A three-dimensional microscopic imaging method and device based on metasurface

Abstract

The present invention discloses a three-dimensional microscopic imaging method based on a metasurface, comprising the following steps: making a metasurface with double-helix point spread function characteristics; building a three-dimensional microscopic imaging device for double-helix point spread function modulation with the metasurface as the core to obtain a double-helix image; determining the lateral position of the sample to be tested by the midpoint of the double-helix light spot in the double-helix image, and determining the axial position of the sample to be tested by the angle between the centers of the two light spots. The present invention also discloses a transmission-type three-dimensional microscopic imaging device based on a metasurface and a reflection-type three-dimensional microscopic imaging device based on a metasurface, and both include an illumination module, a sample stage, an imaging module, and an acquisition module, and the imaging modules are all provided with a metasurface. The present invention uses the metasurface to replace traditional light field control elements to improve the imaging effect. The present invention belongs to the field of optical microscopic imaging and optical manipulation technology, and can be used for three-dimensional microscopic imaging in this field.

Description

Technical Field

[0001] The invention relates to a three-dimensional microscopic imaging method and device based on a metasurface, belonging to the technical field of optical microscopic imaging and optical manipulation. Background Art

[0002] The point spread function describes the response of the imaging system to a point source or point object. The three-dimensional point spread function encodes the depth information in the different morphological features of the detected image, and uses the known point spread function information to restore the axial information corresponding to each lateral position on the two-dimensional image plane. The existing three-dimensional point spread function modulation method mainly designs the amplitude transmittance and phase transmittance of the pupil function. By introducing the corresponding amplitude and phase modulation at the exit pupil plane of the system, the point spread function of the system can be adjusted.

[0003] The control of the light field is usually achieved by traditional light field control elements, including amplitude / phase masks, spatial light modulators, deformable mirrors, and digital micromirror devices, etc. The most commonly used one is the spatial light modulator. The quantitative level distribution of its phase structure and the structural characteristics of the control unit determine the existence of the zero-order diffraction spot. The zero-order diffraction spot often occupies a large part of the energy and is often aliased with the modulated effective image, making the displayed image dim and blurred, seriously reducing the imaging quality. In addition, the spatial light modulator is large in size, making it impossible to integrate the three-dimensional imaging optical system. Summary of the invention

[0004] The present invention provides a three-dimensional microscopic imaging method and device based on a metasurface to solve the problems in the prior art that the spatial light modulator has poor imaging quality, is not conducive to integration and has high cost.

[0005] The technical solution adopted by the present invention to solve the above problems is:

[0006] A three-dimensional microscopic imaging method based on a metasurface comprises the following steps:

[0007] Step 1, making a metasurface with double helix point spread function characteristics;

[0008] Step 2, using the metasurface as the core to construct a three-dimensional microscopic imaging device for double-helix point spread function modulation to obtain a double-helix image;

[0009] Step 3: determine the lateral position of the sample to be tested by the midpoint of the double helix light spot in the double helix image, and determine the axial position of the sample to be tested by the angle between the centers of the two light spots.

[0010] Preferably, in step 1, the method for making the metasurface is as follows:

[0011] Step 11, by performing simulation calculations, when the period of the basic unit structure of the metasurface and the height of the nanorods are constant, by changing the length and width of the nanorods, a length and width with the maximum cross-polarization transmittance is found within a size range suitable for processing, as a unit structure of the geometric phase;

[0012] Step 12, superimposing Laguerre-Gaussian beams with different mode numbers to obtain a double helix point spread function phase distribution;

[0013] Step 13, forming a processing file of a double helix metasurface according to the metasurface unit structure selected in step 11 and the phase distribution obtained in step 12;

[0014] Step 14, processing the processing file of the metasurface obtained in step 13 by electron beam lithography combined with reactive ion beam etching, so as to obtain a metasurface with double helix point spread function characteristics.

[0015] Preferably, the basic unit structure of the metasurface in step 11 is made of sapphire crystal (Al 2 O 3 ) is used as a substrate, and the substrate has nanorods made of high refractive index material Si, the period of the nanorods is P = 400nm, the height is H = 360nm, and under the condition of 632nm incident wave, the cross-polarization transmittance is the largest. At this time, the nanorods have a length of L = 130nm and a width of W = 100nm.

[0016] Preferably, in step 12, the Laguerre-Gaussian beam mode is:

[0017]

[0018] is the normalized radial coordinate, is the normalized radius of the light spot, w 0 is the beam waist radius, To use the Rayleigh distance Normalized axial coordinate, l is the wavelength of incident light, where:

[0019]

[0020]

[0021] Φ m (φ)=exp(imφ)

[0022]

[0023] For the ancient phase, is the Laguerre polynomial, n and m are the Laguerre-Gaussian mode numbers, in the double helix point spread function, nm satisfies n=|m|,|m|+2,|m|+4,|m|+6,...., and the phase and intensity of the double helix point spread function can be obtained by selecting (1, 1), (3, 5), (5, 9), (7, 13), (9, 17) of the Laguerre-Gaussian modes (m, n) for equal weight superposition.

