A single-pixel terahertz detection system and image acquisition method

Abstract

The present application discloses a single-pixel terahertz detection system and an image acquisition method. The system modulates the terahertz beam reflected by the target object to be detected by using a single-pixel speckle pattern, and obtains the light field intensity value of the terahertz beam corresponding to each single-pixel speckle pattern, so that imaging data can be quickly acquired, greatly improving data acquisition efficiency and shortening imaging time. The use of single-pixel imaging has low requirements on the environment and hardware. At the same time, combined with the strong penetration and detection capabilities of terahertz waves, the imaging resolution and detection efficiency of the system are greatly improved, and high-quality imaging and detection can be performed on the surface or interior of a variety of objects, with wide practicality.

Description

Technical Field

[0001] The present application relates to the field of terahertz detection technology, and in particular to a single-pixel terahertz detection system and an image acquisition method using the system. Background Art

[0002] In the electromagnetic spectrum, the frequency of terahertz waves is in the range of 0.1-10THz, and the wavelength is between 3μj and 1000μj. It is an electromagnetic wave between microwaves and infrared rays. The damage caused by terahertz wave radiation to the human body is one thousandth of that caused by X-rays, and it causes almost no harm to the human body, so it can be used in the field of security inspection. At present, security inspections in public places such as high-speed railway stations and airports usually require two steps: the inspected person first passes through a metal security gate (most of the security gates are currently based on X-rays), and then the whole body is scanned and inspected by the staff using a handheld metal detector for a second time. Unlike conventional security inspection methods, terahertz waves have strong penetrating power. It can not only detect metals, but also non-metallic, colloids, powders, ceramics, liquids and other dangerous items carried by the human body can be identified at the same time. Moreover, terahertz security inspection only requires one detection to complete the security inspection task. Therefore, this security inspection method is a very efficient security inspection method and has great application value in real life.

[0003] When using terahertz wave technology for security inspection, high-quality imaging of the inspected person is a crucial step in the security inspection process. There are two main types of terahertz imaging technologies currently in common use: point-by-point scanning and focal plane array imaging. However, the image data acquisition efficiency of these two imaging methods leads to long imaging time, low imaging resolution, and high hardware requirements. Summary of the invention

[0004] The present application provides a single-pixel terahertz detection system and an image acquisition method, which are used to solve the technical problems of image data acquisition efficiency, long imaging time, low imaging resolution and high hardware requirements in existing imaging technologies.

[0005] In view of this, the first aspect of the present application provides a single-pixel terahertz detection system, comprising: a laser source, a spatial light modulator, a projection lens, a terahertz wave source, a terahertz wave imaging lens, a light-controlled terahertz wave modulator, a terahertz wave converging lens and a terahertz wave intensity detector;

[0006] The laser source is used to generate a laser beam and then emit it to the spatial light modulator;

[0007] The spatial light modulator is used to sequentially load the speckle patterns therein according to the pre-stored single-pixel speckle pattern sequence, and at the same time, by limiting its relative position with respect to the laser source so that the laser beam incident on the spatial light modulator completely covers the speckle pattern, thereby modulating the laser beam and outputting the modulated laser beam;

[0008] The projection lens is used to receive the laser beam output by the spatial light modulator, and project the laser beam into the optically controlled terahertz wave modulator to form a laser spot;

[0009] The terahertz wave source is used to generate a terahertz wave beam and then irradiate the target object to be measured;

[0010] The terahertz wave imaging lens is used to image the target object to be measured irradiated by the terahertz wave beam, and at the same time, receive and project the terahertz beam reflected by the target object to be measured to the optically controlled terahertz wave modulator, and limit its relative position relative to the optically controlled terahertz wave modulator so that the terahertz beam projected to the optically controlled terahertz wave modulator completely covers the laser spot, so that the optically controlled terahertz wave modulator can modulate the terahertz beam;

[0011] The optically controlled terahertz wave modulator is used to modulate the terahertz wave beam and then output the modulated terahertz beam to the terahertz wave converging lens;

[0012] The terahertz wave converging lens is used to converge the terahertz wave beam;

[0013] The terahertz wave intensity detector is used to obtain the light field intensity value of the terahertz wave beam converged by the terahertz wave converging lens.

