Terahertz single imaging method and system based on metasurface structure

Abstract

The invention discloses a terahertz single imaging method and system based on a metasurface structure, and the method comprises the steps: placing the metasurface structure above or in front of an imaging object, the metasurface structure comprises a pixel array composed of a plurality of pixel units, and the pixel units and imaging units of the imaging object are in one-to-one correspondence and have consistent parameters; enabling a terahertz light beam to vertically penetrate through the metasurface structure and the imaging object, and respectively obtaining a metasurface terahertz radio-frequency transmission domain spectrum and an imaging object terahertz radio-frequency transmission domain spectrum; and constructing a resonance intensity detection limit model so as to reconstruct pixel distribution of the imaging object and realize terahertz single imaging of the imaging object. According to the invention, an adaptive correction algorithm and an external complex modulation decoding device are not needed, the image of the measured object is reconstructed by using the resonant frequency, the imaging time is reduced, the sampling speed is improved, and the problems of slow sampling speed, low compatibility and incapability of real-time imaging of a terahertz single imaging technology in the prior art are solved.

Description

Technical Field

[0001] The present application relates to the field of terahertz imaging technology, and in particular to a terahertz single-shot imaging method and system based on a metasurface structure. Background Art

[0002] Terahertz waves have a frequency of 1×10 12 Electromagnetic radiation in the order of Hertz. Terahertz technology covers all aspects of military, security, and people's livelihood, including confidential communications, satellite communications, security inspections, biopharmaceuticals, early detection of cancer cells, industrial quality inspections, and so on. As one of the key applications of terahertz technology, terahertz imaging is similar in function to visible light or infrared spectral imaging. However, the photon energy (meV) of terahertz waves is relatively low, and only a few semiconductor materials have a small enough band gap energy to achieve effective terahertz photon detection. Field-effect terahertz sensors, pyroelectric detectors, and terahertz microbolometers can operate at room temperature, but it is difficult to balance indicators such as sensitivity, detection wavelength range, and imaging speed. In addition, the above-mentioned terahertz array sensors can only resolve the intensity response of the imaged object and lack phase information. In contrast, terahertz time-domain scanning imaging can provide amplitude, phase, and ultrafast time and spectral information of the inspected object, but its point-by-point scanning imaging method limits its application in large-area imaging or real-time in-situ detection. How to reduce redundant operations, achieve single-shot imaging through non-point scanning, and improve the efficiency of terahertz imaging is the current technical challenge.

[0003] Existing terahertz single-shot imaging is mainly divided into two categories: pump pulse coded terahertz detection and coded terahertz illumination. The coded modulation of terahertz or detection light generally requires the use of metal masks, artificial metamaterials or digital micromirrors. In the existing technology, since the spatial encoding of terahertz or detection light requires continuous mask changes, the sampling time of computational imaging is long, the imaging speed is slow, and real-time imaging cannot be achieved. In addition, it needs to be used with external modulation and decoding equipment, and has low compatibility.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present application provides a terahertz single-shot imaging method and system based on a metasurface structure, which does not require an adaptive correction algorithm and external complex modulation and decoding equipment, and can use the resonant frequency and intensity parameters in the terahertz transmitted frequency-domain spectrum to reconstruct the image of the object under test, thereby reducing the imaging time, thereby improving the sampling speed and achieving quasi-real-time or even real-time imaging frame rate. In addition, the independence of each pixel unit in the present application makes the method compatible with imaging and near-field sensing applications, solving the problems of slow terahertz single-shot imaging sampling speed, low compatibility, and inability to real-time imaging in the prior art.

[0006] This application is implemented through the following technical solutions:

[0007] The first aspect of the present application is to provide a terahertz single-shot imaging method based on a metasurface structure, comprising the following steps:

[0008] Placing a metasurface structure above or in front of an imaging object, wherein the metasurface structure comprises a pixel array composed of a plurality of pixel units, wherein the pixel units correspond one-to-one to imaging units of the imaging object and have consistent parameters;

[0009] The terahertz beam is vertically penetrated through the metasurface structure and the imaging object to obtain a terahertz-transmitted radio-domain spectrum of the metasurface and a terahertz-transmitted radio-domain spectrum of the imaging object, respectively;

[0010] A resonance intensity detection limit model is constructed according to the terahertz-transmitted radio-frequency spectrum of the metasurface and the terahertz-transmitted radio-frequency spectrum of the imaging object to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object.

[0011] Specifically, the pixel unit is composed of a plurality of microstructure blocks, and any one of the microstructure blocks includes a group of two-dimensional structured inclined elliptical silicon columns based on symmetry breaking; the inclined angle of the inclined elliptical silicon columns is 8° to 12°.

[0012] Specifically, any pixel unit of the metasurface structure generates only one resonance frequency within the terahertz spectrum range of 0.55 THz to 0.75 THz.

[0013] Specifically, the parameter consistency includes that any group of corresponding imaging units and pixel units have the same size and the same spatial position.

