Near-field optical imaging system

Abstract

The invention provides a near-field optical imaging system, and the system comprises a pumping laser source which is suitable for providing pumping laser; the optical window sheet is attached to a sample to be detected; the solid-state color center crystal is attached to the optical window sheet and is suitable for emitting a fluorescence signal under the irradiation of the pumping laser; the light source is suitable for providing an initial light beam of a middle infrared band or a terahertz band, and a fluorescence signal is subjected to energy level pumping under the combined action of the pumping laser and the initial light beam to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal; and the detection light path is suitable for detecting the fluorescence up-conversion signal or the fluorescence down-conversion signal so as to obtain light field distribution images of the surface of the to-be-detected sample and the cross section of the solid color center crystal at different depths.

Description

Technical Field

[0001] At least one embodiment of the present disclosure relates to the field of optical imaging technology, and more specifically to a near-field optical imaging system. Background Art

[0002] The mid-infrared and terahertz bands have a wide range of application scenarios and potential in material analysis and biological tissue testing due to their strong penetration, non-destructiveness, and matching with vibration energy levels. However, traditional imaging technology is limited by the optical diffraction limit and can usually only achieve a resolution of tens to hundreds of microns, which cannot meet the in-depth application needs at the microscopic scale. For example, traditional terahertz waves can measure the conductivity of materials, but due to the optical diffraction limit, they can only measure the average conductivity of all materials and structures in the focused spot, and cannot reflect their microscopic characteristics. Especially in the study of condensed matter systems, such as ultrafast current imaging of two-dimensional materials, hot electron energy dissipation processes, atomic-scale transient electromagnetic fields, and carrier and defect imaging of semiconductors, the demand for higher resolution imaging technology is particularly urgent.

[0003] Related mid-infrared / terahertz near-field imaging technologies all require coherent detection of electromagnetic waves, which usually requires amplitude detection of the mid-infrared / terahertz field intensity in the time domain, followed by Fourier transform, which greatly increases the complexity and cost of the system. Existing mid-infrared / terahertz near-field imaging technologies are mainly divided into the following categories: Scanning Near-field Optical Microscope with an aperture (Apertured SNOM), Apertureless Scanning Near-field Optical Microscope (Apertureless SNOM), Electro-optical effect (EO effect) detection based on sum frequency generation (SFG) materials, and mid-infrared photothermal imaging (IR-PHI).

[0004] In realizing the inventive concept disclosed herein, the inventors have found that there are at least the following problems in the related art: near-field optical microscopy with an aperture excites the sample to be tested through a small hole to improve the resolution, but the signal intensity decreases sharply as the aperture decreases, resulting in increased detection difficulty; near-field optical microscopy without an aperture uses nanoscale metal probes to achieve local electric field enhancement, but the detected signal does not directly reflect the response of the material to mid-infrared / terahertz, and has high requirements for sample flatness and stability; terahertz imaging based on electro-optic crystals uses electro-optic crystals to modulate the refractive index to detect terahertz waves, but the system is complex and the resolution is limited; and mid-infrared photothermal imaging technology detects mid-infrared absorption by monitoring temperature changes, but requires an additional temperature sensing medium, which increases the complexity and limitations of the system. Summary of the invention

[0005] In order to solve at least one of the above-mentioned and other technical problems in the prior art, the present disclosure provides a near-field optical imaging system, which can achieve near-field optical imaging beyond the diffraction limit of the mid-infrared band or the terahertz band, and improve the resolution of imaging in the mid-infrared band and the terahertz band.

[0006] According to one aspect of the present disclosure, there is provided a near-field optical imaging system, comprising:

[0007] A pump laser source, adapted to provide a pump laser;

[0008] Optical window piece, attached to the sample to be tested;

[0009] A solid color center crystal is attached to the optical window, and the solid color center crystal is suitable for emitting a fluorescence signal under the irradiation of the pump laser;

[0010] A light source, adapted to provide an initial light beam in the mid-infrared band or the terahertz band, wherein the above-mentioned fluorescence signal is pumped by energy level under the combined action of the above-mentioned pump laser and the above-mentioned initial light beam to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal; and

[0011] A detection optical path, adapted to detect the fluorescence up-conversion signal or the fluorescence down-conversion signal, so as to obtain images of light field distribution of the surface of the sample to be tested and the cross section of the solid color center crystal at different depths;

[0012] Among them, the above-mentioned fluorescence signal includes the near-field optical information of the above-mentioned initial light beam passing through the above-mentioned sample to be tested, and the above-mentioned near-field optical information includes the transmission spectrum information and intensity information of the above-mentioned initial light beam; the above-mentioned near-field optical information is obtained based on the image of the light field distribution of the surface of the above-mentioned sample to be tested and the cross-section of the above-mentioned solid color center crystal at different depths.

[0013] According to an embodiment of the present disclosure, there is a split in the energy level of the solid color center crystal that matches the mid-infrared band or the terahertz band; and

[0014] There is a radiation relaxation channel between the excited state and the ground state of the solid color center crystal, so that photons are emitted when the ions in the excited state fall to the ground state.

[0015] According to an embodiment of the present disclosure, the metastable lifetime length of the solid color center crystal makes the population accumulation rate caused by the initial light beam in the mid-infrared band or terahertz band pumping faster than the population relaxation rate of the energy level of the solid color center crystal itself.

[0016] According to an embodiment of the present disclosure, the pump laser pumps the plurality of ions in the ground state in the solid color center crystal to the first excited state, and the plurality of ions in the first excited state continue to be pumped to the second excited state under the irradiation of the initial light beam, and a portion of the plurality of ions in the second excited state falls back to the ground state and emits a plurality of corresponding up-conversion photons having an energy greater than that of the pump laser.

[0017] Wherein, the intensity of the initial light beam in the mid-infrared band or the terahertz band is obtained according to the intensity of the fluorescence signal of the up-converted photons.

[0018] According to an embodiment of the present disclosure, the optical window is suitable for isolating the interference of the light field generated by the pump laser scattered by the sample to be tested on the near-field optical information detection, and is suitable for allowing the initial light beam to pass through and blocking background stray light interference.

