CN117870534A - A dual-wavelength dynamic holographic microscopic imaging system and method based on LED illumination - Google Patents

Abstract

The invention relates to an optical microscopic imaging measurement system and method, in particular to a dual-wavelength dynamic holographic microscopic imaging system and method based on LED illumination. The technical problems of low space bandwidth and limited imaging efficiency of the existing LED-based dual-wavelength partially coherent grating off-axis digital holographic microscopic system are solved. The system comprises a light source module, a first interference branch, a second interference branch and an imaging module; the light source module comprises a first beam splitter prism, an LED illumination light path and a laser illumination light path; light of the LED illumination light path and light of the laser illumination light path are commonly emitted into the first beam splitting prism to form combined light, and then the combined light is reflected and transmitted; the reflected combined beam light forms laser target light, LED target light and LED reference light through a first interference branch; the transmitted combined light forms laser reference light through a second interference branch; and the laser target light, the LED reference light and the laser reference light synchronously enter a phase shift imaging module to obtain the spatial multiplexing phase shift hologram.

Description

A dual-wavelength dynamic holographic microscopy imaging system and method based on LED illumination

Technical Field

The present invention relates to an optical microscopic imaging measurement system and method, and in particular to a dual-wavelength dynamic holographic microscopic imaging system and method based on LED lighting for applications in the fields of industrial detection and biomedicine.

Background Art

Digital holographic microscopy introduces an additional coherent reference beam on the basis of the traditional intensity optical microscopy architecture to interfere and superimpose with the target light field, thereby encoding the phase distribution of the target light field containing the target depth information into the intensity holographic pattern that can be recorded by the photodetector. The quantitative phase image of the target light field reconstructed after computational decoding not only has good imaging contrast, but the further inverted deep three-dimensional image can also be used to characterize important physical parameters such as the volume, dry mass and refractive index of biological cells, the surface shape, corrugation and roughness of industrial devices. It has broad application prospects and important research value in the fields of industrial detection and biomedicine.

Partially coherent digital holographic microscope based on LED illumination is one of the important branches of digital holographic microscopy. It uses LED low-coherence light source to replace traditional single-frequency coherent laser for system illumination, which can avoid the influence of coherent noise such as parasitic fringes caused by coherent superposition of multiple reflected light in the optical path, improve imaging quality and enhance the accuracy of quantitative phase measurement. However, due to the short coherence length of LED low-coherence light source, there is a disadvantage of reduced imaging field of view when combined with the commonly used off-axis filtering method of zero-order diffraction and twin image noise suppression. In order to achieve full-field holographic imaging under LED illumination, there are currently two main solutions: grating diffraction 4F filtering method and coaxial asynchronous phase shift method. Among them, the coaxial asynchronous phase shift method requires time-sharing recording of multiple phase-shifted holograms, which is not only greatly affected by environmental interference such as vibration, but also difficult to achieve observation and measurement of fast-moving targets. Therefore, the research and application of grating diffraction 4F filtering method that can achieve snapshot imaging is more extensive.

The off-axis digital holographic microscopy system with partially coherent grating based on LED illumination can simultaneously realize low-noise, full-field and snapshot qualitative amplitude imaging and quantitative phase measurement functions. However, due to the short central wavelength of the LED illumination source, when the optical path corresponding to the depth of the target to be measured exceeds the central wavelength of the light source, the 2π periodicity of the arctangent angle function used in the phase imaging process will introduce folded phase distortion, which seriously limits the accuracy of the measured phase and inversion depth. The dual-wavelength phase unwrapping method that introduces a second illumination light source with a different central wavelength is one of the mainstream methods to correct the folded phase distortion, expand the depth measurement range and improve the depth measurement accuracy. However, due to the fixed relative positions of the diffraction grating, Fourier transform lens, low-pass filter aperture and Fourier inverse transform lens of the imaging field compensation module in the off-axis digital holographic microscopy system with partially coherent grating, the propagation direction of the incident light beam of the field compensation module is limited, resulting in the dual-wavelength partially coherent grating off-axis digital holographic microscopy system based on LED illumination can only record dual-wavelength holographic images in time-sharing, which loses the snapshot imaging advantage and limits the dynamic performance of holographic imaging.

The existing optical path structure of the dual-wavelength partially coherent grating off-axis digital holographic microscopy system based on LED illumination is related to the wavelength of the illumination beam because the +1-order diffraction angle of the diffraction grating is related to the wavelength of the illumination beam. Therefore, in order to achieve filtering of the dual-wavelength diffracted light through a polarization diaphragm with a fixed aperture position, the central wavelength spacing of the dual-wavelength light source must be small. At the same time, it is also necessary to coaxially illuminate the diffraction grating with a dual-wavelength light beam, resulting in the overlap of the dual-wavelength hologram spectrum. It is necessary to control the light source to time-share the illumination to extract the dual-wavelength hologram separately, which limits the efficiency of dual-wavelength holographic imaging (see Guo Rongli. Research on digital holographic microscopy with LED illumination [D]. Graduate School of the Chinese Academy of Sciences (Xi'an Institute of Optics and Precision Mechanics), 2014.).

At present, the mainstream method for realizing dual-wavelength digital hologram snapshot recording is the spectrum angle division multiplexing technology, which uses two lasers to form two plane wave reference beams respectively, uses an adjustable prism to increase the spatial frequency of the first plane wave reference beam, and adjusts the reflector to reduce the spatial frequency of the second plane wave reference beam, so that the spectrum components of the dual-wavelength hologram in the multiplexed recording hologram are separated from each other, and uses a frequency domain low-pass filter to extract the target spectrum components corresponding to different wavelengths in the same multiplexed recording hologram, so as to realize snapshot holographic imaging and folding distortion correction functions. However, the coherent noise introduced by laser illumination will reduce the holographic imaging quality and quantitative phase measurement accuracy. (See Kühn J, Colomb T, Montfort F, et al. Real-time dual-wavelength digital holographic microscopy with a single hologram acquisition [J]. Optics express, 2007, 15 (12): 7231-7242.)

In summary, although the existing LED-based dual-wavelength partially coherent grating off-axis digital holographic microscopy system can simultaneously suppress zero-order diffraction and twin image noise, coherent noise such as parasitic fringes, and the folded phase distortion introduced by the angle-finding function to achieve low-noise, full-field-of-view and large-range holographic amplitude imaging and quantitative phase measurement functions, the grating diffraction angle is related to the incident wavelength and incident direction, and the fixed spectrum selection range in the 4F low-pass filter module behind the grating limits the central wavelength of the dual-wavelength illumination beam to be relatively close to the propagation direction, resulting in the inability to use the traditional angle division multiplexing method to realize the separate extraction of the dual-wavelength target spectral components in the hologram, limiting the snapshot dynamic imaging performance and efficiency.

Summary of the invention

The purpose of the present invention is to solve the technical problems of low imaging quality and limited imaging efficiency in the process of realizing low-noise, full-field-of-view and large-range holographic amplitude imaging and quantitative phase measurement in the existing LED-based dual-wavelength partially coherent grating off-axis digital holographic microscopy system, and to provide a dual-wavelength dynamic holographic microscopy imaging system and method based on LED illumination.