[0024] Preferably, in step 14, the method for processing the processing file of the metasurface is as follows:

[0025] Step 141, selecting a single crystal silicon epitaxial wafer with a sapphire thickness of 360 nm as a processing material substrate;

[0026] Step 142, spin-coating an electron beam photoresist PMMA A4 on the processing material substrate at a speed of 3000 revolutions per minute (RPM) to obtain a photoresist substrate;

[0027] Step 143, using electron beam lithography technology, at an acceleration voltage of 30 kV, a beam current of 360 pA, and a 100×100 μm 2 Under the writing field condition of , preparing a corresponding superlens mask on the photoresist substrate to obtain a superlens mask sample;

[0028] Step 144, exposing the superlens mask sample to a 25% tetramethylammonium hydroxide (TMAH) solution, soaking it at room temperature (25°C) for 2 minutes, rinsing it with deionized water for 20 seconds, soaking it in an isopropyl alcohol (IPA) solution for 10 seconds, and then drying it with nitrogen to obtain a silicon film;

[0029] Step 145, transferring the pattern onto the silicon film by using inductively coupled plasma reactive ion etching to obtain a silicon substrate having a pattern;

[0030] Step 146, immersing the silicon substrate with the pattern in 10% hydrofluoric acid (HF) for 15 seconds to remove the residual photoresist mask, washing with deionized water, and drying with nitrogen to obtain a processed meta-structure surface.

[0031] Preferably, in step 145, the method of plasma reactive ion etching is as follows:

[0032] Step 1451, using carbon tetrafluoride (CF4) at 100W ICP power and 100W bias power, with a gas flow rate of 45 sccm for 5 seconds to remove the oxide layer on the surface of the silicon substrate;

[0033] Step 1452, using hydrogen bromide gas (HBr) to etch silicon, at this time, the gas flow rate is set to 100sccm, 400W ICP power, 100W bias power, and silicon is etched at a speed of 83nm / min. During the etching process, the silicon substrate workbench temperature is set to 20°C, and the chamber pressure is set to 10mTorr to obtain a silicon substrate with a pattern.

[0034] A transmission-type three-dimensional microscopic imaging device based on a metasurface, wherein the transmission-type three-dimensional microscopic imaging device is provided with an illumination module, a sample stage, an imaging module and a collection module in sequence along the same horizontal direction of light propagation, the illumination module comprises a fiber-coupled laser, a collimating lens, a polarizer, a quarter-wave plate, an optical scatterer and a converging lens, and is arranged in sequence along the same horizontal direction of light propagation, the sample stage is provided with a transmission-type sample, the imaging module comprises a microscope objective, a tube lens, a Fourier lens 1, a metasurface, a right-handed circular polarizer and a Fourier lens 2, and is arranged in sequence along the same horizontal direction of light propagation, the rear focal plane of the tube lens coincides with the front focal plane of the Fourier lens 1, the Fourier lens 1 and the Fourier lens 2 have the same focal length and aperture, the rear focal plane of the Fourier lens 1 coincides with the front focal plane of the Fourier lens 2, the metasurface is arranged on the front focal plane of the Fourier lens 2, and the metasurface adopts the metasurface described in any one of claims 2-6.

[0035] Preferably, the wavelength range of the light emitted by the fiber-coupled laser is 400nm-650nm, the optical scattering plate adopts frosted glass with a surface sand count of 1500 mesh, sulfuric acid paper or any high-transmittance optical flat plate with irregular micron-level surface morphology, and the acquisition module adopts a CMOS camera.

[0036] A reflective three-dimensional microscopic imaging device based on a metasurface, the reflective three-dimensional microscopic imaging device comprising an illumination module, a sample stage, an imaging module and a collection module, and the sample stage, the imaging module and the collection module are arranged vertically in sequence, the illumination module comprises a fiber-coupled laser, a collimating lens, a polarizer, a quarter-wave plate, an optical scattering plate and a converging lens, and are arranged in sequence along the same horizontal direction of light propagation, the sample stage is provided with a reflective sample, the imaging module is vertically provided with a microscope objective lens, a half-reflecting half-mirror, a tube lens, a Fourier transform lens, a Lens 1, metasurface, right-handed circular polarizer and Fourier lens 2, the half-reflective half-mirror and the lighting module are located on the same horizontal line and are located behind the converging lens, the rear focal plane of the tube lens coincides with the front focal plane of the Fourier lens 1, the Fourier lens 1 and the Fourier lens 2 have the same focal length and aperture, the rear focal plane of the Fourier lens 1 coincides with the front focal plane of the Fourier lens 2, the metasurface is arranged on the front focal plane of the Fourier lens 2, and the metasurface adopts the metasurface described in any one of claims 2-6.

