CN108801969B - Terahertz detection device - Google Patents
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Abstract
The invention relates to the technical field of safety inspection, and provides a terahertz detection device which comprises a laser system for generating laser, a dispersion compensation system for performing dispersion compensation on the laser, an optical beam splitter, an optical fiber stretching system for performing delay scanning on the laser, a sample detection system for generating and receiving terahertz waves and detecting a sample to be detected, and a data processing system for analyzing test data, wherein the laser system is connected with the dispersion compensation system through an optical fiber; not only can discern multiple material, can automatic identification wait to detect the sample moreover to improve safety inspection's efficiency greatly, satisfied the user demand of different scenes.
Description
Technical Field
The invention relates to the technical field of safety inspection, in particular to a terahertz detection device.
Background
The detection of flammable and explosive materials is related to the safety of public places, so that in places with dense people flow, such as airports, subways, bus stations and the like, safety inspection is generally required so as to eliminate hidden dangers. The liquid dangerous goods are usually in a liquid state at normal temperature, and have the characteristics of uniform components, good fluidity, convenient transportation, easy manufacture and camouflage, strong concealment and the like; in addition, the raw materials of the liquid hazardous materials may be transported separately, or may be mixed with various compounds, thereby increasing the difficulty of safety inspection work.
At present, the common way to eliminate inflammable and explosive materials is: liquid, which is not harmful to the passengers when the passengers drink the liquid, but the method has low efficiency and is easy to cause the passengers to have a feeling of conflict; the solid type, the security check machine provided in the security check area, requires the staff to simply judge whether it is contraband by means of its profile information. At present, in security inspection equipment at home and abroad, although an automatic identification system aiming at major dangerous substances such as explosives, drugs and the like exists, the technology is still imperfect and the price is high. In addition, in the face of a large amount of common dangerous goods in people's daily life, but do not have any kind of safety inspection product to reach automatic identification, all need carry out semi-manual identification to it, even open a packet inspection manual identification.
The existing safety detection equipment comprises technologies such as X-ray, Raman spectrum technology, dielectric constant detection technology and the like. However, the X-ray is strong to the organism damage, for those liquid dangerous goods that are not easy to volatilize, especially the liquid dangerous goods in the closed container, basically unable to detect, for the metal detection, it is easy to be disturbed by the metal sundries and increase the false alarm rate; the laser Raman spectrum adopts a low-power laser light source, and laser beams can penetrate through transparent bottled liquid and cannot be used for a non-transparent container; the dielectric constant technology has a limited range of applications, is generally used for detecting liquid substances in containers, requires close proximity detection of samples, and has limited penetration capability.
The above disadvantages need to be improved.
Disclosure of Invention
The invention aims to provide a terahertz detection device, which aims to solve the technical problems that in the prior art, the safety inspection efficiency is low, and the types of detected dangerous goods are limited.
In order to achieve the purpose, the invention adopts the technical scheme that: the terahertz detection device comprises a laser system for generating laser, a dispersion compensation system for performing dispersion compensation on the laser, an optical beam splitter, an optical fiber stretching system for performing delay scanning on the laser, a sample detection system for generating and receiving terahertz waves and detecting a sample to be detected, and a data processing system for analyzing test data, wherein the laser system is connected with the dispersion compensation system through an optical fiber, the dispersion compensation system is connected with the optical beam splitter through an optical fiber, the optical beam splitter is simultaneously connected with the optical fiber stretching system and the sample detection system through an optical fiber, the optical fiber stretching system is connected with the sample detection system through an optical fiber, and the sample detection system is connected with the data processing system.
Furthermore, the laser system comprises a laser, a saturable absorber, an optical coupler, a gain fiber and a fiber grating which are connected in sequence, wherein a pumping source is further connected to one side of the optical coupler connected with the saturable absorber.
Further, the laser system further comprises a repetition frequency locking mechanism, the repetition frequency locking mechanism is used for locking the frequency of the laser generated by the laser, the laser is provided with piezoelectric ceramics used for adjusting the cavity length of a laser cavity of the laser, the repetition frequency locking mechanism is connected with the piezoelectric ceramics, and meanwhile, the repetition frequency locking mechanism is connected with the laser.
Further, repetition frequency locking mechanical system is including the photoelectric detector, band-pass filter, mixer, loop filter and the high-pressure amplifier that connect gradually, photoelectric detector with the laser instrument links to each other, the high-pressure amplifier with piezoceramics connects, the mixer is connected one side of band-pass filter still is connected with the reference signal generator, the reference signal generator locks on the rubidium clock.
Further, the dispersion compensation system includes an optical fiber ring mechanism for adjusting the laser transmission direction, a first chirped fiber grating and a second chirped fiber grating for performing dispersion compensation on the laser, where the dispersion compensation amount is opposite, the optical fiber ring mechanism is provided with an input end for connecting with an optical fiber, the optical fiber is used for transmitting the laser, the first chirped fiber grating and the second chirped fiber grating are both connected with the optical fiber ring mechanism, the laser sequentially passes through the first chirped fiber grating and the second chirped fiber grating and then exits from the optical fiber ring mechanism, and absolute values of the dispersion compensation amounts of the first chirped fiber grating and the second chirped fiber grating are not equal to each other.
Further, the sample detection system comprises a photoconductive transmitting antenna for generating terahertz waves, a photoconductive receiving antenna for receiving the terahertz waves and an optical component for focusing the terahertz waves, wherein the photoconductive transmitting antenna is connected with the optical beam splitter, the photoconductive receiving antenna is connected with the optical fiber stretching system, and the photoconductive receiving antenna is connected with the data processing system.
Further, the optical assembly comprises a first lens group used for focusing the terahertz waves generated by the photoconductive transmitting antenna on the sample to be detected and a second lens group used for focusing the terahertz waves passing through the sample to be detected on the photoconductive receiving antenna.
Furthermore, the optical fiber stretching system comprises a first coupler for splitting laser, two optical fiber stretchers, a second coupler for combining laser, a photoelectric detector for converting optical signals into electric signals and a display device for converting the electric signals into visual patterns, wherein the optical beam splitter is connected with the first coupler through optical fibers, the first coupler is simultaneously connected with the two optical fiber stretchers through optical fibers, the two optical fiber stretchers are both connected with the second coupler through optical fibers, the second coupler is connected with the photoelectric detector through optical fibers, and the photoelectric detector is connected with the display device.