[0019] According to an embodiment of the present disclosure, the near-field optical imaging system further includes a focusing component, adapted to focus the initial light beam onto the surface of the sample to be measured, so as to facilitate positioning of the light spot formed by the initial light beam; and

[0020] The beam splitter is adapted to reflect the fluorescence up-conversion signal or the fluorescence down-conversion signal to the detection light path.

[0021] According to an embodiment of the present disclosure, the above detection optical path includes:

[0022] A filter, adapted to filter out the pump laser and scattered light; and

[0023] The detector is suitable for detecting the above-mentioned fluorescence up-conversion signal or the above-mentioned fluorescence down-conversion signal.

[0024] According to an embodiment of the present disclosure, the near-field optical imaging system further includes a microscope, which is disposed between the solid color center crystal and the beam splitter, and the microscope is suitable for collecting the fluorescence signal; and

[0025] The three-axis translation stage is configured to movably support the microscope.

[0026] According to an embodiment of the present disclosure, the light source includes any one of a mid-infrared quantum cascade laser, a terahertz quantum cascade laser, a black body radiation light source, and a carbon dioxide laser.

[0027] According to an embodiment of the present disclosure, the solid color center crystal includes any one of a bulk crystal, an ion-implanted solid color center crystal, a substrate of spin-coated solid color center nanoparticles, and a thin film solid color center crystal.

[0028] According to an embodiment of the present disclosure, a pump laser source is provided to provide a pump laser, a light source provides an initial light beam in a mid-infrared band or a terahertz band, an optical window is provided to fit a sample to be tested, a solid-state color center crystal is provided to fit a optical window, and the solid-state color center crystal emits a fluorescence signal under the irradiation of the pump laser; the fluorescence signal is energy-level pumped under the joint action of the pump laser and the initial light beam to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal; and a detection optical path is provided to detect the fluorescence up-conversion signal or the fluorescence down-conversion signal, so as to obtain an image of the light field distribution of the surface of the sample to be tested and the cross-section of the solid-state color center crystal at different depths; wherein the fluorescence signal includes near-field optical information of the initial light beam passing through the sample to be tested, and the near-field optical information includes transmission spectrum information and intensity information of the initial light beam; according to the image of the light field distribution of the surface of the sample to be tested and the cross-section of the solid-state color center crystal at different depths, the near-field optical information is obtained, and near-field optical imaging beyond the diffraction limit of the mid-infrared band or the terahertz band is realized, the complexity of the system is reduced, and the resolution of imaging in the mid-infrared band and the terahertz band is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above contents and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0030] Figure 1 The working principle diagram of the near-field optical imaging system according to an embodiment of the present disclosure is schematically shown;

[0031] Figure 2 A schematic diagram of a sample to be tested and a solid color center crystal in a near-field optical imaging system according to an embodiment of the present disclosure under the irradiation of an initial light beam in the mid-infrared band or the terahertz band is shown;

[0032] Figure 3 Schematically showing the simulation result images of the light field distribution of the surface of the sample to be tested and the solid color center crystal under the irradiation of the initial light beam in the mid-infrared band or the terahertz band in the near-field optical imaging system according to the embodiment of the present disclosure and the cross-section of the solid color center crystal at different depths;

[0033] Figure 4 Schematically showing experimental result images of light field distribution of the surface of the sample to be tested and the solid color center crystal under the irradiation of the initial light beam in the mid-infrared band or the terahertz band in the near-field optical imaging system according to the embodiment of the present disclosure and the cross-section of the solid color center crystal at different depths;

[0034] Figure 5 A schematic diagram of conversion energy levels in the process of up-conversion and down-conversion in the mid-infrared / terahertz band by a solid color center crystal according to an embodiment of the present disclosure is schematically shown; and

[0035] Figure 6 The Nd according to the embodiment of the present disclosure is schematically shown. 3+ Schematic diagram of mid-infrared conversion energy levels of ion-doped YAG crystal;

[0036] Figure 7 The Nd according to the embodiment of the present disclosure is schematically shown. 3+ Spectral response diagram of ion-doped YAG crystal under the irradiation of initial beam in the mid-infrared band or terahertz band;

[0037] Figure 8 Schematically illustrates an embodiment of the present disclosure Figure 7 A locally enlarged spectral response diagram of the initial light beam within the wavelength range of 780nm-825nm;

[0038] Fig. 9 Schematically illustrates an embodiment of the present disclosure Figure 7 A locally enlarged spectral response diagram of the initial light beam within the wavelength range of 860nm-910nm;

[0039] Fig.10 A mid-infrared / terahertz near-field super-resolution system combined with wide-field imaging according to an embodiment of the present disclosure is schematically shown;

[0040] Fig.11 A mid-infrared / terahertz near-field super-resolution system combined with a confocal microscope according to another embodiment of the present disclosure is schematically shown;

[0041] Fig.12 A mid-infrared / terahertz near-field super-resolution system combined with structured light illumination according to another embodiment of the present disclosure is schematically shown; and

[0042] Fig.13 A mid-infrared / terahertz near-field super-resolution system combined with a STED stimulated emission depletion microscope according to yet another embodiment of the present disclosure is schematically shown.

[0043] In the above drawings, the meanings of the reference numerals are as follows:

[0044] 1- Pump laser source;

[0045] 2-sample to be tested;

[0046] 3- Optical window;

[0047] 4- solid crystal color center;

[0048] 5- Light source;

[0049] 6-Detection optical path;

[0050] 61- first lens;

[0051] 62- second lens;

[0052] 63-Detector;

[0053] 64-third lens;

[0054] 65-pinhole;

[0055] 66-first filter;

[0056] 7- beam splitter;

[0057] 8- Focusing component;

[0058] 9- Microscope;

[0059] 10-Three-axis translation stage;

[0060] 11- second filter;

[0061] 12-reflector;

[0062] 13- vortex phase plate;

[0063] 14-Exhaustion of light source;

[0064] 15- cylindrical lens;

[0065] 16-Diffraction grating. DETAILED DESCRIPTION

[0066] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0067] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0068] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0069] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0070] Near-field optical imaging mainly images optical phenomena or structures within one wavelength from the surface of an object. Near-field optical imaging is based on the detection and imaging principles of non-radiative fields. When light waves hit the surface of an object, evanescent waves are generated on the surface of the object. These evanescent waves are strong near the surface of the object, and their intensity decays rapidly once they leave the object. Near-field optical imaging technology converts these evanescent waves into detectable propagation fields through the conversion of tiny objects, which are then recorded by long-distance probes, thereby achieving high-resolution imaging of optical phenomena or structures near the surface of the object to be measured.

