CN111157486A - Three-dimensional terahertz imaging method and imaging system thereof - Google Patents
Three-dimensional terahertz imaging method and imaging system thereof Download PDFInfo
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Abstract
The invention discloses a three-dimensional terahertz imaging method, and particularly relates to a frequency domain terahertz coherent tomography method. The broadband terahertz wave is divided into a detection wave and a reference wave, the detection wave is focused into a spot beam or a line beam to be incident on a measured object, and the reference wave is reflected back by an original path. The detection waves with different frequencies are incident to different depths of an object to generate backscattering, and the optical path difference between the backscattering detection waves carrying object depth information and the reference waves is constant to generate interference; the interference signal is focused on a linear array type or area array type terahertz detector after being subjected to grating frequency division, and different pixels of the detector detect the amplitude information of the interference signal with different frequencies and different positions; and continuously scanning the one-dimensional or two-dimensional plane of the object to be measured and acquiring the scanned coherent information in real time to finally obtain all three-dimensional structural data of the object. The method can remarkably improve the speed of terahertz three-dimensional imaging and can obtain high longitudinal resolution under the condition of high signal-to-noise ratio.
Description
Technical Field
The invention relates to a three-dimensional terahertz imaging method, in particular to a frequency domain terahertz coherent tomography method, and particularly relates to a parallel frequency domain terahertz coherent tomography method.
Background
Terahertz (THz) is an electromagnetic wave with the frequency within a 0.l-10 THz frequency band (the wavelength is 3 mm-30 mu m) and is in a frequency domain transition region from a macroscopic classical theory to a microscopic quantum theory, so that the THz has dual characteristics of electronics and photonics. The terahertz waves have strong reflection characteristics for high-conductivity materials such as metal and the like; the material has strong absorbability to most polar molecules such as water, ammonia gas and the like; the terahertz detection device has good penetration characteristics for a plurality of non-metallic materials and non-polar substances, can penetrate polymer composite materials such as foam, plastic, rubber and resin, and materials which are not permeable to visible light, infrared light and even ultrasonic waves such as insulation and heat insulation, and therefore has wide application prospect.
The application of the terahertz detection technology is mainly focused in the terahertz imaging field, and terahertz imaging can be roughly divided into two categories of terahertz pulse imaging and terahertz continuous wave imaging according to different detection terahertz radiation forms. For terahertz pulse radiation imaging, a point-scanning terahertz time-domain spectrum method is mainly adopted, but the imaging speed of terahertz time-domain spectrum point scanning imaging is low, real-time imaging cannot be realized, the resolution depends on the scanning step distance and the size of a light spot, and the resolution is difficult to be greatly improved, so that the development of the imaging mode is limited in many applications. Terahertz continuous wave imaging is an imaging mode for obtaining images according to intensity information of reflected or transmitted waves of an object to be measured, and the basic principle is that various materials and internal structures forming the object to be measured can generate different scattering effects on terahertz waves, so that intensity distribution of the terahertz waves is influenced, the terahertz waves are reflected to the images of the object and displayed as different light and shade (namely intensity), and accordingly, the internal shape, defects or damage positions of the object can be deduced. The continuous terahertz wave source can obtain relatively high output power, so that enough signal-to-noise ratio can be obtained only by the intensity information, and the requirement of imaging application is met. An effective mode for realizing terahertz continuous wave imaging is to utilize terahertz focal plane array imaging, and amplitude information of a whole measured object can be directly obtained without two-dimensional scanning of the measured object, so that a two-dimensional image of the measured object is obtained, and the defect that the scanning time of terahertz time-domain spectrum point scanning imaging is too long can be overcome.
For the two-dimensional imaging technology of the measured object, the imaging mode is limited in many applications because the two-dimensional imaging technology can only obtain the section or surface information of the measured object and cannot obtain the complete internal appearance of the measured object. The three-dimensional (three-dimensional) image of the measured object can acquire more abundant distribution information than the two-dimensional image, so that the terahertz three-dimensional imaging technology is a research hotspot of the terahertz imaging technology at present. The imaging modes for acquiring the terahertz three-dimensional image of the measured object mainly comprise terahertz holographic imaging, terahertz synthetic aperture imaging, terahertz computer-aided tomography, terahertz coherent tomography and the like. The terahertz holographic imaging technology has many disadvantages, such as the inability to provide accurate refractive index information of the object to be measured, and the dependence on multiple scattering and diffraction effects, the signal-to-noise ratio of the image is very low; the terahertz computer-aided tomography technology using several angle projection slices to synthesize image has low resolution and is not suitable for detecting large-size and non-axisymmetric objects.