[0014] Specifically, the terahertz beam is obtained by the following steps:

[0015] The femtosecond pulse laser excites the terahertz source to produce a divergent terahertz wave;

[0016] The terahertz wave is focused by a plurality of off-axis parabolic mirrors to form a collimated terahertz beam.

[0017] Specifically, the plurality of off-axis parabolic mirrors include a first mirror facing the emission direction of the terahertz source, a third mirror located above the metasurface structure, and a second mirror located between the first mirror and the third mirror;

[0018] The terahertz wave passes through the first mirror to form a collimated terahertz wave;

[0019] The collimated terahertz wave is focused by the second mirror and the third mirror to form a collimated terahertz beam with a reduced spot diameter.

[0020] Specifically, the terahertz beam vertically penetrates the metasurface structure and the imaging object to obtain a terahertz-transmitted radio-domain spectrum of the metasurface and a terahertz-transmitted radio-domain spectrum of the imaging object, respectively, including the following steps:

[0021] The terahertz beam is vertically incident and penetrates the metasurface structure to obtain a terahertz transmission signal of the metasurface structure, and the terahertz transmission signal of the metasurface structure is converted into the metasurface terahertz transmission frequency domain spectrum through Fourier transformation; wherein each of the pixel units has a corresponding metasurface structure resonant frequency in the metasurface terahertz transmission frequency domain spectrum;

[0022] The terahertz light beam passing through the metasurface structure is vertically incident and penetrates the light-transmitting area of ​​the imaging object to generate a terahertz transmission signal of the imaging object, and the terahertz transmission signal of the imaging object is converted into a terahertz transmission frequency domain spectrum of the imaging object through Fourier transformation; wherein each of the imaging units has corresponding spatial information.

[0023] Specifically, the step of constructing a resonant intensity detection limit model according to the terahertz-transmitted radio-domain spectrum of the metasurface and the terahertz-transmitted radio-domain spectrum of the imaging object to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object comprises the following steps:

[0024] Comparing the difference in the resonance frequency intensity between the imaging unit and the corresponding pixel unit, and constructing the resonance intensity detection limit model;

[0025] quantifying the differences in the resonance intensity detection limit models and establishing a determination criterion;

[0026] The pixel distribution of the imaging object is reconstructed according to the judgment standard, the image restoration of the imaging object is achieved, and the terahertz single-shot imaging is completed.

[0027] The second aspect of the present application is to provide a terahertz single-shot imaging system based on a metasurface structure, comprising an excitation device, a transmission device and an imaging processing device;

[0028] an exciting device, used for exciting a terahertz beam;

[0029] A transmission device, used for focusing and transmitting the terahertz light beam, so that the terahertz light beam is vertically incident and sequentially penetrates the metasurface structure and the imaging object, and outputs a terahertz transmission signal;

[0030] An imaging processing device is used to receive the terahertz transmission signal and convert it into a time domain signal, convert the time domain signal into a terahertz transmission frequency domain spectrum through Fourier transform, obtain the terahertz transmission frequency domain spectrum of the metasurface and the terahertz transmission frequency domain spectrum of the imaging object respectively, and construct a resonant intensity detection limit model to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object.

[0031] Specifically, the imaging processing device includes a signal receiving and processing module and an imaging module.

[0032] Specifically, the signal receiving and processing module includes a terahertz receiving antenna, which is used to receive the terahertz transmission signal and convert it into a time domain signal, and convert the time domain signal into the terahertz transmission frequency domain spectrum through Fourier transformation, so as to generate the terahertz transmission frequency domain spectrum of the metasurface and the terahertz transmission frequency domain spectrum of the imaging object;

[0033] Specifically, the imaging module is used to construct a resonant intensity detection limit model based on the terahertz-transmitted radio-domain spectrum of the metasurface and the terahertz-transmitted radio-domain spectrum of the imaging object, so as to reconstruct the pixel distribution of the imaging object, realize image restoration of the imaging object, and complete terahertz single-shot imaging.

[0034] Compared with the prior art, the present application mainly has the following beneficial effects: the present application provides a terahertz single-shot imaging method and system based on a metasurface structure, which does not require an adaptive correction algorithm and external complex modulation and decoding equipment, and can use the resonant frequency and intensity parameters in the terahertz transmissive radio frequency spectrum to reconstruct the image of the object under test, thereby reducing the imaging time, improving the sampling speed, and achieving quasi-real-time or even real-time imaging frame rate. In addition, the independence of each pixel unit of the present application enables the present method to be compatible with imaging and near-field sensing applications, solving the problems of slow sampling speed, low compatibility, and inability to perform real-time imaging of terahertz single-shot imaging technology in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 This is a flow chart of a terahertz single-shot imaging method based on a metasurface structure according to an embodiment of the present application.

[0037] Figure 2 Schematic diagram of a two-dimensional structure of tilted elliptical silicon pillars based on symmetry breaking in a supersurface structure of an embodiment of the present application.

[0038] Figure 3 A schematic diagram of the composition structure of a metasurface according to an embodiment of the present application.