[0071] Related mid-infrared / terahertz near-field imaging technologies all require coherent detection of electromagnetic waves, which usually requires amplitude detection of the mid-infrared / terahertz field intensity in the time domain, followed by Fourier transform, which greatly increases the complexity and cost of the system. Existing mid-infrared / terahertz near-field imaging technologies are mainly divided into the following categories: Scanning Near-field Optical Microscope with an aperture (Apertured SNOM), Apertureless Scanning Near-field Optical Microscope (Apertureless SNOM), Electro-optical effect (EO effect) detection based on sum frequency generation (SFG) materials, and mid-infrared photothermal imaging (IR-PHI).

[0072] In implementing the inventive concept disclosed herein, the inventors found that apertured near-field optical microscopy can improve imaging resolution based on the aperture method, by selecting a small hole with an aperture smaller than the optical diffraction limit (generally λ / 2) to excite the sample to be tested, thereby obtaining a higher spatial resolution. This method usually requires complex sample processing (such as fine small holes and tapered optical fibers). In addition, its signal intensity is proportional to (a / λ) 4 ,When the aperture is continuously reduced to improve the spatial resolution, the signal strength gradually weakens, making detection more difficult.

[0073] Aperture-free near-field optical microscopy can achieve local electric field enhancement based on nanoscale metal probes, and extract local electric field signals by coupling evanescent waves with scattered fields. This method requires high-precision and complex nanoscale needle tip manufacturing processes, and requires frequency modulation and demodulation to obtain evanescent wave information in the scattered field, which often results in the detected signal not directly reflecting the material's response information to mid-infrared / terahertz. In addition, this method has high requirements for sample flatness and stability, which limits the number of samples that can be measured in actual testing.

[0074] Terahertz imaging based on electro-optic crystals, such as LiNbO 3In the case of electro-optical crystals, the material to be detected is placed close to the surface of the crystal. When the terahertz wave irradiates the crystal, its electric field modulates the refractive index of the crystal. The terahertz wave can be detected by monitoring the change in polarization state caused by the change in the refractive index of the crystal with a beam of detection light. However, this method is not only complex in system, but also birefringent crystals will introduce additional aberrations during imaging, resulting in limited resolution.

[0075] Mid-infrared thermal imaging technology uses detection light to monitor temperature changes caused by mid-infrared absorption at local sites. Its disadvantage is that it requires temperature sensing media such as glycerol to be attached to the sample surface, which increases the complexity and limitations of the system.

[0076] In view of this, the present disclosure provides a near-field optical imaging system, which provides a pump laser source by providing a pump laser, provides an initial light beam in the mid-infrared band or the terahertz band by providing an optical window piece to fit a sample to be tested, and provides a solid color center crystal to fit the optical window piece, so that the solid color center crystal emits a fluorescence signal under the irradiation of the pump laser; the fluorescence signal is energy-level pumped under the joint action of the pump laser and the initial light beam to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal; and a detection optical path is provided to detect the fluorescence up-conversion signal or the fluorescence down-conversion signal, so as to obtain an image of the light field distribution of the surface of the sample to be tested and the cross-section of the solid color center crystal at different depths; wherein the fluorescence signal includes near-field optical information of the initial light beam passing through the sample to be tested, and the near-field optical information includes transmission spectrum information and intensity information of the initial light beam; according to the image of the light field distribution of the surface of the sample to be tested and the cross-section of the solid color center crystal at different depths, the near-field optical information is obtained, so as to realize near-field optical imaging beyond the diffraction limit of the mid-infrared band or the terahertz band, reduce the complexity of the system, and improve the resolution of imaging in the mid-infrared band and the terahertz band.

[0077] Figure 1 The working principle diagram of the near-field optical imaging system according to an embodiment of the present disclosure is schematically shown.

[0078] According to some embodiments of the present disclosure, Figure 1As shown, the above-mentioned near-field optical imaging system includes a pump laser source 1, an optical window 3, a solid color center crystal 4, a light source 5 and a detection optical path 6. The pump laser source 1 is suitable for providing pump laser; the optical window 3 is attached to the sample 2 to be tested; the solid color center crystal 4 is attached to the optical window 3, and the solid color center crystal 4 is suitable for emitting a fluorescence signal under the irradiation of the pump laser; the light source 5 is suitable for providing an initial light beam in the mid-infrared band or the terahertz band, and the fluorescence signal is pumped at an energy level under the joint action of the pump laser and the initial light beam to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal; and the detection optical path 6 is suitable for detecting the fluorescence up-conversion signal or the fluorescence down-conversion signal to obtain an image of the light field distribution of the surface of the sample 2 to be tested and the cross section of the solid color center crystal 4 at different depths; wherein the fluorescence signal includes the near-field optical information of the initial light beam passing through the sample 2 to be tested, and the near-field optical information includes the transmission spectrum information and the intensity information of the initial light beam; according to the image of the light field distribution of the surface of the sample 2 to be tested and the cross section of the solid color center crystal 4 at different depths, the near-field optical information is obtained.

