099] In an embodiment of the present invention, after the phase corresponding to each pixel point is determined, a loop is used to traverse all pixel points, and the above step 104 is repeated to obtain the pixel phase, and the calculated phase value is stored in the corresponding position of the phase diagram until all pixel points are processed. The calculated phases of all pixel points are combined to complete the reconstruction of the phase of the element to be tested.

[0100] It should be noted that the loop start condition is: the loop starts from the first pixel point of the four phase-shift holograms (the pixel point in the upper left corner of the image), and the loop end condition is: the loop ends after traversing all the pixel points of the four phase-shift holograms.

[0101] In summary, the embodiment of the present invention provides a microscopic imaging device and a phase reconstruction method thereof, in which a vortex reference module uses a vortex phase plate to modulate a vortex reference light, and uses the special spiral phase distribution of the vortex light to obtain a vortex reference light with a vortex distribution and including four regions, and the vortex reference light with a vortex distribution and including four regions interferes with the four beams of diffracted light from the object light splitting module, and obtains four phase-shifted holograms of the object to be measured through single-frame imaging, effectively avoiding the positioning error caused by multiple movements of the phase shifter and the singularity of the vortex light, and has the advantages of simple operation and real-time imaging measurement, and can be widely used in the field of micro-optical element surface morphology detection. The method uses the acquired amplitude phase shift hologram single and vortex reference light map, effectively avoiding the problem that the multi-CCD recording method requires that the exposure of all cameras must be precisely synchronized; the least squares generalized phase shift algorithm is used to obtain the reconstruction of the pixel phase, canceling the restriction that the phase shift amount must be equal, and improving the system's adaptability to environmental changes.

[0102] Another embodiment of the present invention also provides a computer device, which includes: a processor and a memory; the memory is used to store computer program code, and the computer program code includes computer instructions; when the processor executes the computer instructions, the electronic device executes each step of the phase reconstruction method shown in the above method embodiment.

[0103] Another embodiment of the present invention further provides a computer-readable storage medium, in which computer instructions are stored. When the computer instructions are executed on a computer device, the computer device executes the steps of the phase reconstruction method shown in the above method embodiment.

[0104] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0105] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A microscopic imaging device, characterized in that: include: A first beam splitter prism, which is located at the light output side of the light source module and is used to split the laser beam into a reference beam and an object beam; An object light splitting module, which is used to make the object light carrying the surface information of the sample to be measured form four beams of diffracted light; A vortex reference module, which is used to convert the reference light into a vortex reference light having a spiral phase distribution and including four regions; a second beam splitter prism, which is used to combine the four diffracted lights and the vortex reference lights of four regions, so that the four diffracted lights and the vortex reference lights of four regions form interference fringes on an imaging target surface; The image acquisition system is used to perform single-frame acquisition of the interference fringes to obtain four phase-shifted holograms in a single frame, thereby realizing real-time imaging measurement.

2. The device according to claim 1, characterized in that The objective light splitting module includes a second microscope objective lens, an aperture and a two-dimensional grating splitting system; The second microscope objective lens is used to make the object light carrying the surface information of the sample to be measured form parallel light; An aperture, which is used to limit the beam aperture angle of the parallel object light carrying the surface information of the sample to be measured; A two-dimensional grating spectroscopic system is used to diffract parallel object light carrying surface information of a sample to be measured to obtain four beams of diffracted light.

3. The device according to claim 1, characterized in that The vortex reference module includes a spiral phase plate and a first microscope objective lens; The spiral phase plate is used to modulate the reference light to form a vortex reference light with a spirally distributed phase and including four regions; The first microscope objective lens is used to make the vortex reference lights in four areas form parallel lights.

4. A phase reconstruction method, characterized in that: include: Based on a microscopic imaging device, four single-frame phase-shift holograms of the sample to be tested and an intensity map of a vortex reference light are obtained, the intensity map of the vortex reference light is binarized, and the intensity minimum point in the obtained vortex light intensity map is determined as the coordinate of the vortex phase singular point, and according to the coordinates of each pixel point in the four phase-shift holograms and the coordinates of the vortex phase singular point, the angle of each pixel point in each sub-phase-shift hologram relative to the vortex phase singular point is determined; When the phase shift value of each pixel point in the first sub-phase-shift hologram is zero, the phase shift value of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram is determined in sequence according to the geometric relationship between the four phase-shift holograms; When the phase shift value of each pixel in the four phase-shift holograms does not change with the change of pixels, the least squares error between the actual light intensity and the theoretical light intensity of each pixel is determined according to the least squares theory, and the phase corresponding to each pixel is obtained according to the least squares error. The phase of the sample to be tested is reconstructed according to the phase corresponding to each pixel.

