阅读说明：本技术 一种图像重建方法及反射式太赫兹鬼成像系统 (Image reconstruction method and reflective terahertz ghost imaging system ) 是由 吴衡 吴基标 陈梅云 程良伦 王涛 王卓薇 于 2020-07-31 设计创作，主要内容包括：本申请公开了一种图像重建方法及反射式太赫兹鬼成像系统,方法包括：根据读取至光调制器中的预置散斑图序列对预置激光束进行调制,并将调制后的激光束投射至有效调制区域,得到激光光斑；根据激光光斑对太赫兹波场进行激光调制,得到调制后的太赫兹波束,并将太赫兹波束投射至目标物体上,获取反射太赫兹波束；获取反射太赫兹波束对应的太赫兹波强度值,组合得到太赫兹波强度序列；采用预置全变分优化模型根据太赫兹波强度序列重建目标图像矩阵,得到目标物体图像。本申请能够解决现有太赫兹成像技术中的图像质量较差,且抗干扰能力较弱的技术问题。(The application discloses an image reconstruction method and a reflective terahertz ghost imaging system, wherein the method comprises the following steps: modulating a preset laser beam according to a preset speckle pattern sequence read into the optical modulator, and projecting the modulated laser beam to an effective modulation area to obtain a laser spot; performing laser modulation on a terahertz wave field according to laser spots to obtain a modulated terahertz wave beam, and projecting the terahertz wave beam onto a target object to obtain a reflected terahertz wave beam; acquiring terahertz wave intensity values corresponding to the reflected terahertz wave beams, and combining to obtain a terahertz wave intensity sequence; and reconstructing a target image matrix according to the terahertz wave intensity sequence by adopting a preset total variation optimization model to obtain a target object image. The terahertz imaging device and the terahertz imaging method can solve the technical problems that the image quality in the existing terahertz imaging technology is poor, and the anti-interference capability is poor.)

1. An image reconstruction method, comprising:

modulating a preset laser beam according to a preset speckle pattern sequence read into an optical modulator, and projecting the modulated laser beam to an effective modulation area to obtain a laser spot, wherein the preset speckle pattern sequence comprises a speckle pattern, and the effective modulation area is positioned on the preset optical control terahertz wave modulator;

performing laser modulation on a terahertz wave field according to the laser spot to obtain a modulated terahertz wave beam, and projecting the terahertz wave beam onto a target object to obtain a reflected terahertz wave beam;

acquiring terahertz wave intensity values corresponding to the reflected terahertz wave beams, and combining the terahertz wave intensity values to obtain a terahertz wave intensity sequence, wherein the terahertz wave intensity sequence and the speckle pattern are in a preset corresponding relationship;

and reconstructing a target image matrix according to the speckle pattern and the terahertz wave intensity sequence by adopting a preset total variation optimization model to obtain a target object image.

2. The image reconstruction method according to claim 1, wherein the modulating the preset laser beam according to the preset speckle pattern sequence read into the optical modulator and projecting the modulated laser beam to the effective modulation area to obtain the laser spot further comprises:

generating a speckle pattern matrix according to a preset Hadamard matrix to obtain an initial speckle pattern sequence, wherein the initial speckle pattern sequence comprises the speckle pattern matrix;

and sequentially carrying out decomposition and sequencing operations on the speckle pattern matrix to obtain the preset speckle pattern sequence.

3. The image reconstruction method according to claim 1, wherein reconstructing a target image matrix according to the speckle pattern and the terahertz wave intensity sequence by using a preset total variation optimization model to obtain a target object image comprises:

respectively calculating difference values of the speckle pattern and the terahertz wave intensity sequence to obtain a speckle pattern variation sequence and a terahertz wave intensity variation sequence;

performing column reconstruction processing on the speckle pattern variable quantity sequence to obtain a sensing matrix;

constructing a preset total variation optimization model according to the sensing matrix and the terahertz wave intensity variation sequence;

and solving a target image column vector through the preset total variation optimization model, and reconstructing the target image column vector into the target image matrix to obtain the target object image.

