WO2020125437A1

WO2020125437A1 - Near-field terahertz wave spectral imaging system and method

Info

Publication number: WO2020125437A1
Application number: PCT/CN2019/123441
Authority: WO
Inventors: 鲁远甫; 佘荣斌; 刘文权; 李光元; 焦国华; 吕建成
Original assignee: 深圳先进技术研究院
Priority date: 2018-12-18
Filing date: 2019-12-05
Publication date: 2020-06-25

Abstract

A near-field terahertz wave spectral imaging system and method. A total reflection principle of an attenuated total reflection module (8) is utilized, and a terahertz wave evanescent field is formed on the surface of the attenuated total reflection module (8), so that a sample under test (9) is tightly attached to the surface, and therefore, the purpose of near-field detection is achieved; the attenuated total reflection module (8) used can also directly carry the sample under test (9) without designing a separate clamp, so that the use is more convenient in the detection process of the sample and even in the in-vivo detection process; in addition, single-pixel imaging of a terahertz wave band is realized by using a light control method, and due to the fact that a modulation mask is projected on the attenuated total reflection module (8) of an in-vivo material, the requirement for the accuracy of the position of the projection surface does not need to be high; and in further combination with a terahertz time domain spectral measurement principle, terahertz light field signals at different moments are reconstructed, and therefore, the purpose of high-resolution terahertz multi-spectral imaging can be achieved by using a shorter time.

Description

Near-field terahertz wave spectral imaging system and method

Technical field

The present application relates to the terahertz technical field, in particular to a terahertz near-field imaging system and a terahertz near-field imaging method.

Background technique

Terahertz wave refers to the coherent electromagnetic radiation (frequency 0.1THz-10THz or wavelength 30μm-3000μm) located between the microwave band and the optical band. It is in the special position of the transition from electronics to photonics in the electromagnetic spectrum and has unique properties. For example, many important biomolecules (such as proteins, DNA) and low-frequency vibrations of biological cells (such as collective vibration of the skeleton, rotation and weak forces between molecules) are all in the terahertz spectrum range (spectral fingerprinting) . Based on terahertz spectroscopy, relevant information such as the spatial conformation, reaction kinetics, hydration and biological functions of biomolecules can be analyzed. In addition, terahertz can penetrate a variety of non-polar materials (paper, plastic, ceramics, etc.) to achieve hidden target imaging. In particular, compared to widely used X-rays, the terahertz wave has a lower photon energy (0.41-41 meV), which makes the terahertz wave harmless to biomolecules and ionizing biological cells, and can be used as an ideal biomedicine Non-destructive testing means. In recent years, terahertz technology has shown significant scientific value and application prospects in the fields of basic physics, industrial applications, biomedicine, and national defense security, and has been listed as a forward-looking technology that will change the future world by the United States, the European Union, Japan, and my country.

Terahertz spectroscopy and imaging are regarded as one of the most important application technologies. It analyzes the interaction between the terahertz wave and the sample to obtain rich physical and chemical information of the sample. The terahertz wavelength is on the order of millimeters/submillimeters. For general large target detection, terahertz imaging can obtain satisfactory results. However, with the terahertz technology and its in-depth research and development in many fields such as material characterization and biomedicine, the requirements for terahertz image resolution and fineness are also increasing. Due to the limitation of diffraction limit, the terahertz far-field spectral imaging system and method are difficult to meet these needs. Therefore, breaking the diffraction limit is an urgent problem to be solved in terahertz imaging. Therefore, terahertz near-field technology came into being. Near-field technology can collect and use the evanescent wave (sub-wavelength order) in the measured signal, so as to achieve sub-wavelength scale image resolution, so the resulting near-field image can display a finer structure.