[0014] Preferably, a laser beam expander is provided between the laser source and the spatial light modulator for expanding the laser beam generated by the laser source.

[0015] Preferably, an aperture diaphragm with adjustable aperture size is provided between the laser beam expander and the spatial light modulator, for limiting the intensity of the laser beam incident on the spatial light modulator.

[0016] Preferably, a timer is further included, and the timer is used to set the working cycle of the spatial light modulator and the terahertz wave intensity detector, so that when the spatial light modulator loads the speckle pattern each time, the terahertz wave intensity detector obtains the light field intensity value of the corresponding terahertz beam.

[0017] Preferably, a terahertz wave beam expander is provided between the terahertz wave source and the target object to be measured, for expanding the terahertz wave beam generated by the terahertz wave source.

[0018] The present application also provides a single-pixel terahertz detection image acquisition method, based on the above-mentioned single-pixel terahertz detection system, comprising the following steps:

[0019] Step S1: sequentially loading the speckle patterns in the spatial light modulator according to the pre-stored speckle pattern sequence;

[0020] Step S2: emitting a laser beam to the spatial light modulator through a laser source and making the laser beam completely cover the speckle pattern pre-loaded on the spatial light modulator, thereby modulating the laser beam;

[0021] Step S3: after modulating the laser beam through the spatial light modulator, outputting the laser beam to the projection lens, and projecting the laser beam to the optically controlled terahertz wave modulator through the projection lens, and forming a laser spot in the optically controlled terahertz wave modulator;

[0022] Step S4: The terahertz wave source emits a terahertz beam, which is expanded by a terahertz wave beam expander and then irradiated toward the target object to be measured;

[0023] Step S5: imaging the target object to be measured irradiated by the terahertz wave beam through a terahertz wave imaging lens, and at the same time, receiving and projecting the terahertz beam reflected by the target object to be measured to the optically controlled terahertz wave modulator, and making the terahertz beam projected to the optically controlled terahertz wave modulator completely cover the laser spot, so that the optically controlled terahertz wave modulator can modulate the terahertz beam;

[0024] Step S6: outputting the modulated terahertz wave beam to the terahertz wave converging lens through the optically controlled terahertz wave modulator;

[0025] Step S7: after the terahertz wave converging lens is used to converge the terahertz beam, a light field intensity value of the terahertz beam converged by the terahertz wave converging lens corresponding to each of the speckle patterns is obtained through a terahertz wave intensity detector;

[0026] Step S8: acquiring an image of the target object to be measured based on a compressed sensing algorithm according to the pre-stored speckle pattern sequence and the light field intensity value of the terahertz wave beam acquired by the terahertz wave intensity detector.

[0027] Preferably, the step S2 further comprises expanding the laser beam emitted by the laser source by a laser beam expander, and then limiting the intensity of the laser beam incident on the spatial light modulator by an aperture.

[0028] Preferably, before step S1, the step further includes:

[0029] The computer generates j speckle images of n×n pixels, each of which is denoted as S j (u,v), where j = 1, 2, 3...j, the speckle pattern sequence can be expressed as:

[0030] S j (u,v)=[S1(u,v),S2(u,v),...,S j (u, v)], where (u, v) is the pixel coordinate, and all of the speckle pattern sequences are loaded into the spatial light modulator.

[0031] Preferably, the light field intensity value of the terahertz beam obtained in step S7 is recorded as A j , the sequence of light field intensity values ​​after j measurements is:

[0032] A=[A1,A2,...,A j ].