4. The image reconstruction method according to claim 3, wherein the preset total variation optimization model is:

the terahertz wave intensity variation sequence is a regularization coefficient, D is the sensing matrix, Z is the target image column vector, alpha is an Nx 1-dimensional sparse column vector, Z is Ψ alpha, Ψ is an Nx N-dimensional sparse conversion matrix, and Δ B is the terahertz wave intensity variation sequence.

5. A reflective terahertz ghost imaging system for performing any of the image reconstruction methods of claims 1-4, comprising: the terahertz wave intensity detector comprises a laser light source, a laser beam expander, an iris diaphragm, a reflective mirror, an optical modulator, a terahertz wave source, a terahertz wave beam expander, an optically controlled terahertz wave modulator, a terahertz wave projection lens, a terahertz wave converging mirror and a terahertz wave intensity detector;

the laser beam expanding lens, the iris diaphragm and the reflector are sequentially arranged right in front of the laser light source, the optical axis of the laser beam expanding lens, the optical axis of the iris diaphragm and the optical axis of the laser light source are positioned on the same axis, and the center of the reflector is positioned on the optical axis of the iris diaphragm;

the center of the optical modulator is positioned on the central axis of the reflector reflected light beam and is used for receiving the reflector reflected light beam, and the central axis of the optical modulator is parallel to the optical axis of the laser light source;

the terahertz wave beam expander, the light-controlled terahertz wave modulator and the terahertz projection lens are sequentially arranged right in front of the terahertz wave source, an optical axis of the terahertz wave beam expander, an optical axis of the light-controlled terahertz wave modulator, a central axis of the terahertz projection lens and a central axis of a target object are on the same axis with an optical axis of the terahertz wave source, the light-controlled terahertz wave modulator is used for receiving a laser spot of the light modulator and a terahertz beam of the terahertz wave beam expander, and the terahertz beam completely covers the laser spot;

the central axis of the terahertz wave converging mirror is coincided with the central axis of the terahertz reflected beam reflected by the target object, the terahertz wave converging mirror is positioned right in front of the terahertz wave intensity detector, and the terahertz wave intensity detector is used for acquiring terahertz wave intensity information of the terahertz reflected beam.

6. The reflective terahertz ghost imaging system of claim 5, further comprising: a projection lens;

the projection lens is located between the optical modulator and the light-controlled terahertz wave modulator and used for projecting the laser light spots to an effective modulation area of the light-controlled terahertz wave modulator.

7. The reflective terahertz ghost imaging system of claim 5, further comprising: a main control module;

the main control module is respectively connected with the optical modulator and the terahertz wave intensity detector, and is used for providing a preset speckle pattern sequence for the optical modulator and sending an instruction for acquiring terahertz wave intensity information to the terahertz wave intensity detector.

Technical Field

The application relates to the technical field of terahertz imaging, in particular to an image reconstruction method and a reflective terahertz ghost imaging system.

Background

The terahertz (THz) imaging technology is to irradiate a target object with THz rays, acquire target object information through transmitted or reflected rays of the target object, and further realize imaging; compared with a low-frequency imaging technology, the THz imaging device has higher THz frequency and shorter wavelength, so that the THz imaging device has higher spatial resolution during imaging; in contrast to infrared and higher frequency imaging techniques, terahertz radiation can be transmitted through many common materials, such as paper products, colloids, powders, etc., which can be internally imaged. Therefore, the terahertz imaging technology has important research value in the fields of safety monitoring, biomedical detection, aerospace industry and the like.

There are two main types of commonly used terahertz imaging techniques: point-by-point scanning and array imaging. Point-by-point scanning imaging needs to scan a target object for multiple times to obtain information and then reconstruct an image, and the method is time-consuming and low in imaging resolution; array imaging overcomes the defect of slow speed of point-by-point scanning, but imaging equipment is complex and high in cost. The existing terahertz imaging technology has poor image quality due to defects, is weak in anti-interference capability, and cannot be suitable for meeting more practical application requirements.

Disclosure of Invention

The application provides an image reconstruction method and a reflective terahertz ghost imaging system, which are used for solving the technical problems that the image quality is poor and the anti-interference capability is poor in the existing terahertz imaging technology.