At present, the near-field imaging that breaks through the diffraction limit of the terahertz band is mainly the near-field probe scanning imaging method (see "Liu Hongxiang et al., Overview of Terahertz Wave Near-field Imaging, Journal of Infrared and Millimeter Waves, 2016"). Since the probe detects the evanescent wave signal within one wavelength from the sample surface, the probe must be placed very close to the sample surface during the detection scan. This requires that the probe and its associated optical path must meet this space requirement, which undoubtedly increases the complexity and difficulty of the imaging system. Raster scanning of samples is generally used for imaging, which usually takes a long time to acquire images, and requires precise control of sample scanning. Recently, in order to overcome the shortcomings of near-field probes, foreign RAYKO I. STANTCHEV and others (see "Compressed sensing with near-field THz radiation, Vol. 4, No. 8, Optica, 2017") use light control ultra-thin silicon wafer The near-field illumination solution achieves near-field terahertz imaging with an imaging resolution of 9 μm. But the use of thin silicon wafers makes the projection focal plane control requirements higher, and thin silicon wafers are not conducive to carrying samples. The imaging method is transmissive and cannot achieve in-vivo near-field biomedical imaging.

Application content

In view of this, the present application proposes a near-field terahertz spectral imaging system and method for the technical problems of the above-mentioned prior art. Using the terahertz near-field conditions, combining the light control method and the terahertz time-domain spectroscopy system, no need for any The mechanical scanning can realize single-pixel near-field terahertz spectrum detection, and then achieve high-resolution sub-wavelength terahertz multi-spectral imaging.

Specifically, a near-field terahertz wave spectral imaging system, the basic optical path is: the laser output from the femtosecond laser is divided into two paths; one path is converged on the terahertz transmitting antenna after the delay line; the other path is focused on the terahertz detection antenna ; The terahertz wave signal generated by the terahertz transmitting antenna interacts with the sample to be measured and is focused to the terahertz detecting antenna at the receiving end; further, the system further includes an attenuation total reflection module, the terahertz transmitting antenna generates The terahertz waves are totally reflected in the attenuated total reflection module, and then a terahertz evanescent field is formed on the total reflection surface of the attenuated total reflection module, and the sample to be tested is directly carried on the attenuated total reflection module Imaging is performed on the total reflection surface.

Preferably, the attenuation total reflection module is a triangular prism as a whole, and the cross section is an isosceles triangle; the terahertz wave generated by the terahertz transmitting antenna is incident from the incident surface of the triangular prism, and total reflection occurs through the total reflection surface, Then it is emitted from the exit surface, and an evanescent field is formed on the total reflection surface during the total reflection process. Further, the base angle of the isosceles triangle of the cross section of the attenuation total reflection module is in the range of 20°-60°, and the size of the base angle is preferably 30°.

Further, the system further includes a light source to generate collimated pump light, which illuminates the digital micromirror array to form a mask using the digital micromirror array; or, the system passes a liquid crystal spatial light modulator Or the projector forms a mask. The mask is then projected onto the incident surface of the attenuated total reflection module, so that the attenuated total reflection module forms photo-generated carriers under the irradiation of the pump light mask on the incident surface On the regulation of the incident terahertz wave.

Based on the above-mentioned light control method for modulating terahertz waves, the material of the attenuated total reflection module is preferably intrinsic silicon, gallium arsenide, or intrinsic germanium. The wavelength of the pump light may be ultraviolet light, visible light or near infrared light, for example, less than 1100 nm, preferably 808 nm.

The system also includes a single pixel detector, which uses a single pixel detector combined with a compressed sensing algorithm to reconstruct the terahertz light field.

In order to make the system more compact and more convenient to use, the femtosecond laser and the delay line can be integrated at a fixed end; the terahertz transmitting antenna, the attenuation total reflection module, and the terahertz detecting antenna can be integrated in A mobile terminal. The optical path between the fixed end and the mobile end is coupled through a first optical fiber and a second optical fiber; the light emitted by the femtosecond laser is divided into two paths, wherein the light in the first optical fiber is passed through a delay line Coupled to the terahertz transmitting antenna, the light in the second optical fiber is coupled to the terahertz detecting antenna.

