Deep-shift frequency super-resolution microscopy chip based on nonlinear evanescent field and imaging method thereof

Abstract

The application discloses a deep-shift frequency super-resolution microscopic chip based on a nonlinear evanescent field and an imaging method thereof, and belongs to the field of shift frequency super-resolution microscopic imaging. The deep-shift frequency super-resolution imaging chip comprises, from bottom to top, a substrate layer, a nonlinear optical material film layer, a surface plasmon film system and a microstructure layer which are sequentially stacked. A polygonal hole slot is entirely provided in the central region of the surface plasmon film system and the microstructure layer, and the exposed part of the nonlinear optical material film layer serves as an imaging sample placement area. A plurality of groups of microstructures are engraved on the upper surface of the microstructure layer around the polygonal hole slot. The application utilizes the nonlinear four-wave mixing effect to excite, control and enhance the super-large wave vector evanescent field and applies the super-large wave vector evanescent field to shift frequency super-resolution imaging, solves the problem that the wave vector of the evanescent field provided by a natural waveguide material is limited and the larger the wave vector is, the weaker the signal is, and breaks through the resolution upper limit of the existing linear shift frequency super-resolution imaging technology under the premise of ensuring the imaging quality.

Description

Technical Field

[0001] This invention belongs to the field of frequency-shifting super-resolution microscopy, and particularly relates to a deep frequency-shifting super-resolution microchip based on a nonlinear evanescent field and its imaging method. Background Technology

[0002] Large field-of-view, high-speed, and ultra-high-resolution optical microscopy plays an irreplaceable role in basic research and industrial production in life sciences, physics, materials science, and integrated circuits. Super-resolution microscopy based on spatial domain methods such as single-molecule localization and point spread function modulation can achieve sub-20 nanometer resolution, but requires special fluorescent molecule staining. In contrast, frequency-shifting super-resolution microscopy based on spatial frequency domain methods has significant advantages in terms of large field of view and high speed, and does not require special fluorescent molecule staining. Frequency-shifting super-resolution technology shifts the spatial spectrum of the sample by controlling the wide-field illumination light field, sequentially moving high-frequency information that would otherwise be cut off by the microscopy imaging system to the system's low-frequency passband for reception. Then, iterative reconstruction algorithms are used to restore each high-frequency information to its original position, synthesizing a sample spectrum with an expanded range, ultimately obtaining a super-resolution image that breaks the diffraction limit.

[0003] Early frequency-shifting super-resolution techniques used free-space light as the illumination field, such as structured illumination super-resolution microscopy (SIM) in labeled imaging and Fourier stacked microscopy (FPM) in label-free imaging. However, the frequency shift achievable by these techniques is limited by the aperture of the imaging system. Using a surface evanescent field generated by a chip as the illumination field can overcome this limitation. For example, CN112213865B discloses a high-speed evanescent field frequency-shifting label-free super-resolution microscopy method that uses an on-chip light-emitting device to excite an evanescent field within a strip waveguide to illuminate the sample. The transverse wave vector of this evanescent field depends only on the excitation wavelength and the effective refractive index of the waveguide, and the corresponding frequency shift is therefore independent of the imaging system parameters. By using a smaller excitation wavelength and a waveguide material with a higher refractive index, a larger frequency shift can be achieved. However, the refractive index of natural optical waveguide materials is limited in the visible light band. Currently, frequency-shifting super-resolution chips rely solely on linear optical processes, making it difficult to generate evanescent fields with larger transverse wave vectors, thus failing to further unleash the potential of frequency-shifting super-resolution technology. Summary of the Invention

[0004] To address the problem that current frequency-shifting super-resolution chips based on linear optical processes have limited evanescent field wave vector magnitudes, thus hindering further improvements in frequency-shifting imaging resolution, this invention proposes a deep frequency-shifting super-resolution imaging chip based on a nonlinear evanescent field and its imaging method.