The technical solution of the present invention is:

The present invention discloses a dual-wavelength dynamic holographic microscopic imaging system based on LED illumination, which is special in that it comprises a dual-wavelength light source module, a first interference branch, a second interference branch and an imaging module;

The dual-wavelength light source module comprises a first beam splitter prism, an LED illumination light path and a laser illumination light path respectively located on both sides of the first beam splitter prism; the LED illumination light path is used to provide 0-π linearly polarized LED plane wave wide beam illumination light, and the laser illumination light path is used to provide horizontally polarized laser plane wave wide beam illumination light;

The linearly polarized LED plane wave wide beam illumination light of 0 to π and the horizontally polarized laser plane wave wide beam illumination light are incident together into the first beam splitter prism to form a dual-wavelength illumination combined beam light, and the combined beam light is reflected and transmitted through the first beam splitter prism;

The first interference branch and the second interference branch are respectively arranged on a reflection light path and a transmission light path of the first beam splitter prism;

The reflected combined light beam forms a horizontally linearly polarized laser target light, a horizontally linearly polarized LED target light and a vertically linearly polarized LED reference light through a first interference branch;

The transmitted combined light beam forms a vertically linearly polarized laser reference light through a second interference branch;

The imaging module includes a third beam splitter prism, an achromatic quarter wave plate and a pixel polarization camera arranged in sequence; the optical axis direction of the achromatic quarter wave plate is -π/4, and the pixel polarization camera includes four linear polarization directions of 0, π/4, π/2, and 3π/4;

The horizontally polarized laser target light, the horizontally polarized LED target light, the vertically polarized LED reference light and the vertically polarized laser reference light are synchronously injected into a third beam splitter prism, and then synchronously enter an achromatic quarter-wave plate, the horizontally polarized LED target light and the horizontally polarized laser target light are converted into right-handed circularly polarized LED target light and laser target light; the vertically polarized LED reference light and the vertically polarized laser reference light are converted into left-handed circularly polarized LED reference light and laser reference light; a pair of object light and reference light beams with relative phase shifts of 0, π/2, π, and 3π/2 are formed by a pixel polarization camera, and a spatially multiplexed phase-shifted hologram is obtained by recording the pixel polarization camera.

Further, the first interference branch includes a third achromatic lens and a second beam splitter prism sequentially arranged on the reflected light path of the first beam splitter prism, a dual-wavelength target light module and an LED reference light module respectively arranged on the transmitted light path and the reflected light path of the second beam splitter prism, and a fourth achromatic lens;

The dual-wavelength target light module comprises a third linear polarizer and a third microscope objective lens sequentially arranged along the transmission light path of the second beam splitter prism; the sample to be measured is located near the working plane of the third microscope objective lens; the optical axis direction of the third linear polarizer is 0, and is used to extract the horizontal linear polarization component light of the transmission light of the second beam splitter prism; the target to be measured is illuminated by the third microscope objective lens to form a horizontal linear polarization laser target light and a horizontal linear polarization LED target light;

The LED reference light module comprises a fourth linear polarizer, a fourth microscope objective lens and a first plane reflector which are sequentially arranged along the reflected light path of the second beam splitter prism; the first plane reflector is located near the working plane of the fourth microscope objective lens; the optical axis direction of the fourth linear polarizer is π/2, and is used to extract the vertically linearly polarized LED reference light from the reflected light of the second beam splitter prism; the horizontally linearly polarized laser target light, the horizontally linearly polarized LED target light and the vertically linearly polarized LED reference light respectively return to the second beam splitter prism along their respective optical paths and are incident on the fourth achromatic lens;

The distances from the third linear polarizer, the third microscope objective lens and the sample to be measured to the second beam splitter prism are respectively the same as the distances from the fourth polarizing filter, the fourth microscope objective lens and the first plane reflector to the second beam splitter prism;

The front focal points of the third microscope objective lens and the fourth microscope objective lens coincide with the rear focal points of the third achromatic lens; the front focal points of the fourth achromatic lens coincide with the front focal points of the third microscope objective lens and the fourth microscope objective lens; the focal length of the fourth achromatic lens is respectively greater than the sum of the thicknesses of the second beam splitter prism and the third polarizing filter and the sum of the thicknesses of the second beam splitter prism and the fourth polarizing filter;

The optical path difference between the sample to be tested, the first plane reflector and the second beam splitter prism is smaller than the coherence length of the LED low coherence light source;

The pixel polarization camera and the sample to be measured are located at a conjugate plane formed by the third microscope objective lens and the fourth achromatic lens.

Further, the second interference branch includes a second plane reflector arranged on the transmission light path of the first beam splitter prism, an achromatic half-wave plate and a fifth polarization filter arranged in sequence on the reflection light path of the second plane reflector; the optical axis direction of the achromatic half-wave plate is -π/4, and is used to change the polarization state of the laser reference light in the incident combined light beam from horizontal linear polarization to vertical linear polarization, and to be incident on the fifth polarization filter to maintain the vertical polarization state of the light beam, and the optical axis direction of the fifth polarization filter is π/2;

The optical axis direction reflected by the second plane reflector is parallel to the optical axis direction of the LED low coherence light source;

The optical axes of the achromatic half-wave plate and the fifth polarization filter coincide with the optical axis of the LED low-coherence light source;

There is an angle between the optical axis of the light beam reflected by the third beam splitter prism and the optical axis of the fourth achromatic lens;

The vertically linearly polarized laser reference light emitted from the fifth polarization filter and the horizontally linearly polarized laser target light, the horizontally linearly polarized LED target light and the vertically linearly polarized LED reference light emitted from the fourth achromatic lens are synchronously emitted into the third beam splitter prism.

Further, the LED illumination light path includes an LED low-coherence light source and a first microscope objective lens, a first pinhole aperture, a first achromatic lens and a first polarization filter which are sequentially arranged on the LED low-coherence light source light path;

The light emitting surface of the LED low coherence light source is located at a position twice the focal length of the first microscope objective lens, the first pinhole aperture is located at an imaging plane of the first microscope objective lens, the front focal plane of the first achromatic lens coincides with the plane of the first pinhole aperture, and the optical axis of the first polarizing filter coincides with the optical axis of the first achromatic lens;

The laser illumination optical path comprises a laser coherent light source and a second microscope objective lens, a second pinhole aperture, a second achromatic lens and a second polarization filter which are sequentially arranged on the laser light source optical path;

Among them, the optical axis of the laser coherent light source and the optical axis of the LED low coherence light source are in the same plane and perpendicular to each other, the second pinhole aperture is located at the focal plane of the second microscope objective, the front focal plane of the second achromatic lens coincides with the plane of the second pinhole aperture, and the optical axis of the second polarizing filter coincides with the optical axis of the second achromatic lens; the angles between the normal direction of the semi-transparent and semi-reflective plane of the first beam splitter prism and the optical axis directions of the first achromatic lens and the second achromatic lens are both π/4; the optical axis direction of the second polarizing filter is 0.