Preferably, the mobile end further includes a digital micromirror array or a liquid crystal spatial light modulator or a projector to project a mask to the attenuated total reflection module.

In addition, to facilitate sample placement, a sample cell is directly provided on the attenuation total reflection module, and the sample cell includes a bottom of the sample cell, and the material of the bottom of the sample cell is the same as the material of the attenuation total reflection module.

At the same time, this application also proposes a near-field terahertz wave spectral imaging method, which is characterized by using attenuated total reflection module to meet the near-field imaging conditions; specifically including the following two operations:

A. The terahertz wave generated by the terahertz transmitting antenna is totally reflected in the attenuated total reflection module, thereby forming a terahertz evanescent field on the total reflection surface of the attenuated total reflection module;

B. Load the sample to be tested directly on the total reflection surface of the attenuation total reflection module.

Wherein, the attenuation total reflection module is placed in a terahertz time-domain spectral imaging system, and the terahertz time-domain spectrum is obtained by delay line scanning.

Further, the method further includes the following operations:

C. Use collimated pump light to illuminate the digital micromirror array to form a mask; or, use a liquid crystal spatial light modulator or a projector to form a mask;

D. Project the mask onto the incident surface of the attenuated total reflection module, so that the attenuated total reflection module forms photo-generated carriers under the irradiation of the pump light mask on the incident surface Regulation of incident terahertz waves;

E. Use a single pixel detector combined with a reconstruction algorithm to reconstruct the terahertz light field.

In addition, based on the above-mentioned light control method for modulating terahertz waves, the material of the attenuated total reflection module is preferably intrinsic silicon, gallium arsenide, or intrinsic germanium. The wavelength of the pump light may be ultraviolet light, visible light or near infrared light, for example, less than 1100 nm, preferably 808 nm.

According to the near-field terahertz wave spectral imaging system and method proposed in this application, using the total reflection principle of the attenuated total reflection module, a terahertz wave evanescent field is formed on the surface of the attenuated total reflection module, and the sample to be measured can be close to the above surface For the purpose of near-field detection, such an attenuated total reflection module can directly carry the sample to be tested without designing a separate fixture, so it is easier to use. Using the light control method to achieve single-pixel imaging in the terahertz band, the modulation mask is projected on the side of the attenuation total reflection module. Since the attenuation total reflection module is a bulk material, there is no need to accurately project the modulation mask on the modulator, even The projection focal plane is shifted to the interior of the attenuation total reflection module, which can also realize the modulation of the terahertz wave. Finally, using the principle of terahertz time-domain spectroscopy, by reconstructing the terahertz light field signals at different times, and then using the relative raster scanning imaging method, it can use shorter time to achieve the purpose of terahertz multi-spectral imaging, combined with the principle of near-field detection. Improving resolution of terahertz wave imaging.

The above description is only an overview of the technical solutions of the present application. In order to better understand the technical means of the present application and can be implemented in accordance with the content of the specification, the following is a detailed description of preferred embodiments of the present application and the accompanying drawings.

BRIEF DESCRIPTION

The drawings forming a part of the application are used to provide a further understanding of the application. The schematic embodiments and descriptions of the application are used to explain the application, and do not constitute an undue limitation on the application. In the drawings:

FIG. 1 shows a structural diagram of a near-field terahertz wave spectral imaging system of the present application;

2 shows a structural diagram of an attenuation total reflection module of the present application;

Figure 3 shows the relationship between different design angles of total reflection;

4 shows a schematic diagram of terahertz wave time-domain spectral imaging of the present application;

5 shows a schematic diagram of THz-TDS near-field hyperspectral imaging results of the present application;

FIG. 6 shows a structural diagram of a fiber-coupled near-field terahertz wave spectral imaging system of the present application;

7 shows a sample cell structure diagram of the near-field terahertz wave spectral imaging system of the present application.

detailed description

In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions of the present application will be described clearly and completely in conjunction with specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without making creative efforts fall within the protection scope of the present application.