[0033] Preferably, the step S8 specifically includes:

[0034] S801: Based on the compressed sensing algorithm model, in the speckle pattern sequence S j (u, v) and the light field intensity value A of the terahertz beam j The compressed sensing algorithm model is established as follows:

[0035]

[0036] Among them, Ψ∈R j×j is the orthogonal transformation matrix, Ψ H is the conjugate transpose of Ψ, x is the one-dimensional original signal to be reconstructed, λ>0, λ is the noise control coefficient, f is the sparse coefficient, and H represents the conjugate transpose of the matrix;

[0037] In addition, in the above formula, y=Φx=ΦΨ H f,

[0038] y is the j-th measurement value of x under the measurement matrix Φ, and y is expressed as,

[0039] y=A T =[A1.A2,...,A j ] T , where x = Ψ H f is the representation of the target object to be measured in one-dimensional space, A T represents the transpose of A, and T represents the matrix transpose;

[0040] Φ is the measurement matrix, expressed as, Φ=[B1,B2,...,B j ,...,B 20000 ] T ,

[0041] Among them, B j is a column vector, which can be expressed as,

[0042] B j = reshape(S j (u,v)), where the reshape() function represents a speckle pattern matrix S j (u,v) is transformed into a one-dimensional column vector;

[0043] S802: According to the formula Calculate the minimum sparse coefficient f and solve the approximate value of f through iterative calculation Then through transformation Get the one-dimensional original signal x;

[0044] S803: The one-dimensional original signal x in step S802 is the one-dimensional spatial signal of the target object to be detected. After it is transformed into a two-dimensional space, the image T(u, v) of the target object to be detected is expressed as:

[0045] T(u,v)=imreshape(x,[n,n]), where imreshape(x,[n,n]) represents the transformation of the one-dimensional original signal x into an image of n×n pixels, and (u,v) represents the pixel coordinates.

[0046] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0047] The embodiment of the present application provides a single-pixel terahertz detection system, which can quickly acquire imaging data by using a single-pixel speckle pattern to modulate the terahertz beam reflected by the target to be detected, and obtain the light field intensity value of the terahertz beam corresponding to each single-pixel speckle pattern, thereby greatly improving the data acquisition efficiency and shortening the imaging time. The use of single-pixel imaging has low requirements on the environment and hardware. At the same time, combined with the strong penetration and detection capabilities of terahertz waves, the imaging resolution and detection efficiency of the system are greatly improved, and high-quality imaging and detection can be performed on the surface or interior of a variety of objects, with wide practicality.

[0048] Another embodiment of the present application provides a single-pixel terahertz detection image acquisition method, which reconstructs the image through a compressed sensing algorithm. Compared with the traditional image reconstruction method, the number of measurements is much lower than the number of measurements required by the traditional image reconstruction method, thereby improving the imaging rate. At the same time, the compressed sensing algorithm adopts a noise control coefficient, which is set according to the image quality, so that the image reconstruction quality is high and the anti-interference ability is strong. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic diagram of the structure of a single-pixel terahertz detection system provided in an embodiment of the present application;

[0050] Figure 2 A flowchart of a single-pixel terahertz detection image acquisition method provided in an embodiment of the present application;

[0051] Figure 3 A speckle pattern in a single-pixel terahertz detection image acquisition method provided in another embodiment of the present application;

[0052] Figure 4 A laser spot diagram in a single-pixel terahertz detection image acquisition method provided in another embodiment of the present application;

[0053] Figure 5 A schematic diagram of a terahertz beam covering a laser spot in a single-pixel terahertz detection image acquisition method provided in another embodiment of the present application. DETAILED DESCRIPTION

[0054] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0055] Embodiment 1

[0056] For easier understanding, see Figure 1 , a single-pixel terahertz detection system provided in the present application includes: a laser source 101, a spatial light modulator 104, a projection lens 105, a terahertz wave source 106, a terahertz wave imaging lens 109, a light-controlled terahertz wave modulator 110, a terahertz wave converging lens 111 and a terahertz wave intensity detector 112;

[0057] Furthermore, the laser source 101 is used to generate a laser beam which is then emitted to the spatial light modulator 104;

[0058] Furthermore, the spatial light modulator 104 is used to sequentially load the speckle patterns therein according to the pre-stored single-pixel speckle pattern sequence, and at the same time, by limiting its relative position with respect to the laser source 101 so that the laser beam incident on the spatial light modulator 104 completely covers the speckle pattern, thereby modulating the laser beam and outputting the modulated laser beam;

[0059] It should be noted that the speckle pattern sequentially loaded into the spatial light modulator 104 is a single one, while the pre-stored speckle pattern sequence may be a plurality of speckle patterns, and the pre-stored speckle pattern is generated by the computer 113 and loaded into the spatial light modulator 104. At the same time, there is no limitation on the relative position relative to the laser source 101, as long as the laser beam incident into the spatial light modulator 104 can completely cover the speckle pattern, and when the laser beam incident into the spatial light modulator 104 completely covers the speckle pattern, the amplitude of the laser beam changes, thereby achieving modulation.