Compared with other imaging methods, the terahertz coherent tomography method has an excellent detection effect on defects such as pores, cracks, adhered interlayers and delamination in the material, especially three-dimensional spatial distribution. The terahertz coherent tomography method is to obtain the three-dimensional structure of the measured object by measuring the interference intensity information of the back reflection or scattering signals of different depth layers of the measured object and the reference wave by utilizing the low coherence of the terahertz wave. A terahertz coherent tomography process method is characterized in that a reference mirror of a reference arm is moved, reflected waves from different layers of a measured object can interfere only when the optical path of the reference arm is matched, and therefore the purpose of scanning the measured object is achieved by moving the reference mirror of the reference arm. According to the time-domain terahertz coherent tomography method, the interference intensity distribution of a time domain can be obtained only by changing the optical path length of the reference arm by moving the reference mirror of the reference arm, and the depth information is obtained by performing Fourier transform on an output spectrum to obtain a frequency domain image. The imaging method needs to perform transverse two-dimensional and longitudinal depth scanning, has long imaging time, and can generate interference only when the optical path difference between the reference arm and the detection arm is smaller than the coherence length, which puts high requirements on the scanning positioning precision of a scanning system.
Disclosure of Invention
The invention provides a frequency domain terahertz coherent tomography method, which comprises the following implementation modes: the wide-spectrum light source emits a broadband terahertz wave which is divided into a detection wave and a reference wave; the detection waves are focused into spot beams to be incident on a measured object, the detection waves with different frequencies are incident on different depth positions of the measured object, and backscattering occurs at the different depth positions; the reference wave is reflected by the original path; the optical path difference between the detection wave carrying the depth information of the measured object and the reference wave which are back-scattered is constant, so that interference is generated between the light wave components with the same frequency; interference signals carrying depth information of a measured object are subjected to grating frequency division and then focused on the linear array type terahertz detector, and interference signals with different frequencies are focused on different pixels of the linear array type terahertz detector; further, the object to be measured is continuously scanned on a two-dimensional plane, and the coherent information of each detection point is acquired at the same time, so that all information data of the object are obtained; and finally obtaining the three-dimensional distribution of the internal structure of the measured object through subsequent image processing and three-dimensional reconstruction.
In order to achieve the above object, the present invention can adopt a frequency domain terahertz coherent tomography system to achieve three-dimensional terahertz imaging, which includes: the system comprises a broadband terahertz source modulation system, a Michelson interferometer, a spectrum measurement system and a scanning control and image data processing system.
The broadband terahertz source modulation system comprises: the terahertz source comprises a broadband terahertz source, a first parabolic mirror and a second parabolic mirror; the broadband terahertz source emits broadband terahertz waves, and the broadband terahertz waves are collimated by the first parabolic mirror and the second parabolic mirror and then enter the Michelson interferometer.
The michelson interferometer includes: the device comprises a beam splitter, a reference mirror, a lens and a two-dimensional translation stage; the broadband terahertz wave is divided into two paths by a beam splitter, namely a reference wave and a detection wave; the reference wave is vertically reflected back to the beam splitter through the fixed reference mirror; the detection waves are focused into spot beams through the lens and are incident on the object to be measured, and the detection waves with different frequencies are incident at different depths of the object to be measured; the detection wave carrying the depth information of the object to be measured is backscattered and returned to the beam splitter, and is superposed with the reference wave to generate interference signals carrying the depth information of the object to be measured.
The spectrum measuring system includes: the terahertz detector comprises a reflection grating, a parabolic mirror and a linear array type terahertz detector, wherein the linear array type terahertz detector is one-dimensionally arranged terahertz detector pixels; wherein, the interference signal is received by the frequency spectrum measuring system, and the reflection grating divides the interference signal according to the frequency; and the parabolic mirror focuses the interference signal after frequency division on the linear array type terahertz detector.
