A dual-wavelength digital holography system and method

Abstract

The application relates to a dual-wavelength digital holographic system and method, wherein the system comprises an LED illumination module, a polarizer, a polarization filter device, a stage device, an infinite imaging microscope objective, a lens barrel, a normal incidence grating, a first lens, a spatial filter, a second lens and a monochrome black-and-white image sensor which are sequentially connected. The technical scheme provided by the application improves the precision of holographic imaging while simplifying the system architecture.

Description

Technical Field

[0001] This invention relates to the field of holographic imaging technology, and more specifically, to a dual-wavelength digital holographic system and method. Background Technology

[0002] Digital holographic microscopy is a high-precision optical measurement technique that combines traditional optical microscopy with holographic imaging to quantitatively obtain the phase distribution of a sample. It features non-destructive, full-field-of-view, rapid, non-contact, and high-precision characteristics, and is widely used in surface microstructure measurement and biological cell imaging. Traditional digital holographic microscopy requires first constructing a wrapped phase from the hologram, and then using an unwrapping algorithm to unfold the wrapped phase into a continuous phase map. Its drawbacks are also significant: the unwrapping algorithm is computationally intensive, and unwrapping may fail when the sample exhibits excessively high phase transitions. To address these issues, dual-wavelength digital holography has been proposed.

[0003] The advantage of dual-wavelength digital holography over single-wavelength digital holographic microscopy lies in its ability to obtain a larger composite wavelength by selecting two wavelengths, theoretically allowing for the measurement of samples with greater height and larger abrupt changes. Furthermore, this technique uses two wavelengths of light to measure the sample, enabling the continuous recording of multiple phase images at different wavelengths. By calculating the phase difference between the two wavelengths, a phase map of the equivalent wavelength can be obtained. Because the composite wavelength is larger than either of the introduced wavelengths, this technique significantly expands the measurement range of digital holographic microscopy.

[0004] However, in the field of dual-wavelength digital holography research, two lasers of different wavelengths are usually required to introduce the synthesized wavelength. This is not only costly, but the two coherent light sources of different wavelengths also introduce a lot of noise into the interference optical path, which greatly affects the accuracy of phase recovery. On the other hand, most current dual-wavelength digital holography techniques are based on the non-common-path structure of Mach-Zehnder or Michelson interferometers. Both beams are subject to environmental interference, which leads to poor time stability of the system, unstable fringes, and considerable phase errors.

[0005] Therefore, there is an urgent need for a dual-wavelength digital holographic system with a simpler architecture and higher precision. Summary of the Invention

[0006] In view of this, it is necessary to provide a dual-wavelength digital holographic system and method to address the above problems, thereby improving the accuracy of holographic imaging while simplifying the system architecture.

[0007] To achieve the above objectives, the present invention provides a dual-wavelength digital holographic system, comprising, in sequence, an LED illumination module, a polarizer, a polarization filter, a stage, an infinity imaging microscope objective, a tube lens, an orthogonal grating, a first lens, a spatial filter, a second lens, and a monochrome image sensor, wherein:

[0008] The light emitted from the LED lighting module is adjusted to be positive by the polarizer and then incident perpendicularly on the polarization filter device to generate two lighting light waves with different wavelengths and orthogonal polarization directions.

[0009] The illumination light wave passes through the sample to be tested placed on the stage device. The imaging beam after being scattered by the sample to be tested is collected by the infinity imaging microscope objective, and after being focused by the lens of the microscope tube, it is diffracted through the orthogonal grating.

[0010] The 0th order diffracted light generated by the orthogonal grating propagates along the original path and passes through the spatial filter to serve as the reference light. The two +1st order diffracted lights converge after passing through the first lens and then pass through the spatial filter to serve as the two object lights.

[0011] The object light and reference light filtered by the spatial filter are converged onto the imaging surface of the monochrome image sensor by the second lens, and the monochrome image sensor captures and records orthogonal carrier frequency interference fringes.

[0012] In one embodiment, the polarization filtering device includes a first Wollaston prism, a third lens, a first filter, a second filter, a fourth lens, and a second Wollaston prism arranged sequentially along the beam propagation direction.