Furthermore, the first microscope objective lens, the second microscope objective lens, the third microscope objective lens and the fourth microscope objective lens are of plan-field achromatic type; the first achromatic lens, the second achromatic lens, the third achromatic lens and the fourth achromatic lens are all doublet lenses.

Furthermore, the spectral ranges of the first polarization filter, the second polarization filter, the third polarization filter, the fourth polarization filter, the fifth polarization filter, the achromatic half-wave plate and the achromatic quarter-wave plate cover the spectral ranges of the LED low-coherence light source and the laser coherent light source.

Furthermore, the image sensor model of the pixel polarization camera is any one of SonyIMX250MZR/MYR, IMX264MZR/MYR and IMX253MZR/MYR.

Furthermore, the sample to be tested and the first plane reflector are mounted on a translation stage and a rotation stage, and the third beam splitter prism is mounted on another rotation stage.

The present invention also provides a dual-wavelength dynamic holographic microscopic imaging method based on LED illumination, which adopts the above-mentioned dual-wavelength dynamic holographic microscopic imaging system based on LED illumination, and its special feature is that it includes the following steps:

1) Install each component according to the preset position;

2) Turn on the LED low-coherence light source and the laser coherent light source at the same time; use a pixel polarization camera to record and obtain a spatially multiplexed phase-shifted hologram;

3) Hologram reconstruction

3.1) The spatially multiplexed phase-shift hologram is extracted by 1:1 interval downsampling to obtain four sparse phase-shift holograms;

3.2) discarding the blank pixels in the four sparse phase-shift holograms to form an aligned four-step phase-shift hologram;

3.3) The four-step phase shift algorithm is used to suppress the LED interference light and the remaining zero-order diffraction and twin image noise in the four-step phase shift hologram, and the dual-wavelength target light field complex amplitude image is calculated;

3.4) The dual-wavelength target light field complex amplitude image is separated into the spatial frequency domain by Fourier transformation, and the LED target image spectrum and the laser target image spectrum are respectively extracted by low-pass filter and placed in the central low-frequency area of two newly created blank spectrum images;

3.5) Then, the LED target complex amplitude image and the laser target complex amplitude image are obtained by inverse Fourier transform;

3.6) The LED target complex amplitude image and the laser target complex amplitude image are subjected to modulus and angle calculations to obtain the corresponding amplitude and phase images;

3.7) Performing preliminary phase unwrapping on the two phase images by direct difference calculation to obtain a difference phase image;

3.8) further iteratively obtain the integer folding phase factor in the LED phase diagram using an iterative formula based on the phase diagram after the preliminary phase unwrapping;

3.9) The obtained integer folded phase factor is used to unfold the LED phase image to obtain a low-noise, full-field, large-range and snapshot inversion depth image.

Further, in step 3.7), the direct difference calculation formula is:

is the difference phase diagram;

and These are the reconstructed phase images when illuminated by LED low-coherence light source and laser coherent light source respectively;

Λ ₁₂ =λ ₁ λ ₂ /|λ ₂ -λ ₁ | is the equivalent synthetic wavelength formed by the two beams of central wavelengths λ ₁ and λ ₂ ;

ε ₁₂ is the noise factor in the difference phase unwrapping;

h _o is the equivalent depth of the sample to be tested;

ε ₁ and ε ₂ are the dimensionless residual noise factor and coherent noise factor corresponding to the illumination of LED low-coherence light source and laser coherent light source, respectively, ε ₂ ＞ε ₁ ;

In step 3.8), the iteration formula is:

C ₁ is the folding phase factor;

round is the rounding function;

In step 3.9), the formula for obtaining the inverted depth image is:

_h1 is the inverted depth image.

Beneficial effects of the present invention:

1. The present invention proposes a dual-wavelength dynamic holographic microscopic imaging system and method based on LED illumination. On the basis of low noise, full field of view and large-range holographic amplitude imaging and quantitative phase measurement functions, it can restore the snapshot imaging performance of the dual-wavelength holographic system and improve the imaging efficiency. It has broad application prospects in the fields of three-dimensional morphology characterization and detection of micro-nano devices.

2. The present invention proposes a dual-wavelength dynamic holographic microscopy imaging system based on LED illumination, which adopts the LED low-coherence light source illumination reflective dual-wavelength dynamic holographic microscopy imaging system optical path structure based on the Michelson and Mach-Zehnder interference optical path architecture, combined with partially coherent light source illumination, the synchronous phase shift function of the pixel polarization camera, and the angle division multiplexing recording method to obtain a spatially multiplexed phase-shifted hologram, which has the advantages of high imaging quality and high imaging efficiency.

3. A dual-wavelength dynamic holographic microscopy imaging method based on LED illumination of the present invention combines the existing dual-wavelength partially coherent grating off-axis digital holographic microscopy system based on LED illumination and the dual-wavelength polarization synchronous phase-shift dynamic holographic microscopy system based on laser illumination. The optical path structure of the dual-wavelength dynamic holographic microscopy imaging system based on LED illumination of the present invention is adopted. First, an achromatic quarter-wave plate and a pixel polarization camera are used to replace the traditional grating polarization filter and imaging module. While maintaining the low noise and full-field imaging characteristics, the target spectrum corresponding to the LED illumination is shifted to the low-frequency region; then a laser reference light branch is introduced, and a laser with a longer coherence length is used. Instead of the second LED low-coherence light source with a shorter coherence length in the traditional method, the second light source can record the full-field off-axis hologram, and the target spectrum corresponding to the laser illumination is shifted to the high-frequency area; finally, the traditional low-pass filtering method is used to extract the dual-wavelength phase images respectively, and the iterative phase unwrapping method is combined to avoid the influence of laser coherence noise. While maintaining the low-noise and full-field imaging characteristics, the depth measurement range is further expanded, the snapshot imaging performance of the dual-wavelength holographic system is restored and the imaging efficiency is improved, and low-noise, full-field, large-range and snapshot dynamic holographic imaging functions are realized, which has broad application prospects in the fields of three-dimensional morphology characterization and detection of micro-nano devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a light path diagram of an embodiment of a dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to the present invention;

FIG2 is a schematic diagram of the structure of a pixel polarization camera in an embodiment of a dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to the present invention;

FIG3 is a schematic diagram of an imaging process in an embodiment of an imaging method of a dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to the present invention;

FIG4 is a schematic diagram of a spatial multiplexing hologram reconstruction process in an imaging method embodiment of a dual-wavelength dynamic holographic microscopy imaging system based on LED illumination according to the present invention;

Figure 5 is a schematic diagram of the imaging effect improvement of an embodiment of a dual-wavelength dynamic holographic microscopy imaging method based on LED illumination of the present invention, wherein (a) is a laser depth map, (b) is an LED depth map, and (c) is a dual-wavelength expanded depth map of the present invention.

Figure numerals: 1-LED low-coherence light source, 2-first microscope objective, 3-first pinhole aperture, 4-first achromatic lens, 5-first polarization filter, 6-laser coherent light source, 7-second microscope objective, 8-second pinhole aperture, 9-second achromatic lens, 10-second polarization filter, 11-first beam splitter prism, 12-third achromatic lens, 13-second beam splitter prism, 14-third polarization filter, 15-third microscope objective, 16-sample to be measured, 17-fourth polarization filter, 18-fourth microscope objective, 19-first plane reflector, 20-fourth achromatic lens, 21-second plane reflector, 22-achromatic half-wave plate, 23-fifth polarization filter, 24-third beam splitter prism, 25-achromatic quarter-wave plate, 26-pixel polarization camera.