[0060] Furthermore, the projection lens 105 is used to receive the laser beam output by the spatial light modulator 104 and project the laser beam into the optically controlled terahertz wave modulator 110 to form a laser spot;

[0061] It is understandable that after the laser beam passes through the interference of the speckle pattern, a laser spot will naturally be formed in the output projection.

[0062] Furthermore, the terahertz wave source 106 is used to generate a terahertz wave beam and then irradiate the target object 108 to be measured;

[0063] Further, the terahertz wave imaging lens 109 is used to image the target object 108 to be measured that is irradiated by the terahertz wave beam, and at the same time, receive and project the terahertz beam reflected by the target object 108 to the optically controlled terahertz wave modulator 110, and by limiting its relative position relative to the optically controlled terahertz wave modulator 110, the terahertz beam projected to the optically controlled terahertz wave modulator 110 completely covers the laser spot, so that the optically controlled terahertz wave modulator 110 modulates the terahertz beam;

[0064] It is understandable that after the terahertz beam projected onto the optically controlled terahertz wave modulator 110 completely covers the laser spot, the transmittance of the optically controlled terahertz wave modulator 110 can be changed, thereby modulating the amplitude of the incident terahertz beam and changing the amplitude of the terahertz beam.

[0065] Furthermore, the optically controlled terahertz wave modulator 110 is used to modulate the terahertz beam and output the modulated terahertz beam to the terahertz wave converging lens 111;

[0066] Further, the terahertz wave converging lens 111 is used to converge the terahertz wave beam;

[0067] The terahertz wave intensity detector 112 is used to obtain the light field intensity value of the terahertz wave beam converged by the terahertz wave converging lens 111 .

[0068] It should be noted that after the terahertz wave converging lens 111 converges the terahertz wave beam, the terahertz wave beam enters the terahertz wave intensity detector 112 .

[0069] Furthermore, a laser beam expander 102 is provided between the laser source 101 and the spatial light modulator 104 for expanding the laser beam generated by the laser source 101 .

[0070] It should be noted that, according to actual conditions, the relative positions of the laser beam expander 102, the laser source 101 and the spatial light modulator 104 need to be adjusted so that the laser beam can completely cover the speckle pattern.

[0071] Furthermore, an aperture 103 with an adjustable aperture size is provided between the laser beam expander and the spatial light modulator 104 , so as to limit the intensity of the laser beam incident on the spatial light modulator 104 .

[0072] It should be noted that, according to actual conditions, the relative positions of the aperture 103, the laser beam expander 102, the laser source 101 and the spatial light modulator 104 need to be adjusted so that the laser beam can completely cover the speckle pattern.

[0073] Furthermore, a timer is included, and the timer is used to set the working cycle of the spatial light modulator 104 and the terahertz wave intensity detector 112, so that when the spatial light modulator 104 loads a speckle pattern each time, the terahertz wave intensity detector 112 obtains the light field intensity value of the corresponding terahertz beam.

[0074] Furthermore, a terahertz wave beam expander is provided between the terahertz wave source 106 and the target object 108 to be measured, for expanding the terahertz wave beam generated by the terahertz wave source 106 .

[0075] It should be noted that the technical solution of this embodiment has a compact structure, and by using a single-pixel speckle pattern to modulate the terahertz beam, imaging data can be acquired without scanning, thereby achieving high imaging efficiency and high imaging resolution, while having low hardware requirements.