[0013] Wherein, the first Wollaston prism is located on the front focal plane of the third lens, the second Wollaston prism is placed on the rear focal plane of the fourth lens, and the first filter and the second filter are distributed on different paths between the third lens and the fourth lens;

[0014] The first Wollaston prism is used to cut the linearly polarized illumination light wave output by the polarizer at an angle. The first filter and the second filter are used to generate illumination light waves of different wavelengths. The second Wollaston prism is used to re-bundle the illumination light waves of different wavelengths.

[0015] In one embodiment, the center wavelength of the first filter is 590 nm, the center wavelength of the second filter is 633 nm, and the full width at half maximum (FWHM) of both the first filter and the second filter is 1 nm.

[0016] In one embodiment, the spatial filter includes a first device, a second device, and a third device, wherein the first device is used to filter the 0th order diffracted light passing through the orthogonal grating into an ideal uniform spherical wave and use it as a reference beam in the interference; the second device allows only light polarized along the x-direction to pass through, and obtains a first object beam after filtering; the third device allows only light polarized along the y-direction to pass through, and obtains a second object beam after filtering.

[0017] In one embodiment, the center wavelength of the LED lighting module is 610 nm and the full width at half maximum (FWHM) is 50 nm.

[0018] In one embodiment, the orthogonal grating is located on the back focal plane of the lens barrel and is used to converge two orthogonally polarized beams with a certain angle to the same position to achieve wavefront matching between the reference beam and the object beam.

[0019] To achieve the above objectives, another aspect of the present invention provides a dual-wavelength digital holography method, the method comprising:

[0020] After the emitted light is adjusted to be positive, two illumination light waves with different wavelengths and orthogonal polarization directions are generated.

[0021] The imaging beam, after being scattered by the sample under test, is focused to produce diffracted light.

[0022] The 0th-order diffracted light propagates along its original path and forms a reference light. The two +1st-order diffracted lights converge and are filtered into two object lights.

[0023] The object light and the reference light converge onto the imaging surface to generate orthogonal carrier frequency interference fringes.

[0024] In one embodiment, after the emitted light is adjusted for polarization, two illumination light waves with different wavelengths and orthogonal polarization directions are generated, including:

[0025] The light emitted from the LED lighting module is polarized by a polarizer and then incident perpendicularly onto a polarization filter to generate two beams of lighting light with different wavelengths and orthogonal polarization directions.

[0026] In one embodiment, the imaging beam, after being scattered by the sample under test, is focused to generate diffracted light, including:

[0027] The illumination light wave passes through the sample to be tested placed on the stage device. The imaging beam scattered by the sample to be tested is collected by the infinity imaging microscope objective, and after being focused by the lens in the microscope tube, it is diffracted through the orthogonal grating to produce diffracted light.

[0028] In one embodiment, the object beam and the reference beam converge onto the imaging plane to generate orthogonal carrier frequency interference fringes, including:

[0029] The object light and reference light, after being filtered by the spatial filter, are converged onto the imaging surface of the monochrome image sensor by the second lens, and the monochrome image sensor captures and records the orthogonal carrier frequency interference fringes.

[0030] The beneficial effects of this invention are as follows:

[0031] The technical solution provided by this invention enables dual-wavelength interferometry using only a partially coherent light source, significantly reducing the impact of coherent noise from the coherent light source, improving the overall system's measurement accuracy, saving experimental costs, and lowering the research threshold for dual-wavelength interferometry technology. Furthermore, the unique common-path structure of this invention ensures that the object light path and the reference light path propagate along the same path, making the impact of environmental noise on the two light waves almost identical, greatly improving the system's stability and measurement accuracy. In addition, this invention uses a broadband light source, allowing for flexible selection of filters with different center wavelengths to filter out the desired wavelength according to the actual conditions of the sample under test, thus achieving dual-wavelength digital holography of any two wavelengths.

[0032] Finally, the present invention can simultaneously capture two off-axis interferograms with orthogonal fringe directions, minimizing the overlap of interference fringes at each wavelength, and can easily select spatial frequencies of different wavelengths in the Fourier spectrum to separate phase information at different wavelengths. Attached Figure Description

[0033] Figure 1 A schematic diagram of the structure of a dual-wavelength digital holographic system according to one embodiment of the present invention is shown;

[0034] Figure 2 This is a schematic diagram of the structure of a polarization filtering device in one embodiment of the present invention;

[0035] Figure 3 This is a background hologram captured by a monochrome black-and-white image sensor when no sample is placed.