[0039] Figure 4 This is a schematic diagram of a terahertz single-shot imaging method based on a metasurface structure according to an embodiment of the present application.

[0040] Figure 5 This is a schematic diagram of a terahertz single-shot imaging system based on a metasurface structure according to an embodiment of the present application.

[0041] Figure 6 This is a structural diagram of a terahertz single-shot imaging system based on a metasurface structure according to an embodiment of the present application. DETAILED DESCRIPTION

[0042] The following will be combined with the implementation methods of this application to clearly and completely describe the technical solutions in the implementation methods of this application. Obviously, the described implementation methods are only part of the implementation methods of this application, not all of the implementation methods. Based on the implementation methods in this application, all other implementation methods obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0043] It should be understood that the terms used in this specification of the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application. As used in the specification of the embodiments of the present application and the appended claims, unless the context clearly indicates otherwise, the singular forms of "a", "an" and "the" are intended to include plural forms.

[0044] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0045] Terahertz single-shot imaging is a kind of associative computational imaging, which replaces imaging based on point-by-point scanning by combining a single-pixel detector with spatial coding of the detection light field. The existing terahertz single-shot imaging is mainly divided into two categories: pump pulse coded terahertz detection and coded terahertz illumination. The coded modulation of terahertz or detection light generally requires the use of metal masks, artificial metamaterials or digital micromirrors. The basic process of terahertz single-shot imaging is: first, the terahertz or detection light is spatially encoded; then the spatial distribution of the perturbed light field is transmitted to the metasurface device, so as to sample the terahertz scattering field of the imaging object using the spatially modulated metasurface; finally, the terahertz field intensity value corresponding to different spatial coding is read with an intensity detector. After acquiring a series of data, the image of the object is restored by combining the Hadamard matrix and the compression imaging algorithm, and the imaging resolution, imaging frame rate and other parameters are calculated. This spatial modulation of the perturbation light field avoids the electrically controlled functional element addressing process and greatly reduces the complexity of the spatial light modulation device. The modulation spatial resolution of the device is only limited by the diffraction limit of the short-wavelength perturbation light, so it can achieve extremely high imaging resolution for terahertz waves.

[0046] However, in the prior art, since the spatial encoding of terahertz or detection light requires continuous mask changes (according to the requirements of the Nyquist sampling theorem, the number of masks is at least the same as the number of pixels), the sampling time of computational imaging is longer than that of focal plane imaging. Under the premise of ensuring the image signal-to-noise ratio, how to increase the sampling speed to achieve quasi-real-time or even real-time imaging frame rate (>26frame / s) is a problem that needs to be developed and solved in the current terahertz single-pixel imaging.

[0047] In view of this, the present application proposes a terahertz single-shot imaging method based on bound states in the continuum (BICs) pixelated metasurface, in which each pixel unit generates a BIC resonance spectrum with a high quality factor in a parallel terahertz incident light field, and the resonance spectra of the pixel units in the metasurface structure do not interfere with each other. By utilizing the spatial correspondence between the metasurface pixel units and the imaged object, a resonance intensity detection model is constructed by analyzing the terahertz resonance spectrum after passing through the imaged object, and the image of the object can be reconstructed by performing a terahertz spectrum detection on the imaged object once, thus realizing terahertz single-shot imaging.

[0048] Bound state (BIC) is a concept in quantum mechanics, which refers to the state of an electron confined to an infinite potential well; when extended to photons, it refers to the eigenstate of the photon below the light in the band diagram. A typical example is the eigenmode in the waveguide. When considering the mode coupled with the free space (above the light), there are also bound states, that is, bound states within the continuous state. In theory, this BIC mode can completely confine photons in the optical microcavity without radiating into the free space, thereby obtaining an infinite radiation quality factor. In order to further reduce the non-radiative loss of photon oscillations, the use of dielectric materials to construct the BIC mode can greatly improve the overall quality factor of the BIC mode. This BIC mode is closely related to the symmetry of the functional elements of the metasurface.

[0049] The terahertz single-shot imaging technology based on BIC pixelated metasurface proposed in the present invention does not require adaptive correction algorithms and external complex modulation and coding equipment. It uses the resonant frequency and intensity parameters in the terahertz-transmitted radio-domain spectrum to reconstruct the image of the object under test and reduce the imaging time. In addition, the pixelated metasurface array proposed in the present invention has independent operability of each pixel unit, making it compatible with imaging and near-field sensing applications, providing a new spectral detection method in the terahertz field.

[0050] like Figure 1 As shown, the first aspect of the present application is to provide a terahertz single-shot imaging method based on a metasurface structure, comprising the following steps:

[0051] S1. Placing a metasurface structure above or in front of an imaging object, wherein the metasurface structure comprises a pixel array composed of a plurality of pixel units, wherein the pixel units correspond one-to-one to the imaging units of the imaging object and have the same parameters;

[0052] S2, vertically incident the terahertz beam on the surface of the metasurface structure, and obtaining a terahertz-transmitted radio-domain spectrum of the metasurface and a terahertz-transmitted radio-domain spectrum of the imaging object;

[0053] S3. Constructing a resonant intensity detection limit model according to the terahertz-transmitted radio-frequency spectrum of the metasurface and the terahertz-transmitted radio-frequency spectrum of the imaging object to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object.