In view of the above, a first aspect of the present application provides an image reconstruction method, including:

modulating a preset laser beam according to a preset speckle pattern sequence read into an optical modulator, and projecting the modulated laser beam to an effective modulation area to obtain a laser spot, wherein the preset speckle pattern sequence comprises a speckle pattern, and the effective modulation area is positioned on the preset optical control terahertz wave modulator;

performing laser modulation on a terahertz wave field according to the laser spot to obtain a modulated terahertz wave beam, and projecting the terahertz wave beam onto a target object to obtain a reflected terahertz wave beam;

acquiring terahertz wave intensity values corresponding to the reflected terahertz wave beams, and combining the terahertz wave intensity values to obtain a terahertz wave intensity sequence, wherein the terahertz wave intensity sequence and the speckle pattern are in a preset corresponding relationship;

and reconstructing a target image matrix according to the speckle pattern and the terahertz wave intensity sequence by adopting a preset total variation optimization model to obtain a target object image.

Preferably, the modulating a preset laser beam according to a preset speckle pattern sequence read into the optical modulator, and projecting the modulated laser beam to an effective modulation region to obtain a laser spot, before further comprising:

generating a speckle pattern matrix according to a preset Hadamard matrix to obtain an initial speckle pattern sequence, wherein the initial speckle pattern sequence comprises the speckle pattern matrix;

and sequentially carrying out decomposition and sequencing operations on the speckle pattern matrix to obtain the preset speckle pattern sequence.

Preferably, the reconstructing a target image matrix according to the speckle pattern and the terahertz wave intensity sequence by using a preset total variation optimization model to obtain a target object image includes:

respectively calculating difference values of the speckle pattern and the terahertz wave intensity sequence to obtain a speckle pattern variation sequence and a terahertz wave intensity variation sequence;

performing column reconstruction processing on the speckle pattern variable quantity sequence to obtain a sensing matrix;

constructing a preset total variation optimization model according to the sensing matrix and the terahertz wave intensity variation sequence;

and solving a target image column vector through the preset total variation optimization model, and reconstructing the target image column vector into the target image matrix to obtain the target object image.

Preferably, the preset total variation optimization model is as follows:

the terahertz wave intensity variation sequence is a regularization coefficient, D is the sensing matrix, Z is the target image column vector, alpha is an Nx 1-dimensional sparse column vector, Z is Ψ alpha, Ψ is an Nx N-dimensional sparse conversion matrix, and Δ B is the terahertz wave intensity variation sequence.

A second aspect of the present application provides a reflective terahertz ghost imaging system for performing any one of the image reconstruction methods described in the first aspect, including: the terahertz wave intensity detector comprises a laser light source, a laser beam expander, an iris diaphragm, a reflective mirror, an optical modulator, a terahertz wave source, a terahertz wave beam expander, an optically controlled terahertz wave modulator, a terahertz wave projection lens, a terahertz wave converging mirror and a terahertz wave intensity detector;

the laser beam expanding lens, the iris diaphragm and the reflector are sequentially arranged right in front of the laser light source, the optical axis of the laser beam expanding lens, the optical axis of the iris diaphragm and the optical axis of the laser light source are positioned on the same axis, and the center of the reflector is positioned on the optical axis of the iris diaphragm;

the center of the optical modulator is positioned on the central axis of the reflector reflected light beam and is used for receiving the reflector reflected light beam, and the central axis of the optical modulator is parallel to the optical axis of the laser light source;

the terahertz wave beam expander, the light-controlled terahertz wave modulator and the terahertz projection lens are sequentially arranged right in front of the terahertz wave source, an optical axis of the terahertz wave beam expander, an optical axis of the light-controlled terahertz wave modulator, a central axis of the terahertz projection lens and a central axis of a target object are on the same axis with an optical axis of the terahertz wave source, the light-controlled terahertz wave modulator is used for receiving a laser spot of the light modulator and a terahertz beam of the terahertz wave beam expander, and the terahertz beam completely covers the laser spot;

the central axis of the terahertz wave converging mirror is coincided with the central axis of the terahertz reflected beam reflected by the target object, the terahertz wave converging mirror is positioned right in front of the terahertz wave intensity detector, and the terahertz wave intensity detector is used for acquiring terahertz wave intensity information of the terahertz reflected beam.