Furthermore, a phase-locked amplifying module is arranged between the photoconductive receiving antenna and the data processing mechanism.
Further, the data processing system comprises a data processing module and a computer for identifying the sample to be detected, the data processing module is connected with the computer through a network cable, and the data processing module is connected with the phase-locked amplification module.
The terahertz detection device provided by the invention has the beneficial effects that:
(1) the terahertz time-domain spectroscopy technology has the characteristics of capability of carrying out nondestructive detection and sample detection, convenience and rapidness in acquiring substance information, low requirement on external conditions and the like, so that the terahertz detection device can identify various substances, and the application scene of the terahertz detection device is expanded.
(2) The terahertz detection device can automatically identify a sample to be detected without manual auxiliary identification, so that the efficiency of safety inspection is greatly improved, and the use requirements of different scenes are met.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed for the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic system diagram of a terahertz detection device according to an embodiment of the present invention;
fig. 2 is a schematic diagram illustrating a laser mode locking principle of a terahertz detection device according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a repetition frequency locking mechanism of a terahertz detection device according to an embodiment of the present invention;
fig. 4 is a schematic structural diagram of a dispersion compensation system of a terahertz detection apparatus according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of another dispersion compensation system of a terahertz detection apparatus according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of a negative-dispersion chirped fiber grating of a dispersion compensation system of a terahertz detection device according to an embodiment of the present invention;
fig. 7 is a schematic structural diagram of a positively-dispersive chirped fiber grating of a dispersion compensation system of a terahertz detection apparatus according to an embodiment of the present invention;
FIG. 8 is a schematic structural diagram of an optical fiber stretching system of a terahertz detection device according to an embodiment of the present invention;
FIG. 9 is a schematic structural diagram of an optical fiber stretcher of a terahertz detection device provided in an embodiment of the present invention;
fig. 10 is a schematic structural diagram of a phase-locked amplification module of a terahertz detection apparatus according to an embodiment of the present invention;
FIG. 11 is a schematic view of a terahertz detection device provided by an embodiment of the present invention for measuring a beverage;
fig. 12 is a schematic waveform diagram of a reflected pulse when the terahertz detection device provided by the embodiment of the invention measures a sample to be detected.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
Referring to fig. 1, a terahertz detection device includes a laser system 1 for generating laser, a dispersion compensation system 2 for performing dispersion compensation on the laser, an optical splitter 3, an optical fiber stretching system 4 for performing delay scanning on the laser, a sample detection system 5 for emitting and receiving terahertz waves and detecting a sample 6 to be detected, and a data processing system 7 for analyzing test data, where the laser system 1 is connected with the dispersion compensation system 2 through an optical fiber 10, the dispersion compensation system 2 is connected with the optical splitter 3 through an optical fiber 10, the optical splitter 3 is simultaneously connected with the optical fiber stretching system 4 and the sample detection system 5 through an optical fiber 10, the optical fiber stretching system 4 is connected with the sample detection system 5 through an optical fiber 10, and the sample detection system 5 is connected with the data processing system 7.
The working principle of the terahertz detection device provided by the embodiment is as follows: firstly, laser generated by a laser system 1 is transmitted to a dispersion compensation system 2 through an optical fiber 10, and dispersion compensation is performed in advance through the dispersion compensation system 2; then laser is divided into two beams after passing through the optical beam splitter 3, one beam of laser is used for emitting terahertz waves after reaching the sample detection system 5, the terahertz waves carry information of the sample 6 to be detected after irradiating the sample 6 to be detected, and then the terahertz waves carrying the information of the sample 6 to be detected are received by the sample detection system 5; the other laser beam passes through the optical fiber stretching system 4 and then reaches the sample detection system 5, and is coupled with terahertz waves carrying information of a sample 6 to be detected to form test data; and then the test data is transmitted to a data processing system 7 for processing, and the sample 6 to be detected is identified, so that the judgment and the alarm of inflammable and explosive articles are realized.
Due to the unique property of terahertz waves, the terahertz time-domain spectroscopy technology has the following advantages:
(1) bandwidth: having a bandwidth of from about 0.1THz to about 5 THz.
(2) The signal-to-noise ratio is high: the signal-to-noise ratio of the terahertz time-domain spectroscopy system can reach as high as 10 when the terahertz time-domain spectroscopy system is less than 3THz4The method is much higher than the Fourier transform infrared spectroscopy technology and has better stability.
(3) Nondestructive testing and sample detection can be carried out: the terahertz time-domain spectroscopy technology can be used for effectively detecting various physical information, chemical information and other information of a sample to be detected, which are reflected in a terahertz waveband, so that the terahertz time-domain spectroscopy technology can be used for qualitative identification and analysis of substances. In addition, due to the safety and penetrability of the terahertz waves, the terahertz waves are suitable for nondestructive detection of biological tissues. The terahertz time-domain spectroscopy also has the characteristics of high detection sensitivity, capability of working stably at room temperature and the like, so that the terahertz time-domain spectroscopy can be widely applied to detection of samples.
(4) The media information acquisition is convenient and fast: by utilizing the terahertz time-domain spectroscopy technology, various material information such as amplitude and phase information of dielectric materials, biomacromolecules, semiconductor materials and the like can be conveniently and rapidly acquired, and carrier information in conductive materials can also be directly reflected; meanwhile, due to the coherence of the terahertz time-domain spectrum, the electric field waveform contains complete information such as the intensity, the phase, the time and the like of the terahertz pulse, and the terahertz pulse is converted into a spectrum signal through Fourier transform, so that an absorption spectrum and a dispersion spectrum can be obtained.
(5) The requirement on external conditions is low: the terahertz time-domain spectroscopy system can work at room temperature, and a complex refrigeration system is omitted.
(6) Non-contact measurement: terahertz radiation can directly reflect information of current carriers in the conductive material, so that the terahertz time-domain spectroscopy system is more convenient and effective than non-contact measurement based on Hall (Hall) effect.
(7) Safety and harmlessness: the single photon energy of the terahertz wave is low, 1THz corresponds to 4.1meV, the components of the detected substance cannot be damaged when the substance is detected, and the terahertz wave is safe for operators.
The terahertz detection device provided by the embodiment has the beneficial effects that:
(1) the terahertz time-domain spectroscopy technology has the characteristics of capability of carrying out nondestructive detection and sample detection, convenience and rapidness in acquiring substance information, low requirement on external conditions and the like, so that the terahertz detection device can identify various substances and expand the application scene of the terahertz detection device.