[0076] Embodiment 2

[0077] For easier understanding, see Figure 2 Embodiment 2 provides a single-pixel terahertz detection image acquisition method, which is based on the single-pixel terahertz detection system in the above embodiment 1, and includes the following steps:

[0078] Step S1: sequentially loading the speckle patterns in the spatial light modulator according to the pre-stored speckle pattern sequence;

[0079] It should be noted that the pixel values ​​of the speckle pattern are randomly distributed in [0,1], and a number of speckle patterns are stored in a hard disk, and the speckle patterns can be read from the hard disk.

[0080] Step S2: emitting a laser beam to the spatial light modulator through a laser source and making the laser beam completely cover the speckle pattern pre-loaded in the spatial light modulator, thereby modulating the laser beam;

[0081] Step S3: after modulating the laser beam through the spatial light modulator, output the laser beam to the projection lens, and project the laser beam to the optically controlled terahertz wave modulator through the projection lens, and form a laser spot in the optically controlled terahertz wave modulator;

[0082] Step S4: The terahertz wave source emits a terahertz beam, which is expanded by a terahertz wave beam expander and then irradiated toward the target object to be measured;

[0083] Step S5: imaging the target object to be measured irradiated by the terahertz wave imaging lens, and at the same time, receiving and projecting the terahertz beam reflected by the target object to be measured to the optically controlled terahertz wave modulator, so that the terahertz beam projected to the optically controlled terahertz wave modulator completely covers the laser spot, so as to realize the optically controlled terahertz wave modulator to modulate the terahertz beam;

[0084] Step S6: outputting the modulated terahertz wave beam to the terahertz wave converging lens through the optically controlled terahertz wave modulator;

[0085] Step S7: After the terahertz beam is converged by the terahertz wave converging lens, the light field intensity value of the terahertz beam converged by the terahertz wave converging lens corresponding to each speckle pattern is obtained by a terahertz wave intensity detector;

[0086] Step S8: acquiring an image of the target object to be measured based on a compressed sensing algorithm according to the pre-stored speckle pattern sequence and the light field intensity value of the terahertz wave beam acquired by the terahertz wave intensity detector.

[0087] Furthermore, step S2 also includes expanding the laser beam emitted by the laser source by a laser beam expander, and then limiting the intensity of the laser beam incident on the spatial light modulator by an aperture.

[0088] Furthermore, before step S1, the following steps are also included:

[0089] Generate j speckle patterns of n×n pixels by computer, each speckle pattern is denoted as S j(u,v), where j = 1, 2, 3...j, the speckle pattern sequence can be expressed as:

[0090] S j (u,v)=[S1(u,v),S2(u,v),...,S j (u,v)], where (u,v) is the pixel coordinate, and the speckle pattern sequence is loaded into the spatial light modulator.

[0091] Furthermore, the light field intensity value of the terahertz beam obtained in step S7 is recorded as A j , the sequence of light field intensity values ​​after j measurements is:

[0092] A=[A1,A2,...,A j ].

[0093] Furthermore, step S8 specifically includes:

[0094] S801: Based on the compressed sensing algorithm model, in the speckle pattern sequence S j (u, v) and the light field intensity value A of the terahertz beam j The compressed sensing algorithm model is established as follows:

[0095]

[0096] Among them, Ψ∈R j×j is the orthogonal transformation matrix, Ψ H is the conjugate transpose of Ψ, x is the one-dimensional original signal to be reconstructed, λ>0, λ is the noise control coefficient, f is the sparse coefficient, and H represents the conjugate transpose of the matrix; in addition, y=Φx=ΦΨ in the above formula H f,

[0097] y is the j-th measurement value of x under the measurement matrix Φ, and y is expressed as,

[0098] y=A T =[A1.A2,...,A j ] T , where x = Ψ H f is the representation of the target object to be measured in one-dimensional space, A T represents the transpose of A, and T represents the transpose of the matrix;

[0099] Φ is the measurement matrix, expressed as, Φ=[B1,B2,...,B j ,...,B 20000 ] T ,

[0100] Among them, B j is a column vector, which can be expressed as,

[0101] B j = reshape(S j (u,v)), where the reshape() function represents a speckle pattern matrix S j (u,v) is transformed into a one-dimensional column vector;

[0102] S802: According to the formula Calculate the minimum sparse coefficient f and solve the approximate value of f through iterative calculation Then through transformation Get the one-dimensional original signal x;

[0103] S803: The one-dimensional original signal x in step S802 is a one-dimensional spatial signal of the target object to be measured. After it is transformed into a two-dimensional space, the image T(u,v) of the target object to be measured is expressed as:

[0104] T(u,v)=imreshape(x,[n,n]), where imreshape(x,[n,n]) represents the transformation of the one-dimensional original signal x into an image of n×n pixels, and (u,v) represents the pixel coordinates.