DETAILED DESCRIPTION

The present invention is described in detail below through examples and drawings.

The present invention discloses a dual-wavelength dynamic holographic microscopic imaging system based on LED illumination, as shown in Fig. 1, comprising a dual-wavelength light source module, a first interference branch, a second interference branch and an imaging module. The imaging module comprises a third beam splitter prism 24, an achromatic quarter-wave plate 25 and a pixel polarization camera 26 arranged in sequence.

The dual-wavelength light source module includes a first beam splitter prism 11, an LED illumination light path and a laser illumination light path respectively located on both sides of the first beam splitter prism 11; the LED illumination light path is used to provide 0-π linearly polarized LED plane wave wide beam illumination light, and the laser illumination light path is used to provide horizontally polarized laser plane wave wide beam illumination light. The 0-π linearly polarized LED plane wave wide beam illumination light and the horizontally polarized laser plane wave wide beam illumination light are jointly incident on the first beam splitter prism 11 to form a dual-wavelength illumination combined beam light, and the combined beam light is reflected and transmitted through the first beam splitter prism 11.

The LED illumination optical path includes an LED low coherence light source 1, and a first microscope objective lens 2, a first pinhole aperture 3, a first achromatic lens 4, and a first polarization filter 5 sequentially arranged on the optical path of the LED low coherence light source 1. Among them, the light emitting surface of the LED low coherence light source 1 is located at a position of twice the focal length of the first microscope objective lens 2, the first pinhole aperture 3 is located at the imaging plane of the first microscope objective lens 2, the front focal plane of the first achromatic lens 4 coincides with the plane of the first pinhole aperture 3, and the optical axis of the first polarization filter 5 coincides with the optical axis of the first achromatic lens 4.

The laser illumination optical path includes a laser coherent light source 6 and a second microscope objective lens 7, a second pinhole aperture 8, a second achromatic lens 9 and a second polarizing filter 10 arranged in sequence on the optical path of the laser light source 6. The optical axis of the laser coherent light source 6 and the optical axis of the LED low coherence light source 1 are in the same plane and perpendicular to each other, the second pinhole aperture 8 is located at the focal plane of the second microscope objective lens 7, the front focal plane of the second achromatic lens 9 coincides with the plane of the second pinhole aperture 8, and the optical axis of the second polarizing filter 10 coincides with the optical axis of the second achromatic lens 9; the angles between the normal direction of the semi-transparent and semi-reflective plane of the first beam splitter prism 11 and the optical axis directions of the first achromatic lens 4 and the second achromatic lens 9 are both π/4; the optical axis direction of the second polarizing filter 10 is 0.

The first interference branch and the second interference branch are respectively arranged on the reflected light path and the transmitted light path of the first beam splitter prism 11. The reflected combined light beam forms horizontally linearly polarized laser target light, horizontally linearly polarized LED target light and vertically linearly polarized LED reference light through the first interference branch; the transmitted combined light beam forms vertically linearly polarized laser reference light through the second interference branch.

The first interference branch includes a third achromatic lens 12 and a second beam splitter prism 13 sequentially arranged on the reflected light path of the first beam splitter prism 11, a dual-wavelength target light module and an LED reference light module respectively arranged on the transmitted light path and the reflected light path of the second beam splitter prism 13, and a fourth achromatic lens 20. The dual-wavelength target light module includes a third linear polarizer 14 and a third microscope objective lens 15 sequentially arranged along the transmitted light path of the second beam splitter prism 13. The sample 16 to be measured is located near the working plane of the third microscope objective lens 15. The optical axis direction of the third linear polarizer 14 is 0, which is used to extract the horizontal linear polarization component light of the transmitted light of the second beam splitter prism 13; the target 16 to be measured is illuminated by the third microscope objective lens 15 to form a horizontal linear polarization laser target light and a horizontal linear polarization LED target light. The LED reference light module includes a fourth linear polarizer 17, a fourth microscope objective lens 18 and a first plane reflector 19 sequentially arranged along the reflected light path of the second beam splitter prism 13. The first plane reflector 19 is located near the working plane of the fourth microscope objective lens 18. The optical axis direction of the fourth linear polarizer 17 is π/2, and is used to extract the vertically linearly polarized LED reference light from the reflected light of the second beam splitter prism 13. The horizontally linearly polarized laser target light, the horizontally linearly polarized LED target light, and the vertically linearly polarized LED reference light return to the second beam splitter prism 13 along their respective optical paths and are incident on the fourth achromatic lens 20.

Among them, the distances from the third linear polarizer 14, the third microscope objective lens 15 and the sample to be measured 16 to the second beam splitter prism 13 are respectively the same as the distances from the fourth polarizing filter 17, the fourth microscope objective lens 18 and the first plane reflector 19 to the second beam splitter prism 13. The front focus of the third microscope objective lens 15 and the fourth microscope objective lens 18 coincides with the back focus of the third achromatic lens 12. The front focus of the fourth achromatic lens 20 coincides with the front focus of the third microscope objective lens 15 and the fourth microscope objective lens 18. The focal length of the fourth achromatic lens 20 is respectively greater than the sum of the thickness of the second beam splitter prism 13 and the third polarizing filter 14, and the sum of the thickness of the second beam splitter prism 13 and the fourth polarizing filter 17. The optical path difference from the sample to be measured 16 and the first plane reflector 19 to the second beam splitter prism 13 is less than the coherence length of the LED low coherence light source 1.

The second interference branch includes a second plane reflector 21 arranged on the transmission light path of the first beam splitter prism 11, an achromatic half-wave plate 22 and a fifth polarization filter 23 arranged in sequence on the reflection light path of the second plane reflector 21. The optical axis direction of the achromatic half-wave plate 22 is -π/4, and is used to change the polarization state of the laser reference light in the incident combined beam from horizontal linear polarization to vertical linear polarization, and to be incident on the fifth polarization filter 23 to maintain the vertical polarization state of the light beam, and the optical axis direction of the fifth polarization filter 23 is π/2. The optical axis direction reflected by the second plane reflector 21 is parallel to the optical axis direction of the LED low coherence light source 1; the optical axes of the achromatic half-wave plate 22 and the fifth polarization filter 23 coincide with the optical axis of the LED low coherence light source 1; there is an angle of 1 to 2 degrees between the optical axis of the light beam reflected by the third beam splitter prism 24 and the optical axis of the fourth achromatic lens 20 for separating the spectral components of the LED and the laser hologram; the vertically linearly polarized laser reference light and LED interference light emitted by the fifth polarization filter 23 and the horizontally linearly polarized laser target light, the horizontally linearly polarized LED target light and the vertically linearly polarized LED reference light emitted by the fourth achromatic lens 20 are synchronously emitted into the third beam splitter prism 24.