The main method to break through the diffraction limit of terahertz waves is to use near-field imaging technology. In order to achieve near-field imaging conditions, a sub-wavelength radiation source is required and the distance between the radiation source and the imaging target is controlled within a wavelength range. Based on this, this application proposes the advantage that the evanescent field based on the attenuated total reflection module satisfies the near field conditions. The light control method is used to realize the near-field sub-wavelength radiation source. Combined with the single-pixel imaging algorithm, the THz near-field imaging without scanning mechanism is realized. .

The structural diagram of the terahertz wave spectral imaging system is exemplified in the attached drawing 1 of the specification. The laser light output by the femtosecond laser 1 is divided into two paths by a beam splitter. One path passes through the right-angle mirror 2 and the delay line 3 and then converges to the terahertz transmitting antenna 4, and the other path passes through the mirror 5 to focus on the terahertz detecting antenna 6. After the terahertz wave signal generated by the terahertz transmitting antenna 4 is collimated by the off-axis parabolic mirror 7, it interacts with the sample 9 to be tested carried on the attenuation total reflection module 8, and then the off-axis parabolic mirror 10 interacts with the above-mentioned interaction The terahertz wave signal is focused on the terahertz detection antenna 6 at the receiving end. The basic structure of the system is the terahertz time-domain spectroscopy system THz-TDS. By scanning the delay line 3, the terahertz time-domain spectrum can be obtained.

In order to improve the resolution of terahertz spectral imaging, this application uses near-field imaging technology. The terahertz wave generated by the terahertz transmitting antenna 4 undergoes total reflection through the attenuated total reflection module 8, and then forms a terahertz evanescent field on the surface of the attenuated total reflection module 8. The evanescent field and the sample to be measured are directly placed in the Both of the surfaces of the total reflection module 8 are attenuated to satisfy the near-field imaging condition that the sub-wavelength radiation source and the distance between the radiation source and the imaging target are controlled within a wavelength range.

For the design of the evanescent field generating module, namely the attenuation total reflection module 8, please refer to the attached drawing 2 of the specification. The attenuation total reflection module 8 is made of intrinsic silicon with low absorption of terahertz waves. The whole module is modeled with a triangular prism and the cross section is an isosceles triangle . The terahertz wave generated by the terahertz transmitting antenna 4 enters from the incident surface 81 of the triangular prism, undergoes total reflection through the reflection surface 82, and then exits from the exit surface 83. During the total reflection, an evanescent field 84 is formed on the reflection surface 82. The sample 9 to be tested can be directly placed on the reflective surface 82 that generates the evanescent field 84 to satisfy the near-field imaging conditions. Compared with the thin-film silicon material in the prior art, the present application can conveniently place the sample to be tested without making an additional fine base structure or jig.

2 in the accompanying drawings shows a cross section of an isosceles triangle base angles α, environmental test sample refractive index n _1, a refractive index of attenuated total reflection module 8, n _2, and the other angle β, θ and γ, since the terahertz wave The catadioptric reflection between the interfaces satisfies Snell's theory and therefore has the following relationship:

n ₂ sinβ＝n ₁ (1)

n ₁ sinθ=n ₂ sinγ (2)

θ＝90°-β+γ (3)

α+θ＝90° (4)