[0079] According to some embodiments of the present disclosure, a pump laser source 1 is provided to provide a pump laser, a light source 5 provides an initial light beam in a mid-infrared band or a terahertz band, an optical window 3 is provided to be attached to a sample 2 to be tested, a solid color center crystal 4 is provided to be attached to the optical window 3, and the solid color center crystal 4 emits a fluorescence signal under the irradiation of the pump laser; the fluorescence signal is energy-level pumped under the combined action of the pump laser and the initial light beam to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal; and a detection optical path 6 is provided to detect the fluorescence up-conversion signal or the fluorescence down-conversion signal, so as to obtain the sample to be tested. The image of the light field distribution of the surface of the sample 2 and the cross-section of the solid color center crystal 4 at different depths is obtained; wherein, the fluorescence signal includes the near-field optical information of the initial light beam passing through the sample 2 to be tested, and the near-field optical information includes the transmission spectrum information and intensity information of the initial light beam; according to the image of the light field distribution of the surface of the sample 2 to be tested and the cross-section of the solid color center crystal 4 at different depths, the near-field optical information is obtained, and the near-field optical imaging beyond the diffraction limit of the mid-infrared band or the terahertz band is realized, the complexity of the system is reduced, and the resolution of imaging in the mid-infrared band and the terahertz band is improved.

[0080] According to some embodiments of the present disclosure, the above-mentioned near-field optical imaging system realizes near-field optical detection by combining the initial light beam in the mid-infrared band or the terahertz band with the excitation light path and the detection light path where the pump laser source 1 is located, thereby reducing the complexity of the system.

[0081] Figure 2 A schematic three-dimensional diagram of a sample to be tested and a solid color center crystal in a near-field optical imaging system according to an embodiment of the present disclosure under the irradiation of an initial light beam in the mid-infrared band or the terahertz band is shown.

[0082] According to some embodiments of the present disclosure, Figure 2 The solid color center crystal 4 is a YAG crystal with a refractive index of 1.82. The sample 2 to be tested can be, for example, a metal E-shaped mask with a size of 25 μm×25 μm. The wavelength of the mid-infrared laser is 10.6 μm. Figure 2 As shown, Figure 2 The z axis takes the cross section of the sample 2 to be tested as the origin, and the cross section of the solid color center crystal 4 far away from the sample 2 to be tested as the positive direction. As the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested gradually increases, the larger the value of z, the greater the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested in micrometers.

[0083] Figure 3 The schematic diagram shows the simulated result images of the light field distribution of the surface of the sample to be tested and the solid color center crystal under the irradiation of the initial light beam in the mid-infrared band or the terahertz band in the near-field optical imaging system according to the embodiment of the present disclosure, and the cross-section of the solid color center crystal at different depths.

[0084] According to some embodiments of the present disclosure, Figure 3 As shown, the light field distribution of the cross section of the solid color center crystal 4 at different depths is different. Figure 3 (a) is the simulated result image of the light field distribution at the metal mask plane when z=0μm, Figure 3 In (a), the decrease in transmittance caused by reflection in the metal mask area can be observed.

[0085] Figure 3 (b) is a simulation result image of the light field distribution when the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested is z=5μm; Figure 3 (c) is a simulation result image of the light field distribution when the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested is z=10 μm; Figure 3 (d) is an image of the simulation result of the light field distribution when the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested is z=20 μm. Figure 3 The horizontal and vertical axes of (a), (b), (c) and (d) are all distances, with the unit being μm. Figure 3 It can be seen from (a), (b), (c) and (d) that as the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be measured gradually increases, the evanescent wave information in the near field range of the surface of the sample 2 to be measured is gradually lost. When the distance from the surface of the object is more than one wavelength, the evanescent wave information is almost completely lost. Therefore, the "near field" area is generally referred to as the range of one wavelength of the material to be imaged.

[0086] Figure 4The experimental result images of the light field distribution of the surface of the sample to be tested and the solid color center crystal under the irradiation of the initial light beam in the mid-infrared band or the terahertz band in the near-field optical imaging system according to the embodiment of the present disclosure and the cross-section of the solid color center crystal at different depths are schematically shown.

[0087] According to some embodiments of the present disclosure, Figure 4 As shown, the light field distribution of the cross section of the solid color center crystal 4 at different depths is different. Figure 4 (a) is the experimental result image of the light field distribution at the metal mask plane when z=0μm, Figure 4 In (a), the decrease in transmittance caused by reflection in the metal mask area can be observed.

[0088] Figure 4 (b) is an experimental result image of the light field distribution when the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested is z=5μm; Figure 4 (c) is an experimental result image of the light field distribution when the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested is z=10 μm; Figure 4 (d) is an experimental result image of the light field distribution when the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested is z=20 μm. Figure 4 The horizontal and vertical axes of (a), (b), (c) and (d) are all distances, with the unit being μm. Figure 4 It can be seen from (a), (b), (c) and (d) that as the distance between the cross section of the solid color center crystal 4 and the surface of the sample 2 to be tested gradually increases, the evanescent wave information in the near-field range of the surface of the sample 2 to be tested is gradually lost. When the distance from the surface of the object is more than one wavelength, the evanescent wave information is almost completely lost.

[0089] According to some embodiments of the present disclosure, the solid color center crystal 4 can realize the conversion of the initial light beam in the mid-infrared band or the terahertz band into visible light, thereby obtaining a fluorescence signal. When the solid color center crystal 4 is irradiated by the pump laser and the initial light beam in the mid-infrared band or the terahertz band, the solid color center crystal 4 will undergo an up-conversion process or a down-conversion process, so that the fluorescence signal is pumped at the energy level under the joint action of the pump laser and the initial light beam to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal, and the intensity of the fluorescence signal of a specific wavelength will change with the change of the intensity of the initial light beam in the mid-infrared band or the terahertz band. By detecting the fluorescence signal of a specific band through the detection optical path 6, the intensity of the initial light beam in the mid-infrared band or the terahertz band at a certain point on the surface of the sample 2 to be tested can be obtained. In this process, the excitation light in the detection optical path 6 is equivalent to an optical probe, whose resolution is limited by the diffraction limit of the pump laser (hundreds of nm scale) rather than the diffraction limit of the mid-infrared / terahertz wave (μm to mm scale), thereby enabling near-field super-resolution imaging in the mid-infrared band or terahertz band.

[0090] According to some embodiments of the present disclosure, there is a splitting in the energy level of the solid color center crystal 4 that matches the mid-infrared band or the terahertz band; and there is a channel for radiative relaxation between the excited state and the ground state of the solid color center crystal 4, so that photons are emitted when ions in the excited state fall to the ground state.