In the imaging module, the optical axis direction of the achromatic quarter wave plate 25 is -π/4, and the pixel polarization camera 26 includes four linear polarization directions of 0, π/4, π/2, and 3π/4. The pixel polarization camera 26 and the sample to be measured 16 are located at a conjugate plane formed by the third microscope objective 15 and the fourth achromatic lens 20. The structural schematic diagram of the pixel polarization camera 26 is shown in Figure 2, including a three-layer structure of a microlens array, a polarizer array, and a pixel array, wherein the microlens array is used to enhance the light field energy collected by the pixel, and the polarizer array includes four polarization directions of 0, π/4, π/2, and 3π/4 distributed in a 2×2 ring-shaped periodic manner, which are used to realize the polarization synchronous phase shift function, and finally the pixel array records the spatial multiplexing phase shift hologram through the polarizer array.

The first microscope objective 2, the second microscope objective 7, the third microscope objective 15 and the fourth microscope objective 18 are of plan-field achromatic type. The first achromatic lens 4, the second achromatic lens 9, the third achromatic lens 12 and the fourth achromatic lens 20 are all double-cemented lenses. The spectral range of the first polarizing filter 5, the second polarizing filter 9, the third polarizing filter 14, the fourth polarizing filter 17, the fifth polarizing filter 23, the achromatic half-wave plate 22 and the achromatic quarter-wave plate 25 covers the spectral range of the LED low-coherence light source 1 and the laser coherent light source 6. The image sensor model of the pixel polarization camera 26 is any one of SonyIMX250MZR/MYR, IMX264MZR/MYR and IMX253MZR/MYR. The sample to be tested 16 and the first plane reflector 19 are both installed on a displacement stage and a rotating stage, and the third beam splitter prism 24 is installed on another rotating stage, and is used to fine-tune the optical axis directions of the laser target light, LED target light and LED reference light reflected by the first plane reflector 19 reflected by the sample to be tested 16 through the rotating stage, so that the three light path directions are coaxial, and the axial positions of the sample to be tested 16 and the first plane reflector 19 are adjusted through the displacement stage, so that the optical path difference between the LED target light and the LED reference light is within the coherence length range of the LED low coherence light source 1; the optical axis direction of the laser reference light reflected by the third beam splitter prism 24 is adjusted through the rotating stage, so that the branches of the laser reference light and the laser target light are off-axis.

The optical principle of the system of the present invention is realized as follows: the LED low-coherence light source 1 and the laser coherent light source 6 are turned on at the same time; the LED divergent light beam of the spatial and temporal partial coherence LED low-coherence light source 1 with a spectral width of tens of nanometers is incident on the first microscope objective lens 2 and is imaged and focused at the first pinhole aperture 3 to form a reduced image with enhanced brightness; the middle highlight area of the light source conjugate image is intercepted through the first pinhole aperture 3 to improve the spatial coherence of the illumination light beam; the intercepted light source conjugate image is imaged to infinity through the first achromatic lens 4 to eliminate the internal structure of the light source. The laser parallel beam is incident on the second microscope objective 7 and focused on the second pinhole aperture 8 to form an Airy spot light source. The second pinhole aperture 8 intercepts the zero-order Airy spot to reduce the light intensity noise. The point light source is imaged to infinity by the second achromatic lens 9 to form a plane wave, which is then passed through the second polarization filter 10 to form horizontal linear polarized light. The 0-π linear polarized LED beam and the horizontal linear polarized laser beam are combined by the first beam splitter prism 11 to form a dual-wavelength illumination combined light, which is then synchronously split. In the first interference branch, the dual-wavelength combined light reflected by the first beam splitter prism 11 is focused again by the third achromatic lens 12 to form an image, and the focused light beam is incident on the second beam splitter prism 13 for transmission and reflection. The transmitted light of the second beam splitter prism 13 is formed into horizontal linear polarized light by the third polarization filter 14, and the parallel light emitted by the third microscope objective lens 15 is irradiated onto the sample to be tested 16. The sample to be tested 16 is illuminated to form a dual-wavelength target light field, and the dual-wavelength target light field includes horizontally linear polarized laser target light and horizontally linear polarized LED target light; the dual-wavelength target light passes through the second beam splitter prism 13 in sequence. The third microscope objective 15, the third polarizing filter 14, and the second beam splitter prism 13 are incident on the fourth achromatic lens 20; the reflected light of the second beam splitter prism 13 is formed into vertical linear polarized light through the fourth polarizing filter 17 and the horizontal linear polarized laser component in the dual-wavelength reference beam is filtered out, and the parallel light emitted through the fourth microscope objective 18 is irradiated onto the first plane reflector 19 to form vertical linear polarized LED reference light, and the LED reference light is incident on the fourth microscope objective 18, the fourth polarizing filter 17, and the second beam splitter prism 13 in sequence and is incident on the fourth achromatic lens 20. In the second interference branch, the dual-wavelength combined beam transmitted by the first beam splitter prism 11 passes through the second plane reflector 21, and then passes through the achromatic half-wave plate 22 to change the polarization state of the 0-π linearly polarized LED plane wave wide-beam illumination light in the combined beam to π/2-3π/2, and the polarization state of the horizontally polarized laser plane wave wide-beam illumination light component is changed to vertical linear polarization, and is filtered out through the fifth polarization filter 23 to obtain the vertically linearly polarized laser reference light and LED interference light. The horizontally polarized laser target light, the horizontally polarized LED target light, the vertically polarized LED reference light, the vertically polarized laser reference light and the LED interference light are synchronously incident into the third beam splitter prism 24, and then synchronously enter the achromatic quarter-wave plate 25, the horizontally polarized LED target light and the horizontally polarized laser target light are converted into right-handed circularly polarized LED target light and laser target light; the vertically polarized LED reference light and the vertically polarized laser reference light are converted into left-handed circularly polarized LED reference light and laser reference light, wherein the LED interference light is filtered out; the object light and the reference light beam pairs with relative phase shifts of 0, π/2, π, 3π/2 are formed by the pixel polarization camera 26, and the spatially multiplexed phase-shifted hologram is obtained by recording the pixel polarization camera 26, as shown in FIG3 .