The scanning control and image data processing system adopts a computer and comprises a scanning control system and an image data processing system; the two-dimensional translation stage of the Michelson interferometer is connected to a scanning control and image data processing system; the scanning control system controls the two-dimensional translation table to realize continuous scanning of the measured object on a two-dimensional plane, and meanwhile, the linear array type terahertz detector collects coherent information of each detection point, so that all information data of the measured object are obtained; the image data processing system carries out subsequent image processing and three-dimensional reconstruction, and finally obtains the three-dimensional distribution of the internal structure of the measured object
In order to further improve the imaging speed and realize quick imaging, the invention also provides a parallel frequency domain terahertz coherent tomography method, which is characterized in that a cylindrical mirror replaces a lens, and an area array type terahertz detector replaces a linear array type terahertz detector; the detection waves in the parallel frequency domain terahertz coherent tomography method are focused by a cylindrical mirror into line beams to be incident on a measured object to form a line of detection points, the detection waves with different frequencies are incident on different depth positions of the measured object to generate back scattering at the different depth positions, and the detection waves back scattered to the back interfere with the reference waves reflected back with the same frequency; interference signals carrying different frequency information on a line of detection points are focused after being subjected to grating frequency division and are incident on an area array type terahertz detector, one dimension of the area array type terahertz detector records spectral information distribution of a measured object along the depth direction, and the other dimension of the area array type terahertz detector samples a line of detection point information of a line beam focusing position; further obtaining all information data of the measured object through one-dimensional scanning in the direction perpendicular to the line wave beam; and finally obtaining the three-dimensional distribution of the internal structure of the measured object through subsequent image processing and three-dimensional reconstruction.
In order to achieve the above object, the present invention may adopt a parallel frequency domain terahertz coherent tomography system, including: the system comprises a broadband terahertz source modulation system, a Michelson interferometer, a spectrum measurement system and a scanning control and image data processing system.
The michelson interferometer includes: the device comprises a beam splitter, a reference mirror, a cylindrical mirror and a one-dimensional translation table; after entering a Michelson interferometer, a broadband terahertz wave emitted by a broadband terahertz source modulation system is divided into a reference wave and a detection wave by a beam splitter; the reference wave returns to the beam splitter after being reflected by the reference mirror; the detection wave is focused by the cylindrical mirror into a line of beam to be incident on the object to be detected to form a line of detection points, the depth of the detection wave entering the object to be detected is related to the frequency, the detection wave scattered back to the beam splitter returns to be combined with the reference wave and superposed together to generate an interference signal.
The spectrum measuring system includes: the terahertz detector comprises a reflection grating, a parabolic mirror and an area array type terahertz detector, wherein the area array type terahertz detector is arranged into terahertz detector pixels in a two-dimensional array; interference signals carrying different frequency information on a row of detection points are received by a frequency spectrum measuring system, and the interference signals are divided by a reflection grating according to the frequency; the parabolic mirror focuses the interference signal after frequency division on the area-array terahertz detector, one dimension of the area-array terahertz detector records the spectral information distribution of the measured object along the depth direction, and the other dimension of the area-array terahertz detector samples a line of detection point information of the line beam focusing position; the method comprises the steps of controlling a measured object to be scanned in a one-dimensional transverse direction perpendicular to a line beam direction, and simultaneously carrying out coherent information acquisition on each section, so as to obtain all information of the measured object; and sending the data to a scanning control and image data processing system.
In general, the invention provides a frequency domain terahertz coherent tomography method for realizing three-dimensional imaging of a measured object, and compared with other imaging methods, the method has the following advantages:
1) the frequency domain terahertz coherent tomography method uses a broad spectrum light source, depth structure information is obtained by performing inverse Fourier transform on backscattered spectrum information of different depths of a measured object, all the depth structure information of the measured object is synchronously obtained, and time-consuming depth scanning is replaced by spectrum measurement, so that depth scanning is not needed, and the imaging speed is improved;
2) the method can obtain high image acquisition speed and longitudinal resolution under the condition of high signal-to-noise ratio, and compared with the defects that the signal-to-noise ratio of a time-domain terahertz coherent tomography method is contradictory to the image acquisition speed and the longitudinal resolution, the signal-to-noise ratio of a frequency-domain terahertz coherent tomography method is irrelevant to the bandwidth of a light source and the longitudinal scanning depth, so that the high image acquisition speed and the longitudinal resolution can be obtained under the condition of high signal-to-noise ratio;
3) compared with a frequency domain terahertz coherent tomography method, the parallel frequency domain terahertz coherent tomography method can synchronously acquire two-dimensional interference spectrum information of a longitudinal section without two-dimensional scanning of a measured object, and the image acquisition speed is mainly determined by the reading speed and the one-dimensional scanning speed of the area array type terahertz detector, so that the overall imaging speed can be obviously improved.