[0005] The specific technical solution adopted in this invention is as follows:

[0006] In a first aspect, the present invention provides a deep frequency-shifting super-resolution imaging chip based on a nonlinear evanescent field, comprising a substrate layer, a nonlinear optical material film layer, a surface plasmon polariton (SPT) film system, and a microstructure layer stacked sequentially from bottom to top; a polygonal aperture is integrally formed through the central region of the SPT film system and the microstructure layer, and the portion of the nonlinear optical material film layer exposed at the bottom of the polygonal aperture serves as an imaging sample placement area; surrounding the polygonal aperture, a plurality of microstructures are etched on the upper surface of the microstructure layer, the microstructures providing corresponding reciprocal lattice vector momentum for exciting target SPTs in the lower SPT film system; the microstructures at different locations have different spatial periods and orientations, used to excite SPTs with different wave vector magnitudes and directions.

[0007] Preferably, if the operating wavelength is in the visible light band, the materials of both the substrate layer and the microstructure layer are SiO2 or Al2O3.

[0008] Preferably, the nonlinear optical material film is LiNbO3 or ITO.

[0009] Preferably, a nonlinear optical material film is prepared on the upper surface of the substrate by sputtering, vapor deposition, or pulsed laser deposition.

[0010] Preferably, the surface plasmon polariton film system is a hyperbolic metasurface type film system, which is composed of periodically stacked non-metallic thin films and metallic thin films, and the first layer on the upper surface of the nonlinear optical material film layer is a metallic material thin film;

[0011] Furthermore, the metal thin film material is Ag or Au, and the non-metal thin film is SiO2, Al2O3 or MgF2.

[0012] Preferably, a surface plasmon film system is prepared on the surface of the nonlinear optical material film by sputtering, vapor deposition or pulsed laser deposition.

[0013] Preferably, a microstructure layer is prepared on the surface of a surface plasmon film system using magnetron sputtering or vapor deposition techniques, and then microstructures are fabricated on the surface of the microstructure layer using laser direct writing etching, focused ion beam etching, electron beam etching, or nanoimprinting techniques.

[0014] Preferably, polygonal holes are formed throughout the central region of the surface plasmon film and microstructure layer using focused ion beam etching or electron beam etching techniques.

[0015] Preferably, the side lengths of the polygonal slots correspond sequentially to the microstructures, and each microstructure has multiple elongated slots that are parallel to the corresponding side lengths and spaced apart along the axial direction.

[0016] Secondly, the present invention provides an imaging method utilizing any of the deep frequency-shifting super-resolution imaging chips based on nonlinear evanescent fields as described in the first aspect, specifically as follows:

[0017] Step 1: Place the target sample in the polygonal aperture, use a monochromatic light source as the signal source and illuminate the sample area vertically from above, and use an optical microscope to take a picture to obtain a low-frequency image carrying the low-frequency information of the sample.

[0018] Step 2: Change the wavelength and incident angle of the signal light source in Step 1 to adjust the magnitude and direction of the free space light transverse wave vector, thereby adjusting the magnitude and direction of the frequency shift of the frequency-shifted illumination. Use an optical microscope to capture the frequency-shifted image carrying high-frequency information from all directions of the sample.

[0019] Step 3: A monochromatic light source is used as the signal source and illuminates the sample area from above. Two other monochromatic light sources are used as excitation sources and illuminate the same or two microstructures on the microstructure layer from above. Large-wave vector surface plasmons are excited in the surface plasmon film structure, and large-wave vector surface plasmons propagating perpendicularly to the corresponding side length are generated from the edge of the polygonal slot as pump sources. Due to the presence of nonlinear materials and the local field characteristics of surface plasmons, the surface plasmon pump light can undergo efficient four-wave mixing with the free-space signal light to generate a nonlinear evanescent field. Thanks to the frequency superposition, momentum superposition, and optical parametric amplification properties of four-wave mixing, this nonlinear evanescent field has a new optical frequency, a larger and tunable transverse wave vector, and sufficient intensity, which can achieve a larger frequency shift illumination when transmitted to the sample position. By adding a corresponding narrowband filter in front of the optical microscope, a frequency-shifted image carrying the high-frequency information of the sample is obtained.