5. The phase reconstruction method according to claim 4, characterized in that: The angle of each pixel point in each sub-phase shift hologram relative to the vortex phase singular point is expressed by the following formula: Among them, o(x0,y0) represents the coordinates of the vortex phase singularity, p m (x m,n ,y m,n ) represents the coordinates of each pixel in the hologram, θ m,n represents the angle of the nth pixel in the mth sub-phase shift hologram relative to the vortex phase singularity, y m,n represents the coordinate of the nth pixel in the mth sub-phase shift hologram on the y-axis, x m,n represents the coordinate of the nth pixel point in the mth sub-phase shift hologram on the x-axis, y0 represents the coordinate of the vortex phase singularity on the y-axis, x0 represents the coordinate of the vortex phase singularity on the x-axis, m=1,2,3,4, n=1,2,....N, N represents a positive integer.

6. The phase reconstruction method according to claim 4, characterized in that: The phase shift values ​​of each pixel point in the second sub-phase-shift hologram, the third sub-phase-shift hologram and the fourth sub-phase-shift hologram relative to each pixel point in the first sub-phase-shift hologram are as follows: Among them, δ 2,n represents the phase shift value of the nth pixel in the second sub-phase shift hologram, δ 3,n represents the phase shift value of the nth pixel in the third sub-phase shift hologram, δ 4,n represents the phase shift value of the nth pixel in the fourth sub-phase shift hologram, θ 1,n represents the angle of the nth pixel of the first sub-phase-shifted hologram relative to the vortex phase singularity, θ 2,n represents the angle of the nth pixel of the second sub-phase-shifted hologram relative to the vortex phase singularity, θ 3,n represents the angle of the nth pixel of the third sub-phase-shifted hologram relative to the vortex phase singularity, θ 4,n Represents the angle of the nth pixel of the fourth sub-phase-shifted hologram relative to the vortex phase singularity.

7. The phase reconstruction method according to claim 4, characterized in that: The least square error between the actual light intensity of each pixel and the theoretical light intensity is determined by the following formula: Among them, L(x,y) represents the least square error between the actual light intensity and the theoretical light intensity of each pixel. represents the actual light intensity of four phase-shifted holograms in a single frame, I m,n (x, y) represents the theoretical light intensity of a single-frame four-phase-shifted hologram, I m,n (x,y)=A+B cos[δ m,n (x,y)]+C sin[δ m,n (x, y)], A represents the background light intensity of the hologram, A=I m,0 (x, y), B represents the product of the modulation degree of the hologram and the phase cosine, C represents the product of the modulation degree of the hologram and the sine of the phase, cos[δ m,n (x, y)] represents the phase shift cosine value of all measurement frames m at the nth pixel; sin[δ m,n (x,y)] represents the sine value of the phase shift of all measurement frames m at the nth pixel, ΔI m (x,y) represents the modulation degree of the hologram; Represents the phase cosine value of the nth pixel; Indicates the phase sine value of the nth pixel.

8. The phase reconstruction method according to claim 4, characterized in that: The phase corresponding to each pixel is determined by the following formula: in, Indicates the phase corresponding to each pixel, {X n }=[ABC] T =[H n ] -1 [K n ],{X n } represents a set of linear equations, H n represents a linear system of equations containing sine and cosine terms of phase shift values, K n represents a vector containing the actual light intensity of four phase-shifted holograms in a single frame; represents the sum of the phase shift cosine values ​​of all measurement frames m at the nth pixel point, represents the sum of the squared cosine values ​​of the phase shift of all measurement frames m at the nth pixel point, represents the sum of the products of the sine and cosine values ​​of the phase shift of all measurement frames m at the nth pixel point, represents the sum of the phase shift sine values ​​of all measurement frames m at the nth pixel point, represents the sum of the squared sine values ​​of the phase shift of all measurement frames m at the nth pixel point, It means summing the light intensity values ​​of all measurement frames m at the nth pixel point. It is the sum of the total light intensity of the nth pixel and the cosine value of the phase shift. It is the sum of the total light intensity of the nth pixel and the sine value of the phase shift.

9. A computer device, characterized in that: The computer device comprises a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the phase reconstruction method according to any one of claims 4 to 8.

10. A computer-readable storage medium, characterized in that: A computer program is stored, and when the computer program is executed by a processor, the processor executes the phase reconstruction method according to any one of claims 4 to 8.

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