Drawings
FIG. 1 is an overall optical path diagram of a frequency-domain terahertz coherent tomography system of the present invention;
FIG. 2 is an overall optical path diagram of the parallel frequency domain terahertz coherent tomography system of the present invention;
FIG. 3 is a schematic diagram of a top view structure of a linear array type terahertz detector in the frequency domain terahertz coherent tomography system according to the present invention;
FIG. 4 is a schematic view of a top view structure of a planar array terahertz detector in the parallel frequency domain terahertz coherent tomography system of the invention
Detailed Description
The invention will be further elucidated by means of specific embodiments in the following with reference to the drawing.
Example one
As shown in fig. 1, for the frequency-domain terahertz coherent tomography method, an imaging system can be implemented by using a frequency-domain terahertz coherent tomography system, and the system includes a broadband terahertz source modulation system 1, a michelson interferometer 2, a spectrum measurement system 3, and a scanning control and image data processing system 4. The broadband terahertz source modulation system 1 includes: a broadband terahertz source 101, a first parabolic mirror 102 and a second parabolic mirror 103; the michelson interferometer 2 includes: a beam splitter 201, a reference mirror 202, a lens 203 and a two-dimensional translation stage 205; the frequency spectrum measuring system 3 comprises a reflection grating 301, a parabolic mirror 302 and a linear array type terahertz detector 5, wherein the overlooking structure of the linear array type terahertz detector 5 is shown in fig. 3, and a pixel 501, a pixel 502, a pixel 503, a pixel 504, a pixel 505, a pixel 506, a pixel 507 and a pixel 508 respectively and correspondingly detect interference signal data with different frequencies; the scan control and image data processing system 4 employs a computer 401, including a scan control system and an image data processing system. The two-dimensional translation stage 205 moves in the x-y plane with the depth of the object being measured along the z-direction. The imaging method specifically comprises the following steps:
1) the broadband terahertz source 101 emits broadband terahertz waves, and the broadband terahertz waves are collimated by the first parabolic mirror 102 and the second parabolic mirror 103 and then enter the Michelson interferometer 2;
2) the broadband terahertz wave is divided into two paths in proportion by a beam splitter 201 in the Michelson interferometer 2, namely a reference wave and a detection wave; the reference wave is reflected by the reference mirror 202 and then returns to the beam splitter 201; the probe wave is focused into a spot beam through the lens 203 and is incident on the object to be measured 204, and the depth of the probe wave entering the object to be measured is related to the frequency; the detection wave carrying the depth information of the object to be measured returns to the beam splitter 201, and is combined with the reference wave and superposed together to generate an interference signal;
3) an interference signal carrying depth information of a measured object is received by the frequency spectrum measuring system 3, frequency-divided by the reflection grating 301, and focused on the linear array type terahertz detector 5 by the parabolic mirror 302;
4) the scanning control and image data processing system 4 controls the x-y direction movement of the two-dimensional translation stage 205 to realize the continuous scanning of the object 204 to be measured on the two-dimensional plane; the linear array terahertz detector 5 simultaneously acquires coherent information to obtain all information data of the object to be measured, and sends the data to the scanning control and image data processing system 4;
5) and performing subsequent data processing in the computer 401, performing three-dimensional reconstruction, and finally obtaining the three-dimensional distribution of the internal structure of the measured object.
In the embodiment, the broadband terahertz source 101 is a broadband continuously adjustable counter-wave oscillator type BWO terahertz light source, the bandwidth covers 160GHz to 2100GHz, and the maximum power of the fundamental frequency of the light source can reach 50 mW; the beam splitter 201 is made of high-resistance silicon material, and the transmission reflectance is 54:46 (%); the linear array type terahertz detector 5 can be a linear array type terahertz detector, and can also be one or more detection pixel arrays of an area array type terahertz detector, and the working principle can be photoelectric type or thermoelectric type.