[0020] Step four: Change the illumination positions of the two excitation light sources in step three to excite microstructures in different orientations in sequence. At the same time, change the incident angle of the signal light source to fine-tune the four-wave mixing momentum superposition result, thereby generating nonlinear evanescent fields with different wave vector magnitudes and directions, realizing large frequency shift illumination of different magnitudes and directions. Repeat the imaging process in step three to obtain frequency shift images carrying high-frequency information of the sample in different orientations in sequence.

[0021] Step 5: Input all the images captured in steps 1 to 4 into the iterative reconstruction algorithm. The low-frequency, higher-frequency, and high-frequency spatial spectrum information contained in the images are restored to the correct spectral positions in sequence, and finally a deep frequency-shifting super-resolution image with a greatly expanded spatial spectrum range is obtained, realizing the imaging of the target sample.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention utilizes the nonlinear four-wave mixing effect to excite, modulate, and enhance ultra-large wave vector evanescent fields and applies them to frequency-shifting super-resolution imaging. It solves the problem that the evanescent field wave vectors provided by natural waveguide materials are limited and the signal is weaker when the wave vector is larger. It can break through the resolution limit of existing linear frequency-shifting super-resolution imaging technology while ensuring imaging quality. Attached Figure Description

[0024] Figure 1 This is a perspective view of the structure of a deep frequency-shifting super-resolution imaging chip.

[0025] Figure 2 This is a cross-sectional view of the structure of a deep frequency-shifting super-resolution imaging chip.

[0026] Figure 3 This is a top view of the deep frequency-shifting super-resolution imaging chip.

[0027] Figure 4 This is a schematic diagram of the physical principle of four-wave mixing excitation to enhance the nonlinear evanescent field of ultra-large wave vector.

[0028] In the figure, 101 is the substrate layer, 102 is the nonlinear optical material film layer, 103 is the surface plasmon resonance film system, 104 is the microstructure layer, 105 is the microstructure, 106 is the imaging sample placement area, 201 is the excitation source, and 202 is the signal source. Detailed Implementation

[0029] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0030] like Figure 1As shown, this invention provides a deep frequency-shifting super-resolution imaging chip based on a nonlinear evanescent field. The deep frequency-shifting super-resolution imaging chip includes a substrate layer 101, a nonlinear optical material film layer 102, a surface plasmon film system 103, and a microstructure layer 104 stacked sequentially from bottom to top. The substrate 101 has a flat surface and a low refractive index. A nonlinear optical material film 102 is fabricated above the substrate 101, capable of efficiently exciting nonlinear optical frequency conversion and optical parametric amplification effects. A surface plasmon polariton (SPP) film system 103 supporting large wave vector surface plasmons (SPPs) is fabricated above the nonlinear optical material film 102. A microstructure layer 104 is fabricated above the SPP film system 103, used to couple free-space light into the SPP film system and excite SPPs with specific wave vector magnitudes and directions. A polygonal aperture is integrally formed through the central region of the SPP film system 103 and the microstructure layer 104, with the exposed portion of the nonlinear optical material film 102 at the bottom of the polygonal aperture serving as an imaging sample placement area 106. Surrounding the polygonal aperture, several sets of microstructures 105 are etched on the upper surface of the microstructure layer 104, providing corresponding reciprocal lattice momentum for exciting target SPPs in the underlying SPP film system 103. Microstructures 105 at different locations have different spatial periods and orientations, which are used to excite surface plasmons with different wave vector magnitudes and directions.