Under normal circumstances, the sample to be tested can be placed in the air, and the air n ₁ =1. The attenuation total reflection module 8 may use, for example, high-resistance silicon or the like, which is n ₂ =3.418 in the terahertz band. Therefore, in the case where the refractive indexes of the above air and high-resistance silicon materials are known, the critical angle β = 17.1° can be calculated according to formula (1). Therefore, for an incident terahertz wave, as long as β>17.1°, a terahertz wave evanescent field can be formed on the reflection surface 82. For an isosceles triangle module, the angle α ∈ (0°, 90°), combined with formulas (2)-(4), can obtain β and θ corresponding to different α, as shown in FIG. 3 of the specification. Therefore, it is easy for a person skilled in the art to select a suitable angle design according to the detection environment. For example, the range of the base angle α is suitable in the range of 20°-60°. Too small a base angle is not conducive to the design of the overall sample bearing structure. In the present embodiment, α is preferably 30°, and accordingly θ is 60° and β is 44.68°. In the case where the above angles are known, if the length of the reflective surface 82 is set to 50 mm, the dimensions of the incident surface 81 and the exit surface 83 can also be calculated to be 28.87 mm.

In order to further overcome the long-time scanning problem of the prior art, the present application also proposes to use single-pixel imaging technology in conjunction with light control or aperture coding technology to quickly obtain high-resolution spectral imaging. Since the aperture coding technology also needs a lot of hardware to implement, the present application preferably uses a light control method combined with a single-pixel imaging algorithm to achieve terahertz near-field imaging without a scanning mechanism. For details, refer to FIG. 1 of the specification. An 808 nm light source 11 generates collimated 808 nm pump light. The pump light irradiates the controllable digital micromirror array 12. The digital micromirror array 12 is used to form a mask. The film is projected onto the incident surface 81 which is the side surface of the attenuation total reflection module 8. The material of the attenuated total reflection module 8 in this application is preferably made of high-resistance silicon, so the attenuated total reflection module 8 forms photo-generated carriers under the irradiation of the pump photomask, and the incident terahertz is incident on the incident surface 81 Wave conductivity is regulated. The material selection of the attenuating total reflection module 8 is aimed at semiconductors that are transparent in the terahertz band, such as intrinsic silicon, gallium arsenide, or intrinsic germanium. Different materials are suitable for different lighting environments to achieve higher terahertz wave modulation efficiency .

Regarding the modulation of terahertz waves, specifically the concentration of photogenerated carriers depends on the illumination conditions and the basic properties of semiconductors, which satisfy the following formula:

Where I ₀ represents the average power of the light source, R represents the reflectivity, hω represents the semiconductor energy band width, A represents the area, τ represents the carrier lifetime, and d represents the penetration depth.

The change of carrier concentration n will cause the complex refractive index of the semiconductor to change, so that the transmittance of the semiconductor to the terahertz wave also changes. The complex refractive index of the semiconductor is given by the crude formula:

Where ε _∞ = 11.7, Γ is the electron collision time, and ω _p is the plasma frequency

ε ₀ is the vacuum dielectric constant, m* is the effective mass, e is the charge quantity, ω=2πf is the angular frequency, where f is in the terahertz range of 0.1-10THz, and n is the carrier concentration. The change in transmittance caused by light is defined as the modulation depth

It is expressed as the difference between the corresponding transmittance when the output power of the pump laser is 0 and the maximum, and then the transmittance when the output power of the upper pump laser is 0. In the present application, the wavelength of the pumping light is less than 1100 nm, preferably a 808 nm laser is used, the power density is 2 W/cm ² , and the modulation depth is about 30% at 0.3 THz. It can be seen that for different semiconductor materials, different concentrations of photo-generated carriers will be generated, and then the change of the photo-generated carrier concentration will lead to the change of the plasma frequency, which in turn will affect the transmittance of the terahertz wave and realize the modulation effect.

Based on the above-mentioned control of the terahertz wave through the projection mask, when the single-pixel detector signal and the projection mask are known, the terahertz light field distribution at a specific time can be calculated. Since the attenuation total reflection module 8 of the present application has a certain body thickness, even if the focal plane position of the above-mentioned mask projection is not so accurate, for example, the focal plane is located inside the attenuation total reflection module 8, it will not affect the incident terahertz wave. Compared with the conventional technology, which can only project a mask on the surface of a thin silicon wafer, the technical solution of the present application has a higher fault tolerance rate. Alternatively, the above-mentioned mask can be generated without using the digital micromirror array 12, for example, the mask can be generated through a liquid crystal spatial light modulator or directly using a commercial projector. For the mask to be projected onto the attenuating total reflection block 8, a conventional projection method may be used.