Example two
As shown in fig. 2, for the parallel frequency domain terahertz coherent tomography method, a parallel frequency domain terahertz coherent tomography system can be used to realize imaging, and the system includes: the system comprises a broadband terahertz source modulation system 1, a Michelson interferometer 2, a spectrum measurement system 3 and a scanning control and image data processing system 4. The broadband terahertz source modulation system comprises: a broadband terahertz source 101, a first parabolic mirror 102 and a second parabolic mirror 103; the michelson interferometer includes: a beam splitter 201, a reference mirror 202, a cylindrical mirror 206 and a one-dimensional translation stage 207; the frequency spectrum measurement system comprises a reflection grating 301, a parabolic mirror 302 and an area array type terahertz detector 6, wherein the overlooking structure of the area array type terahertz detector 6 is shown in fig. 4, pixels 601 and 606 respectively and correspondingly detect interference signal data of different detection points at the same frequency, and the pixel 601 and the pixel 605 respectively and correspondingly detect the interference signal data of the same detection point at different frequencies; the scan control and image data processing system employs a computer 401, including a scan control system and an image data processing system. The imaging method specifically comprises the following steps:
1) the broadband terahertz source 101 emits broadband terahertz waves, and the broadband terahertz waves are collimated by the first parabolic mirror 102 and the second parabolic mirror 103 and then enter the Michelson interferometer 2;
2) the broadband terahertz wave is divided into two paths in proportion by a beam splitter 201 in the Michelson interferometer 2, namely a reference wave and a detection wave; the reference wave is reflected by the reference mirror 202 and then returns to the beam splitter 201; the probe waves are focused into a line beam by the cylindrical mirror 206 and are incident on the object to be detected 204 to form a line of probe points, and the depth of the probe waves entering the object to be detected is related to the frequency; the backscattered detection waves return to the beam splitter 201, are combined with the reference waves, and are superposed to generate interference signals carrying information of different frequencies on a row of detection points;
3) the interference signal is received by the frequency spectrum measuring system 3, frequency-divided by the reflection grating 301, and focused on the area array type terahertz detector 6 by the parabolic mirror 302;
4) the scanning control and image data processing system 4 controls the one-dimensional translation table to realize one-dimensional transverse scanning (such as the x direction or the y direction) of the measured object in the direction perpendicular to the linear beam direction, the area array terahertz detector simultaneously acquires coherent information of each section, so that all information data of the measured object are obtained, and the data are sent to the scanning control and image data processing system 4;
5) the computer 401 performs subsequent data processing, performs three-dimensional reconstruction, and finally obtains three-dimensional distribution of the internal structure of the object to be measured.
In the embodiment, the broadband terahertz source 101 is a broadband continuously adjustable counter-wave oscillator type BWO terahertz light source, the bandwidth covers 160GHz to 2100GHz, and the maximum power of the fundamental frequency of the light source can reach 50 mW; the beam splitter 201 is made of high-resistance silicon material, and the transmission reflectance is 54:46 (%); the cylindrical lens 206 may be a lens made of high density polyethylene material, or a lens made of high-resistance silicon material; the working principle of the area array type terahertz detector 6 can be photoelectric type or thermoelectric type.
Finally, it is noted that the disclosed embodiments are intended to aid in further understanding of the invention, but those skilled in the art will appreciate that: various substitutions and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.
Claims (10)
1. A frequency domain terahertz coherent tomography method is characterized by comprising the following implementation modes: the wide-spectrum light source emits a broadband terahertz wave which is divided into a detection wave and a reference wave; the probe wave is focused into a spot beam to be incident on the measured object, and the reference wave is reflected by the original path. The detection waves with different frequencies are incident to different depth positions of a measured object, back scattering occurs at the different depth positions, and the optical path difference between the detection waves carrying the depth information of the measured object and the reference waves which are back scattered is constant, so that the detection waves with the same frequency and the reference waves are interfered; an interference signal carrying depth information of a measured object is subjected to grating frequency division and then focused on a linear array type terahertz detector, and different pixels of the terahertz detector detect amplitude information of terahertz interference signals with different frequencies and different positions; further, the object to be measured is continuously scanned on a two-dimensional plane, and the coherent information of each detection point is acquired at the same time, so that all the information data of the object are obtained; and reconstructing a three-dimensional image through subsequent image processing, and finally obtaining the three-dimensional distribution of the internal structure of the measured object.
2. The method of claim 1, wherein three-dimensional terahertz imaging can be achieved by a frequency-domain terahertz coherence tomography system, the frequency-domain terahertz coherence tomography system comprising: the system comprises a broadband terahertz source modulation system, a Michelson interferometer, a spectrum measurement system, a scanning control system and an image data processing system.
3. The frequency domain terahertz coherence tomography system of claim 2, wherein the broadband terahertz source modulation system comprises: the terahertz source comprises a broadband terahertz source, a first parabolic mirror and a second parabolic mirror; the broadband terahertz source emits broadband terahertz waves, and the broadband terahertz waves are collimated by the first parabolic mirror and the second parabolic mirror and then enter the Michelson interferometer.