[0037] Preferably, the wavelength range of the light emitted by the fiber-coupled laser is 400nm-650nm, the optical scattering plate adopts frosted glass with a surface sand count of 1500 mesh, sulfuric acid paper or any high-transmittance optical flat plate with irregular micron-level surface morphology, and the acquisition module adopts a CMOS camera.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The imaging device of the present invention uses a metasurface to generate double-helix point spread function modulation, and places the metasurface that generates double-helix point spread function phase modulation on the Fourier plane of the 4f system to replace the traditional spatial light modulator. It has no zero-order diffraction spot, which not only avoids the influence of the zero-order diffraction spot, but also improves the energy utilization and imaging efficiency, thereby improving the imaging quality.

[0040] 2. The present invention combines the characteristics of the three-dimensional point spread function with the advantages of the metasurface, greatly reducing the size of the component, while being able to perform high-precision three-dimensional imaging, reducing the complexity of the system. It is also easy to integrate, improving the integration and lightweight of the system, making the system easier to integrate and meeting the current use requirements of three-dimensional detection systems.

[0041] 3. In the present invention, the metasurface compatible with semiconductor processing technology has a much lower cost than a spatial light modulator composed of a controller, a liquid crystal panel, and a communication module during mass production, which leads to a significant reduction in the cost of the entire system and increases its practicality.

[0042] 4. The imaging device of the present invention encodes the three-dimensional information of the sample on the rotation angles of the two main lobes of the double-helix spot, and by solving the collected two-dimensional intensity information, it can obtain the three-dimensional depth information while obtaining the two-dimensional morphology distribution on the imaging plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A flow chart of a three-dimensional microscopic imaging method and system based on a metasurface provided by the present invention;

[0044] Figure 2 A schematic diagram of the structure of a transmission-type three-dimensional microscopic imaging device based on a metasurface provided by the present invention;

[0045] Figure 3 A schematic structural diagram of a reflective three-dimensional microscopic imaging device based on a metasurface provided by the present invention;

[0046] Figure 4 is a unit structure of the metasurface in the present invention;

[0047] Figure 5 Schematic diagram of the unit structure orientation angle of the metasurface in the present invention;

[0048] Figure 6 is the phase distribution of the metasurface in the present invention;

[0049] Figure 7 is the amplitude distribution of the metasurface in the present invention;

[0050] Figure 8 The micro-nano processing process of the superstructure surface in the present invention is as follows;

[0051] Fig. 9 This is the electron microscope imaging result of a local part of the metastructure surface in the present invention. DETAILED DESCRIPTION

[0052] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0053] In describing the present invention, it is noted that, for the sake of clarity and conciseness, not all features of actual implementations are described in the specification. However, it should be understood that many implementation-specific decisions must be made in the process of developing any such actual implementation in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and these constraints may vary from implementation to implementation. In addition, it should be understood that although the development work may be very complex and time-consuming, it is only a routine task for those skilled in the art who benefit from the disclosure of the present invention.

[0054] It is also necessary to explain here that, in order to avoid obscuring the present invention due to unnecessary details, only the device structure and / or processing steps closely related to the scheme according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0055] The present invention introduces the concept of metasurfaces. Metasurface structures are used to replace traditional optical elements for imaging. Metasurfaces are artificial elements composed of nanostructures that can arbitrarily control the phase, intensity and polarization response of the incident field with sub-wavelength resolution. Figure 1 As shown, the three-dimensional microscopic imaging method based on the metasurface provided by the present invention comprises the following steps:

[0056] Step 1, designing and processing a metasurface with double helix point spread function characteristics by simulation means;

[0057] Step 2, using the metasurface as the core, constructing a three-dimensional microscopic imaging device for double-helix point spread function modulation, imaging the molecule to be measured (i.e., the sample) through the metasurface to obtain a double-helix image;

[0058] Step 3, determining the lateral position of the molecule to be detected by the midpoint of the double helix light spot in the double helix image, and determining the axial position of the molecule to be detected by the angle between the centers of the two light spots.