[0054] In the specific operation process, a metasurface structure is first manufactured according to the size and shape of the pixel point of the imaging object, that is, the imaging unit. In the imaging process, after the terahertz beam is excited, the metasurface structure is first placed in the device, so that the terahertz beam penetrates the metasurface structure to form a terahertz transmission signal of the metasurface structure, thereby obtaining the terahertz transmission frequency domain spectrum of the metasurface after processing, and then the imaging object is placed under or behind the metasurface structure to obtain the terahertz transmission frequency domain spectrum of the imaging object. Therefore, the above steps S1 and S2 can also be expressed as:

[0055] The terahertz beam is vertically incident on the surface of the metasurface structure to obtain the metasurface terahertz transmission frequency domain spectrum, wherein the metasurface structure includes a pixel array composed of a plurality of pixel units;

[0056] The terahertz beam is kept unchanged, and the imaging object is placed below or behind the metasurface structure to obtain the terahertz transmission frequency domain spectrum of the imaging object. The imaging unit of the imaging object corresponds to the pixel unit one by one and the parameters are consistent.

[0057] like Figure 2 (a) is a schematic diagram of the two-dimensional structure of the BIC metasurface based on the symmetry-breaking inclined elliptical silicon pillars proposed in this application. Its corresponding terahertz-transmitting frequency-domain spectrum is shown in Figure 2 As shown in (b) in the figure. The metasurface structure designed in the present application only produces one high-quality resonant frequency within a wider terahertz frequency range, which is crucial for single-shot imaging. The uniqueness of the resonant frequency of each pixel unit of the metasurface determines the uniqueness of the spatial modulation of parallel terahertz light. If more than one resonant frequency appears in the transmitted frequency-domain spectrum of a pixel array within a selected wavelength range, the transmitted frequency-domain spectra of multiple pixel arrays are superimposed to form an envelope, and the BICs resonances corresponding to each pixel array will be difficult to distinguish. The BIC-based metasurface structure proposed in the present application can adjust the frequency range by modifying the structural parameters, as long as it ensures that within a wider terahertz frequency range, each pixel unit of the metasurface structure only produces one high-quality resonant frequency.

[0058] The structural parameters refer to the structural parameters of the inclined elliptical silicon columns that make up the pixel unit. Figure 3 , which is a schematic diagram of the composition structure of the pixelated super surface structure of the present application, Figure 3 (a) is a schematic diagram of a planar structure of a metasurface structure including four pixel units i, ii, iii, and iv. The four pixel units are arranged in pairs with a certain interval. The interval is determined according to the arrangement of the imaging units of the imaging object to ensure that the size and spatial position of each pixel unit are consistent with the corresponding imaging unit. The consistency of spatial position can be understood as when the metasurface structure is above the imaging object, the one-to-one corresponding imaging units and pixel units are on the same vertical axis. Figure 3 (b) is Figure 3 (a) is a schematic diagram of the enlarged structure of one pixel unit iv of the metasurface structure, where the pixel unit iv comprises 3*3 adjacently arranged microstructure blocks, each of which comprises a group of symmetry-broken inclined elliptical silicon pillars. Figure 3 As shown in (c), Figure 3The enlarged three-dimensional structure diagram of the first pixel in the third row in (b). Preferably, any pixel unit may include a plurality of microstructure blocks including inclined elliptical silicon columns, and adjacent microstructure blocks are closely connected to ensure that the pixel unit completely corresponds to the corresponding imaging unit.

[0059] Specifically, the structural parameters of the inclined elliptical silicon column include the major axis r of the elliptical silicon column: a 、Short axis r b , thickness h and the tilt angle α in the two-dimensional direction (xy direction), as well as the length Px and width P of the microstructure block where the tilted elliptical silicon column is located y The parameters of several micro-structure blocks of each pixel unit are the same. These structural parameters are adjusted so that each pixel unit only produces one high-quality resonance frequency within a wider terahertz frequency range, and the resonance frequencies of adjacent pixel units are different. This ensures that the resonance frequencies produced by several pixel units of the same metasurface structure are different, thereby ensuring the uniqueness of the metasurface structure in spatial modulation of parallel terahertz light.

[0060] Preferably, any pixel unit is composed of several microstructure blocks containing inclined elliptical silicon pillars, adjacent microstructure blocks are tightly connected without gaps, and one microstructure block includes at least one group of inclined elliptical silicon pillars. The number of microstructure blocks that make up the pixel unit can be determined according to the size of the imaging unit of the imaging object, the size of the silicon pillars, and actual needs.

[0061] Specifically, Figure 2 As shown, the tilt angle α of the tilted elliptical silicon column is 8° to 12°, preferably, the tilt angle α is 10°. Optionally, the microstructure block can also be tilted silicon columns of other two-dimensional structures, such as circular, rectangular, etc. Among them, the silicon column can be made of high-resistance silicon with a conductivity greater than 10000 ohm / cm.