Preferably, the method further comprises the following steps: a projection lens;

the projection lens is located between the optical modulator and the light-controlled terahertz wave modulator and used for projecting the laser light spots to an effective modulation area of the light-controlled terahertz wave modulator.

Preferably, the method further comprises the following steps: a main control module;

the main control module is respectively connected with the optical modulator and the terahertz wave intensity detector, and is used for providing a preset speckle pattern sequence for the optical modulator and sending an instruction for acquiring terahertz wave intensity information to the terahertz wave intensity detector.

According to the technical scheme, the embodiment of the application has the following advantages:

the application provides an image reconstruction method, which comprises the following steps: modulating a preset laser beam according to a preset speckle pattern sequence read into the optical modulator, and projecting the modulated laser beam to an effective modulation area to obtain a laser spot, wherein the preset speckle pattern sequence comprises a speckle pattern, and the effective modulation area is positioned on the preset light-controlled terahertz wave modulator; performing laser modulation on a terahertz wave field according to laser spots to obtain a modulated terahertz wave beam, and projecting the terahertz wave beam onto a target object to obtain a reflected terahertz wave beam; acquiring terahertz wave intensity values corresponding to the reflected terahertz wave beams, and combining the terahertz wave intensity values to obtain a terahertz wave intensity sequence, wherein the terahertz wave intensity sequence and the speckle pattern are in a preset corresponding relation; and reconstructing a target image matrix by adopting a preset total variation optimization model according to the speckle pattern and the terahertz wave intensity sequence to obtain a target object image.

According to the image reconstruction method, the modulated laser is adopted to modulate the terahertz wave field, modulation of invisible terahertz wave beams is achieved, and due to the fact that laser modulation is simple and feasible, the flexibility of terahertz wave modulation is enhanced, and meanwhile the anti-jamming capability of imaging is enhanced; preset speckle pattern sequence not only can realize image reconstruction under the condition of nyquist sampling, can also carry out high quality image reconstruction under the condition that is less than the nyquist sampling to, can effectively get rid of the noise interference in the image through presetting total variation optimization model, strengthen the image detail characteristic, can further promote the quality of rebuilding the image, consequently, image quality among the present terahertz imaging technique is relatively poor can be solved to this application, and the technical problem that interference killing feature is relatively weak.

Drawings

Fig. 1 is a schematic flowchart of an image reconstruction method according to an embodiment of the present disclosure;

fig. 2 is a schematic structural diagram of a reflective terahertz ghost imaging system according to an embodiment of the present disclosure;

fig. 3 is a schematic diagram of laser modulation in an effective modulation region according to an embodiment of the present disclosure;

reference numerals:

the terahertz wave laser device comprises a laser light source 101, a laser beam expander 102, an iris diaphragm 103, a reflector 104, an optical modulator 105, a projection lens 106, a terahertz wave source 107, a terahertz wave beam expander 108, an optically controlled terahertz wave modulator 109, a terahertz wave projection lens 110, a target object 111, a terahertz wave converging lens 112, a terahertz wave intensity detector 113, a main control module 114, a laser spot 201, a terahertz light beam 202, a speckle pattern 203 and an effective modulation region 204.

Detailed Description

In order to make the technical solutions of the present application better understood, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

For easy understanding, referring to fig. 1, a first embodiment of an image reconstruction method provided in the present application includes:

step 101, modulating a preset laser beam according to a preset speckle pattern sequence read into an optical modulator, and projecting the modulated laser beam to an effective modulation area to obtain a laser spot, wherein the preset speckle pattern sequence comprises a speckle pattern, and the effective modulation area is located on the preset light-controlled terahertz wave modulator.

It should be noted that the preset speckle pattern sequence is obtained from a Hadamard matrix, and the preset laser beam is modulated according to the preset speckle pattern sequence, so that the method of the embodiment can realize reconstruction of a high-quality image under the condition of no matter equal to or lower than nyquist sampling. The modulated laser beam is projected to an effective modulation area of the light-controlled terahertz wave modulator to form a laser spot. The preset speckle pattern sequence is composed of speckle patterns.