[0091] According to some embodiments of the present disclosure, the absorption cross section of the solid color center crystal 4 is relatively large, and the absorption cross section area range is at least greater than 10 -21 cm 2 .

[0092] According to some embodiments of the present disclosure, the metastable lifetime of the solid color center crystal 4 is such that the population accumulation rate caused by pumping with an initial light beam in the mid-infrared band or the terahertz band is faster than the population relaxation rate of the energy level of the solid color center crystal itself.

[0093] According to some alternative embodiments of the present disclosure, the metastable lifetime of the solid color center crystal 4 is longer than 10 microseconds.

[0094] According to some embodiments of the present disclosure, by selecting a solid-state color center crystal 4 that simultaneously satisfies the following conditions: there is a splitting in the energy level of the solid-state color center crystal 4 that matches the mid-infrared band or the terahertz band; there is a radiation relaxation channel between the excited state and the ground state of the solid-state color center crystal 4, so that photons are emitted when the ions in the excited state fall to the ground state; the absorption cross-section of the solid-state color center crystal 4 is large; and the metastable lifetime of the solid-state color center crystal 4 is long enough that the population accumulation rate caused by the initial light beam in the mid-infrared band or the terahertz band pumping is faster than the population relaxation rate of the energy level of the solid-state color center crystal itself, it is possible to realize the up-conversion and down-conversion process in the mid-infrared / terahertz band, thereby realizing near-field optical imaging beyond the diffraction limit of the mid-infrared band or the terahertz band.

[0095] According to some embodiments of the present disclosure, the solid-state color center crystal is equivalent to a multi-pixel optical conversion device, and taking the rare earth doped crystal as an example, its cost is low and can be mass-produced. The transfer of the sample to be tested to the solid-state color center crystal and the subsequent cleaning with organic reagents (such as ethanol) are very friendly, which reduces the cost of the system. The above-mentioned near-field optical imaging system is based on the energy level transition inside the solid-state color center crystal, and directly reflects the mid-infrared and terahertz wave intensity in the change of the solid-state color center fluorescence intensity, without the need for complex coherent detection means.

[0096] Figure 5 A schematic diagram of conversion energy levels in the process of up-conversion and down-conversion in the mid-infrared / terahertz band by a solid-state color center crystal according to an embodiment of the present disclosure is schematically shown.

[0097] According to some embodiments of the present disclosure, according to the properties of the initial light beam in the mid-infrared band or the terahertz band and the splitting resonance of the ground state or the excited state energy level, the solid color center crystal 4 realizes the up-conversion and down-conversion process in the mid-infrared band / terahertz band and is divided into a ground state resonance-up-conversion process, a ground state resonance-down-conversion process, an excited state resonance-up-conversion process and an excited state resonance-down-conversion process. The classification of the up-conversion / down-conversion process is based on the comparison of the photon energy of the converted fluorescence with the photon energy of the pump laser. When the converted fluorescence signal photon energy is greater than the pump laser, it is called an up-conversion process, otherwise it is called a down-conversion process. Figure 5 As shown, Figure 5 (a) is a schematic diagram of the conversion energy levels in the ground state resonance-upconversion process. First, the electrons in the first ground state are pumped to the second ground state by a mid-infrared / terahertz laser, and then a pump laser that matches the energy splitting of the second ground state and the excited state is used to pump the second ground state electrons to the excited state. By monitoring the intensity of the fluorescence signal emitted when the excited state electrons fall to the first ground state, the corresponding mid-infrared / terahertz wave intensity can be inferred.

[0098] Figure 5(b) is a schematic diagram of the conversion energy level in the ground state resonance-down conversion process. First, the electrons in the first ground state are pumped to the excited state by a pump laser. A part of the excited state electrons will fall to the second ground state and emit a down-conversion fluorescence signal. When an external mid-infrared / terahertz laser splits and resonates with the first and second ground state energy levels, the population number of the first ground state decreases, and the population number of the excited state decreases accordingly. The down-conversion fluorescence signal of the second ground state gradually decreases. The intensity of the mid-infrared / terahertz laser signal can be inferred by monitoring the intensity value of the down-conversion fluorescence signal.

[0099] Figure 5 (c) is a schematic diagram of the conversion energy level in the excited state resonance-upconversion process; Figure 5 (d) is a schematic diagram of the conversion energy levels in the excited state resonance-down conversion process. First, the electrons in the ground state are pumped to the second excited state by a pump laser that matches the splitting of the ground state and the second excited state energy levels. When irradiated with mid-infrared / terahertz waves, the electron population of the second excited state is transferred to the first excited state, resulting in an enhancement of the down-conversion fluorescence signal emitted by the first excited state electrons transitioning to the ground state. The mid-infrared / terahertz wave intensity can be detected by monitoring the down-conversion fluorescence signal.

[0100] According to some embodiments of the present disclosure, Figure 5 As shown in (c), the pump laser pumps multiple ions in the ground state in the solid color center crystal 4 to the first excited state, and the multiple ions in the first excited state continue to be pumped to the second excited state under the irradiation of the initial light beam. A part of the multiple ions in the second excited state falls back to the ground state and emits multiple corresponding up-conversion photons with energy greater than the pump laser, wherein the intensity of the initial light beam in the mid-infrared band or the terahertz band is obtained according to the fluorescence signal intensity of the up-conversion photons.

[0101] Figure 6 The Nd according to the embodiment of the present disclosure is schematically shown. 3+ Schematic diagram of the mid-infrared conversion energy levels of ion-doped YAG crystal.