Specifically, regarding the above digital projection and image reconstruction, it is preferable to operate according to the following process:

1) Construct the mask matrix

The matrix is, for example, one of a random matrix, a Hadamard matrix, or a Bernoulli matrix;

2) Put the matrix

Take out each row in and construct an N×N mask

3) Use digital projection technology to

The mask is projected on the incident surface 81 of the attenuated total reflection module 8 to generate photo-generated carriers in the attenuated total reflection module 8 to achieve modulation of the incident terahertz wave;

4) A single pixel detector collects the modulated terahertz wave signal after passing through the sample;

5) Use compressed sensing algorithm to reconstruct the terahertz light field.

The terahertz light field distribution at a specific time is obtained according to the above procedure, for example, see (b) in FIG. 4 of the specification, and the two-dimensional light field distribution at each time is obtained according to the above procedure. Further, in conjunction with (a) in FIG. 4 of the specification, the terahertz light field distribution at different times is calculated by the delay line using the terahertz wave time-domain spectral imaging principle, and then the terahertz multispectral image of the sample can be calculated. Figure 5 of the specification further exemplarily shows the THz-TDS near-field hyperspectral imaging results at a time, where (a) in FIG. 5 is the time-domain spectrum, and (b) in FIG. 5 is the frequency-domain spectrum, and its spectrum The resolving power can further characterize the substance. The resonance absorption of a substance in the terahertz band shows the relevant properties of the substance molecule, which can be characterized separately in the time domain and the frequency domain. The time-domain spectrum is obtained by scanning the delay line. The time-domain spectrum collected without the sample is the reference signal R, and the time-domain spectrum collected with the sample to be tested is the sample signal S. The reference signal peak in the figure is represented by P1, and the sample signal peak is represented by P2 It shows that the difference between peak and peak value is ΔP=P1-P2. This value can characterize the absorption status of substances, especially solution substances. The difference is positively correlated with the water content, so it can monitor the water activity of biological tissues online. In addition, the characteristic frequency difference Δα _f characterizes the change of the configuration of the substance to a certain extent, especially the biological macromolecules such as protein transcription, and the concentration change will affect the increase or decrease of certain frequency components. The method of this application can be monitored online Changes in the content of biological macromolecules. Further, combined with light-controlled single-pixel imaging, the image changes of peak-to-peak differences and the image changes of characteristic frequency differences can be observed online to achieve a more intuitive observation effect.

Unlike the free-space optical path of FIG. 1 of the specification, FIG. 6 of the specification shows an embodiment of using optical fiber coupling to build an optical path. The use of the reference numerals in the figure is the same as in FIG. 1 of the specification, that is, the same reference numerals refer to the same devices. The laser light emitted by the femtosecond laser 1 is divided into two paths, which are coupled to the first optical fiber 13 and the second optical fiber 14, respectively. The light in the first optical fiber 13 is coupled to the terahertz transmitting antenna 4 through the delay line 3, and then the terahertz wave signal generated by the terahertz transmitting antenna 4 is irradiated onto the attenuating total reflection module 8, and is directly carried on the attenuating total reflection module After the sample 9 on 8 interacts, it is focused to the terahertz detection antenna 6 at the receiving end.