[0062] Specifically, in one embodiment, any pixel unit of the metasurface structure generates only one resonance frequency in the terahertz spectrum range of 0.55 THz to 0.75 THz, and the resonance frequency is unique.

[0063] Specifically, the one-to-one correspondence and consistent parameters of the pixel units and the imaging units of the imaging object mentioned in step S1 means that, under the premise of ensuring the consistency of the number of pixel units and imaging units, the size and spatial position of any group of corresponding imaging units and the pixel units are guaranteed to be consistent. For example, in one embodiment, the imaging object includes N pixels (pixel units), and it is necessary to ensure that the pixel units of the metasurface structure also have N pixels, the spatial positions correspond one-to-one, and the sizes are equal.

[0064] Specifically, S2, vertically penetrating the terahertz beam through the metasurface structure and the imaging object to obtain a terahertz-transmitted radio-domain spectrum of the metasurface and a terahertz-transmitted radio-domain spectrum of the imaging object, comprising the following steps:

[0065] S21, the terahertz light beam is vertically incident and penetrates the metasurface structure to generate a terahertz signal of the metasurface structure, and the terahertz transmission signal of the metasurface structure is converted into the metasurface terahertz transmission frequency domain spectrum through Fourier transformation; wherein each of the pixel units has a corresponding metasurface structure resonant frequency in the metasurface terahertz transmission frequency domain spectrum;

[0066] S22. The terahertz light beam passing through the metasurface structure is vertically incident and penetrates the light-transmitting area of ​​the imaging object to generate a terahertz transmission signal of the imaging object, and the terahertz transmission signal of the imaging object is converted into a terahertz transmission frequency domain spectrum of the imaging object through Fourier transform; wherein each of the imaging units has corresponding spatial information.

[0067] Specifically, S3, constructing a resonant intensity detection limit model according to the terahertz-transmitted radio-domain spectrum of the metasurface and the terahertz-transmitted radio-domain spectrum of the imaging object to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object, comprises the following steps:

[0068] S31, comparing the difference in the resonance frequency intensity between the imaging unit and the corresponding pixel unit, obtaining the resonance information at different spatial positions, and constructing the resonance intensity detection limit model;

[0069] S32, quantifying the difference of the resonance intensity detection limit model and establishing a judgment standard;

[0070] S33. Reconstruct the pixel distribution of the imaging object according to the judgment criterion, restore the image of the imaging object, and complete the terahertz single-shot imaging.

[0071] like Figure 4 As shown in FIG. 1 , it is a schematic diagram of a terahertz single-shot imaging method based on a metasurface structure of the present application. In this embodiment, as Figure 4 As shown in (c), the imaging object includes 4 square imaging units, black represents opaque imaging units that terahertz light cannot penetrate, and white represents imaging units that terahertz light can penetrate, which are arranged in pairs, and the corresponding metasurface structure has four pixel units i, ii, iii, iv, as shown in FIG. Figure 4 In the vertical direction, the imaging units and the pixel units correspond to each other one by one and have the same size. The number and size of the pixel units of the metasurface structure can be set according to the number and size of the imaging units of the imaging object.

[0072] First, the pixelated metasurface structure is placed in the terahertz collimated light path. The linearly polarized parallel terahertz light field ( Figure 4 (a)) is incident vertically onto the pixelated metasurface ( Figure 4 (b)) and covers the entire metasurface. After the terahertz light is vertically incident and passes through the metasurface, the generated terahertz transmission signal is a time domain signal, which is converted into a frequency domain signal through Fourier transform. The four pixel units i, ii, iii, and iv arranged in two dimensions are excited to generate four independent high Q value resonance peaks in the spectrum (such as Figure 4 (e)), the resonance frequencies 1, 2, 3, and 4 correspond to the four pixel units i, ii, iii, and iv, respectively. Based on this, the resonance peaks in the spectrum carry two-dimensional spatial information. The resonance frequencies in the broadband spectrum accurately correspond to the spatial positions of the pixel units, thus establishing a one-to-one mapping between spectrum information and spatial information. Therefore, the pixelated metasurface achieves the modulation of the terahertz light field and uses frequency information to encode the terahertz spatial information.

[0073] Continue to keep the terahertz light incident vertically, and then place the imaging object below or behind the metasurface ( Figure 4 (c)), the imaging unit, size, and spatial position of the imaging object are consistent with the metasurface pixel unit. The black area in the imaging object represents the area where the terahertz light cannot penetrate, and the white area refers to the area with high terahertz transmittance. After inserting the imaging object into the terahertz optical path, the terahertz transmission signal penetrating the imaging object is measured, and the time domain signal is transformed by Fourier transform (FFT) to obtain the terahertz transmission frequency domain spectrum of the imaging object. Figure 4 As shown in (f). Since the spatial position of the imaging unit and the pixel unit of the metasurface are mapped to each other, when the terahertz structure light field cannot penetrate the position of the non-light-transmitting imaging unit of the imaging object, the resonance corresponding to the spatial position in the terahertz-transmitting frequency-domain spectrum of the imaging object disappears. Figure 4 The black imaging unit positions corresponding to pixel units ii and iv in (c) are terahertz non-light-transmitting areas, so Figure 4 The resonance frequencies of 2 and 4 in (f) disappear. In contrast, the resonances of frequencies 1 and 3 barely change. Based on this, the distribution of imaging units of the imaging object in the terahertz light field is obtained by the resonance frequency.