And 102, performing laser modulation on the terahertz wave field according to the laser spot to obtain a modulated terahertz wave beam, and projecting the terahertz wave beam onto a target object to obtain a reflected terahertz wave beam.

It should be noted that the laser spot is covered by the terahertz wave beam on the effective modulation region, and the adjusted wave beam completely covers the laser spot, so that the modulation of the terahertz wave field is realized, and the terahertz wave beam successfully modulated is obtained. The modulated terahertz wave beam is adopted to irradiate the target object, the information of the target object can be reflected by the reflected terahertz wave beam obtained by the modulation, and the reflected terahertz wave beam is the key information for reconstructing the image of the target object.

And 103, acquiring terahertz wave intensity values corresponding to the reflected terahertz wave beams, and combining the terahertz wave intensity values to obtain a terahertz wave intensity sequence, wherein the terahertz wave intensity sequence and the speckle pattern are in a preset corresponding relationship.

It should be noted that in this embodiment, image reconstruction may be performed under the condition of sampling below nyquist, that is, the total number of times K for acquiring terahertz wave intensity values is less than the total number of speckle patterns 2N, where K is greater than 0 and less than or equal to 2N, and K is an even number, but each time one speckle pattern is loaded in the optical modulator, a corresponding terahertz wave intensity sequence B, denoted as B ═ B₁,B₂,...,B_k,...B_K]Namely, the terahertz wave intensity sequence corresponds to the speckle pattern one by one.

And step 104, reconstructing a target image matrix according to the speckle pattern and the terahertz wave intensity sequence by adopting a preset total variation optimization model to obtain a target object image.

The number of the speckle patterns is determined according to the number of the acquired terahertz wave intensity sequences, and other speckle patterns in the preset speckle pattern sequences are discarded; and performing difference value calculation, matrix reconstruction, modeling, optimization solution and form transformation of a column vector of the target image on the speckle pattern and the terahertz wave intensity sequence to obtain a reconstructed target object image. The preset total variation optimization model can effectively remove noise, is more favorable for reconstruction of images and improves the quality of reconstructed images.

According to the image reconstruction method provided by the embodiment, the modulated laser is adopted to modulate the terahertz wave field, so that the modulation of invisible terahertz wave beams is realized, and the laser modulation is simple and feasible, so that the modulation flexibility of terahertz waves is enhanced, and the imaging anti-interference capability is enhanced; the preset speckle pattern sequence can realize image reconstruction under the condition of Nyquist sampling, and can also carry out high-quality image reconstruction under the condition of being lower than the Nyquist sampling, and can effectively remove noise interference in the image through presetting the total variation optimization model, and the image detail characteristics are enhanced, and the quality of the reconstructed image can be further improved, so that the image quality in the existing terahertz imaging technology is poorer, and the technical problem that the anti-interference capability is weaker can be solved by the embodiment.

Further, step 101 is preceded by: generating a speckle pattern matrix according to a preset Hadamard matrix to obtain an initial speckle pattern sequence, wherein the initial speckle pattern sequence comprises the speckle pattern matrix; and sequentially carrying out decomposition and sequencing operations on the speckle pattern matrix to obtain a preset speckle pattern sequence.

It should be noted that an N × N Hadamard matrix can be generated by a computer, and is represented as follows:

wherein N is 2^mM > 0 is a positive integer, H₂Can be expressed as:

will Hadamard matrix H_NMiddle ith row H_iConversion to initial speckle pattern matrix:

wherein an initial speckle pattern matrix P_i(x, y) has a size of

reshape () is a process of converting a row vector into a matrix, i 1,2, N,

is a positive integer; combining the initial speckle pattern matrixes to obtain an initial speckle pattern sequence:

P＝[P₁(x,y),P₂(x,y),...,P_i(x,y),...,P_N(x,y)]；

the decomposition of the speckle pattern matrix can be expressed as:

P_i(x,y)＝A_i(x,y)-B_i(x,y)；

from the above expression, it is possible to obtain:

B_i(x,y)＝1-A_i(x,y)；

handle A_i(x, y) and B_iWhen 1 in the expression (x, y) is changed to 255, A is calculated by the 4-connected domain method_i(x, y) and B_iThe number of connected domains centered at 255 in (x, y) is denoted as a_iAnd b_iThen the initial speckle pattern matrix P_iThe total number of connected domains after (x, y) decomposition is c_iDenoted by c_i＝a_i+b_i(ii) a At this time, the sequence of the number of connected domains c ═ c is known₁,c₂,...,c_i,...,c_N]In the initial speckle patternColumn P and connected component sequence c, speckle pattern matrix P_i(x, y) and c_iThe positions are in one-to-one correspondence; sequencing the connected domain sequences c in an ascending order, sequencing the corresponding initial speckle pattern sequences P according to the same rule, and still keeping the element positions in the sequences in one-to-one correspondence; recording the elements in the sorted initial speckle pattern sequence P as Q_i(x, y); according to the method, a new speckle pattern sequence can be obtained, namely a preset speckle pattern sequence Q:

wherein the content of the first and second substances,

wherein j is 1,2, and N, and the total number of speckle patterns in the preset speckle pattern sequence Q obtained by decomposition and sorting is 2N.

Further, step 104 includes: respectively calculating difference values of the speckle pattern and the terahertz wave intensity sequence to obtain a speckle pattern variation sequence and a terahertz wave intensity variation sequence; performing column reconstruction processing on the speckle pattern variable quantity sequence to obtain a sensing matrix; constructing a preset total variation optimization model according to the sensing matrix and the terahertz wave intensity variation sequence; and solving a target image column vector through a preset total variation optimization model, and reconstructing the target image column vector into a target image matrix to obtain a target object image.

It should be noted that, K speckle pattern matrices with the same data quantity as the element data quantity of the terahertz wave intensity sequence are selected from the obtained preset speckle pattern sequence Q, and the rest are discarded, and the difference value calculation is performed on the selected preset speckle pattern sequence and the terahertz wave intensity sequence respectively to obtain a speckle pattern variation sequence Δ Q and a terahertz wave intensity variation sequence Δ B, which are expressed as follows:

ΔB＝[B₁-B₂,...,B_k-B_k-1,...,Β_K-B_K-1]；

through difference value calculation, the number of the terahertz wave intensity values in the speckle pattern matrix in the delta Q and the terahertz wave intensity value in the delta B are both K/2. The nth speckle pattern matrix delta Q in the speckle pattern variation sequence_nReconstructing to obtain an Nx 1 column vector D_nIn the reconstruction process, the second column in the matrix is taken out and connected to the tail of the first column, the third column is taken out and connected to the tail of the second column, and the like; and performing the same operation on all the speckle pattern matrixes in the speckle pattern variation sequence to obtain column vectors with the same dimension, and combining the column vectors to obtain a sensing matrix D:

D＝[D₁,D₂,...,D_n...,D_K]^T；

where T denotes transposition.

Constructing a preset total variation optimization model through a sensing matrix D and a terahertz wave intensity variation sequence delta B; the preset total variation optimization model is expressed as:

the regularization coefficient is greater than 0, D is a sensing matrix, Z is a target image column vector, alpha is an N multiplied by 1-dimensional sparse column vector, Z is psi alpha, and psi is an N multiplied by N-dimensional sparse conversion matrix. The column vector Z of the target image can be obtained by carrying out minimum iterative computation on alpha, and the Z is subjected to structural transformation and converted intoThe target image matrix Z (x, y) of (1) is an image of the target object obtained by reconstruction, but normalization processing is also required to output the reconstructed image, and the normalization processing mode is as follows:

Z'(x,y)＝Z(x.y)/Z_max；

wherein Z is_maxRepresenting the maximum value in the column vector Z. Z' (x, y) is the reconstructed target object image.

For ease of understanding, referring to fig. 2, the present application further provides an embodiment of a reflective terahertz ghost imaging system, comprising: the image reconstruction method for performing any one of the above method embodiments, comprising: the terahertz wave intensity detector comprises a laser light source 101, a laser beam expander 102, an iris diaphragm 103, a reflector 104, an optical modulator 105, a terahertz wave source 107, a terahertz wave beam expander 108, an optically controlled terahertz wave modulator 109, a terahertz wave projection lens 110, a terahertz wave converging mirror 112 and a terahertz wave intensity detector 113.