[0102] According to some alternative embodiments of the present disclosure, the solid color center crystal 4 is Nd 3+ Ion-doped YAG crystal, Nd 3+ The infrared near-field imaging mechanism of ion-doped YAG crystals is as follows Figure 6 As shown, Nd:YAG crystal is used as solid color center crystal 4, that is, as the response medium of infrared / terahertz detector, and the ground state electrons are pumped to 4 F 3 / 2 The first excited state (lifetime of about 300μs is a long-lived metastable state), when the mid-infrared laser (4-11μm) is injected, the electrons inside the rare earth ions will jump and change the energy level distribution, making4 F 3 / 2 Energy level electron transition to 4 F 5 / 2 Energy level, among which 4 F 5 / 2 Electrons on each energy level have a certain probability of falling to 4 I 9 / 2 , and emits photons with a wavelength of 806nm. By monitoring the up-conversion fluorescence intensity through a filter (for example, a bandpass filter with a central wavelength of 810nm and a half-width of 10nm) and a single-photon detector, the mid-infrared wave intensity irradiated on the Nd:YAG crystal infrared detector can be inferred. The 850nm pump laser is focused on the plane of the sample 2 to be tested through the confocal optical path. Its spatial resolution as an optical probe is about 400nm, which is much better than the original diffraction limit (2-5.5μm) of the mid-infrared band to be detected, realizing near-field optical imaging beyond the diffraction limit of the mid-infrared band and improving the resolution of mid-infrared band imaging.

[0103] Figure 7 The Nd according to the embodiment of the present disclosure is schematically shown. 3+ Spectral response diagram of ion-doped YAG crystal under the irradiation of the initial beam in the mid-infrared band or the terahertz band.

[0104] According to some embodiments of the present disclosure, Figure 7 The horizontal axis represents the wavelength in nm, and the vertical axis represents the fluorescence intensity in au. Figure 7 The solid line in the middle is the fluorescence wavelength-intensity correspondence diagram of the solid-state color center crystal 4 under the combined action of the mid-infrared laser and the pump laser when the light source 1 is turned on; the dotted line is the fluorescence wavelength-intensity correspondence diagram of the solid-state color center crystal 4 under the action of the pump laser when the light source 1 is turned off. Figure 8 Schematically illustrates an embodiment of the present disclosure Figure 7 A locally enlarged spectral response diagram of the initial light beam within the wavelength range of 780nm-825nm; Fig. 9 Schematically illustrates an embodiment of the present disclosure Figure 7 A locally enlarged spectral response diagram of the initial light beam with a wavelength range of 860nm-910nm.

[0105] According to some embodiments of the present disclosure, Figure 8 As shown, the light source 1 is turned on, and on the basis of irradiating the solid color center crystal 4 with the pump laser, the solid color center crystal 4 is irradiated with the mid-infrared laser with a wavelength range of 780nm-825nm, so that 4 F 5 / 2 The electrons on the energy level undergo energy level transition and fall to 4 I 9 / 2 energy level.

[0106] According to some embodiments of the present disclosure, Fig. 9 As shown, the light source 1 is turned on, and on the basis of irradiating the solid color center crystal 4 with the pump laser, the solid color center crystal 4 is irradiated with the mid-infrared laser with a wavelength range of 860nm-910nm, so that 4 F 3 / 2 Energy level electron transition to 4 I 9 / 2 energy level.

[0107] According to some embodiments of the present disclosure, when Nd:YAG crystal is used as a solid color center crystal, 850nm is used as a pump laser, and its diffraction limit is about 400nm, which is much larger than the diffraction limit of the mid-infrared wave (um). It can study the mid-infrared super-resolution imaging of micro-nanoscale physical properties, and improve the resolution of imaging in the mid-infrared band and terahertz band.

[0108] According to some embodiments of the present disclosure, the optical window 3 is suitable for isolating the interference of the light field generated by the pump laser scattered by the sample 2 to the near-field optical information detection, and is suitable for allowing the initial light beam to pass through and blocking the background stray light interference.

[0109] According to some embodiments of the present disclosure, the near-field optical imaging system further includes a focusing component and a beam splitter 7. The focusing component is adapted to focus the initial light beam onto the surface of the sample 2 to be tested, so as to facilitate the positioning of the light spot formed by the initial light beam; the beam splitter 7 is adapted to reflect the fluorescence up-conversion signal or the fluorescence down-conversion signal to the detection optical path 6.

[0110] According to some embodiments of the present disclosure, the initial light beam is focused onto the surface of the sample 2 to be tested by using a focusing assembly, which facilitates the positioning of the light spot formed by the initial light beam and enhances the power density of the initial light beam, which is beneficial for monitoring the relevant information of the absorption of the initial light beam by the sample 2 to be tested. By using a beam splitter 7, the excitation light path of the solid color center crystal 4 excited by the pump laser can be separated from the detection light path 6, thereby avoiding interference between the excitation light path and the detection light path 6.

[0111] According to some embodiments of the present disclosure, the focusing component includes any one of a focusing lens, a parabolic mirror and a ZnSe lens. The beam splitter 7 divides the pump laser into two parts, and one part of the pump laser is transmitted to the solid color center crystal 4 .

[0112] According to some alternative embodiments of the present disclosure, the beam splitter 7 may be replaced by a polarization beam splitter or a dichroic mirror.

[0113] According to some embodiments of the present disclosure, the near-field optical imaging system further comprises a microscope and a three-axis translation stage. The microscope is disposed between the solid color center crystal 4 and the beam splitter 7, and is suitable for collecting fluorescence signals; and the three-axis translation stage is configured to movably support the microscope.

[0114] According to some embodiments of the present disclosure, surface positioning (i.e., z-axis positioning) of the interface between the solid color center crystal 4 and the sample to be tested 2 can be achieved by setting a three-axis translation stage, and after positioning on the surface of the solid color center crystal 4, the near-field optical distribution image of the initial light beam in the mid-infrared band or the terahertz band in a two-dimensional plane is obtained by using confocal scanning imaging technology, super-resolution scanning imaging technology, and wide-field imaging technology. By comparing and analyzing the near-field optical distribution data of the solid color center crystal 4 at the sample to be tested 2 with the near-field optical distribution data of the solid color center crystal 4 at the sample to be tested 2, the transmission spectrum information of the initial light beam in the mid-infrared band or the terahertz band of the sample to be tested 2 can be obtained.

[0115] According to some embodiments of the present disclosure, by fitting the sample to be tested 2, the optical window 3 and the solid color center crystal 4, the solid color center crystal 4 can receive the near-field optical information after the initial light beam in the mid-infrared band or the terahertz band passes through the sample to be tested 2. The pump laser is focused on the interface between the sample to be tested 2 and the optical window 3 through a microscope.