4. The frequency-domain terahertz coherence tomography system of claim 2, wherein the michelson interferometer comprises: the device comprises a beam splitter, a reference mirror, a lens and a two-dimensional translation stage; the broadband terahertz wave is divided into two paths by a beam splitter, namely a reference wave and a detection wave; the reference wave is vertically reflected back to the beam splitter through the fixed reference mirror; the detection waves are focused into point beams by the lens and are incident on the object to be detected, and the detection waves with different frequencies are incident at different depths of the object to be detected; the detection wave carrying the depth information of the object to be measured returns to the beam splitter and is superposed with the reference wave to generate interference signals carrying the depth information of the object to be measured.
5. The frequency domain terahertz coherent tomography system of claim 2 wherein the spectral measurement system comprises a reflection grating, a parabolic mirror and a linear array terahertz detector consisting of one-dimensional arranged terahertz detector pixels.
6. The spectral measurement system of claim 5, wherein the spectral measurement system receives michelson interferometer interference signals, and a reflection grating separates the interference signals by frequency; the parabolic mirror focuses the interference signals after frequency division on the linear array type terahertz detector, and the interference signals of different depth information are incident on different pixels of the linear array type terahertz detector. The continuous scanning of the measured object on a two-dimensional plane is realized by moving the two-dimensional translation table, and the coherent information acquisition of each detection point is carried out simultaneously, so that all information data of the measured object are obtained.
7. The frequency domain terahertz coherent tomography method as claimed in claim 1, wherein the lens is replaced by a cylindrical lens, the linear terahertz detector is replaced by an area terahertz detector, forming a parallel frequency domain terahertz coherent tomography method; the detection waves in the parallel frequency domain terahertz coherent tomography method are focused by a cylindrical mirror into line beams to be incident on a measured object to form a line of detection points, the detection waves with different frequencies are incident on different depth positions of the measured object to generate back scattering at the different depth positions, and the optical path difference between the detection waves back scattered and the reference waves reflected back at the same frequency is constant, so that interference is generated between light wave components at the same frequency; interference signals carrying different frequency information on a line of detection points are focused on an area array type terahertz detector after being subjected to grating frequency division, one dimension of the area array type terahertz detector records spectral information distribution of a measured object along the depth direction, and the other dimension of the area array type terahertz detector samples a line of detection point information of a line beam focusing position; further, by one-dimensional scanning in the direction perpendicular to the line beam and simultaneously carrying out coherent information acquisition on each section, all information data of the object to be measured are obtained; and finally obtaining the three-dimensional distribution of the internal structure of the measured object through subsequent image processing and three-dimensional reconstruction.
8. The parallel frequency domain terahertz coherent tomography method according to claim 7, characterized in that a parallel frequency domain terahertz coherent tomography system can be adopted to realize three-dimensional imaging, the imaging system comprises: the system comprises a broadband terahertz source modulation system, a Michelson interferometer, a spectrum measurement system and a scanning control and image data processing system.
9. The parallel frequency-domain terahertz coherence tomography system of claim 8, wherein the michelson interferometer comprises: the device comprises a beam splitter, a reference mirror, a cylindrical mirror and a one-dimensional translation table; broadband terahertz waves emitted by a broadband terahertz source are divided into reference waves and detection waves through a beam splitter; the reference wave returns to the beam splitter after being reflected by the reference mirror; the detection waves are focused into a line of beam beams through the cylindrical mirror and are incident on an object to be detected to form a line of detection points, the detection waves with different frequencies are incident to different depths of the object to be detected and are subjected to back scattering, the detection waves which are back scattered back return to the beam splitter and are superposed with the reference waves to generate interference.
10. The parallel frequency domain terahertz coherent tomography system of claim 8, wherein the spectral measurement system comprises a reflection grating, a parabolic mirror and a planar array terahertz detector, the planar array terahertz detector is terahertz detector pixels arranged in a two-dimensional array; the spectrum measurement system receives interference signals carrying different frequency information on a row of detection points, and the reflection grating divides the frequency of the interference signals according to the frequency; the parabolic mirror focuses the interference signal after frequency division on the area-array terahertz detector, one dimension of the area-array terahertz detector records the spectral information distribution of the measured object along the depth direction, and the other dimension of the area-array terahertz detector samples a line of detection point information of the line beam focusing position. The one-dimensional scanning of the measured object in the direction perpendicular to the line beam is realized by controlling the one-dimensional translation table, and the coherent information acquisition of each section is carried out simultaneously, so that all depth information data of the measured object are obtained.
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