The laser beam expander 102, the iris diaphragm 102 and the reflector 104 are sequentially arranged right in front of the laser light source 101, the optical axis of the laser beam expander, the optical axis of the iris diaphragm and the optical axis of the laser light source are on the same axis, and the center of the reflector is positioned on the optical axis of the iris diaphragm;

the center of the optical modulator 105 is on the central axis of the reflected beam of the mirror 104 for receiving the reflected beam of the mirror, and the central axis of the optical modulator 105 is parallel to the optical axis of the laser light source;

the terahertz wave beam expander 108, the light-controlled terahertz wave modulator 109 and the terahertz projection lens 110 are sequentially arranged right in front of the terahertz wave source 107, an optical axis of the terahertz wave beam expander, an optical axis of the light-controlled terahertz wave modulator, a central axis of the terahertz projection lens and a central axis of a target object are on the same axis with an optical axis of the terahertz wave source, the light-controlled terahertz wave modulator 109 is used for receiving a laser spot of the optical modulator 105 and a terahertz beam of the terahertz wave beam expander 108, and the terahertz beam completely covers the laser spot;

the central axis of the terahertz wave converging mirror coincides with the central axis of the terahertz reflected beam reflected by the target object 111, the terahertz wave converging mirror 112 is located right in front of the terahertz wave intensity detector 113, and the terahertz wave intensity detector 113 is used for acquiring terahertz wave intensity information of the terahertz reflected beam.

Please refer to fig. 2, the modulation process of the reflective terahertz ghost imaging system is as follows: firstly, a laser beam expander 102, an iris diaphragm 103 and a reflector 104 are arranged right in front of a laser source 101 of a single light path to perform necessary processing on laser, the laser beam expander 102 can amplify laser of the single light path into a plurality of beams so as to be more convenient to cover a speckle pattern, the iris diaphragm 103 is used for controlling and adjusting the thickness of a laser beam, the reflector 104 can reflect the laser to an optical modulator 105, and the optical modulator 105 is provided with a loaded Hadamard speckle pattern sequence which is used for modulating the laser beam to obtain a laser spot; the light modulator 105 projects the modulated laser light spot onto the light-controlled terahertz wave modulator 109, referring to fig. 3, which includes an effective modulation region 204, a speckle pattern 203, a terahertz light beam 202, and a laser light spot 201; the light-controlled terahertz wave modulator 109 comprises a laser spot 201 and a terahertz light beam 202 emitted by a terahertz wave source 107 through a terahertz wave beam expander 108, wherein the terahertz light beam 202 needs to completely cover the laser spot 201, so that modulation of a terahertz wave field is realized on the light-controlled terahertz wave modulator 109; the terahertz wave beams which are successfully modulated are projected onto a target object 111 through a terahertz wave projection lens 110, the target object 111 reflects the terahertz wave beams, the reflected terahertz wave beams have a certain angle and reach a terahertz wave intensity detector 113 through a terahertz wave converging mirror 112, the terahertz wave intensity detector 113 obtains corresponding terahertz wave intensity values according to intensity information of the reflected terahertz wave beams, a pair of speckle patterns corresponds to a terahertz wave intensity sequence, and the terahertz wave intensity sequence comprises a plurality of terahertz wave intensity values.

Further, still include: a projection lens 106; the projection lens 106 is located between the optical modulator 105 and the optically controlled terahertz wave modulator 109, and is used for projecting the laser spot 201 to an effective modulation region 204 of the optically controlled terahertz wave modulator 109.

Further, still include: a master control module 114; the main control module 114 is connected to the optical modulator 105 and the terahertz wave intensity detector 113, and is configured to provide a preset speckle pattern sequence for the optical modulator 105, and send an instruction for acquiring terahertz wave intensity information to the terahertz wave intensity detector 109. The master control module 114 may be a computer to assist in the modulation process.

In the several embodiments provided in the present application, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application may be substantially implemented or contributed to by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for executing all or part of the steps of the method described in the embodiments of the present application through a computer device (which may be a personal computer, a server, or a network device). And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.

The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.