[0105] It should be noted that traditional image reconstruction is based on the Nyquist sampling theorem, which requires at least n samples. 2 The image reconstruction can be realized by using the compressed sensing algorithm, and the number of measurements can be lower than the number of measurements required by the Nyquist sampling theorem, so as to realize image reconstruction, thereby greatly improving the imaging efficiency. The selection of the noise control coefficient λ can be adjusted according to the image quality, which is beneficial to further improve the imaging quality. In this embodiment, λ=16.

[0106] Embodiment 3

[0107] In this embodiment, a single-pixel terahertz detection image acquisition method is described by combining specific implementation data, specifically,

[0108] Step S1: Generate 4000 128×128 pixel speckle images by computer, such as Figure 3 As shown, each speckle pattern is denoted by S j (u,v), j = 1, 2, 3...4000, the speckle pattern sequence is:

[0109] S j (u,v)=[S1(u,v),S2(u,v),...,S 4000 (u, v)], (u, v) represents the pixel coordinates, and all the speckle patterns are sequentially loaded into the spatial light modulator according to the speckle pattern sequence, and the speckle patterns therein are sequentially loaded through the spatial light modulator according to the pre-stored speckle pattern sequence.

[0110] Step S2: emitting a laser beam to the spatial light modulator through a laser source and making the laser beam completely cover the speckle pattern pre-loaded in the spatial light modulator, thereby modulating the laser beam;

[0111] Step S3: After the laser beam is modulated by the spatial light modulator, the laser beam is output to the projection lens, and the laser beam is projected to the optically controlled terahertz wave modulator through the projection lens, and a laser spot is formed in the optically controlled terahertz wave modulator. Figure 4 As shown;

[0112] Step S4: The terahertz wave source emits a terahertz beam, which is expanded by a terahertz wave beam expander and then irradiated toward the target object to be measured;

[0113] Step S5: The target object to be measured irradiated by the terahertz wave is imaged by the terahertz wave imaging lens, and at the same time, the terahertz beam reflected by the target object to be measured is received and projected to the optically controlled terahertz wave modulator, and the terahertz beam projected to the optically controlled terahertz wave modulator completely covers the laser spot, such as Figure 5 As shown, the optically controlled terahertz wave modulator is used to modulate the terahertz beam;

[0114] Step S6: outputting the modulated terahertz wave beam to the terahertz wave converging lens through the optically controlled terahertz wave modulator;

[0115] Step S7: Each time a speckle pattern is loaded into the spatial light modulator, the corresponding light field intensity value is collected by the terahertz wave intensity detector, which is recorded as A j , j = 1, 2, 3...4000, and the sequence of light field intensity values ​​after 4000 measurements is A = [A1, A2, ..., A 4000 ].

[0116] Step S8 specifically includes:

[0117] S801: Based on the compressed sensing algorithm model, in the speckle pattern sequence S j (u, v) and the light field intensity value A of the terahertz beam j The compressed sensing algorithm model is established as follows:

[0118]

[0119] Among them, Ψ∈R 4000×4000 is the orthogonal transformation matrix, Ψ H is the conjugate transpose of Ψ, x is the one-dimensional original signal to be reconstructed, λ>0, λ is the noise control coefficient, f is the sparse coefficient, and H represents the conjugate transpose of the matrix; in addition, y=Φx=ΦΨ in the above formula H f,

[0120] y is the 4000 measurement values ​​of x under the measurement matrix Φ, and y is expressed as,

[0121] y=A T =[A1.A2,...,A 4000 ] T , where x = Ψ H f is the representation of the target object to be measured in one-dimensional space, A T represents the transpose of A, and T represents the transpose of the matrix;