The use of optical fiber coupling optical path will make the whole system more compact, in which the terahertz transmitting antenna 4, the attenuation total reflection module 8, the terahertz detecting antenna 6, the pump laser 11, the digital micromirror array 12, etc. can be integrated together to form the movement of the system End M. The femtosecond laser 1 and the delay line 3 can be integrated in the fixed end F of the system. The mobile end M and the fixed end F are coupled and connected by a first optical fiber 13 and a second optical fiber 14. In this way, when using the system, the position of the mobile terminal M can be conveniently adjusted according to needs, so that, for example, biological tissues, organs, and solutions waiting to be measured are conveniently and directly placed on the total reflection surface of the attenuation total reflection module 8 for detection . At the same time, the design can also meet the needs of in-vivo detection. Since the mobile terminal M can be made to a size that is convenient to move, it can totally reflect the attenuation in the mobile terminal M by moving the mobile terminal M without moving the object to be measured. The total reflection surface of the module 8 is attached to the object to be measured to realize detection.

Further, the mobile terminal M may have a housing, and a detection window is left at the position of the total reflection surface of the attenuation total reflection module 8, so that the sample to be tested is directly placed on the module. In particular, for a solution or other sample to be tested that is not suitable to be placed directly on the attenuation total reflection module 8, see FIG. 7 of the specification, a sample cell convenient for containing a solution can be made, and the sample cell 15 is directly seated in the On the total reflection surface of the attenuation total reflection module 8, the sample cell 15 also has a sample cell bottom 16 of the same material as the attenuation total reflection module 8, so that the terahertz wave can be totally reflected on the upper surface of the sample cell bottom 16, To meet near-field conditions.

The above describes a near-field terahertz wave spectral imaging system and method of the present application. This technical solution combines a terahertz time-domain spectroscopy system based on an attenuated total reflection module, utilizes the space-time characteristics of semiconductor photo-induced carriers, and combines light projection technology to realize single-pixel terahertz wave near-field imaging. Generally speaking, the traditional terahertz time-domain spectroscopy system is far-field detection. In this application, an attenuated total reflection module is introduced. The terahertz light generates a strong evanescent wave (the evanescent wave is near-field) through the module and interacts with the sample placed on the surface of the module. Therefore, in near-field detection, the sample only needs to be close to the surface of the attenuation total reflection module. Compared with the prior art, the present application can directly carry samples on the attenuation total reflection module without designing a separate fixture. Further combined with an advanced digital projection system, through the projection mask, using the photo-generated carrier characteristics of the high-resistance silicon of the attenuated total reflection module, the terahertz wave is modulated and then collected to realize the function of single-pixel imaging. It is sufficient to attenuate the sides of the total reflection module. Therefore, compared with the prior art in which the mask is projected onto a thin silicon wafer, the present application has lower requirements for the projection of the modulation mask, and the operation is more direct and convenient. Finally, the spectral resolution of terahertz time-domain spectroscopy is used to reconstruct the terahertz light field signals at different times to achieve fast and high-resolution near-field multi-spectral imaging.

It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other if there is no conflict.

The above are only preferred embodiments of the present application, and are not intended to limit the present application in any way. Any simple modifications, equivalent changes, and modifications to the above embodiments based on the technical essence of the present application still belong to the present application. Apply for technical solutions.

Claims

A near-field terahertz wave spectral imaging system, the basic optical path of the system is: the laser light output by the femtosecond laser (1) is divided into two paths; one path passes through the delay line (3) and converges on the terahertz transmitting antenna (4) ; The other way focuses on the terahertz detecting antenna (6); the terahertz wave signal generated by the terahertz transmitting antenna (4) interacts with the sample to be measured (9) and is focused to the terahertz detecting antenna (6) ); characterized by:

The system further includes an attenuated total reflection module (8), and the terahertz waves generated by the terahertz transmitting antenna (4) undergo total reflection in the attenuated total reflection module (8), and then the attenuated total reflection module The total reflection surface (82) of (8) forms a terahertz evanescent field, and the sample (9) to be tested is directly carried on the total reflection surface (82) of the attenuation total reflection module (8).
The system according to claim 1, characterized in that: the attenuation total reflection module (8) is a triangular prism as a whole, and the cross section is an isosceles triangle;