[0059] Specifically, in step 1, the method for making a metasurface having double helix point spread function characteristics is as follows:

[0060] Step 11, using the frequency domain calculation module based on the finite element method in the electromagnetic simulation software CST to perform simulation operations to optimize the material, shape, geometric parameters, etc. of the metasurface. When the period of the unit structure of the metasurface and the height of the nanorods are constant, by changing the length and width of the nanorods, the length and width with the maximum cross-polarization transmittance are found within the size range suitable for processing, as the unit structure of the geometric phase;

[0061] Step 12, superimposing Laguerre-Gaussian beams with different mode numbers to obtain a double helix point spread function phase distribution;

[0062] Step 13, according to the unit structure selected in step 11, combined with the phase distribution of the geometric phase obtained in step 12, through FDTD algorithm simulation, periodically arranging to form a complete double helix metasurface processing file;

[0063] Step 14, for the processing file of the metasurface obtained in step 13, the metasurface is processed by electron beam lithography combined with reactive ion beam etching, so as to obtain a metasurface with double helix point spread function characteristics.

[0064] like Figure 4 As shown, according to the metasurface unit structure designed in step 11, a sapphire crystal (Al 2 O 3 ) as a substrate. On it are nanorods made of high refractive index material Si.

[0065] like Figure 5 As shown, the orientation angle of the metasurface unit structure designed according to step 11 is θ.

[0066] The period P = 400nm and the nanorod height H = 360nm were selected. The length and width of the nanorod were scanned to obtain the corresponding S parameter curve. This was used to analyze the cross-polarization transmittance of left-handed circularly polarized light, and finally a structure with a higher cross-polarization transmittance under the condition of 632nm incident wave was found. At this time, the length L of the nanorod was 130nm and the width W was 100nm.

[0067] The double helix point spread function described in step 12 is a special rotating light beam. Its focused spot is composed of two main lobes, and the angle between the centroids of the two main lobes changes with the axial position, which is manifested as the rotation of the main lobe, and the rotation angle has an approximately linear relationship with the axial position. It can also ensure that the main lobe size, main lobe spacing and clarity remain unchanged during the rotation process. Based on such characteristics, the rotating light beam can be used to measure three-dimensional displacement.

[0068] The double helix point spread function is formed by superimposing Laguerre-Gaussian functions whose modes are located on the same straight line, and the slope of the straight line is related to the rotation speed of the main lobe.

[0069] The Laguerre-Gaussian function mathematical model is:

[0070]

[0071] is the normalized radial coordinate, is the normalized radius of the light spot, w 0 is the beam waist radius, To use the Rayleigh distance Normalized axial coordinate, l is the wavelength of incident light, where:

[0072]

[0073]

[0074] Φ m (φ)=exp(imφ)

[0075]

[0076] For the ancient phase, is the Laguerre polynomial, n and m are the Laguerre-Gaussian mode numbers, in the double helix point spread function, nm satisfies n=|m|,|m|+2,|m|+4,|m|+6,...., and the phase and intensity of the double helix point spread function can be obtained by selecting (1, 1), (3, 5), (5, 9), (7, 13), (9, 17) of the Laguerre-Gaussian modes (m, n) for equal weight superposition.

[0077] Amplitude-type masks have a high absorption rate for light, which results in the loss of most of the energy.

[0078] Therefore, if Figure 6-7 As shown in the figure, only the phase is selected as the basis for constructing the metasurface, and the amplitude is fixed to 1. The size of the two main lobes of the point spread function, the distance between the main lobes, and the degree of image blur are basically unchanged, and the rotation rate remains unchanged, that is, the angle between the centers of the two main lobes of the double helix image is roughly linearly related to the change in defocus.

[0079] like Figure 8 As shown, in step 14, the processing file of the metasurface is processed by electron beam lithography (EBL) combined with reactive ion etching (RIE), and the method is as follows:

[0080] Step 141, selecting a single crystal silicon epitaxial wafer grown on double-sided polished sapphire with a thickness of 360 nm as a processing material substrate;

[0081] Step 142, spin-coating an electron beam photoresist PMMA A4 on the processing material substrate at a speed of 3000 revolutions per minute (RPM) to obtain a photoresist substrate;

[0082] Step 143, using electron beam lithography technology, at an acceleration voltage of 30 kV, a beam current of 360 pA, and a 100×100 μm 2 Under the writing field condition of , a corresponding superlens mask is prepared on the photoresist, thereby obtaining a superlens mask sample;

[0083] Step 144, then exposing the superlens mask sample to a 25% tetramethylammonium hydroxide (TMAH) solution, soaking it at room temperature (25°C) for 2 minutes, rinsing it with deionized water for 20 seconds, soaking it in an isopropyl alcohol (IPA) solution for 10 seconds, and then drying it with nitrogen to obtain a silicon film;

[0084] Step 145, then, transferring the pattern onto the silicon film by using inductively coupled plasma reactive ion etching to obtain a silicon substrate with a pattern;

[0085] Step 146, finally immerse the silicon substrate with the pattern in 10% hydrofluoric acid (HF) for 15 seconds to remove the residual photoresist mask, wash it with deionized water, and then blow dry it with nitrogen to obtain a processed meta-structure surface.