[0116] According to some alternative embodiments of the present disclosure, the near-field optical imaging system includes a pump laser source 1, a solid color center crystal 4, a light source 5, and a detection optical path 6. By placing the sample to be tested 2 and the solid color center crystal 4 in close proximity, the solid color center crystal 4 can receive the near-field optical information after the initial light beam in the mid-infrared band or the terahertz band passes through the sample to be tested 2. The pump laser is focused on the interface between the sample to be tested 2 and the solid color center crystal 4 through a microscope.

[0117] According to some embodiments of the present disclosure, the detection optical path 6 includes a filter and a detector. The filter is suitable for filtering out pump laser and scattered light; and the detector is suitable for detecting fluorescence up-conversion signals or fluorescence down-conversion signals.

[0118] According to some embodiments of the present disclosure, by fitting the sample to be tested 2, the optical window piece 3 and the solid color center crystal 4 together, the near-field optical information after the mid-infrared / terahertz light wave passes through the sample to be tested 2 can be sensed with low loss to the cross-sections of different depths of the solid color center crystal 4, and the mid-infrared / terahertz light field is converted to visible light / near-infrared through the solid color center crystal 4, and then the light field distribution information of the surface of the sample to be tested 2 and the cross-section of the solid color center crystal 4 at different depths is read out through a microscope to form an image; the detector in the detection optical path 6 is a detector in the visible light / near-infrared band, which is used to detect the intensity of the converted fluorescent photons.

[0119] According to some embodiments of the present disclosure, different types of detectors are selected according to the band and strength of the fluorescence up-conversion signal or the fluorescence down-conversion signal. If the band of the fluorescence up-conversion signal or the fluorescence down-conversion signal is in the visible light band, the detector includes any one of a conventional photodiode, an avalanche photodiode, and a photomultiplier tube. If the band of the fluorescence up-conversion signal or the fluorescence down-conversion signal is in the near-infrared band, the detector includes an InGaAs photodiode with higher sensitivity in the near-infrared band. In the actual measuring device, it is necessary to add a filter corresponding to the fluorescence band to be detected to screen out the fluorescence signal and filter out interference such as background excitation light and scattered light.

[0120] According to some embodiments of the present disclosure, based on the solid color center crystal material that meets the up-conversion or down-conversion fluorescence detection conditions, different optical systems can be selected in the actual experimental system for near-field super-resolution imaging. While keeping the mid-infrared / terahertz band optical path unchanged, the pump laser excitation optical path and the detection optical path under the solid color center crystal 4 have many optional schemes, such as: confocal, super-resolution, wide-field imaging, structured light illumination excitation and corresponding detection optical paths. Different excitation optical paths and detection optical paths have common characteristics: the sensing of evanescent wave information is achieved by contacting the sample to be tested 2 with the solid color center crystal 4, the up-conversion / down-conversion process inside the solid color center crystal 4 is used to achieve fluorescence conversion from the mid-infrared / terahertz band to a shorter wavelength, and the near-field optical information in the plane of the sample to be tested 2 is collected by the detector to achieve near-field super-resolution imaging.

[0121] Fig.10 A mid-infrared / terahertz near-field super-resolution system combined with wide-field imaging according to an embodiment of the present disclosure is schematically shown. Fig.10As shown, the mid-infrared / terahertz near-field super-resolution system combined with wide-field imaging includes a pump laser source 1, a solid color center crystal 4, a light source 5, a detection optical path 6, a beam splitter 7, a focusing component 8, and a microscope 9. The detection optical path 6 in the system includes a first lens 61, a second lens 62, and a detector 63. The system focuses the pump laser onto the back focal plane of the microscope 9 through the focusing component 8, and realizes parallel light illumination and collects conversion fluorescence through the microscope 9. It has the advantages of a large field of view and no need for scanning, but the required excitation power is high and the signal-to-noise ratio is low. In the actual experimental process, the wide-field imaging uses a solid color center crystal in the form of an ion implantation / nanoparticle spin-coated substrate for the best effect.

[0122] Fig.11 A mid-infrared / terahertz near-field super-resolution system combined with a confocal microscope according to another embodiment of the present disclosure is schematically shown. Fig.11 As shown, the mid-infrared / terahertz near-field super-resolution system combined with a confocal microscope includes a pump laser source 1, a solid color center crystal 4, a light source 5, a detection optical path 6, a beam splitter 7, a focusing component 8, a microscope 9, and a three-axis translation stage 10. The detection optical path 6 in the system includes a first lens 61, a pinhole 65, a second lens 62, a first filter 66, a third lens 64, and a detector 63. The pinhole 65 is an optical precision pinhole 65. The system injects the pump laser parallel into the rear focal plane of the microscope 9 and focuses it on the solid color center crystal 4. Its spatial resolution is limited by the diffraction limit of the pump laser. The converted fluorescence signal is collected after filtering through the optical precision pinhole 65, which has the advantage of high z-axis spatial resolution, but requires point-by-point scanning imaging through a three-axis translation stage 10 or a scanning galvanometer, and the speed is slow.

[0123] Fig.12 A mid-infrared / terahertz near-field super-resolution system combined with structured light illumination according to another embodiment of the present disclosure is schematically shown. Fig.12 As shown, the system includes a pump laser source 1, a solid color center crystal 4, a light source 5, a detection optical path 6, a beam splitter 7, a focusing component 8, a microscope 9, a cylindrical lens 15, and a diffraction grating 16. The diffraction grating 16 can be replaced by a spatial light modulator. The system generates a structured light field through devices such as the diffraction grating 16 or the spatial light modulator, which can convert the high-frequency information emitted by the sample 2 to be tested into low-frequency information that can be collected by the detector 63 through an interference method, thereby improving the resolution of the final near-field optical imaging.