[0074] Obtaining the terahertz-transmitting radio-domain spectrum of the metasurface ( Figure 4 (e)) and the THz-transmitted radio-domain spectrum of the imaged object ( Figure 4 After (f)), the resonance intensity detection limit model was constructed ( Figure 4 (g)) to reconstruct the pixel distribution of the imaged object to be measured ( Figure 4(d)). The judgment standard is established by quantifying the difference in the terahertz-transmittance radio-domain spectrum, namely, ΔTi(ω) = |T0(ω)-Tr(ω)| / ΔIi, where Tr(ω) represents the reference spectrum, i.e., the terahertz-transmittance radio-domain spectrum of the metasurface structure measured when there is no imaging object, T0(ω) is the spectrum modulated by the imaging object, i.e., the terahertz-transmittance radio-domain spectrum of the imaging object, and ΔIi is defined as the peak intensity of the resonance peak of each individual pixel unit of the metasurface. By judging whether the difference is greater than or equal to a threshold (defined as 0.5), the spatial distribution of terahertz transparent and opaque areas can be directly visualized ( Figure 4 (d)). This makes it possible to achieve real-time imaging without the need for external modulation and decoding equipment.

[0075] Specifically, the terahertz beam is obtained by the following steps:

[0076] The femtosecond pulse laser excites the terahertz source to produce a divergent terahertz wave;

[0077] The terahertz wave is focused by a plurality of off-axis parabolic mirrors to form a collimated terahertz beam.

[0078] In order to realize a terahertz single-shot imaging method based on a metasurface structure, the second aspect of the present application is to provide a terahertz single-shot imaging system based on a metasurface structure, such as Figure 6 FIG. 1 is a schematic diagram of a terahertz single-shot imaging system based on a metasurface structure of the present application, comprising:

[0079] An exciting device 10, for exciting a terahertz beam;

[0080] A transmission device 20, used for focusing and transmitting the terahertz light beam, so that the terahertz light beam is vertically incident and sequentially penetrates the metasurface structure and the imaging object, and outputs a terahertz transmission signal;

[0081] The imaging processing device 30 is used to receive the terahertz transmission signal and convert it into a time domain signal, convert the time domain signal into the terahertz transmission frequency domain spectrum through Fourier transform, obtain the terahertz transmission frequency domain spectrum of the metasurface and the terahertz transmission frequency domain spectrum of the imaging object respectively, and construct a resonant intensity detection limit model to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object.

[0082] Specifically, the excitation device 10 includes a femtosecond laser, a terahertz transmitting antenna, and an optical fiber connecting the femtosecond laser and the terahertz transmitting antenna, wherein the laser is a 1550nm femtosecond pulse laser.

[0083] Specifically, the transmission device 20 includes an off-axis parabolic mirror for transmitting terahertz waves and terahertz beams, and a metasurface structure and an imaging object located between the off-axis parabolic mirrors. Specifically, when the imaging object is located below the metasurface structure, such as Figure 5 As shown, the several off-axis parabolic mirrors include a first mirror PM1 located facing the emission direction of the terahertz source, a third mirror PM3 located above the metasurface structure, a second mirror PM2 located between the first mirror PM1 and the third mirror PM3, and a fourth mirror PM4 located behind the adult object.

[0084] The terahertz wave emitted from the terahertz transmitting antenna Tx passes through the first mirror PM1 to form a vertical collimated terahertz wave;

[0085] The collimated terahertz wave is focused by the second mirror PM2 and the third mirror PM3 to form a collimated terahertz beam with a smaller spot diameter;

[0086] The terahertz beam passes through the pixelated metasurface and / or the imaging object, passes through the fourth mirror PM4, and sends the terahertz transmission signal (optical signal) to the terahertz receiving antenna (Rx) to be converted into an electrical signal. At this time, the terahertz transmission electrical signal is a frequency domain signal, which needs to be converted into a frequency domain signal by Fourier transform.

[0087] The imaging processing device 30 includes a signal receiving and processing module 31 and an imaging module 32;

[0088] The signal receiving and processing module 31 includes a terahertz receiving antenna (Rx), which is used to receive the optical signal of the terahertz transmission signal and convert it into an electrical signal. At this time, the electrical signal is a time domain signal, which is converted into a frequency domain signal through Fourier transformation, that is, to generate a terahertz transmission frequency domain spectrum of the metasurface and a terahertz transmission frequency domain spectrum of the imaging object;

[0089] The imaging module 32 is used to construct a resonant intensity detection limit model based on the terahertz-transmitted radio-domain spectrum of the metasurface and the terahertz-transmitted radio-domain spectrum of the imaging object, so as to reconstruct the pixel distribution of the imaging object, realize image restoration of the imaging object, and complete terahertz single-shot imaging.