[0122] Φ is the measurement matrix, expressed as, Φ=[B1,B2,...,B j ,...,B 20000 ] T ,

[0123] Among them, B j is a column vector, which can be expressed as,

[0124] B j = reshape(S j (u,v)), where the reshape() function represents a speckle pattern matrix S j (u,v) is transformed into a one-dimensional column vector;

[0125] S802: According to the formula Calculate the minimum sparse coefficient f and solve the approximate value of f through iterative calculation Then through transformation Get the one-dimensional original signal x;

[0126] S803: The one-dimensional original signal x in step S802 is a one-dimensional spatial signal of the target object to be measured. After it is transformed into a two-dimensional space, the image T(u,v) of the target object to be measured is expressed as:

[0127] T(u,v)=imreshape(x,[128,128]), where imreshape(x,[128,128]) means transforming the one-dimensional original signal x into an image of 128×128 pixels, and (u,v) represents the pixel coordinates, that is, obtaining a high-quality image of the target object to be measured.

[0128] In the several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0129] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0130] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0131] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application 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 the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A single-pixel terahertz detection system, characterized in that: include: Laser source, spatial light modulator, projection lens, terahertz wave source, terahertz wave imaging lens, light-controlled terahertz wave modulator, terahertz wave converging lens and terahertz wave intensity detector; The laser source is used to generate a laser beam and then emit it to the spatial light modulator; The spatial light modulator is used to sequentially load the speckle patterns therein according to the pre-stored single-pixel speckle pattern sequence, and at the same time, by limiting its relative position with respect to the laser source so that the laser beam incident on the spatial light modulator completely covers the speckle pattern, thereby modulating the laser beam and outputting the modulated laser beam; A laser beam expander is provided between the laser source and the spatial light modulator, for expanding the laser beam generated by the laser source; An aperture diaphragm with adjustable aperture size is provided between the laser beam expander and the spatial light modulator, for limiting the intensity of the laser beam incident on the spatial light modulator; The projection lens is used to receive the laser beam output by the spatial light modulator, and project the laser beam into the optically controlled terahertz wave modulator to form a laser spot; The terahertz wave source is used to generate a terahertz wave beam and then irradiate the target object to be measured; The terahertz wave imaging lens is used to image the target object to be measured irradiated by the terahertz wave beam, and at the same time, receive and project the terahertz beam reflected by the target object to be measured to the optically controlled terahertz wave modulator, and limit its relative position relative to the optically controlled terahertz wave modulator so that the terahertz beam projected to the optically controlled terahertz wave modulator completely covers the laser spot, so that the optically controlled terahertz wave modulator can modulate the terahertz beam; The optically controlled terahertz wave modulator is used to modulate the terahertz wave beam and then output the modulated terahertz beam to the terahertz wave converging lens; The terahertz wave converging lens is used to converge the terahertz wave beam; The terahertz wave intensity detector is used to obtain the light field intensity value of the terahertz beam after being converged by the terahertz wave converging lens; It also includes a timer, which is used to set the working cycle of the spatial light modulator and the terahertz wave intensity detector, so that when the spatial light modulator loads the speckle pattern each time, the terahertz wave intensity detector obtains the light field intensity value of the corresponding terahertz beam.

2. The single-pixel terahertz detection system according to claim 1, characterized in that: A terahertz wave beam expander is provided between the terahertz wave source and the target object to be measured, and is used to expand the terahertz wave beam generated by the terahertz wave source.