[0036] Figure 4 This is a hologram with phase information of the object, acquired by a monochrome black-and-white image sensor after the sample is placed.

[0037] Figure 5 The spectrum is obtained by calculating the Fourier transform algorithm after a hologram containing object phase information acquired by a monochrome black and white image sensor is processed.

[0038] Figure 6 To calculate the phase map of the sample at the synthesized wavelength based on the obtained spectrum;

[0039] Figure 7 A schematic diagram illustrating the steps of a dual-wavelength digital holographic method according to one embodiment of the present invention is shown. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be further described clearly and completely below in conjunction with the embodiments of this invention. It should be noted that the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] Example 1

[0042] Please see Figure 1 One embodiment of the present invention provides a dual-wavelength digital holographic system, the system comprising, in sequence, an LED illumination module 101, a polarizer 102, a polarization filter 103, a stage device 104, an infinity imaging microscope objective 105, a tube lens 106, an orthogonal grating 107, a first lens 108, a spatial filter 109, a second lens 110, and a monochrome image sensor 111, wherein:

[0043] The light emitted from the LED lighting module 101 is adjusted to be positive by the polarizer 102 and then incident vertically on the polarization filter 103 so that the polarization filter 103 generates two beams of lighting light waves with different wavelengths and orthogonal polarization directions.

[0044] The illumination light wave passes through the sample to be tested placed on the stage device 104. The imaging beam after being scattered by the sample to be tested is collected by the infinity imaging microscope objective 105, and after being converged by the lens 106, it is diffracted through the orthogonal grating 107.

[0045] The zeroth-order diffraction light generated by the orthogonal grating 107 propagates along the original path and passes through the spatial filter 109 to serve as the reference light. The two +1st-order diffraction lights converge after passing through the first lens 108 and then pass through the spatial filter 109 to serve as the two object lights, respectively.

[0046] The object light and reference light filtered by the spatial filter 109 are converged by the second lens 110 onto the imaging surface of the monochrome image sensor 111, and the monochrome image sensor 111 captures and records orthogonal carrier frequency interference fringes.

[0047] In practical applications, the center wavelength of the LED lighting module 101 is 610nm and the half-width at half-maximum (WHM) is 50nm.

[0048] The light transmission axis of the polarizer 102 lies in the xy plane of the coordinate axis and makes an angle of 45° with the x-axis.

[0049] The center wavelengths of the two filters in the polarization filter device 103 are 590nm and 633nm, respectively; the full width at half maximum (FWHM) of both filters is 1nm.

[0050] During operation, the light emitted from the LED lighting module 101 is polarized by the polarizer 102 and then incident perpendicularly on the polarization filter 103, generating two orthogonally linearly polarized lights with different wavelengths and strictly consistent transmission paths. This beam passes through the sample to be tested placed on the stage device 104. The image beam scattered by the sample is collected by the infinity imaging microscope objective 105 and converged by the tube lens 106. It then undergoes diffraction through the orthogonal grating 107. The strongest 0th-order diffracted light continues to propagate along its original path and is filtered by device a (first device) on the spatial filter 109, becoming the reference light. The two weaker +1st-order diffracted lights are converged by the first lens 108 and then pass through devices b (second device) and c (third device) on the spatial filter 109 to become the object light. Device b only allows light polarized along the x-direction to pass through, resulting in object light λ1 (first object light); device c only allows light polarized along the y-direction to pass through, resulting in object light λ2 (second object light). The object light and reference light, filtered by spatial filter 109, are converged by second lens 110 onto the imaging surface of monochrome image sensor 111, where they are simultaneously captured and recorded by monochrome image sensor 111 to obtain orthogonal carrier frequency interference fringes. Phase reconstruction of the dual-wavelength digital hologram can then be achieved based on the digital hologram acquired by monochrome image sensor 111.

[0051] In this embodiment, the transmission axis of the polarizer in the polarizer 102 lies in the xy-plane, which is used to split the illumination light emitted from the LED lighting module 101 into linearly polarized light along the x-axis and y-axis. The intensity ratio of the two polarized beams can be arbitrarily adjusted by adjusting the direction of the transmission axis of the polarizer.

[0052] The polarization filter device 103, such as Figure 2 As shown, it includes a first Wollaston prism 1031, a third lens 1032, a first filter 1033, a second filter 1034, a fourth lens 1035, and a second Wollaston prism 1036 arranged sequentially along the beam propagation direction, for filtering out two illumination light waves with different wavelengths and mutually orthogonal polarization directions.