(2) The terahertz detection device can automatically identify the sample 6 to be detected without manual auxiliary identification, so that the efficiency of safety inspection is greatly improved, and the use requirements of different scenes are met.
The terahertz detection device provided by the embodiment is internally provided with the lithium battery, can conveniently carry out outdoor detection, and can prevent the situation that the detection cannot be carried out due to instantaneous power failure and can protect equipment. The bottom of the terahertz detection device is also provided with universal wheels, so that the terahertz detection device can be moved at will, and detection can be performed at any position according to needs.
Referring to fig. 2, the laser system 1 further includes a laser 11, a saturable absorber 12, an optical coupler 13, a gain fiber 14, and a fiber grating 15, which are connected in sequence, and a pump source 16 is connected to a side of the optical coupler 13 connected to the saturable absorber 12. Preferably, the laser 11 is a femtosecond laser, so that femtosecond laser pulses can be generated.
Since the saturable absorber 12 has a large absorption for weak light and a small absorption for strong light, when the intensity of the laser light generated by the laser 11 is too low, the laser light is absorbed by the saturable absorber 12, and when the intensity of the laser light generated by the laser 11 becomes high, the laser light penetrates through the saturable absorber 12, so that the output power of the laser 11 can be ensured to meet the requirement by using the saturable absorber 12. In the present embodiment, the output power of the laser 11 is higher than 80mW, and the pulse width of the femtosecond laser pulse is less than 100 fs.
The pump source 16 and the laser passing through the saturable absorber 12 are coupled in the optical coupler 13, and the coupled laser is gained through the gain fiber 14 and filtered through the fiber grating 15, so that the laser with a specific wavelength can be obtained, and the use requirement can be met.
Referring to fig. 3, the laser system 1 further includes a repetition frequency locking mechanism, which is used for locking the frequency of the laser generated by the laser 11; the laser 11 is provided with piezoelectric ceramics, preferably PZT piezoelectric ceramics 111, which can be used for adjusting the cavity length of the laser cavity, and the PZT piezoelectric ceramics work under the control of the PZT drive 110; the repetition frequency locking mechanism is connected to PZT piezoelectric ceramics 111, and the repetition frequency locking mechanism is connected to the laser 11. A small part of laser light generated by the laser enters the repetition frequency locking mechanism after being split by the coupler, a corresponding high-voltage signal is generated after passing through the repetition frequency locking mechanism, and then the high-voltage signal controls the PZT piezoelectric ceramic 111 to move through the PZT drive 110, so that the cavity length of a laser cavity is changed, the frequency of the laser is adjusted, and the repetition frequency of the output laser is stable.
In the present embodiment, the repetition frequency locking mechanism includes a photodetector 171, a band pass filter 172, a mixer 173, a loop filter 174, and a high voltage amplifier 175, which are connected in this order, the photodetector 171 is connected to the laser 11, the high voltage amplifier 175 is connected to the PZT piezoelectric ceramic 111, a reference signal generator 176 is connected to the mixer 173 on the side connected to the band pass filter 172, and the reference signal generator 176 is locked to a rubidium clock 177.
A small portion of the laser light generated by the femtosecond laser is split by the coupler, and then is irradiated onto the photodetector 171 and captured by the photodetector 171. The output frequency of the photodetector 171 is an integer multiple of the repetition frequency (denoted as Nf)rep) May be filtered by the band pass filter 172 to obtain a signal of a desired frequency (i.e., Nf)repSignal(s) of (a). Preferably, N is 4, i.e. the output frequency of the photodetector 171 is 4 times the repetition frequency, and the fourth harmonic of the repetition frequency is obtained after passing through the band-pass filter 172; of course, higher harmonics can also be obtained; in fact, the higher the number of harmonics of the mixing input, the more sensitive the system is to frequency variations, so that a closed-loop control system can be formed with a higher degree of stability.
The signal having passed through the band pass filter 172 and the reference signal generated by the reference signal generator 176 enter the mixer 173 to be mixed, and a difference frequency signal can be obtained. The reference signal generator 76 is locked to the rubidium clock 177 and sets the frequency of the reference signal, which in this embodiment is 1000MHz, according to the repetition frequency to be locked. The difference frequency signal enters the loop controller 174 and then outputs a compensation control signal, the compensation control signal passes through the high-voltage amplifier 175 to obtain a high-voltage signal for controlling the PZT drive 110, so that the PZT piezoelectric ceramic 111 is controlled, the cavity length of the laser cavity is changed through the micro displacement of the PZT piezoelectric ceramic 111, so that the micro fluctuation of the repetition frequency can be inhibited, and finally the upper reference signal (namely, the upper reference signal is locked) is dynamically tracked, so that the repetition frequency f is enabled to berepThe same stability as that of rubidium clock 177 is obtained, and the repetition frequency of the output laser is ensured to be stable.
The loop controller 174 is the core of the entire repetition frequency locking mechanism, and not only has the function of low-pass filtering, but also can improve the dynamic response characteristic and stability characteristic of the system.
Further, the loop controller 174 includes a proportional integral controller and a dc bias circuit, wherein the function of the proportional integral controller is to improve the dynamic response characteristic of the system, and the dc bias circuit is to find a suitable frequency point before locking, so as to provide for fast locking. The proportional-integral controller comprises a bandwidth selection part, an integral link part and a Low Frequency Gain Limit (LFGL for short); the bandwidth selection part is used for selecting proper bandwidth, switching the loop to the position of the broadband when the loop is not locked, so that the frequency can be swept quickly, switching the loop to the position of the narrow band when the loop is locked, reducing errors and improving the locking performance; the low-frequency gain limiting part is used for limiting low-frequency gain, preventing integral saturation caused by improper conditions at the locking moment, limiting the low-frequency gain before locking, searching a locking point, and removing the limitation after locking so as to enter a pure integral link. The setting makes the operation of the repeated frequency locking process more flexible, is beneficial to quickly finding the locking point and efficiently and accurately completing the locking. The stability of the repetition frequency of the commonly used femtosecond laser is about 20Hz (namely, the repetition frequency is +/-20 Hz), and in the embodiment, the repetition frequency of the femtosecond laser can be stabilized at 100MHz +/-1 mHz, so that the stability of the femtosecond laser is greatly improved.