At the same time, the present invention also provides a dual-wavelength dynamic holographic microscopic imaging method based on LED illumination, using the above-mentioned dual-wavelength dynamic holographic microscopic imaging system based on LED illumination, comprising the following steps:

1) Install each component according to the preset position;

The light emitting surface of the LED low coherence light source 1 is located near the double focal length of the first microscope objective lens 2, the first pinhole aperture 3 is located at the imaging plane of the first microscope objective lens 2, the front focal plane of the first achromatic lens 4 coincides with the plane of the first pinhole aperture 3, and the optical axis of the first polarizing filter 5 coincides with the optical axis of the first achromatic lens 4; the optical axis of the laser coherent light source 6 and the optical axis of the LED low coherence light source 1 are located in the same plane and are perpendicular to each other, the second pinhole aperture 8 is located at the focal plane of the second microscope objective lens 7, the front focal plane of the second achromatic lens 9 coincides with the plane of the second pinhole aperture 8, and the optical axis of the second polarizing filter 10 coincides with the optical axis of the second achromatic lens 9 ; Make the angle between the normal direction of the semi-transparent and semi-reflective plane of the first beam splitter prism 11 and the optical axis direction of the first achromatic lens 4 and the second achromatic lens 9 be π/4; Make the distance from the third achromatic lens 12 to the first beam splitter prism 11 greater than the sum of the thicknesses of the achromatic half-wave plate 22 and the fifth polarizing filter 23, and the focal length greater than the sum of the thicknesses of the second beam splitter prism 13 and the third polarizing filter 14 or the fourth polarizing filter 17; Make the front focus of the third microscope objective lens 15 and the fourth microscope objective lens 18 coincide with the rear focus of the third achromatic lens 12; Make the sample to be measured 16 and the first plane reflector 19 respectively located between the third microscope objective lens 15 and the fourth microscope objective lens 18; The working plane of the micro-objective lens 18 is near, and the optical path difference to the second beam splitter prism 13 is less than the coherence length of the LED low coherence light source 1; the front focus of the fourth achromatic lens 20 coincides with the front focus of the third microscope objective lens 15 and the fourth microscope objective lens 18, and the focal length of the fourth achromatic lens 20 is greater than the sum of the thicknesses of the second beam splitter prism 13 and the third polarizing filter 14 or the fourth polarizing filter 17; the optical axis direction reflected by the second plane reflector 21 is parallel to the optical axis direction of the LED low coherence light source 1, and the optical axes of the achromatic half wave plate 22 and the fifth polarizing filter 23 coincide with the optical axis of the LED low coherence light source 1; the third beam splitter prism There is a small angle between the optical axis of the light beam reflected by the mirror 24 and the optical axis of the fourth achromatic lens 20; the pixel polarization camera 26 and the sample to be measured 16 are located at the approximate conjugate plane of the wireless conjugate microscopy module composed of the third microscope objective 15 and the fourth achromatic lens 20; the polarization directions of the second polarization filter 10 and the third polarization filter 14 are rotated to the horizontal direction, the polarization directions of the fourth polarization filter 17 and the fifth polarization filter 23 are rotated to the vertical direction, the optical axis directions of the achromatic half wave plate 22 and the achromatic quarter wave plate 25 are rotated to -π/4, and the polarization direction of the first polarization filter 5 is rotated so that the target light field and the reference light field have similar intensities.

2) Turn on the LED low-coherence light source 1 and the laser coherent light source 6 at the same time; use the pixel polarization camera 26 to record and obtain the spatial multiplexing phase-shifted hologram. The 2θ phase-shifted sub-hologram recorded by the pixel array behind the linear polarization filter in the direction of θ in the pixel polarization camera 26 can be expressed as shown in formula (1):

Where: Δk = 1/Λ is the wave number width of the LED low coherence light source, is the coherence length of the LED low coherence light source, λ ₁ and Δλ are the central wavelength and spectral width of the LED low coherence light source respectively, and λ ₂ is the central wavelength of the laser coherent light source; O ₁ ＝|O ₁ |exp(j 2πh _o /λ ₁ ), R ₁ ＝|R ₁ |exp(j 2πh _r1 /λ ₁ ), N ₁ ＝|N ₁ |exp(j 2πh _n1 /λ ₁ ) respectively represent the complex amplitude distributions of the object light field, reference light field and noise light field when illuminated by the LED low coherence light source; O ₂ ＝|O ₂ |exp(j 2πh _o /λ ₂ ), R ₂ ＝|R ₂ |exp(j 2πh _r2 /λ ₂ ), N ₂ ＝|N ₂ |exp(j 2πh _n2 /λ ₂ ) respectively represent the complex amplitude distributions of the object light field, reference light field and noise light field when illuminated by the laser coherent light source; |O ₁ |, |R 1 | ₁ |, |N ₁ | and |O ₂ |, |R ₂ |, |N ₂ | are the corresponding complex amplitude modulus values, h _o represents the equivalent depth of the sample to be tested, h _r1 , h _r2 and h _n1 , h _n2 are the equivalent depths of the reference light and the noise light when illuminated by the LED low coherence light source and the laser coherent light source, wherein h _r1 and h _r2 can be controlled by adjusting the angle and axial position of the reflector 19 and the angle of the beam combining prism 24, respectively, so that |h _o -h _r1 |＜Λ. When the polarizer direction is θ＝0, π/4, π/2, 3π/4, four-step phase shift of 0, π/2, π, 3π/2 can be achieved.

3) Hologram reconstruction, see Figure 4;

3.1) The spatially multiplexed phase-shift hologram is extracted by 1:1 interval downsampling to obtain four sparse phase-shift holograms.

3.2) The blank pixels in the four sparse phase-shift holograms are discarded to form an aligned four-step phase-shift hologram.

3.3) The four-step phase shift algorithm is used to suppress the LED interference light and other zero-order diffraction and twin image noises, and the dual-wavelength target light field complex amplitude image is calculated. The dual-wavelength target light field complex amplitude image is reconstructed by the four-step phase shift algorithm shown in formula (2):

3.4) The dual-wavelength target light field complex amplitude image The spectrum of the LED target image and the spectrum of the laser target image are extracted by Fourier transform to the spatial frequency domain and separated by low-pass filter, and placed in the central low-frequency area of two newly created blank spectrum images.

3.5) Then obtain the LED target complex amplitude image through inverse Fourier transform and laser target complex amplitude image As shown in formula (3) and formula (4):

3.6) Obtain the LED target complex amplitude image and the laser target complex amplitude image through inverse Fourier transform. The two target complex amplitude images can obtain the amplitude map and phase map through modulus and angle calculation. Assume that the reconstructed phase when the LED low coherence light source and the laser coherent light source are illuminated and As shown in formula (5) and formula (6):

Wherein, h _o (＞λ ₁ ,λ ₂ ) is the equivalent depth of the sample to be tested, C ₁ and C ₂ are the corresponding folding phase factors when illuminated by LED low coherence light source and coherent laser, respectively, and ε ₁ and ε ₂ (＞ε ₁ ) are the corresponding dimensionless residual noise factor and coherent noise factor when illuminated by LED low coherence light source and laser coherent light source, respectively.

3.7) Perform a preliminary phase unwrapping of the two phase images by direct difference calculation to obtain a difference phase image; the dual-wavelength difference phase unwrapping method shown in formula (7) can remove the influence of phase folding distortion and obtain a difference phase image under equivalent synthetic wavelength illumination:

is the difference phase diagram;

and These are the reconstructed phase images when illuminated by LED low-coherence light source and laser coherent light source respectively;

Λ ₁₂ =λ ₁ λ ₂ /|λ ₂ -λ ₁ |, which is the equivalent synthetic wavelength formed by the two beams of central wavelengths λ ₁ and λ ₂ ;

ε ₁₂ is the noise factor in the difference phase unwrapping;

h _o is the equivalent depth of the sample to be tested;

ε ₁ and ε ₂ are the dimensionless residual noise factor and coherent noise factor corresponding to the illumination of LED low-coherence light source and laser coherent light source, respectively, ε ₂ ＞ε ₁ ;

Although the dual-wavelength difference phase unwrapping method can remove the folding phase distortion and improve the phase measurement accuracy, there is a noise amplification problem in the inverted depth image. The measured depth accuracy ε ₁₂ Λ ₁₂ is much lower than the depth accuracy ε ₁ λ ₁ and ε ₂ λ ₂ of the single-wavelength phase image reconstruction without folding distortion in the ideal case.