The terahertz wave generated by the terahertz transmitting antenna (4) enters from the incident surface (81) of the triangular prism, undergoes total reflection through the total reflection surface (82), then exits from the exit surface (83), and is totally reflected In the process, an evanescent field is formed on the total reflection surface (82).
The system according to claim 2, characterized in that the base angle of the isosceles triangle of section of the attenuation total reflection module (8) is 20°-60°.
The system of claim 2, further comprising a light source (11) to generate collimated pump light, the pump light illuminating the digital micromirror array (12) to utilize the digital micromirror The array (12) forms a mask; or, the mask is formed by a liquid crystal spatial light modulator or a projector;

The mask is projected onto the incident surface (81) of the attenuation total reflection module (8), so that the attenuation total reflection module (8) forms photo-generated carriers under the projection illumination of the mask , The incident terahertz wave is regulated on the incident surface (81).
The system according to claim 4, characterized in that the material of the attenuated total reflection module (8) is intrinsic silicon, gallium arsenide or intrinsic germanium.
The system of claim 4, wherein the pump light is ultraviolet light, visible light, or near infrared light.
The system according to claim 6, wherein the wavelength of the pump light is 808 nm.
The system according to claim 1 or 4, further comprising a single pixel detector, which uses a single pixel detector combined with a compressed sensing algorithm to reconstruct the terahertz light field.
The system of claim 1, wherein:

The femtosecond laser (1), the delay line (3) are integrated at the fixed end (F) of the system; the terahertz transmitting antenna (4), the attenuated total reflection module (8), the The terahertz detection antenna (6) is integrated in the mobile end (M) of the system;

The optical path between the fixed end (F) and the mobile end (M) is coupled through a first optical fiber (13) and a second optical fiber (14); the light emitted by the femtosecond laser (1) is divided into two Road, wherein the light in the first optical fiber (13) is coupled to the terahertz transmitting antenna (4) via a delay line (3), and the light in the second optical fiber (14) is coupled to the too Hertz probe antenna (6).
The system of claim 9, wherein:

The mobile terminal (M) further includes a digital micromirror array (12), a liquid crystal spatial light modulator or a projector to project a mask to the attenuated total reflection module (8).
The system according to claim 1 or 9, characterized in that a sample cell (15) is directly provided on the attenuation total reflection module (8), the sample cell (15) includes a sample cell bottom (16), The material of the bottom (16) of the sample cell is the same as the material of the attenuated total reflection module (8).
A near-field terahertz wave spectral imaging method, characterized by:

The attenuation total reflection module (8) is used to meet the near-field imaging conditions; the specific operations include the following two operations:

A. The terahertz wave generated by the terahertz transmitting antenna (4) is totally reflected in the attenuated total reflection module (8), and then a terahertz wave is formed on the total reflection surface (82) of the attenuated total reflection module (8) Hertz's death

B. Load the sample to be tested (9) directly on the total reflection surface (82) of the attenuation total reflection module (8).
The method according to claim 12, characterized in that the attenuated total reflection module (8) is placed in a terahertz time-domain spectral imaging system, and the terahertz time-domain spectrum is obtained by scanning with a delay line (3).
The method according to claim 12 or 13, further comprising the following operations:

C. Use collimated pump light to illuminate the digital micromirror array (12) to form a mask; or use a liquid crystal spatial light modulator or a projector to form a mask;

D. Project the mask onto the incident surface (81) of the attenuated total reflection module (8), so that the attenuated total reflection module (8) forms a photogenerated load under the irradiation of the pump light mask Flow, regulating the incident terahertz wave on the incident surface (81);

E. Use a single pixel detector combined with a reconstruction algorithm to reconstruct the terahertz light field.
The method according to any one of claims 12 to 14, wherein the material of the attenuated total reflection module (8) uses intrinsic silicon, gallium arsenide, or intrinsic germanium.
The method of claim 14, wherein the pump light is ultraviolet light, visible light, or near infrared light.
The method of claim 16, wherein the wavelength of the pump light is 808 nm.