[0086] In step 145, the method of plasma reactive ion etching is as follows:

[0087] Step 1451, using carbon tetrafluoride (CF4) at 100W ICP power and 100W bias power, with a gas flow rate of 45sccm for 5s, to remove the surface oxide layer by dry etching;

[0088] Step 1452, using hydrogen bromide gas (HBr) to etch silicon, at this time, the gas flow rate is set to 100sccm, 400W ICP power, 100W bias power, and silicon is etched at a speed of 83nm / min. During the etching process, the silicon substrate workbench temperature is set to 20°C, and the chamber pressure is set to 10mTorr to obtain a silicon substrate with a pattern.

[0089] The imaging results of the processed metasurface under an electron microscope are as follows: Fig. 9 shown.

[0090] The present invention also provides a transmission-type three-dimensional microscopic imaging device based on the metasurface.

[0091] like Figure 2 As shown, the transmission type three-dimensional microscopic imaging device is provided with an illumination module, a sample stage 7, an imaging module and a collection module in sequence along the same horizontal direction of light propagation.

[0092] The sample stage 7 is provided with a transmission sample (ie, a transparent sample).

[0093] The acquisition module uses a CMOS camera 14 .

[0094] The lighting module comprises a fiber-coupled laser 1, a collimating lens 2, a polarizer 3, a quarter-wave plate 4, an optical scattering plate 5 and a converging lens 6, which are sequentially arranged along the same horizontal direction of light propagation.

[0095] The fiber-coupled laser 1 emits a laser with strong monochromaticity and coherence, and the laser wavelength can be any wavelength in the visible light band (400nm-650nm). The laser passes through the collimating lens 2 to form a parallel beam with good collimation. The incident parallel beam passes through the polarizer 3 and the quarter-wave plate 4 to generate left-handed circularly polarized light. The incident light spot of the generated left-handed circularly polarized light is projected onto the optical scattering plate 5 by adjusting the quarter-wave plate 4, wherein the distance between the incident light spot and the edge of the optical scattering plate 5 should be less than twice the diameter of the incident light spot. The optical scattering plate 5 is driven to rotate by a micro motor to weaken the coherence of the incident laser, thereby generating partially coherent divergent light (i.e., scattered light). The divergent light generated by the optical scattering plate 5 is converged on the transmission sample via the converging lens 6. The optical scattering plate 5 can be frosted glass with a surface sand count of 1500 mesh, sulfuric acid paper, or any high-transmittance optical flat plate with an irregular micron-level surface morphology.

[0096] The imaging module includes a microscope objective 8, a tube lens 9, a Fourier lens 1 10, a metasurface 11, a right-handed circular polarizer 12 and a Fourier lens 2 13.

[0097] The microscope objective lens 8 collects the light reflected by the transmission sample and focuses it through the tube lens 9, thereby imaging the transmission sample. The microscope objective lens 8 has a numerical aperture that matches the size of the details to be resolved on the sample on the sample stage 7. If imaging a fluorescent sample, filters that are adapted to the characteristics of the fluorescent sample should be added before and after the sample.

[0098] It should be noted that the positioning accuracy and detection range of the double helix point spread function are determined by the numerical aperture of the microscope objective 8. The larger the numerical aperture, the higher the axial positioning accuracy of the particles after the double helix point spread function is modulated, but the smaller the detection range is.

[0099] Moreover, the rear focal plane of the tube lens 9 coincides with the front focal plane of the Fourier lens 10, and the rear focal plane of the Fourier lens 10 coincides with the front focal plane of the Fourier lens 2 13, and the Fourier lens 10 and the Fourier lens 2 13 have the same focal length and aperture, and the two form a 4f system. The metasurface 11 capable of generating double-helix phase modulation is placed on the rear focal plane of the Fourier lens 10, that is, the front focal plane of the Fourier lens 2 13, that is, on the Fourier plane of the 4f system. The right-handed circular polarizer 12 behind the metasurface 11 is used to eliminate the output light having the same circular polarization state as the input light, and to minimize the crosstalk of the incident light.

[0100] The image after phase modulation is collected by the CMOS camera 14 .

[0101] The collected image of the transmission sample is modulated by a double helix point spread function, and two non-overlapping images of the particles are obtained on the CMOS camera 14, and the line connecting the centroids of the two images shows a trend of continuous rotation as the axial position changes.

[0102] The present invention also provides a reflective three-dimensional microscopic imaging device based on the metasurface.

[0103] like Figure 3 As shown, the transmission type three-dimensional microscopic imaging device includes an illumination module, a sample stage 7, an imaging module and a collection module, and the sample stage 7, the imaging module and the collection module are arranged vertically in sequence.