[0031] In practical applications, the following options can also be selected based on the specific circumstances:

[0032] If the incident light operates in the visible light band, the substrate 101 material can be selected from materials with good interface properties and low refractive index, such as SiO2 and Al2O3, so as to form a large refractive index difference with the nonlinear optical material film 102 above, thereby reducing the leakage of light field energy from the nonlinear optical material film 102 to the substrate 101.

[0033] The nonlinear optical material film 102 can use materials with high second- and third-order nonlinear coefficients, such as LiNbO3 and ITO, to support nonlinear optical frequency conversion effects such as sum-frequency, difference-frequency, and four-wave mixing.

[0034] A nonlinear optical material film 102 is fabricated on the substrate 101 using micro-nano fabrication methods, including sputtering, vapor deposition, and pulsed laser deposition. The thickness of the film needs to be comprehensively designed in conjunction with the surface plasmon film system 103.

[0035] The surface plasmon polariton film system 103 can be a hyperbolic metasurface film system. This type of film system is composed of periodically stacked non-metallic thin films and metallic thin films, and has special hyperbolic dispersion properties. It can support specific ultra-large wave vector surface plasmon polariton modes and filter out other modes. The hyperbolic metasurface film system is prepared by stacking on top of the nonlinear optical material film layer 102 using micro-nano fabrication methods, including magnetron sputtering, vapor deposition, and other techniques. The metallic thin film material can be Ag, Au, etc., which have negative refractive indices in the visible light band, and the non-metallic thin film material can be SiO2, Al2O3, MgF2, etc. The first layer deposited on the nonlinear optical material film layer 102 is a metallic thin film, the second layer is a non-metallic thin film, the third layer is a metallic thin film, the fourth layer is a non-metallic thin film, and so on, alternating in this order. The number of film layers and the thickness of each film layer need to be optimized for the target surface plasmon polariton modes.

[0036] If the operating wavelength is in the visible light band, the microstructure layer 104 can be made of materials that are transparent in the visible light band, such as SiO2 or Al2O3. Several microstructures 105 distributed around the central through hole are etched on it to provide the corresponding reciprocal lattice vector momentum for exciting the target surface plasmons in the lower surface plasmon film system 103. The microstructures 105 at different positions have different spatial periods and orientations, which can be used to excite surface plasmons with different wave vector magnitudes and directions.

[0037] A microstructure layer 104 is fabricated on the surface plasmon film system 103 using micro-nano fabrication methods. First, a uniform material film is prepared by techniques such as magnetron sputtering and vapor deposition. Then, microstructure morphology is fabricated on the material film by techniques such as laser direct writing etching, focused ion beam etching, electron beam etching, and nanoimprinting. The position and morphology of the microstructure need to be designed and optimized by comprehensively considering the wave vector and excitation efficiency of the plasmon mode on the target surface.

[0038] Micro-nano fabrication methods are used to create through polygonal holes in the center of the surface plasmon film 103 and the microstructure layer 104, including techniques such as focused ion beam etching and electron beam etching. The exposed surface of the nonlinear optical material film layer 102 serves as the imaging sample placement area. The hole shape is generally polygonal, with each side corresponding to a microstructure. The more sides of the polygon, the higher the adjustable precision of the frequency shift. The specific size of the polygon depends on the expected transmission distance of the surface plasmon mode. In other words, each side of the polygonal hole corresponds to a microstructure 105, and each microstructure 105 has multiple elongated slots parallel to their corresponding side lengths and spaced apart along the axial direction.

[0039] like Figure 2 As shown, the present invention also provides an imaging method using the above-mentioned deep frequency-shifting super-resolution imaging chip, as detailed below:

[0040] Step 1: Place the target sample in the polygonal aperture slot, use a monochromatic light source as the signal light source 202 to illuminate the sample area vertically from above, and use an optical microscope to take a picture to obtain a low-frequency image carrying the low-frequency information of the sample.