[0053] Specifically, the first Wollaston prism is located on the front focal plane of the third lens, the second Wollaston prism is placed on the rear focal plane of the fourth lens, and the first filter and the second filter are distributed on different paths between the third lens and the fourth lens;

[0054] The first Wollaston prism is used to cut the linearly polarized illumination light wave output by the polarizer at an angle. The first filter and the second filter are used to generate illumination light waves of different wavelengths. The second Wollaston prism is used to re-bundle the illumination light waves of different wavelengths.

[0055] For example, in practical applications, the first Wollaston prism is located at the front focal plane of the third lens, and its slow axis is along the x-axis, which is used to cut linearly polarized illumination waves with polarization directions along the x-axis and y-axis at small angles.

[0056] The center wavelengths of the first filter and the second filter can be arbitrarily selected within the spectral range of the illumination source to obtain two illumination light waves λ1 and λ2 of different wavelengths.

[0057] The second Wollaston prism is placed on the back focal plane of the fourth lens in the xy plane, mirroring the first Wollaston prism. Its slow axis is along the x-axis, and it is used to re-bundle the two wavelengths of illumination light waves filtered out by the first and second filters, and to ensure that the transmission paths of the two light waves are consistent. The illumination light wave λ1 is polarized along the x-axis, and the illumination light wave λ2 is polarized along the y-axis.

[0058] The orthogonal grating 107 is located on the back focal plane of the lens barrel 106 to ensure that two beams of orthogonally polarized light with a certain angle are converged to the same position, thereby achieving wavefront matching between the reference light wave and the object light wave, and finally obtaining interference fringes with high contrast.

[0059] The spatial filter 109 may include three devices. Device a is used to filter the 0th order diffracted light passing through the orthogonal grating into an ideal uniform spherical wave and use it as a reference beam in the interference; device b of the spatial filter only allows light polarized along the x-direction to pass through, and obtains the object beam λ1 after filtering; device c only allows light polarized along the y-direction to pass through, and obtains the object beam λ2 after filtering.

[0060] To test the feasibility of the technical solution provided by this invention, it is possible to target... Figure 1 The system shown was used for experimental verification.

[0061] During measurement, the optical path is first adjusted until the monochrome image sensor 111 acquires orthogonal carrier frequency fringes as background information. The acquired background information is as follows: Figure 3 As shown. After acquiring the background information, the sample is placed on the stage device 104 and focused by the infinity imaging microscope objective 105. An interferogram containing the sample's phase information is acquired by the monochrome black and white image sensor 111. The acquired interferogram containing the sample's phase information is shown in the figure. Figure 4 As shown. The spectrum obtained by the Fourier transform algorithm is shown below. Figure 5 As shown, the phase information of the sample at the synthesized wavelength can finally be recovered from the obtained spectrum. Figure 6 As shown.

[0062] The technical solution provided by this invention enables dual-wavelength interferometry using only a partially coherent light source, significantly reducing the impact of coherent noise from the coherent light source, improving the overall system's measurement accuracy, saving experimental costs, and lowering the research threshold for dual-wavelength interferometry technology. Furthermore, the unique common-path structure of this invention ensures that the object light path and the reference light path propagate along the same path, making the impact of environmental noise on the two light waves almost identical, greatly improving the system's stability and measurement accuracy. In addition, this invention uses a broadband light source, allowing for flexible selection of filters with different center wavelengths to filter out the desired wavelength according to the actual conditions of the sample under test, thus achieving dual-wavelength digital holography of any two wavelengths.

[0063] Finally, the present invention can simultaneously capture two off-axis interferograms with orthogonal fringe directions, minimizing the overlap of interference fringes at each wavelength, and can easily select spatial frequencies of different wavelengths in the Fourier spectrum to separate phase information at different wavelengths.

[0064] Example 2

[0065] In another aspect, the present invention also provides a dual-wavelength digital holography method, such as... Figure 7 As shown, the method may include the following steps.

[0066] S1: After the emitted light is adjusted to be positive, two illumination light waves with different wavelengths and orthogonal polarization directions are generated.