[0104] The sample stage 7 is provided with a reflective sample (ie, an opaque sample).

[0105] The acquisition module uses a CMOS camera 14 .

[0106] The lighting module comprises a fiber-coupled laser 1, a collimating lens 2, a polarizer 3, a quarter-wave plate 4, an optical scattering plate 5 and a converging lens 6, which are sequentially arranged along the same horizontal direction of light propagation.

[0107] The fiber-coupled laser 1 emits a laser with strong monochromaticity and coherence. The wavelength of the laser can be any wavelength in the visible light band (400nm-650nm). The laser passes through the collimating lens 2 to form a parallel beam with good collimation. The incident parallel beam passes through the polarizer 3 and the quarter-wave plate 4 to generate left-handed circularly polarized light. The incident light spot of the generated left-handed circularly polarized light is projected onto the optical scattering plate 5 by adjusting the quarter-wave plate 4, wherein the distance between the incident light spot and the edge of the optical scattering plate 5 should be less than twice the diameter of the light spot. The optical scattering plate 5 is driven to rotate by a micro motor to weaken the coherence of the incident laser, thereby generating partially coherent divergent light. The divergent light generated by the optical scattering plate 5 is converged via the converging lens 6. The optical scattering plate 5 can be frosted glass with a surface sand count of 1500 mesh, sulfuric acid paper, or any high-transmittance optical flat plate with an irregular micron-level surface morphology.

[0108] The imaging module is vertically provided with a microscope objective lens 8, a semi-reflective mirror 15, a tube lens 9, a Fourier lens 10, a metasurface 11, a right-handed circular polarizer 12, and a Fourier lens 2 13. The semi-reflective mirror 15 is located on the same horizontal line as the illumination module and is located behind the converging lens 6. The divergent light generated by the optical scattering sheet 5 is converged on the rear focal plane of the microscope objective lens 8 via the converging lens 6 and the semi-reflective mirror 15, and the sample stage 7 is arranged on the rear focal plane of the microscope objective lens 8, so as to image the reflective sample.

[0109] The sample stage 7, microscope objective 8, half-reflective half-mirror 15, tube lens 9, Fourier lens 10, metasurface 11, right-handed circular polarizer 12, Fourier lens 2 13 and CMOS camera 14 are all located in the same vertical direction, and the central axes of the microscope objective 8, tube lens 9, Fourier lens 10, metasurface 11 and Fourier lens 2 13 in the vertical direction coincide with each other.

[0110] The microscope objective lens 8 collects the light reflected by the reflective sample, and then focuses the light through the half-reflective mirror 15 and then through the tube lens 9. The microscope objective lens 8 has a numerical aperture that matches the size of the details to be resolved on the sample on the sample stage 7, and can evenly project the light beam processed by the half-reflective mirror 15 onto the reflective sample to be inspected.

[0111] When imaging a fluorescent sample, the semi-reflective mirror 15 can be replaced by a dichroic mirror that matches the wavelength of the fluorescent sample to provide uniform illumination light to illuminate the sample.

[0112] It should be noted that the positioning accuracy and detection range of the double helix point spread function are determined by the numerical aperture of the microscope objective 8. The larger the numerical aperture, the higher the axial positioning accuracy of the particles after the double helix point spread function is modulated, but the smaller the detection range is.

[0113] Moreover, the rear focal plane of the tube lens 9 coincides with the front focal plane of the Fourier lens 10, and the rear focal plane of the Fourier lens 10 coincides with the front focal plane of the Fourier lens 2 13, and the Fourier lens 10 and the Fourier lens 2 13 have the same focal length and aperture, and the two form a 4f system. The metasurface 11 capable of generating double-helix phase modulation is placed on the rear focal plane of the Fourier lens 10, that is, the front focal plane of the Fourier lens 2 13, that is, on the Fourier plane of the 4f system. The right-handed circular polarizer 12 behind the metasurface 11 is used to eliminate the output light having the same circular polarization state as the input light, and to reduce the crosstalk of the incident light as much as possible.

[0114] The image after phase modulation is collected by a CMOS camera 14 .

[0115] The collected image of the reflective sample is modulated by a double helix point spread function, and two non-overlapping images of the particles are obtained on the CMOS camera, and the line connecting the centroids of the two images shows a trend of continuous rotation as the axial position changes.

[0116] The technical feature of the present invention is to use a metasurface to replace the traditional light field control element to modulate the three-dimensional point spread function, thereby avoiding the influence of the zero diffraction spot on the modulation efficiency and imaging effect caused by incomplete modulation.