[0041] Step 2: Change the wavelength and incident angle of the signal light source 202 in Step 1 to adjust the magnitude and direction of the free space light transverse wave vector, thereby adjusting the magnitude and direction of the frequency shift of the frequency-shifted illumination. Use an optical microscope to capture the frequency-shifted image carrying high-frequency information from various directions of the sample.

[0042] Step three: A monochromatic light source serves as the signal source 202, illuminating the sample area from above. Two other monochromatic light sources serve as excitation sources 201, illuminating the same or two microstructures 105 on the microstructure layer 104 from above. Large-wave vector volume plasmons are excited in the surface plasmon film system 103, and large-wave vector surface plasmons propagating perpendicularly to the corresponding side length are generated from the edges of the polygonal slots, serving as the pump source. Due to the presence of nonlinear materials and the local field characteristics of surface plasmons, the surface plasmon pump light can undergo efficient four-wave mixing with the free-space signal light, generating a nonlinear evanescent field. Benefiting from the frequency superposition, momentum superposition, and optical parametric amplification properties of four-wave mixing, this nonlinear evanescent field possesses a new optical frequency, a larger and tunable transverse wave vector, and sufficient intensity, enabling illumination with a larger frequency shift when transmitted to the sample location. By adding a corresponding narrowband filter in front of an optical microscope, a frequency-shifted image carrying high-frequency information of the sample is obtained.

[0043] Step four: Change the illumination positions of the two excitation light sources 201 in step three to excite the microstructures 105 in different orientations in sequence. At the same time, change the incident angle of the signal light source 202 to fine-tune the four-wave mixing momentum superposition result, thereby generating nonlinear evanescent fields with different wave vector magnitudes and directions, realizing large frequency shift illumination of different magnitudes and directions. Repeat the imaging process of step three to obtain frequency shift images carrying high-frequency information of the sample in different orientations in sequence.

[0044] Step 5: Input all the images captured in steps 1 to 4 into the iterative reconstruction algorithm. The low-frequency, higher-frequency, and high-frequency spatial spectrum information contained in the images are restored to the correct spectral positions in sequence, and finally a deep frequency-shifting super-resolution image with a greatly expanded spatial spectrum range is obtained, realizing the imaging of the target sample.

[0045] Example

[0046] In this embodiment, frequency-shift imaging of a two-dimensional sample structure is taken as an example, such as... Figure 1 As shown, the polygonal sample placement area uses a hexagonal groove. Six microstructures are etched on the microstructure layer and are centrally symmetrically distributed around the hexagonal groove, which can be used to excite six different types of surface plasmons.

[0047] The sample is illuminated vertically from above using a monochromatic light source, and low-frequency images are acquired using an optical microscope; the wavelength and incident angle of the monochromatic light source are then changed, and higher-frequency images are acquired using an optical microscope.

[0048] A monochromatic light source is used as the signal light to illuminate the groove area where the sample is placed from above, while two other monochromatic light sources are used as pump light to illuminate and excite the microstructure from above. There are a total of 36 microstructure excitation options, namely excitation microstructures 1 and 1, 1 and 2, 1 and 3, 1 and 4, 1 and 5, 1 and 6, 2 and 1, ..., 6 and 6. Figure 3 The diagram illustrates the excitation of microstructures 1 and 2. This results in four-wave mixing between the generated surface plasmons and the free-space signal light. The frequency and wave vector of the newly generated nonlinear evanescent mixing field are determined by the attached... Figure 4 The physical mechanism shown determines this.

[0049] like Figure 3 The image shown is a top view of a deep frequency-shifting super-resolution imaging chip, illustrating the process of four-wave mixing to excite a nonlinear evanescent field: the gray circle on the left represents the illumination area of ​​the microstructure excitation source, and the gray circle in the middle represents the illumination area of ​​the signal source. Under the illumination of the excitation source, surface plasmons (SPPs) propagating perpendicular to the side length of the groove are generated. After four-wave mixing of the surface plasmons and the signal light, a nonlinear evanescent field is generated.