3.8) To solve the problem of deep noise amplification in the dual-wavelength difference phase unwrapping method, the iterative phase unwrapping process shown in equations (8) and (9) is adopted. First, the dual-wavelength difference phase map Get the folding phase factor C ₁ when illuminated by LED low coherence light source:

3.9) Then use the folding phase factor C ₁ to adjust the folding phase The phase unwrapping process is iterated and multiplied by the depth inversion proportional coefficient λ ₁ /2π, as shown in formula (9), thereby expanding the depth measurement range and improving the depth measurement accuracy, while restoring the depth measurement accuracy to the partially coherent single wavelength level ε ₁ λ ₁ without coherent noise interference, and obtaining a low-noise, full-field, large-range and snapshot inversion depth image h ₁ . The formula for obtaining the inversion depth image h ₁ by unwrapping the LED phase image using the obtained folding phase factor C ₁ is:

_h1 is the inverted depth image.

In order to solve the problem of depth noise amplification in the dual-wavelength difference phase unwrapping method, round is a rounding function, and its establishment condition is approximately Λ ₁₂ ≤λ ₁ /2ε ₁₂ , which can usually be satisfied in the fields of biological cell imaging and MEMS industrial device detection at a depth of micrometers. Figure 4 shows the above-mentioned hologram reconstruction flow chart, and Figure 5 shows a schematic diagram of the imaging effect obtained by the dual-wavelength dynamic holographic microscopy imaging method based on LED illumination of the present invention, wherein (a) is a depth image of the measured target under laser illumination that is severely affected by coherent noise in the above-mentioned dual-wavelength digital holography, and (b) is a depth image of the measured target under LED illumination in which coherent noise is suppressed in the above-mentioned dual-wavelength digital holography. The depth range between the minimum and maximum depths measured by both is less than a single illumination wavelength,

Figure (c) shows the depth image measured by the proposed method, which suppresses coherent noise while expanding the depth measurement range. The measurement range depends on the equivalent synthetic wavelength of the LED and the laser.

Claims (10)