[0117] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent replacement and improvement made to the above embodiments without departing from the content of the technical solution of the present invention, based on the technical essence of the present invention, within the spirit and principles of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims

1. A three-dimensional microscopic imaging method based on metasurfaces, Features: The following steps are included: Step 1, manufacturing a metasurface having double helix point spread function characteristics, wherein the method for manufacturing the metasurface is as follows: Step 11, by performing simulation calculations, when the period of the basic unit structure of the metasurface and the height of the nanorods are constant, by changing the length and width of the nanorods, the length and width with the maximum cross-polarization transmittance are found within a size range suitable for processing, as the unit structure of the geometric phase; Step 12, superimposing Laguerre-Gaussian beams with different mode numbers to obtain a double helix point spread function phase distribution; Step 13, forming a processing file of a double helix metasurface according to the metasurface unit structure selected in step 11 and the phase distribution obtained in step 12; Step 14, processing the processing file of the metasurface obtained in step 13 by electron beam lithography combined with reactive ion beam etching, so as to obtain a metasurface with double helix point spread function characteristics; Step 2, using the metasurface as the core to construct a three-dimensional microscopic imaging device for double-helix point spread function modulation, and obtaining a double-helix image, wherein: a fiber-coupled laser (1) in the three-dimensional microscopic imaging device emits laser light, and the laser light passes through a collimating lens (2) to form a parallel light beam, and the incident parallel light beam passes through a polarizer (3) and a quarter-wave plate (4) to generate left-handed circularly polarized light, and the left-handed circularly polarized light incident light spot is adjusted to hit an optical scattering plate (5), and the divergent light generated by the optical scattering plate (5) is converged by a converging lens (6), and the light reflected or transmitted by the sample stage (7) is reflected by a microscope objective lens (8). Collecting, focusing the image by the tube lens (9), the rear focal plane of the tube lens (9) coincides with the front focal plane of the Fourier lens one (10), the rear focal plane of the Fourier lens one (10) coincides with the front focal plane of the Fourier lens two (13), the metasurface (11) is placed on the rear focal plane of the Fourier lens one (10), a right-handed circular polarizer (12) is arranged behind the metasurface (11), the metasurface (11) performs double-helix point spread function modulation on the collected image, and two non-overlapping images of the particles are obtained on the CMOS camera (14), and the centroid line of the two images shows a continuous rotation trend as the axial position changes; Step 3, determining the lateral position of the sample to be tested by the midpoint of the double helix light spot in the double helix image, and determining the axial position of the sample to be tested by the angle between the centers of the two light spots, wherein the sample to be tested is placed on a sample stage (7), and the sample to be tested is a transmission sample or a reflection sample.

2. The three-dimensional microscopic imaging method based on a metasurface according to claim 1, Features: The basic unit structure of the metasurface in step 11 is made of sapphire crystal (Al 2 O 3 ) is used as a substrate, and the substrate has nanorods made of high refractive index material Si, the period of the nanorods is P = 400nm, the height is H = 360nm, and under the condition of 632nm incident wave, the cross-polarization transmittance is the largest. At this time, the nanorods have a length of L = 130nm and a width of W = 100nm.

3. The three-dimensional microscopic imaging method based on a metasurface according to claim 1, Features: In step 12, the Laguerre-Gaussian beam mode is: is the normalized radial coordinate, is the normalized radius of the light spot, w 0 is the beam waist radius, To use the Rayleigh distance Normalized axial coordinate, l is the wavelength of incident light, where: F m (φ)=exp(imφ) For the ancient phase, is the Laguerre polynomial, n and m are the Laguerre-Gaussian mode numbers, in the double helix point spread function, nm satisfies n=|m|,|m|+2,|m|+4,|m|+6,...., and the phase and intensity of the double helix point spread function can be obtained by selecting (1, 1), (3, 5), (5, 9), (7, 13), (9, 17) of the Laguerre-Gaussian modes (m, n) for equal weight superposition.

4. The three-dimensional microscopic imaging method based on a metasurface according to claim 1, Features: In step 14, the method for processing the processing file of the metasurface is as follows: Step 141, selecting a single crystal silicon epitaxial wafer with a sapphire thickness of 360 nm as a processing material substrate; Step 142, spin-coating the electron beam photoresist PMMA A4 on the processing material substrate at a speed of 3000 revolutions per minute (RPM) to obtain a photoresist substrate; Step 143, using electron beam lithography technology, at an acceleration voltage of 30 kV, a beam current of 360 pA, and a 100×100 μm 2 Under the writing field condition of , preparing a corresponding superlens mask on the photoresist substrate to obtain a superlens mask sample; Step 144, exposing the superlens mask sample to a 25% tetramethylammonium hydroxide (TMAH) solution, soaking it at room temperature (25°C) for 2 minutes, rinsing it with deionized water for 20 seconds, soaking it in an isopropyl alcohol (IPA) solution for 10 seconds, and then drying it with nitrogen to obtain a silicon film; Step 145, transferring the pattern onto the silicon film by using inductively coupled plasma reactive ion etching to obtain a silicon substrate having a pattern; Step 146, immersing the silicon substrate with the pattern in 10% hydrofluoric acid (HF) for 15 seconds to remove the residual photoresist mask, washing with deionized water, and drying with nitrogen to obtain a processed meta-structure surface.