Referring to fig. 4, further, the dispersion compensation system 2 includes an optical fiber ring mechanism for adjusting a laser transmission direction, a first chirped fiber grating 221 and a second chirped fiber grating 222 for performing dispersion compensation on the laser, where the first chirped fiber grating 221 and the second chirped fiber grating 222 have opposite dispersion compensation amounts, the optical fiber ring mechanism is provided with an input end for connecting with the optical fiber 10, the optical fiber 10 is used for transmitting the laser 100, the first chirped fiber grating 221 and the second chirped fiber grating 222 are both connected with the optical fiber ring mechanism, the laser 100 sequentially passes through the first chirped fiber grating 221 and the second chirped fiber grating 222 and then exits from the optical fiber ring mechanism, and absolute values of the dispersion compensation amounts of the first chirped fiber grating 221 and the second chirped fiber grating 222 for the laser 100 are not equal to each.
The operating principle of the dispersion compensation system 2 is as follows: firstly, the optical fiber 10 for transmitting the laser light 100 is connected with the optical fiber ring mechanism, and simultaneously, the first chirped fiber grating 221 and the second chirped fiber grating 222 are sequentially connected with the optical fiber ring mechanism, so that the laser light 100 enters the optical fiber ring mechanism through the optical fiber 3, then, the laser light sequentially passes through the first chirped fiber grating 221 and the second chirped fiber grating 222 for dispersion compensation, and then, the laser light is emitted from the optical fiber ring mechanism. Since the dispersion compensation of the first chirped fiber grating 221 and the second chirped fiber grating 222 are opposite and the dispersion compensation amount is not equal, after the laser 100 passes through the first chirped fiber grating 221 and the second chirped fiber grating 222 in sequence, the total dispersion compensation amount is the sum of the dispersion compensation amount of the first chirped fiber grating 221 and the dispersion compensation amount of the second chirped fiber grating 222, and the total dispersion compensation amount can reach the fs/nm (femtosecond/nanometer) level, so that the micro dispersion amount of the femtosecond laser can be compensated.
The beneficial effect that so set up lies in: because the first chirped fiber grating 221 and the second chirped fiber grating 222 which are used for performing dispersion compensation on the laser 100 and have opposite dispersion compensation are arranged, after the laser 100 sequentially passes through the first chirped fiber grating 221 and the second chirped fiber grating 222, the total dispersion compensation amount can reach the magnitude of fs/nm, so that the micro dispersion amount of the femtosecond laser can be compensated, and the reliability of laser transmission can be effectively guaranteed.
Referring to fig. 4, in one embodiment, the fiber ring mechanism includes a first fiber ring device 211, the first fiber ring device 211 includes a first input port 2110, a first port 2111, a second port 2112, and a third port 2113 arranged along a laser transmission direction, the first input port 2110 is connected to the optical fiber 10, the first port 2111 is connected to the first chirped fiber grating 221, and the second port 2112 is connected to the second chirped fiber grating 222. The first chirped fiber grating 221 and the second chirped fiber grating 222 are connected through the first fiber circulator 211, so that not only can the tiny dispersion compensation of the laser 100 be realized, but also the structure is compact, and the installation is convenient. Preferably, the first fiber optic circulator 211 is a four-port fiber optic circulator.
Referring to fig. 5, in one embodiment, the fiber ring mechanism includes a second fiber circulator 212 and a third fiber circulator 213, the second fiber circulator 212 includes a second input port 2120, a fourth port 2121 and a fifth port 2122 arranged along the laser transmission direction, the third fiber circulator 213 includes a third input port 2130, a seventh port 2131 and an eighth port 2132 arranged along the laser transmission direction, the second input port 2120 is connected with the optical fiber 10, the fourth port 2121 is connected with the first chirped fiber grating 221, the fifth port 2122 is connected with the third input port 2130, and the seventh port 2131 is connected with the second chirped fiber grating 222. Preferably, the second fiber circulator 212 is a three-port fiber circulator, the third fiber circulator 213 is a three-port fiber circulator, and the second fiber circulator 212 and the third fiber circulator 213 are connected to each other by the optical fiber 103. The first chirped fiber grating 221 and the second chirped fiber grating 222 are respectively connected through the two fiber circulators, so that not only can the micro dispersion compensation of the laser 100 be realized, but also the connection can be performed as required, and the installation is more flexible.
It should be understood that the second fiber optic circulator 212 and the third fiber optic circulator 213 can be other types of fiber optic circulators, such as a four port fiber optic circulator, in which only three of the ports are used in sequence.
Referring to fig. 6 and 7, in one embodiment, the refractive index variation period in the first chirped fiber grating 221 gradually increases along the incident direction of the laser light 100, and the refractive index variation period in the second chirped fiber grating 222 gradually decreases along the incident direction of the laser light 100. Specifically, the first chirped fiber grating 221 is a negative dispersion chirped fiber grating, laser components with different frequencies in the laser 100 are totally reflected at different positions of the negative dispersion chirped fiber grating, wherein the position where the high-frequency laser component 1001 is totally reflected is deeper than the position where the low-frequency laser component 1002 is totally reflected, so that the optical path of the high-frequency laser component 1001 is greater than that of the low-frequency laser component 1002, thereby generating negative dispersion; the second chirped fiber grating 222 is a positive dispersion chirped fiber grating, laser components with different frequencies in the laser 100 are totally reflected at different positions of the positive dispersion chirped fiber grating, wherein the position where the high-frequency laser component 1001 is totally reflected is shallower than the position where the low-frequency laser component 1002 is totally reflected, so that the optical path of the high-frequency laser component 1001 is smaller than that of the low-frequency laser component 1002, thereby generating positive dispersion. In fact, in practical use, the negative dispersion chirped fiber grating can be obtained only by connecting the negative dispersion chirped fiber grating with the fiber circulator reversely.
In one embodiment, the period of the refractive index variation in the first chirped fiber grating 221 gradually decreases along the incident direction of the laser light 100, i.e., the first chirped fiber grating 221 is a positive dispersion chirped fiber grating; the period of the refractive index change in the second chirped fiber grating 222 gradually increases along the incident direction of the laser light 100, that is, the second chirped fiber grating 222 is a negative dispersion chirped fiber grating.
Since the dispersion compensation generated by the first chirped fiber grating 221 and the second chirped fiber grating 222 are opposite, when the laser light 100 sequentially passes through the first chirped grating 221 and the second chirped fiber grating 222, the sum of the dispersion compensation amount of the first chirped fiber grating 221 and the dispersion compensation amount of the second chirped fiber grating 222 is the dispersion compensation amount actually obtained by the laser light 100.