[0050] like Figure 4 The diagram shows the physical principle of four-wave mixing to enhance a nonlinear evanescent field with a large wave vector. Energy conservation determines the superposition of optical frequencies during the mixing process, while momentum conservation determines the superposition of optical wave vectors. In the diagram, k... spp k is the transverse wave vector of the surface plasmon polariton, k0 is the wave vector of the signal light in free space, and k ne It is the transverse wave vector of a nonlinear evanescent field.

[0051] Different microstructures were used to excite nonlinear evanescent fields with different wave vector magnitudes and directions. An optical microscope with a narrowband filter corresponding to the optical frequency of the nonlinear evanescent field was used to acquire images carrying high-frequency information from different orientations.

[0052] All images carrying low-frequency, high-frequency, and high-frequency information are input into an iterative reconstruction algorithm to recover a deep frequency-shifting super-resolution image with a greatly expanded spectral range.

[0053] Specifically, the chip substrate uses SiO2 material, on which a 100 nm thick LiNbO3 thin film is deposited. The surface plasmon resonance (SPR) system consists of eight alternately stacked Ag metal layers (10 nm thick) and SiO2 non-metal layers (6 nm thick), supporting an equivalent refractive index of 7.2 (@532 nm wavelength). The microstructure layer uses SiO2 material, on which six centrally symmetrically distributed rectangular gratings are etched. Each grating has a length and width of 200 μm, a grating period of 500 nm, and a grating duty cycle of 0.1. The microstructure excitation light source uses a wavelength of 532 nm, the signal light source uses a wavelength of 780 nm, the imaging objective has a numerical aperture of 0.4, the nonlinear evanescent field wavelength is approximately 404 nm, the equivalent refractive index is approximately 10.9 (@404 nm wavelength), and the maximum resolution of approximately 36 nm can be achieved for label-free frequency-shifting imaging.

[0054] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A nonlinear evanescent field-based deep-shift super-resolution imaging chip, characterized in that, The system comprises a substrate layer (101), a nonlinear optical material film layer (102), a surface plasmon polariton film system (103), and a microstructure layer (104) stacked sequentially from bottom to top. A polygonal hole is formed through the central region of the surface plasmon polariton film system (103) and the microstructure layer (104). The portion of the nonlinear optical material film layer (102) exposed at the bottom of the polygonal hole serves as an imaging sample placement area (106). Surrounding the polygonal hole, a number of microstructures (105) are etched on the upper surface of the microstructure layer (104). The microstructures (105) provide corresponding reciprocal lattice vector momentum for exciting target surface plasmons in the lower surface plasmon polariton film system (103). The microstructures (105) at different locations have different spatial periods and orientations, which are used to excite surface plasmons with different wave vector magnitudes and directions.

2. The nonlinear evanescent field-based deep frequency-multiplexed super-resolution imaging chip of claim 1, wherein, If the working waveband is in the visible light waveband, the material of the substrate layer (101) and the microstructure layer (104) are both made of or .

3. The nonlinear evanescent field-based deep frequency-multiplexed super-resolution imaging chip of claim 1, wherein, The nonlinear optical material film layer (102) is made of or .

4. The nonlinear evanescent-based deep frequency-multiplexed super-resolution imaging chip of claim 1, wherein, A nonlinear optical material film (102) is prepared on the upper surface of the substrate (101) by sputtering, vapor deposition or pulsed laser deposition.

5. The nonlinear evanescent-based deep frequency-multiplexed super-resolution imaging chip of claim 1, wherein, The surface plasmon film system (103) adopts a hyperbolic metasurface type film system, which is composed of periodically stacked non-metallic thin films and metal thin films. The first layer on the upper surface of the nonlinear optical material film layer (102) is a metal thin film.

6. The nonlinear evanescent-based deep-tunneling super-resolution imaging chip of claim 5, wherein, The metal thin film is or The non-metal thin film is , or .