3. A single-pixel terahertz detection image acquisition method, based on the single-pixel terahertz detection system according to any one of claims 1-2, characterized in that: The following steps are involved: Step S1: sequentially loading the speckle patterns in the spatial light modulator according to the pre-stored speckle pattern sequence; Step S2: emitting a laser beam to the spatial light modulator through a laser source and making the laser beam completely cover the speckle pattern pre-loaded on the spatial light modulator, thereby modulating the laser beam; Step S3: after modulating the laser beam through the spatial light modulator, outputting the laser beam to the projection lens, and projecting the laser beam to the optically controlled terahertz wave modulator through the projection lens, and forming a laser spot in the optically controlled terahertz wave modulator; Step S4: The terahertz wave source emits a terahertz beam, which is expanded by a terahertz wave beam expander and then irradiated toward the target object to be measured; Step S5: imaging the target object to be measured irradiated by the terahertz wave beam through a terahertz wave imaging lens, and at the same time, receiving and projecting the terahertz beam reflected by the target object to be measured to the optically controlled terahertz wave modulator, and making the terahertz beam projected to the optically controlled terahertz wave modulator completely cover the laser spot, so that the optically controlled terahertz wave modulator can modulate the terahertz beam; Step S6: outputting the modulated terahertz wave beam to the terahertz wave converging lens through the optically controlled terahertz wave modulator; Step S7: after the terahertz wave converging lens is used to converge the terahertz beam, a light field intensity value of the terahertz beam converged by the terahertz wave converging lens corresponding to each of the speckle patterns is obtained through a terahertz wave intensity detector; Step S8: acquiring an image of the target object to be measured based on a compressed sensing algorithm according to the pre-stored speckle pattern sequence and the light field intensity value of the terahertz wave beam acquired by the terahertz wave intensity detector.

4. The single-pixel terahertz detection image acquisition method according to claim 3, characterized in that: The step S2 further includes expanding the laser beam emitted by the laser source by a laser beam expander, and then limiting the intensity of the laser beam incident on the spatial light modulator by an aperture.

5. The single-pixel terahertz detection image acquisition method according to claim 3, characterized in that: Before step S1, the following steps are also included: Generate j speckle images of n×n pixels by computer, each of which is denoted as S j (u,v), where j = 1, 2, 3...j, the speckle pattern sequence can be expressed as: S j (u,v)=[S1(u,v),S2(u,v),...,S j (u, v)], where (u, v) is the pixel coordinate, and all of the speckle pattern sequences are loaded into the spatial light modulator.

6. The single-pixel terahertz detection image acquisition method according to claim 5, characterized in that: The light field intensity value of the terahertz beam obtained in step S7 is recorded as A j , the sequence of light field intensity values ​​after j measurements is: <h2 style=";text-align:left;direction:ltr">A=[A1,A2,...,A<h2 style=";text-align:left;direction:ltr"> j <h2 style=";text-align:left;direction:ltr"> ]。 7. The single-pixel terahertz detection image acquisition method according to claim 6, characterized in that: The step S8 specifically includes: S801: Based on the compressed sensing algorithm model, in the speckle pattern sequence S j (u, v) and the light field intensity value A of the terahertz beam j The compressed sensing algorithm model is established as follows: Among them, Ψ∈R j×j is the orthogonal transformation matrix, Ψ H is the conjugate transpose of Ψ, x is the one-dimensional original signal, λ>0, λ is the noise control coefficient, f is the sparse coefficient, and H represents the conjugate transpose of the matrix; In addition, in the above formula, y=Φx=ΦΨ H f, y is the jth measurement value of x under the measurement matrix Φ, and y is expressed as, y=A T =[A1.A2,...,A j ] T , where x = Ψ H f is the one-dimensional original signal, A T represents the transpose of A, and T represents the matrix transpose; Φ is the measurement matrix, expressed as, Φ=[B1,B2,...,B j ,...,B 20000 ] T , Among them, B j is a column vector, which can be expressed as, B j = reshape(S j (u,v)), where the reshape() function represents a speckle pattern matrix S j (u,v) is transformed into a one-dimensional column vector; S802: According to the formula Calculate the minimum sparse coefficient f and solve the approximate value of f through iterative calculation Then through transformation Get the one-dimensional original signal x; S803: The one-dimensional original signal x in step S802 is the one-dimensional spatial signal of the target object to be detected. After it is transformed into a two-dimensional space, the image T(u, v) of the target object to be detected is expressed as: T(u,v)=imreshape(x,[n,n]), where imreshape(x,[n,n]) represents the transformation of the one-dimensional original signal x into an image of n×n pixels, and (u,v) represents the pixel coordinates.

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