[0067] S2: The imaging beam, after being scattered by the sample under test, is focused to produce diffracted light;

[0068] S3: The 0th order diffracted light propagates along the original path and forms the reference light. The two +1st order diffracted lights converge and are filtered into two object lights.

[0069] S4: The object light and the reference light converge onto the imaging surface to generate orthogonal carrier frequency interference fringes.

[0070] In one embodiment, after the emitted light is adjusted for polarization, two illumination light waves with different wavelengths and orthogonal polarization directions are generated, including:

[0071] The light emitted from the LED lighting module is polarized by a polarizer and then incident perpendicularly onto a polarization filter to generate two beams of lighting light with different wavelengths and orthogonal polarization directions.

[0072] In one embodiment, the imaging beam, after being scattered by the sample under test, is focused to generate diffracted light, including:

[0073] The illumination light wave passes through the sample to be tested placed on the stage device. The imaging beam scattered by the sample to be tested is collected by the infinity imaging microscope objective, and after being focused by the lens in the microscope tube, it is diffracted through the orthogonal grating to produce diffracted light.

[0074] In one embodiment, the object beam and the reference beam converge onto the imaging plane to generate orthogonal carrier frequency interference fringes, including:

[0075] The object light and reference light, after being filtered by the spatial filter, are converged onto the imaging surface of the monochrome image sensor by the second lens, and the monochrome image sensor captures and records the orthogonal carrier frequency interference fringes.

[0076] In a specific application example, the above solution can be implemented through the following specific steps:

[0077] Step 1: The light emitted from the LED lighting module is polarized by a polarizer and then incident directly into the polarization filter, which then generates two beams of orthogonally linearly polarized light with different wavelengths and strictly consistent transmission paths.

[0078] Step 2: Two linearly polarized beams of different wavelengths are scattered by the sample on the stage and then collected by the infinity imaging microscope objective and collimated by the lens in the microscope tube for imaging.

[0079] Step 3: Place an orthogonal grating on the imaging plane of the lens tube to generate different diffraction orders carrying sample information. The 0th order diffracted light propagates along the original optical axis, while the ±1st order diffracted light continues to propagate after being separated by a certain angle.

[0080] Step 4: Place the first lens behind the orthogonal grating, ensuring that the orthogonal grating is located on the front focal plane of the first lens, so that the beams diffracted by the orthogonal grating converge to a single point after passing through the first lens. Simultaneously, the first lens and the second lens together form a 4f system.

[0081] Step 5: Place the spatial filter on the Fourier plane of the 4f system described above. Specifically, device a of the spatial filter is used to filter the 0th-order diffracted light passing through the orthogonal grating into an ideal uniform spherical wave, which serves as the reference beam in the interference; devices b and c of the spatial filter are used to filter the +1st-order diffracted light passing through the orthogonal grating to obtain object beams λ1 and λ2, respectively, containing complete sample information.

[0082] Step 6: The object beams λ1 and λ2, carrying complete sample information, interfere with the reference light at the back focal plane of the 4f system, generating orthogonal carrier frequency interference fringes. These fringes are captured and recorded in one go by a monochrome black and white image sensor, and the phase information of the sample is recovered by a Fourier transform algorithm.

[0083] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0084] (1) The technical solution provided by the present invention can realize dual-wavelength interferometric measurement by using only a partially coherent light source, which greatly reduces the influence of coherent noise brought by the coherent light source, improves the measurement accuracy of the whole system, saves experimental costs, and lowers the research threshold of dual-wavelength interferometric measurement technology.

[0085] (2) The technical solution provided by the present invention has a unique common path structure that makes the object optical path and the reference optical path propagate along the same path. The interference of environmental noise has almost the same effect on the two light waves, which greatly improves the stability and measurement accuracy of the system.

[0086] (3) The technical solution provided by the present invention uses a broadband light source and can flexibly select filters with different center wavelengths to filter out the desired wavelength according to the actual situation of the sample to be tested, so as to realize dual-wavelength digital holography of any two wavelengths.

[0087] (4) The technical solution provided by the present invention captures two off-axis interference patterns with orthogonal fringe directions simultaneously by a monochrome black and white image sensor, so that the overlap of interference fringes at each wavelength is minimized. In this way, the spatial frequencies of different wavelengths in the Fourier spectrum can be easily selected to separate the phase information at that wavelength.