7. The nonlinear evanescent-based deep frequency-multiplexed super-resolution imaging chip of claim 1, wherein, A surface plasmon film system (103) is prepared on the surface of the nonlinear optical material film layer (102) by sputtering, vapor deposition or pulsed laser deposition.

8. The nonlinear evanescent-based deep-tunneling super-resolution imaging chip of claim 1, wherein, A microstructure layer (104) is prepared on the surface of a surface plasmon film system (103) using magnetron sputtering or vapor deposition techniques. Then, microstructures (105) are fabricated on the surface of the microstructure layer (104) using laser direct writing etching, focused ion beam etching, electron beam etching or nanoimprinting techniques.

9. The nonlinear evanescent-based deep frequency-multiplexed super-resolution imaging chip of claim 1, wherein, Polygonal holes are formed throughout the central region of the surface plasmonic film system (103) and microstructure layer (104) using focused ion beam etching or electron beam etching techniques.

10. A deep frequency-shifting super-resolution imaging chip based on a nonlinear evanescent field according to claim 1, characterized in that, Each side length of the polygonal slot corresponds to each microstructure (105) in sequence, and each microstructure (105) has multiple elongated slots that are parallel to the corresponding side length and spaced apart along the axial direction.

11. An imaging method using the deep-tunneling frequency super-resolution imaging chip based on nonlinear evanescent field according to any one of claims 1-10, characterized in that, Specifically as follows: Step 1: Place the target sample in the polygonal aperture slot, use a monochromatic light source as the signal light source (202) and illuminate the sample area vertically from above, and use an optical microscope to take a picture to obtain a low-frequency image carrying the low-frequency information of the sample. Step 2: Change the wavelength and incident angle of the signal light source (202) in Step 1 to adjust the magnitude and direction of the free space light transverse wave vector, thereby adjusting the magnitude and direction of the frequency shift of the frequency shift illumination, and use an optical microscope to take pictures to obtain frequency shift images carrying high-frequency information of the sample in various directions. Step 3: A monochromatic light source is used as a signal source (202) and illuminates the sample area from above. Two other monochromatic light sources are used as excitation sources (201) and illuminate the same or two microstructures (105) on the microstructure layer (104) from above. Large-wave vector plasmons are excited in the surface plasmon film system (103) structure, and large-wave vector surface plasmons propagating perpendicularly to the corresponding side length are generated from the edge of the polygonal slot as pump sources. Due to the presence of nonlinear materials and the local field characteristics of surface plasmons, the surface plasmon pump light can undergo efficient four-wave mixing with the free space signal light to generate a nonlinear evanescent field. Thanks to the frequency superposition, momentum superposition and optical parametric amplification properties of four-wave mixing, the nonlinear evanescent field has a new light frequency, a larger and tunable transverse wave vector and sufficient intensity. When transmitted to the sample position, it can achieve illumination with a larger frequency shift. By adding a corresponding narrowband filter in front of the optical microscope, a frequency-shifted image carrying the high-frequency information of the sample is obtained. Step four: Change the illumination positions of the two excitation light sources (201) in step three to excite microstructures (105) in different orientations in sequence. At the same time, change the incident angle of the signal light source (202) to fine-tune the four-wave mixing momentum superposition result, thereby generating nonlinear evanescent fields with different wave vector magnitudes and directions, realizing large frequency shift illumination of different magnitudes and directions. Repeat the imaging process in step three to obtain frequency shift images carrying high-frequency information of the sample in different orientations in sequence. Step 5: Input all the images captured in steps 1 to 4 into the iterative reconstruction algorithm. The low-frequency, higher-frequency, and high-frequency spatial spectrum information contained in the images are restored to the correct spectral positions in sequence, and finally a deep frequency-shifting super-resolution image with a greatly expanded spatial spectrum range is obtained, realizing the imaging of the target sample.

Images