[0090] like Figure 4 In a specific embodiment, the imaging object includes four imaging units with a side length of 4.5 mm in the positive direction, which are arranged in pairs, and the corresponding metasurface structure also has four pixel units i, ii, iii, and iv with a side length of 4.5 mm in the positive direction, wherein the structural parameters of the microstructure blocks of the four pixel units and the inclined elliptical silicon pillars are shown in Table 1.

[0091] Structural parameters <![CDATA[r a ]]> <![CDATA[r b ]]> <![CDATA[p x ]]> <![CDATA[p y ]]> α Pixel unit i 206 62 231 205 12 Pixel unit ii 196 60 221 195 10 Pixel unit iii 186 57 210 186 9 Pixel unit iv 176 54 200 177 8

[0092] like Figure 5 In the experiment, a 1550nm femtosecond pulse laser is divided into two beams. One beam of laser excites the terahertz source through optical fiber transmission to generate a divergent terahertz wave, which forms a terahertz beam after passing through off-axis parabolic mirrors PM1, PM2, and PM3. The terahertz transmission signal is vertically penetrated through the metasurface structure to be received by the terahertz receiving antenna Rx, and the imaging object is placed under the metasurface structure to generate the imaging object terahertz transmission signal to be received by the receiving antenna Rx. The first mirror PM1, equipped with an off-axis parabolic mirror with a diameter of two inches and a focal length of 50.8 mm, is placed behind the terahertz transmitting antenna (Tx) to convert the divergent terahertz source into a collimated beam. Subsequently, the beam is adjusted by the second mirror PM2 with a diameter of two inches and a focal length of 50.8 mm and the third mirror PM3 with a diameter of one inch (12.7 mm), achieving a 4:1 beam reduction and generating a collimated terahertz beam with a diameter of about 10 mm. Finally, the beam is focused onto the receiving antenna (Rx) by a fourth mirror PM4 with a one-inch diameter and a focal length of 25.4 mm.

[0093] The receiving antenna Rx receives the terahertz transmission signal in the form of light waves, converts it into an electrical signal, then amplifies it through a phase-locked amplifier, and finally collects it by the computer. The computer converts the terahertz transmission signal in the time domain into a terahertz transmission frequency domain spectrum through Fourier transform, thereby obtaining the terahertz transmission frequency domain spectrum of the super surface and the terahertz transmission frequency domain spectrum of the imaging object, and then constructs a resonant intensity detection limit model to reconstruct the pixel distribution of the imaging object, realize the image restoration of the imaging object, and complete terahertz single-shot imaging. The terahertz single-shot imaging method based on the super surface structure of the present application does not require an adaptive correction algorithm and external complex modulation and decoding equipment, and can use the resonant frequency and intensity parameters in the terahertz transmission frequency domain spectrum to reconstruct the image of the object being measured, reduce the imaging time, thereby improving the sampling speed, and achieving quasi-real-time or even real-time imaging frame rate, and the independence of each pixel unit of the present application makes the present method compatible with imaging and near-field sensing applications, solving the problems of slow sampling speed, low compatibility, and inability to image in real time of terahertz single-shot imaging in the prior art.

[0094] In summary, the present application provides a terahertz single-shot imaging method and system based on a metasurface structure, the method comprising: placing a metasurface structure above or in front of an imaging object, the metasurface structure comprising a pixel array composed of a plurality of pixel units, the pixel units corresponding one to one with the imaging units of the imaging object and having consistent parameters; vertically penetrating the terahertz beam through the metasurface structure and the imaging object to obtain a terahertz-transmitted radio frequency spectrum of the metasurface and a terahertz-transmitted radio frequency spectrum of the imaging object, respectively; constructing a resonant intensity detection limit model based on the terahertz-transmitted radio frequency spectrum of the metasurface and the terahertz-transmitted radio frequency spectrum of the imaging object to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object. The present application does not require an adaptive correction algorithm and external complex modulation and decoding equipment, and utilizes the resonant frequency to reconstruct the image of the object being measured, thereby reducing the imaging time and increasing the sampling speed, thereby solving the problems of slow sampling speed, low compatibility, and inability to perform real-time imaging of the terahertz single-shot imaging technology in the prior art.

[0095] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A terahertz single-shot imaging method based on a metasurface structure, characterized in that: The following steps are involved: Placing a metasurface structure above or in front of an imaging object, wherein the metasurface structure comprises a pixel array composed of a plurality of pixel units, wherein the pixel units correspond one-to-one to imaging units of the imaging object and have consistent parameters; The terahertz beam is vertically penetrated through the metasurface structure and the imaging object to obtain a terahertz-transmitted radio-domain spectrum of the metasurface and a terahertz-transmitted radio-domain spectrum of the imaging object, respectively; A resonance intensity detection limit model is constructed according to the terahertz-transmitted radio-frequency spectrum of the metasurface and the terahertz-transmitted radio-frequency spectrum of the imaging object to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object.