In this embodiment, the refractive index variation amplitude in the chirped fiber grating can be controlled by changing the exposure power density I and the exposure time t. The refractive index n (I, t) has the following relationship with the exposure power density I and the exposure time t:
n(I,t)＝AIatb(I)
wherein A is 3.6X 10-7Is a constant; a is 0.78 and is a constant; b is an exposure intensity dependent coefficient, and b (I) ═ 0.165+0.028exp (-I × 1 × 10)-5)。
As can be seen from the above formula, when the exposure power density I is in the range of 0-600 mW/cm under the same exposure time t2In this case, the change in the refractive index n (I, t) and the change in the exposure power density I are approximately linear, and therefore the change in the refractive index n (I, t) of the optical fiber can be well controlled by changing the exposure power density I. Obtaining the small difference of the refractive index n (I, t) in the fiber grating, and obtaining the Bragg reflection wavelength lambda of different positions in the fiber gratingBThe relationship satisfies:
λB＝2neffΛ
wherein n iseffLambda is the effective index of the fiber and lambda is the grating period.
Small difference lambda of Bragg reflection wavelength at different positionsBIt means that the wavelengths meeting the reflection condition have a slight difference at the same position of the chirped fiber grating, or the reflection positions of two beams of light having the same frequency in the chirped fiber grating have a slight difference, which is considered as a whole that the dispersion compensation amount of the chirped fiber grating has a slight difference.
The value of the exposure power density I was set to 450mW/cm2The fiber grating with dispersion compensation amount of 14ps/nm can be obtained, and the setting value of the exposure power density I is 440mW/cm2The fiber grating with dispersion compensation amount of 13.95ps/nm can be obtained. In practical use, the two fiber gratings are reversely connected with the fiber circulator, and the total dispersion compensation amount of the fiber gratings is the sum of the dispersion compensation amounts of the two fiber gratings, namely 50fs/nm (namely 0.05ps/nm), so that the total dispersion compensation amount can reach the magnitude of fs/nm, and the micro dispersion amount of the femtosecond laser can be compensated.
Further, the absolute value of the total dispersion compensation amount of the first chirped fiber grating 21 and the second chirped fiber grating 22 ranges from 50fs/nm to 100 fs/nm. Preferably, the absolute value of the total dispersion compensation amount is 50fs/nm, so that the micro dispersion amount of the femtosecond laser can be compensated, and the reliability of laser transmission is effectively guaranteed.
Referring to fig. 1, further, the sample detection system 5 includes a photoconductive transmitting antenna 51 for transmitting the terahertz wave, a photoconductive receiving antenna 52 for receiving the terahertz wave, and an optical component 52 for focusing the terahertz wave, the photoconductive transmitting antenna 51 is connected to the optical beam splitter 3, the photoconductive receiving antenna 52 is connected to the optical fiber stretching system 4, and the photoconductive receiving antenna 52 is connected to the data processing system 7. The optical assembly 53 includes a first lens group for focusing the terahertz wave generated by the photoconductive transmitting antenna 51 on the sample 6 to be detected and a second lens group for focusing the terahertz wave after passing through the sample 56 to be detected on the photoconductive receiving antenna 52.
Preferably, an optical fiber delay line 54 is further provided between the optical splitter 3 and the photoconductive transmitting antenna 51. The delay line of the existing terahertz time-domain spectrometer is a free space delay line, and most of the delay line is delayed by using a mobile platform. Such devices lack stability and are susceptible to vibration and temperature fluctuations resulting in delay misalignment. And the optical fiber delay line is adopted in the embodiment, so that the stability is high, and the integration is easy.
In this embodiment, the optical assembly 53 includes four polyolefin lenses, wherein the first lens group includes two polyolefin lenses, and the second lens group includes another two polyolefin lenses, and the polyolefin lenses may be aspheric mirrors or spherical mirrors for collimating and focusing terahertz waves. The terahertz waves emitted by the photoconductive transmitting antenna 51 firstly pass through the two polyolefin lenses of the first lens group and then are focused on the surface of the sample 6 to be detected, the terahertz waves carry the information of the sample 6 to be detected after being reflected on the surface of the sample 6 to be detected, and then the terahertz waves pass through the two polyolefin lenses of the second lens group and then are received by the photoconductive receiving antenna 52 and are converted into corresponding electric signals.
Referring to fig. 8 and 9, the conventional optical fiber stretcher stretches the optical fiber by using piezoelectric ceramics, these piezoelectric bodies are usually driven by high-power high-voltage sources, the cost of the driver is high, and the high-voltage sources are also liable to cause interference to the surrounding circuits, which is not favorable for device integration. The optical fiber drawing system 4 provided by the present embodiment includes a first coupler 43 for splitting laser light, two optical fiber drawing devices, a second coupler 44 for combining laser light, a photodetector 45 for converting optical signals into electrical signals, and a display device 46 for converting the electrical signals into visual graphics. Preferably, the display device 46 is an oscilloscope, so that the electrical signal can be converted into a visualized time-domain waveform.
For ease of description, the two fiber stretchers are referred to as a first fiber stretcher 4101 and a second fiber stretcher 4102, respectively. The optical splitter 3 is connected to a first coupler 43 through an optical fiber 10, the first coupler 43 is connected to a first optical fiber stretcher 4101 and a second optical fiber stretcher 4102 through the optical fiber 10, both the first optical fiber stretcher 4101 and the second optical fiber stretcher 4102 are connected to a second coupler 44 through the optical fiber 10, the second coupler 44 is connected to a photodetector 45 through the optical fiber 10, and the photodetector 45 is connected to a display device 46.
Here, the optical fiber 10 connected to the first optical fiber stretcher 4101 is wound around the outer surface of the first optical fiber stretcher 4101, and the optical fiber 10 connected to the second optical fiber stretcher 4102 is wound around the outer surface of the second optical fiber stretcher 4102. The end where the first fiber stretcher 4101 is located serves as a reference arm, and the end where the second fiber stretcher 102 is located serves as a signal arm.