[0088] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A dual-wavelength digital holographic system, characterized in that, The system includes, in sequence, an LED illumination module, a polarizer, a polarization filter, a stage, an infinity imaging microscope objective, a tube lens, an orthogonal grating, a first lens, a spatial filter, a second lens, and a monochrome image sensor, wherein: The light emitted from the LED lighting module is adjusted to be positive by the polarizer and then incident perpendicularly on the polarization filter device to generate two lighting light waves with different wavelengths and orthogonal polarization directions. The illumination light wave passes through the sample to be tested placed on the stage device. The imaging beam after being scattered by the sample to be tested is collected by the infinity imaging microscope objective, and after being focused by the lens of the microscope tube, it is diffracted through the orthogonal grating. The 0th order diffracted light generated by the orthogonal grating propagates along the original path and passes through the spatial filter to serve as the reference light. The two +1st order diffracted lights converge after passing through the first lens and then pass through the spatial filter to serve as the two object lights. The object light and reference light filtered by the spatial filter are converged onto the imaging surface of the monochrome image sensor by the second lens, and the monochrome image sensor captures and records orthogonal carrier frequency interference fringes. The polarization filtering device includes a first Wollaston prism, a third lens, a first filter, a second filter, a fourth lens, and a second Wollaston prism arranged sequentially along the beam propagation direction. Wherein, the first Wollaston prism is located on the front focal plane of the third lens, the second Wollaston prism is placed on the rear focal plane of the fourth lens, and the first filter and the second filter are distributed on different paths between the third lens and the fourth lens; The first Wollaston prism is used to cut the linearly polarized illumination light wave output by the polarizer at an angle. The first filter and the second filter are used to generate illumination light waves of different wavelengths. The second Wollaston prism is used to re-bundle the illumination light waves of different wavelengths.

2. The system according to claim 1, characterized in that, The center wavelength of the first filter is 590nm, the center wavelength of the second filter is 633nm, and the full width at half maximum (FWHM) of both the first filter and the second filter is 1nm.

3. The system according to claim 1, characterized in that, The spatial filter includes a first device, a second device, and a third device. The first device is used to filter the 0th-order diffracted light passing through the orthogonal grating into an ideal uniform spherical wave and use it as a reference beam in the interference. The second device only allows light polarized along the x-direction to pass through, and obtains a first object beam after filtering. The third device only allows light polarized along the y-direction to pass through, and obtains a second object beam after filtering.

4. The system according to claim 1, characterized in that, The LED lighting module has a center wavelength of 610nm and a half-width at half-maximum (WWHM) of 50nm.

5. The system according to claim 1, characterized in that, The orthogonal grating is located on the back focal plane of the lens barrel and is used to converge two orthogonally polarized beams with a certain angle to the same position to achieve wavefront matching between the reference beam and the object beam.

6. A dual-wavelength digital holographic method applied to the system described in any one of claims 1 to 5, characterized in that, The method includes: After the emitted light is adjusted to be positive, two illumination light waves with different wavelengths and orthogonal polarization directions are generated. The imaging beam, after being scattered by the sample under test, is focused to produce diffracted light. The 0th-order diffracted light propagates along its original path and forms a reference light. The two +1st-order diffracted lights converge and are filtered into two object lights. The object light and the reference light converge onto the imaging surface to generate orthogonal carrier frequency interference fringes.

7. The method according to claim 6, characterized in that, After the emitted light is adjusted to a positive polarization direction, two illumination light waves with different wavelengths and orthogonal polarization directions are generated, including: The light emitted from the LED lighting module is polarized by a polarizer and then incident perpendicularly onto a polarization filter to generate two beams of lighting light with different wavelengths and orthogonal polarization directions.

8. The method according to claim 6, characterized in that, The imaging beam, after being scattered by the sample under test, is focused to produce diffracted light, including: The illumination light wave passes through the sample to be tested placed on the stage device. The imaging beam scattered by the sample to be tested is collected by the infinity imaging microscope objective, and after being focused by the lens in the microscope tube, it is diffracted through the orthogonal grating to produce diffracted light.

9. The method according to claim 6, characterized in that, The object beam and the reference beam converge onto the imaging plane to generate orthogonal carrier frequency interference fringes, including: The object light and reference light, after being filtered by the spatial filter, are converged onto the imaging surface of the monochrome image sensor by the second lens, and the monochrome image sensor captures and records the orthogonal carrier frequency interference fringes.

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