1. A dual-wavelength dynamic holographic microscopic imaging system based on LED illumination, characterized in that it comprises a dual-wavelength light source module, a first interference branch, a second interference branch and an imaging module; The dual-wavelength light source module comprises a first beam splitter prism (11), an LED illumination light path and a laser illumination light path respectively located on both sides of the first beam splitter prism (11); the LED illumination light path is used to provide 0-π linearly polarized LED plane wave wide beam illumination light, and the laser illumination light path is used to provide horizontally polarized laser plane wave wide beam illumination light; Linearly polarized LED plane wave wide beam illumination light of 0 to π and horizontally polarized laser plane wave wide beam illumination light are jointly incident on a first beam splitter prism (11) to form a dual-wavelength illumination combined beam light, and the combined beam light is reflected and transmitted through the first beam splitter prism (11); The first interference branch and the second interference branch are respectively arranged on a reflection light path and a transmission light path of a first beam splitter prism (11); The reflected combined light beam forms a horizontally linearly polarized laser target light, a horizontally linearly polarized LED target light and a vertically linearly polarized LED reference light through a first interference branch; The transmitted combined light beam forms a vertically linearly polarized laser reference light through a second interference branch; The imaging module comprises a third beam splitter prism (24), an achromatic quarter wave plate (25) and a pixel polarization camera (26) which are arranged in sequence; the optical axis direction of the achromatic quarter wave plate (25) is -π/4, and the pixel polarization camera (26) comprises four linear polarization directions of 0, π/4, π/2 and 3π/4; The horizontally polarized laser target light, the horizontally polarized LED target light, the vertically polarized LED reference light and the vertically polarized laser reference light are synchronously injected into a third beam splitter prism (24), and then synchronously enter an achromatic quarter-wave plate (25); the horizontally polarized LED target light and the horizontally polarized laser target light are converted into right-handed circularly polarized LED target light and laser target light; the vertically polarized LED reference light and the vertically polarized laser reference light are converted into left-handed circularly polarized LED reference light and laser reference light; a pixel polarization camera (26) forms an object light and reference light beam pair with relative phase shifts of 0, π/2, π, and 3π/2, and the pixel polarization camera (26) records the spatially multiplexed phase-shifted hologram. 2. The dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to claim 1, characterized in that: The first interference branch comprises a third achromatic lens (12) and a second beam splitter prism (13) which are sequentially arranged on a reflected light path of the first beam splitter prism (11), a dual-wavelength target light module and an LED reference light module which are respectively arranged on a transmitted light path and a reflected light path of the second beam splitter prism (13), and a fourth achromatic lens (20); The dual-wavelength target light module comprises a third linear polarizing plate (14) and a third microscope objective lens (15) which are sequentially arranged along the transmission light path of the second beam splitter prism (13); the sample to be measured (16) is located near the working plane of the third microscope objective lens (15); the optical axis direction of the third linear polarizing plate (14) is 0, and is used to extract the horizontal linear polarization component light of the transmission light of the second beam splitter prism (13); the target to be measured (16) is illuminated by the third microscope objective lens (15) to form horizontal linear polarized laser target light and horizontal linear polarized LED target light; The LED reference light module comprises a fourth linear polarizing plate (17), a fourth microscope objective lens (18) and a first plane reflector (19) which are sequentially arranged along the reflected light path of the second beam splitter prism (13); the first plane reflector (19) is located near the working plane of the fourth microscope objective lens (18); the optical axis direction of the fourth linear polarizing plate (17) is π/2, and is used to extract vertical linear polarized LED reference light from the reflected light of the second beam splitter prism (13); the horizontal linear polarized laser target light, the horizontal linear polarized LED target light and the vertical linear polarized LED reference light respectively return to the second beam splitter prism (13) along their respective optical paths and are incident on the fourth achromatic lens (20); The distances from the third linear polarizing plate (14), the third microscope objective lens (15) and the sample to be measured (16) to the second beam splitter prism (13) are respectively the same as the distances from the fourth polarizing filter (17), the fourth microscope objective lens (18) and the first plane reflector (19) to the second beam splitter prism (13); The front focal points of the third microscope objective lens (15) and the fourth microscope objective lens (18) coincide with the rear focal point of the third achromatic lens (12); the front focal point of the fourth achromatic lens (20) coincides with the front focal points of the third microscope objective lens (15) and the fourth microscope objective lens (18); the focal length of the fourth achromatic lens (20) is respectively greater than the sum of the thicknesses of the second beam splitter prism (13) and the third polarizing filter (14), and the sum of the thicknesses of the second beam splitter prism (13) and the fourth polarizing filter (17); The optical path difference between the sample to be tested (16), the first plane reflector (19) and the second beam splitter prism (13) is smaller than the coherence length of the LED low-coherence light source (1); The pixel polarization camera (26) and the sample to be measured (16) are located at a conjugate plane formed by the third microscope objective lens (15) and the fourth achromatic lens (20). 3. A dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to claim 1 or 2, characterized in that: The second interference branch comprises a second plane reflector (21) arranged on the transmission light path of the first beam splitter (11), an achromatic half-wave plate (22) and a fifth polarization filter (23) arranged in sequence on the reflection light path of the second plane reflector (21); the optical axis direction of the achromatic half-wave plate (22) is -π/4, and is used to change the polarization state of the laser reference light in the incident combined light beam from horizontal linear polarization to vertical linear polarization, and to be incident on the fifth polarization filter (23) to maintain the vertical polarization state of the light beam; the optical axis direction of the fifth polarization filter (23) is π/2; The optical axis direction reflected by the second plane reflector (21) is parallel to the optical axis direction of the LED low-coherence light source (1); The optical axes of the achromatic half-wave plate (22) and the fifth polarization filter (23) coincide with the optical axis of the LED low-coherence light source (1); There is an angle between the optical axis of the light beam reflected by the third beam splitter prism (24) and the optical axis of the fourth achromatic lens (20); The vertically linearly polarized laser reference light emitted by the fifth polarization filter (23) and the horizontally linearly polarized laser target light, the horizontally linearly polarized LED target light and the vertically linearly polarized LED reference light emitted by the fourth achromatic lens (20) are synchronously emitted into the third beam splitter prism (24). 4. The dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to claim 3, characterized in that: The LED illumination light path comprises an LED low-coherence light source (1), and a first microscope objective lens (2), a first pinhole aperture (3), a first achromatic lens (4), and a first polarization filter (5) which are sequentially arranged on the light path of the LED low-coherence light source (1); The light emitting surface of the LED low-coherence light source (1) is located at a position twice the focal length of the first microscope objective lens (2), the first pinhole diaphragm (3) is located at an imaging plane of the first microscope objective lens (2), the front focal plane of the first achromatic lens (4) coincides with the plane of the first pinhole diaphragm (3), and the optical axis of the first polarization filter (5) coincides with the optical axis of the first achromatic lens (4); The laser illumination optical path comprises a laser coherent light source (6), and a second microscope objective lens (7), a second pinhole aperture (8), a second achromatic lens (9) and a second polarization filter (10) which are sequentially arranged on the optical path of the laser light source (6); The optical axis of the laser coherent light source (6) and the optical axis of the LED low coherent light source (1) are in the same plane and perpendicular to each other; the second pinhole diaphragm (8) is located at the focal plane of the second microscope objective (7); the front focal plane of the second achromatic lens (9) coincides with the plane of the second pinhole diaphragm (8); the optical axis of the second polarizing filter (10) coincides with the optical axis of the second achromatic lens (9); the angles between the normal direction of the semi-transparent and semi-reflective plane of the first beam splitting prism (11) and the optical axis directions of the first achromatic lens (4) and the second achromatic lens (9) are both π/4; and the optical axis direction of the second polarizing filter (10) is 0. 5. The dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to claim 4, characterized in that: The first microscope objective lens (2), the second microscope objective lens (7), the third microscope objective lens (15) and the fourth microscope objective lens (18) are of plan-field achromatic type; The first achromatic lens (4), the second achromatic lens (9), the third achromatic lens (12) and the fourth achromatic lens (20) are all doublet lenses. 6. The dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to claim 5, characterized in that: The spectral ranges of the first polarization filter (5), the second polarization filter (9), the third polarization filter (14), the fourth polarization filter (17), the fifth polarization filter (23), the achromatic half-wave plate (22) and the achromatic quarter-wave plate (25) cover the spectral ranges of the LED low-coherence light source (1) and the laser coherent light source (6). 7. The dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to claim 6, characterized in that: The image sensor model of the pixel polarization camera (26) is any one of SonyIMX250MZR/MYR, IMX264MZR/MYR and IMX253MZR/MYR. 8. The dual-wavelength dynamic holographic microscopic imaging system based on LED illumination according to claim 7, characterized in that: The sample to be tested (16) and the first plane reflector (19) are mounted on a displacement stage and a rotation stage, and the third beam splitter prism (24) is mounted on another rotation stage. 9. A dual-wavelength dynamic holographic microscopy imaging method based on LED illumination, using the dual-wavelength dynamic holographic microscopy imaging system based on LED illumination according to any one of claims 1 to 8, characterized in that it comprises the following steps: 1) Install each component according to the preset position; 2) simultaneously turning on the LED low-coherence light source (1) and the laser coherent light source (2); using a pixel polarization camera (26) to record and obtain a spatially multiplexed phase-shifted hologram; 3) Hologram reconstruction 3.1) The spatially multiplexed phase-shift hologram is extracted by 1:1 interval downsampling to obtain four sparse phase-shift holograms; 3.2) discarding the blank pixels in the four sparse phase-shift holograms to form an aligned four-step phase-shift hologram; 3.3) The four-step phase shift algorithm is used to suppress the LED interference light and the remaining zero-order diffraction and twin image noise in the four-step phase shift hologram, and the dual-wavelength target light field complex amplitude image is calculated; 3.4) The dual-wavelength target light field complex amplitude image is separated into the spatial frequency domain by Fourier transformation, and the LED target image spectrum and the laser target image spectrum are respectively extracted by low-pass filter and placed in the central low-frequency area of two newly created blank spectrum images; 3.5) Then, the LED target complex amplitude image and the laser target complex amplitude image are obtained by inverse Fourier transform; 3.6) The LED target complex amplitude image and the laser target complex amplitude image are subjected to modulus and angle calculations to obtain the corresponding amplitude and phase images; 3.7) Performing preliminary phase unwrapping on the two phase images by direct difference calculation to obtain a difference phase image; 3.8) further iteratively obtain the integer folding phase factor in the LED phase diagram using an iterative formula based on the phase diagram after the preliminary phase unwrapping; 3.9) The obtained integer folded phase factor is used to unfold the LED phase image to obtain a low-noise, full-field, large-range and snapshot inversion depth image. 10. The dual-wavelength dynamic holographic microscopic imaging method based on LED illumination according to claim 9, characterized in that: In step 3.7), the direct difference calculation formula is: is the difference phase diagram; and These are the reconstructed phase images when illuminated by LED low-coherence light source and laser coherent light source respectively; Λ ₁₂ =λ ₁ λ ₂ /|λ ₂ -λ ₁ | is the equivalent synthetic wavelength formed by the two beams of central wavelengths λ ₁ and λ ₂ ; ε ₁₂ is the noise factor in the difference phase unwrapping; h ₀ is the equivalent depth of the sample to be tested; ε ₁ and ε ₂ are the dimensionless residual noise factor and coherent noise factor corresponding to the illumination of LED low-coherence light source and laser coherent light source, respectively, v ₂ >ε ₁ ; In step 3.8), the iteration formula is: C ₁ is the integer folding phase factor; round is the rounding function; In step 3.9), the formula for obtaining the inverted depth image is: _h1 is the inverted depth image.