The working principle of the optical fiber drawing system 4 provided in this embodiment is as follows:
the laser is transmitted to the first coupler through the optical fiber 10;
the laser light is divided into two bundles after passing through the first coupler 43, one bundle is transmitted to the second coupler 44 through the optical fiber 10 wound around the first optical fiber stretcher 4101, and the other bundle is transmitted to the second coupler 44 through the optical fiber 10 wound around the second optical fiber stretcher 4102;
two laser beams reaching the second coupler 44 are combined into one beam after passing through the second coupler 44, and are transmitted to the photoelectric sensor 45 through the optical fiber 10;
the photoelectric sensor 45 converts the received optical signal into an electrical signal and transmits the electrical signal to the display device 46;
the display device 46 converts the electric signal into a visual figure and displays it.
Specifically, when the stretched lengths of the optical fiber 10 at the first optical fiber stretcher 4101 as a reference arm and the optical fiber 10 at the second optical fiber stretcher 4102 as a signal arm coincide, the optical paths experienced by the two laser beams are the same, and thus the optical path difference is zero; then, a triangular wave modulation signal is applied to the second optical fiber stretcher 4102 as a signal arm so that the optical path of the laser light transmitted through the optical fiber 10 at the second optical fiber stretcher 4102 is different from the optical path of the laser light transmitted through the optical fiber 10 at the first optical fiber stretcher 4101, thereby generating an optical path difference; because the two laser beams are transmitted to the second coupler and then combined into one laser beam, the combined laser beams interfere with each other when being transmitted to the photoelectric sensor 45; the optical path difference can be obtained by analyzing the interference signal, so that the stretching length of the optical fiber can be obtained.
It should be understood that the first optical fiber stretcher 4101 is identical to the second optical fiber stretcher 4102, so that it is effectively ensured that the optical path difference is zero when the motor is in the initial state and the optical fiber 10 is wound around the first optical fiber stretcher 4101 or the second optical fiber stretcher 4102 in the same manner. The end where the first optical fiber stretcher 4101 is located is used as a reference arm to solve the problem of contrast reduction of optical effect interference fringes caused by the winding bending.
Referring to fig. 9, further, the optical fiber stretcher includes a telescopic rod 411, a motor 412 capable of driving the telescopic rod 411 to stretch and retract, and a stretching portion 413 for winding the optical fiber 10, wherein one end of the telescopic rod 411 is connected to the motor 412, and the other end of the telescopic rod 411 is connected to the stretching portion 413 and is capable of driving the stretching portion 413 to expand or contract.
The working principle of the optical fiber stretcher is as follows: firstly, fixing the motor 412, connecting the motor 412 with one end of the telescopic rod 411, then connecting the other end of the telescopic rod 411 with the telescopic part 413, and then winding the optical fiber 10 on the telescopic part 413; when the optical fiber 10 needs to be stretched, the motor 412 is powered on, and drives the telescopic rod 411 to stretch as required, so that the telescopic part 413 can be driven to expand, and the optical fiber 10 wound on the telescopic part 413 can be driven to stretch; when the optical fiber 10 does not need to be stretched, the motor 412 drives the telescopic rod 411 to retract, so as to drive the telescopic part 413 to retract, and further to retract the optical fiber 10 wound on the telescopic part 413.
The beneficial effect that so set up lies in: because the optical fiber 10 is stretched by the way that the motor 412 drives the telescopic rod 411 to move and further drives the telescopic part 413 to move, the stretching length of the optical fiber 10 can be effectively increased, the transmission length of laser in the optical fiber 10 can be further increased, and the optical path scanning range is enlarged.
Further, the telescopic part 413 comprises a first telescopic part 4131 and a second telescopic part 4132, the motor 412 is disposed between the first telescopic part 4131 and the second telescopic part 4132, the motor 412 is fixedly connected with the first telescopic part 4131, the telescopic rod 411 is also disposed between the first telescopic part 4131 and the second telescopic part 4132, the other end of the telescopic rod 411 is connected with the second telescopic part 4132, and the optical fiber 10 is wound on the outer surfaces of the first telescopic part 4131 and the second telescopic part 4132.
When the optical fiber 10 needs to be stretched, the motor 412 drives the telescopic rod 411 to stretch, and the telescopic rod 411 drives the second stretching part 4132 to move in a direction away from the first stretching part 4131, so that the whole stretching part 413 is expanded outwards, and the optical fiber 10 wound on the surfaces of the first stretching part 4131 and the second stretching part 4132 is further driven to be stretched; when the optical fiber 10 is not required to be stretched, the motor 412 drives the telescopic rod 411 to retract, so that the second stretching part 4132 moves towards the direction close to the first stretching part 4131, and the whole stretching part 413 is shrunk, thereby driving the optical fiber 10 wound on the surfaces of the first stretching part 4131 and the second stretching part 4132 to shrink.
Because the expansion part 413 comprises the first expansion part 4131 and the second expansion part 4132 which can be relatively applied, the optical fiber 10 is driven to stretch and contract through the relative movement of the first expansion part 4131 and the second expansion part 4132, the movement mode is simple and flexible, the stretching length of the optical fiber 10 is easy to adjust, the stretching length of the optical fiber 10 can be effectively increased, and the optical path scanning range is enlarged.
Further, the first stretching part 4131 is a first semi-cylinder, and the surface of the first semi-cylinder wound with the optical fiber 10 is a curved surface; the second extensible part 4132 is a second semi-cylinder, and the surface of the second extensible semi-cylinder wound with the optical fiber 10 is a curved surface. Preferably, the first and second expansion parts 4131 and 4132 constitute a cylindrical body, and the first and second expansion parts 4131 and 4132 are the same size. Since the optical fiber 10 is wound on the curved surfaces of the first and second semicylinders, the optical fiber 10 is more smoothly stretched and contracted, thereby making the stretching and contraction of the optical fiber 10 more natural and precise and also preventing the optical fiber 10 from being damaged during the stretching and contraction.
Preferably, the first extensible part 4131 is made of metal, and the second extensible part 4132 is made of metal. Therefore, the first and second expansion parts 4131 and 4132 are hard and can better pull the optical fiber 10 to stretch and contract. It should be understood that the material of the first telescoping portion 4131 may be other sturdy materials and the material of the second telescoping portion 4132 may be other sturdy materials.
Further, the number of the motors 412 is two, the number of the telescopic rods 411 is two correspondingly, the two motors 412 are arranged and fixed along the axial direction of the first telescopic part 4131, each motor 412 is connected with one telescopic rod 411, and the other ends of the two telescopic rods 411 are connected with the second telescopic part 4132. Preferably, the two electrodes 412 are fixedly connected at positions near both ends of the first expansion part 4131, respectively, so that the first expansion part 4131 is more stable during the movement, and thus the stretching and contraction of the optical fiber 10 is more stable.