2. The terahertz single-shot imaging method based on a metasurface structure according to claim 1, characterized in that: The pixel unit is composed of a plurality of microstructure blocks, and any one of the microstructure blocks includes a group of inclined elliptical silicon columns based on symmetry breaking in a two-dimensional structure; the inclined angle of the inclined elliptical silicon columns is 8° to 12°.

3. The terahertz single-shot imaging method based on a metasurface structure according to claim 1, characterized in that: Any pixel unit of the metasurface structure generates only one resonance frequency within the terahertz spectrum range of 0.55 THz to 0.75 THz.

4. The terahertz single-shot imaging method based on a metasurface structure according to claim 1, characterized in that: The parameter consistency includes that any group of corresponding imaging units and pixel units have the same size and the same spatial position.

5. The terahertz single-shot imaging method based on a metasurface structure according to claim 1, characterized in that: The terahertz beam is obtained by the following steps: The femtosecond pulse laser excites the terahertz source to produce a divergent terahertz wave; The terahertz wave is focused by a plurality of off-axis parabolic mirrors to form a collimated terahertz beam.

6. The terahertz single-shot imaging method based on a metasurface structure according to claim 5, characterized in that: The plurality of off-axis parabolic mirrors include a first mirror facing the emission direction of the terahertz source, a third mirror located above the metasurface structure, and a second mirror located between the first mirror and the third mirror; The terahertz wave passes through the first mirror to form a collimated terahertz wave; The collimated terahertz wave is focused by the second mirror and the third mirror to form a collimated terahertz beam with a reduced spot diameter.

7. The terahertz single-shot imaging method based on a metasurface structure according to claim 1, characterized in that: The terahertz beam vertically penetrates the metasurface structure and the imaging object to obtain a terahertz-transmitted radio-domain spectrum of the metasurface and a terahertz-transmitted radio-domain spectrum of the imaging object, respectively, including the following steps: The terahertz beam is vertically incident and penetrates the metasurface structure to obtain a terahertz transmission signal of the metasurface structure, and the terahertz transmission signal of the metasurface structure is converted into the metasurface terahertz transmission frequency domain spectrum through Fourier transformation; wherein each of the pixel units has a corresponding metasurface structure resonant frequency in the metasurface terahertz transmission frequency domain spectrum; The terahertz light beam passing through the metasurface structure is vertically incident and penetrates the light-transmitting area of ​​the imaging object to generate a terahertz transmission signal of the imaging object, and the terahertz transmission signal of the imaging object is converted into a terahertz transmission frequency domain spectrum of the imaging object through Fourier transformation; wherein each of the imaging units has corresponding spatial information.

8. The terahertz single-shot imaging method based on a metasurface structure according to claim 3, characterized in that: The step of constructing a resonant intensity detection limit model according to the terahertz-transmitted radio-domain spectrum of the metasurface and the terahertz-transmitted radio-domain spectrum of the imaging object to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object comprises the following steps: Comparing the difference in the resonance frequency intensity between the imaging unit and the corresponding pixel unit, and constructing the resonance intensity detection limit model; quantifying the differences in the resonance intensity detection limit models and establishing a determination criterion; The pixel distribution of the imaging object is reconstructed according to the judgment standard, the image restoration of the imaging object is achieved, and the terahertz single-shot imaging is completed.

9. A terahertz single-shot imaging system based on a metasurface structure, characterized in that: include: an exciting device, used for exciting a terahertz beam; A transmission device, used for focusing and transmitting the terahertz light beam, so that the terahertz light beam is vertically incident and sequentially penetrates the metasurface structure and the imaging object, and outputs a terahertz transmission signal; An imaging processing device is used to receive the terahertz transmission signal and convert it into a time domain signal, convert the time domain signal into a terahertz transmission frequency domain spectrum through Fourier transform, obtain the terahertz transmission frequency domain spectrum of the metasurface and the terahertz transmission frequency domain spectrum of the imaging object respectively, and construct a resonant intensity detection limit model to reconstruct the pixel distribution of the imaging object and realize terahertz single-shot imaging of the imaging object.

10. The terahertz single-shot imaging system based on a metasurface structure according to claim 9, characterized in that: The imaging processing device comprises a signal receiving and processing module and an imaging module; The signal receiving and processing module includes a terahertz receiving antenna, which is used to receive the terahertz transmission signal and convert it into a time domain signal, and convert the time domain signal into the terahertz transmission frequency domain spectrum through Fourier transformation, so as to generate the terahertz transmission frequency domain spectrum of the metasurface and the terahertz transmission frequency domain spectrum of the imaging object; The imaging module is used to construct a resonant intensity detection limit model according to the terahertz-transmitted radio-frequency spectrum of the metasurface and the terahertz-transmitted radio-frequency spectrum of the imaging object, so as to reconstruct the pixel distribution of the imaging object, realize image restoration of the imaging object, and complete terahertz single-shot imaging.

Images