5. The three-dimensional microscopic imaging method based on a metasurface according to claim 4, Features: In step 145, the method of plasma reactive ion etching is as follows: Step 1451, using carbon tetrafluoride (CF4) at 100 W ICP power and 100 W bias power, with a gas flow rate of 45 sccm for 5 seconds to remove the oxide layer on the surface of the silicon substrate; Step 1452, using hydrogen bromide gas (HBr) to etch silicon, at this time, set the gas flow rate to 100sccm, 400W ICP power, 100W bias power, and etch silicon at a speed of 83nm / min. During the etching process, the silicon substrate workbench temperature is set to 20°C and the chamber pressure is set to 10mTorr to obtain a silicon substrate with a pattern.

6. A transmission-type three-dimensional microscopic imaging device based on a metasurface. Features The transmission-type three-dimensional microscopic imaging device is provided with an illumination module, a sample stage (7), an imaging module and a collection module in sequence along the same horizontal direction of light propagation, the illumination module comprises a fiber-coupled laser (1), a collimating lens (2), a polarizer (3), a quarter-wave plate (4), an optical scattering plate (5) and a converging lens (6), and is arranged in sequence along the same horizontal direction of light propagation, the sample stage (7) is provided with a transmission-type sample, the imaging module comprises a microscope objective lens (8), a tube lens (9), a Fourier lens 1 (10), a metasurface (11), a right-handed circular polarizer (12) and a Fourier lens 2 (13), and is arranged in sequence along the same horizontal direction of light propagation. The same horizontal direction of light propagation is arranged in sequence, the rear focal plane of the tube lens (9) coincides with the front focal plane of the Fourier lens one (10), the Fourier lens one (10) and the Fourier lens two (13) have the same focal length and aperture, the rear focal plane of the Fourier lens one (10) coincides with the front focal plane of the Fourier lens two (13), the metasurface (11) is arranged on the front focal plane of the Fourier lens two (13), the metasurface (11) is a metasurface (11) obtained by the three-dimensional microscopic imaging method according to any one of claims 1 to 5, and the metasurface (11) performs double helix point spread function modulation on the collected image.

7. The metasurface-based transmission-type three-dimensional microscopic imaging device according to claim 6, Features: The wavelength range of the light emitted by the fiber-coupled laser (1) is 400nm-650nm, the optical scattering plate (5) is made of frosted glass with a surface grit of 1500 mesh, sulfuric acid paper or any high-transmittance optical flat plate with an irregular micron-level surface morphology, and the acquisition module is made of a CMOS camera.

8. A reflective three-dimensional microscopic imaging device based on a metasurface. Features The reflective three-dimensional microscopic imaging comprises an illumination module, a sample stage (7), an imaging module and a collection module, and the sample stage (7), the imaging module and the collection module are arranged vertically in sequence. The illumination module comprises a fiber-coupled laser (1), a collimating lens (2), a polarizer (3), a quarter-wave plate (4), an optical scattering plate (5) and a converging lens (6), and is arranged in sequence along the same horizontal direction of light propagation; the sample stage (7) is provided with a reflective sample; the imaging module is vertically provided with a microscope objective lens (8), a semi-reflective semi-mirror (15), a tube lens (9), a Fourier lens 1 (10), a metasurface (11), a right-handed circular polarizer (12) and a Fourier lens 2 (13); the semi-reflective semi-mirror (15) and the illumination module are located on the same horizontal line and are located on the converging lens. After the lens (6), the rear focal plane of the tube lens (9) coincides with the front focal plane of the Fourier lens one (10), the Fourier lens one (10) and the Fourier lens two (13) have the same focal length and aperture, the rear focal plane of the Fourier lens one (10) coincides with the front focal plane of the Fourier lens two (13), the metasurface (11) is arranged on the front focal plane of the Fourier lens two (13), the metasurface (11) is a metasurface (11) obtained by the three-dimensional microscopic imaging method according to any one of claims 1 to 5, and the metasurface (11) performs double helix point spread function modulation on the collected image.

9. The reflective three-dimensional microscopic imaging device based on a metasurface according to claim 8, Features: The wavelength range of the light emitted by the fiber-coupled laser (1) is 400nm-650nm, the optical scattering plate (5) is made of frosted glass with a surface grit of 1500 mesh, sulfuric acid paper or any high-transmittance optical flat plate with an irregular micron-level surface morphology, and the acquisition module is made of a CMOS camera.

Images