In this embodiment, the motor 412 is connected to a motor driver, and the motor driver is controlled to control the movement mode of the motor 412 and further control the optical fiber stretcher. The maximum drawing amount of the optical fiber 10 wound on the expansion part 413 by the optical fiber stretcher is 6cm, so that the time delay of 200ps can be realized.
Referring to fig. 10, a phase-locked amplifying module 8 is further disposed between the photoconductive receiving antenna 52 and the data processing mechanism 7. Because the energy of the electrical signal converted by the photoconductive receiving antenna 52 is low, the electrical signal needs to be amplified by a current amplifier, enters the phase-locked amplification module 8 for secondary amplification, and then is transmitted to the data processing system 7 for processing and analysis.
In order to compress the bandwidth of the noise and improve the signal-to-noise ratio, the signal needs to be amplified and de-noised. The phase-locked amplification module 8 has the characteristics of strong anti-interference capability, high signal accuracy and the like when extracting weak signals in strong noise, and can acquire the change of the size and the direction of a measured signal, so that the phase-locked amplification module can be widely applied to signal detection.
The phase-locked amplification block 8 includes a signal path, a reference path, a phase sensitive detector 84 (abbreviated as PSD), and a low pass filter 85. The signal path includes a lock-in amplifier 81 connected to the photoconductive receiving antenna 52 and which functions to initially amplify the input signal, which is modulated at the same frequency as the reference signal, with accompanying noise and to initially reduce the noise by selective amplification. The reference channel comprises a square wave signal source 82 and a phase shifter 83 connected in series and operative to provide a reference signal in phase with the input signal, the reference signal being a square wave signal. The phase shifter 83 and the lock-in amplifier 81 are connected to a phase sensitive detector 84, and the phase sensitive detector 84 is used for mixing the input signal and the reference signal and outputting a sum frequency signal and a difference frequency signal. The phase sensitive detector 84 is connected to a low pass filter 85, the low pass filter 85 being operative to filter out the sum frequency signal and to retain only the difference frequency signal. And the reserved difference frequency signal is output after being amplified. In this embodiment, in order to realize a low-cost and small-volume lock-in amplifier, a balanced modem is used for performing lock-in amplification to extract a weak terahertz signal submerged by noise, and the dynamic range of the lock-in amplifier is wide and reaches 100dB, and the lock-in amplifier can detect pA-level signals.
Further, the data processing system 7 includes a data processing module 71 and a computer 72 for identifying the sample 6 to be detected, the data processing module 71 is connected to the computer 72 through a network cable, and the data processing module 71 is connected to the phase-locked amplifying module 8.
Further, the data processing module 71 also has a control function, and can control the working state of each system of the terahertz detection device. Specifically, the data processing module 71 may control the operating state of the laser system 1, so as to control whether the laser system 1 starts to operate. The data processing module 71 can control the motion state of the motor 412 through the motor driver, thereby controlling the operation state of the optical fiber drawing system 4. The data processing module 71 can control the operating state of the photoconductive transmitting antenna 51, thereby controlling whether the photoconductive transmitting antenna 51 transmits the terahertz waves. Meanwhile, the data processing module 71 can also control the working state of the phase-locked amplifying module 8.
The data processing module 71 extracts a time-domain electric field signal by using an equivalent sampling method, changes the time delay between two laser pulses through the optical fiber stretching system 4, and converts a high-frequency and fast signal into a low-frequency and slow signal for processing, thereby accurately reconstructing a terahertz waveform, and realizing effective acquisition and analysis of a terahertz signal and noise suppression.
Although a transient current proportional to the terahertz radiation field can be obtained by utilizing the photoconductive detection technology, the terahertz time-domain signal is about picosecond (ps) magnitude or even shorter, the rising edge of the current response time is basically in the sub-picosecond magnitude, and the signal is difficult to be detected by a common current detector, so that the terahertz time-domain electric field signal needs to be extracted by utilizing the equivalent time sampling technology. Because the laser pulse is a femtosecond laser pulse, the duration time of the laser pulse is far shorter than that of the terahertz pulse, high-frequency and fast signals can be converted into low-frequency and slow-speed signals for processing by changing the time delay between the two laser pulses, a sample is taken at each period or every few periods of a repeated signal, each sampling point is respectively taken from different positions of each input signal waveform, and a plurality of sampling points form a period, so that a waveform similar to one period of an original signal can be formed, and the terahertz waveform can be extracted.
Further, the computer 72 adopts an algorithm for identifying flammable and combustible materials, which is an algorithm for identifying a reflective terahertz time-domain spectroscopy system (abbreviated as THz-TDS system).
Common THz-TDS systems can be divided into two categories: transmissive and reflective. The transmission THz-TDS technology is utilized to extract optical parameters by measuring the transmission spectrum of various substances, thereby identifying the substances. However, when the transmission-type THz-TDS technique is used for measurement, the transmission-type THz-TDS technique needs to be in contact with two ends of a substance, and has a great bottleneck in practicality and universality for liquid, especially liquid with strong absorption in the terahertz wave band. In contrast, when the reflective THz-TDS technology is adopted, the terahertz wave only acts on the liquid at the interface of the inner wall of the container, and does not need to transmit the liquid, so that the terahertz wave has superiority in the problem of strong absorptivity of the liquid.
When the traditional reflective THz-TDS technology is used for identifying and detecting different liquids, time domain signals need to be converted into frequency domains in the data processing process; however, in practical application, the reference signal and the detection signal are very close to each other due to the fact that the container wall is often very thin, so that data processing is difficult, and therefore the method is not practical and can not adapt to containers or packages with different thicknesses.
The terahertz detection device provided in the present embodiment utilizes the characteristic that the refractive indexes of different substances are different, which causes the amplitude and shape of the detection signal light pulse to be different, and discriminates the component of the article in the container or package by using a pattern recognition method with respect to the detection signal light pulse in the time domain.
The procedure of the flammable and explosive article identification algorithm of the terahertz detection device provided by the embodiment is as follows:
firstly, performing data dimension reduction by using principal component analysis to realize feature extraction of data;
and (3) judging whether the article is safe or not by using an artificial intelligence algorithm (for example, linear discriminant analysis or support vector machine algorithm design can be adopted).
Since it is not necessary to perform fourier transform into a frequency domain and then analyze, the time for substance discrimination can be reduced.