[0124] Fig.13 A mid-infrared / terahertz near-field super-resolution system combined with a STED stimulated emission depletion microscope according to another embodiment of the present disclosure is schematically shown. Fig.13As shown, the system includes a pump laser source 1, a solid color center crystal 4, a light source 5, a depletion light source 14, a reflector 12, a vortex phase plate 13, a detection light path 6, a beam splitter 7, a focusing assembly 8, a microscope 9, and a second filter 11. The detection light path 6 in the system includes a first lens 61, a first filter 66, and a detector 63. The pump laser source 1 emits a laser beam to excite the fluorescence of the solid color center, and the depletion light source 14 is used to generate a ring laser to suppress the fluorescence emission of the fluorophore outside the excitation center, thereby achieving imaging beyond the diffraction limit.

[0125] According to some embodiments of the present disclosure, the light source 5 includes any one of a mid-infrared quantum cascade laser, a terahertz quantum cascade laser, a black body radiation light source, and a carbon dioxide laser.

[0126] According to some embodiments of the present disclosure, the band and type of the mid-infrared / terahertz band light source 5 are changed according to the different bands of the optical "fingerprint" characteristics of different samples 2 to be tested.

[0127] According to some embodiments of the present disclosure, the solid color center crystal 4 includes any one of a bulk crystal, an ion-implanted solid color center crystal, a substrate of spin-coated solid color center nanoparticles, and a thin film solid color center crystal.

[0128] According to some embodiments of the present disclosure, the solid color center conversion ions in the bulk crystal are uniformly distributed throughout the crystal, and the signal intensity is high and the background fluorescence intensity is large; the ion implanted solid color center crystal is a layer of color center that can emit conversion fluorescence is implanted on the surface of the crystal by ion implantation, and the detector prepared in this way has low background interference; the substrate of spin-coated solid color center nanoparticles is prepared by preparing solid color center-doped nanoparticles and spin-coating them on a transparent substrate, which can also be used as a near-field optical detector, with weak background signal, and only the nanoparticle plane contributes to the fluorescence signal. The thin film type solid color center crystal is a thin film material type solid color center crystal that can be prepared by ion cutting and other technologies, which can be transferred to a transparent optical substrate medium as a mid-infrared / terahertz near-field optical detector. Since the thin film type solid color center crystal is thin, it has the characteristics of high z-axis spatial resolution and high signal-to-noise ratio.

[0129] It will be appreciated by those skilled in the art that the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways, even if such combinations and / or combinations are not explicitly described in the present disclosure. In particular, the features described in the various embodiments and / or claims of the present disclosure may be combined and / or combined in a variety of ways without departing from the spirit and teachings of the present disclosure. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0130] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. The scope of the present disclosure is defined by the attached claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A near-field optical imaging system, comprising: A pump laser source, adapted to provide a pump laser; Optical window piece, attached to the sample to be tested; A solid color center crystal is attached to the optical window, and the solid color center crystal is suitable for emitting a fluorescence signal under the irradiation of the pump laser; A light source, adapted to provide an initial light beam in a mid-infrared band or a terahertz band, wherein the fluorescence signal is pumped to emit a fluorescence up-conversion signal or a fluorescence down-conversion signal under the combined action of the pump laser and the initial light beam; and A detection optical path, adapted to detect the fluorescence up-conversion signal or the fluorescence down-conversion signal, so as to obtain images of light field distribution of the surface of the sample to be tested and the cross section of the solid color center crystal at different depths; Among them, the fluorescence signal includes near-field optical information of the initial light beam passing through the sample to be tested, and the near-field optical information includes transmission spectrum information and intensity information of the initial light beam; the near-field optical information is obtained based on images of light field distribution of the surface of the sample to be tested and the cross-section of the solid color center crystal at different depths.

2. The near-field optical imaging system according to claim 1, wherein: The energy level of the solid color center crystal has a cleavage matching the mid-infrared band or the terahertz band; and There is a radiation relaxation channel between the excited state and the ground state of the solid color center crystal, so that photons are emitted when the ions in the excited state fall to the ground state.

3. The near-field optical imaging system according to any one of claims 1 to 2, wherein: The metastable lifetime of the solid color center crystal makes the population accumulation rate caused by the initial light beam in the mid-infrared band or the terahertz band pumping faster than the population relaxation rate of the energy level of the solid color center crystal itself.

4. The near-field optical imaging system according to claim 1, wherein: The pump laser pumps a plurality of ions in the ground state in the solid color center crystal to a first excited state, and the plurality of ions in the first excited state continue to be pumped to a second excited state under the irradiation of the initial light beam, and a portion of the plurality of ions in the second excited state falls back to the ground state and emits a plurality of corresponding up-conversion photons with energy greater than that of the pump laser. Wherein, the intensity of the initial light beam in the mid-infrared band or the terahertz band is obtained according to the intensity of the fluorescence signal of the up-converted photons.

5. The near-field optical imaging system according to claim 1, wherein: The optical window is suitable for isolating the interference of the light field generated by the pump laser scattered by the sample to be tested on the near-field optical information detection, and is suitable for allowing the initial light beam to pass through and blocking the interference of background stray light.

6. The near-field optical imaging system according to claim 1, wherein: It also includes a focusing assembly, which is adapted to focus the initial light beam onto the surface of the sample to be measured, so as to facilitate positioning of the light spot formed by the initial light beam; as well as The beam splitter is adapted to reflect the fluorescence up-conversion signal or the fluorescence down-conversion signal to the detection light path.

7. The near-field optical imaging system according to claim 1, wherein: The detection optical path includes: A filter, adapted to filter out the pump laser and scattered light; and The detector is suitable for detecting the fluorescence up-conversion signal or the fluorescence down-conversion signal.

8. The near-field optical imaging system according to claim 6, wherein: Also included is a microscope, disposed between the solid color center crystal and the beam splitter, the microscope being suitable for collecting the fluorescence signal; as well as A three-axis translation stage is configured to movably support the microscope.

9. The near-field optical imaging system according to claim 1, wherein: The light source includes any one of a mid-infrared quantum cascade laser, a terahertz quantum cascade laser, a black body radiation light source and a carbon dioxide laser.

10. The near-field optical imaging system according to claim 1, wherein: The solid color center crystal includes any one of a bulk crystal, an ion implanted solid color center crystal, a substrate of spin-coated solid color center nanoparticles, and a thin film solid color center crystal.

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