Referring to fig. 11 and 12, a method for identifying a hazardous material by using the terahertz time-domain spectroscopy in the present embodiment is described by taking a beverage component as an example. When the terahertz pulse 611 propagates through the air, the liquid bottle 602, and the liquid 601, two reflections occur at a contact point between the air and the bottle outer wall 603 and a contact point between the bottle inner wall 604 and the liquid 601, respectively. The fresnel formula for the reflectivity is:
wherein n is1、n2The angle θ is the angle of incidence, which is the refractive index of the two materials in contact.
The first measurement terahertz pulse 611 propagates on the air, the liquid bottle 602 and the air interface, and a first reflected pulse 612 can be obtained, so that the dielectric constant and the thickness of the material of the liquid bottle 602 can be measured; when the material parameters of the liquid bottle 602 are obtained, the second reflected pulse 613 can be obtained by performing the measurement on the interface between the air, the bottle inner wall 604 of the liquid bottle 602 and the liquid 601 again, and the dielectric constant of the liquid 601 can be obtained by data processing.
wherein N is the number of samples in the calibration sample set,
is the ith reference value of the sample,
is the ith predictor for the sample. And judging the threshold value of the accumulated variance value, and determining dangerous goods if the accumulated variance value exceeds the threshold value.
The above description is only exemplary of the present invention and should not be taken as limiting the invention, and any modifications, equivalents, improvements, etc. that are made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A terahertz detection device is characterized in that: the system comprises a laser system for generating laser, a dispersion compensation system for performing dispersion compensation on the laser, an optical beam splitter, an optical fiber stretching system for performing delay scanning on the laser, a sample detection system for generating and receiving terahertz waves and detecting a sample to be detected, and a data processing system for analyzing test data, wherein the laser system is connected with the dispersion compensation system through an optical fiber, the dispersion compensation system is connected with the optical beam splitter through an optical fiber, the optical beam splitter is simultaneously connected with the optical fiber stretching system and the sample detection system through an optical fiber, the optical fiber stretching system is connected with the sample detection system through an optical fiber, and the sample detection system is connected with the data processing system;
the dispersion compensation system comprises an optical fiber ring mechanism used for adjusting the transmission direction of the laser, a first chirped fiber grating and a second chirped fiber grating which are used for performing dispersion compensation on the laser and have opposite dispersion compensation amounts, the optical fiber ring mechanism is provided with an input end used for being connected with an optical fiber, the optical fiber is used for transmitting the laser, the first chirped fiber grating and the second chirped fiber grating are both connected with the optical fiber ring mechanism, the laser sequentially passes through the first chirped fiber grating and the second chirped fiber grating and then is emitted out of the optical fiber ring mechanism, and the absolute values of the dispersion compensation amounts of the first chirped fiber grating and the second chirped fiber grating are not equal;
if the refractive index change period inside the first chirped fiber grating is gradually increased along the laser incidence direction, the refractive index change period inside the second chirped fiber grating is gradually decreased along the laser incidence direction; if the refractive index change period inside the first chirped fiber grating is gradually decreased along the laser incidence direction, the refractive index change period inside the second chirped fiber grating is gradually increased along the laser incidence direction.
2. The terahertz detection device of claim 1, wherein: the laser system comprises a laser, a saturable absorber, an optical coupler, a gain optical fiber and an optical fiber grating which are connected in sequence, wherein a pumping source is further connected to one side of the optical coupler, which is connected with the saturable absorber.
3. The terahertz detection device of claim 2, wherein: the laser system further comprises a repetition frequency locking mechanism, the repetition frequency locking mechanism is used for locking the frequency of laser light generated by the laser, the laser is provided with piezoelectric ceramics which can be used for adjusting the cavity length of a laser cavity of the laser, the repetition frequency locking mechanism is connected with the piezoelectric ceramics, and meanwhile, the repetition frequency locking mechanism is connected with the laser.
4. The terahertz detection device of claim 3, wherein: repetition frequency locking mechanical system is including the photoelectric detector, band-pass filter, mixer, loop filter and the high-pressure amplifier that connect gradually, photoelectric detector with the laser instrument links to each other, high-pressure amplifier with piezoceramics connects, the mixer is connected one side of band-pass filter still is connected with the reference signal generator, the reference signal generator locks on rubidium clock.
5. The terahertz detection device of claim 1, wherein: the sample detection system comprises a photoconductive transmitting antenna for generating terahertz waves, a photoconductive receiving antenna for receiving the terahertz waves and an optical component for focusing the terahertz waves, wherein the photoconductive transmitting antenna is connected with the optical beam splitter, the photoconductive receiving antenna is connected with the optical fiber stretching system, and the photoconductive receiving antenna is connected with the data processing system.
6. The terahertz detection device of claim 5, wherein: the optical component comprises a first lens group used for focusing the terahertz waves generated by the photoconductive transmitting antenna on the sample to be detected and a second lens group used for focusing the terahertz waves passing through the sample to be detected on the photoconductive receiving antenna.
7. The terahertz detection device of claim 5, wherein: the optical fiber stretching system comprises a first coupler for splitting laser, two optical fiber stretchers, a second coupler for combining the laser, a photoelectric detector for converting optical signals into electric signals and a display device for converting the electric signals into visual graphs, wherein the optical beam splitter is connected with the first coupler through optical fibers, the first coupler is simultaneously connected with the two optical fiber stretchers through optical fibers, the two optical fiber stretchers are both connected with the second coupler through optical fibers, the second coupler is connected with the photoelectric detector through optical fibers, and the photoelectric detector is connected with the display device.
8. The terahertz detection device of claim 5, wherein: and a phase-locked amplifying module is also arranged between the photoconductive receiving antenna and the data processing system.
9. The terahertz detection device of claim 8, wherein: the data processing system comprises a data processing module and a computer for identifying the sample to be detected, the data processing module is connected with the computer through a network cable, and the data processing module is connected with the phase-locked amplification module.
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| CN110620329B (en) * | 2019-10-18 | 2020-07-28 | 华东师范大学重庆研究院 | Terahertz saturable absorption device for quantum cascade laser |
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| CN104568819B (en) * | 2015-01-15 | 2017-02-22 | 南开大学 | All-fiber transmission reflection integrated terahertz time-domain spectroscopy system |
| CN205843813U (en) * | 2016-06-16 | 2016-12-28 | 中国工程物理研究院流体物理研究所 | A kind of device of all-fiber formula time domain short scan tera-hertz spectra based on fiber stretcher |
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