WO2019183952A1 - 一种太赫兹检测装置 - Google Patents
一种太赫兹检测装置 Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
- G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
Definitions
- the present invention relates to the field of security inspection technology, and more particularly to a terahertz detection device.
- Liquid dangerous goods are usually liquid at normal temperature, and have the characteristics of uniform composition, good fluidity, convenient transportation, easy manufacture and camouflage, and strong concealment.
- the raw materials of liquid dangerous goods can be transported separately, or can be combined with various compounds. Mixing, which increases the difficulty of security inspections.
- the existing safety detection devices include X-ray, Raman spectroscopy, and dielectric constant detection technology.
- X-rays are highly damaging to living organisms.
- An object of the embodiments of the present invention is to provide a terahertz detecting device to solve the technical problem that the safety inspection efficiency in the prior art is low and the dangerous types of detection are limited.
- the technical solution adopted by the embodiment of the present invention is to provide a terahertz detecting device, including a laser system for generating laser light, a dispersion compensation system for performing dispersion compensation on the laser beam, and optical splitting.
- a fiber stretching system for performing delayed scanning of the laser
- a sample detecting system for generating and receiving terahertz waves and detecting a sample to be detected
- a data processing system for analyzing the test data
- the laser system is connected to the dispersion compensation system via an optical fiber
- the dispersion compensation system is connected to the optical beam splitter through an optical fiber
- the optical beam splitter simultaneously detects the optical fiber stretching system and the sample through an optical fiber.
- the system is connected, the fiber draw system is coupled to the sample detection system via an optical fiber, and the sample detection system is coupled to the data processing system.
- the laser system includes a laser connected in sequence, a saturable absorber, a photocoupler, a gain fiber, and a fiber grating, and a pump source is further connected to a side of the photocoupler connected to the saturable absorber. .
- the laser system further includes a repetition frequency locking mechanism for locking the frequency of the laser generated by the laser, the laser being provided with a piezoelectric ceramic that can be used to adjust the cavity length of the laser cavity thereof
- the repeating frequency locking mechanism is coupled to the piezoelectric ceramic while the repeating frequency locking mechanism is coupled to the laser.
- the repetition frequency locking mechanism includes a photodetector, a band pass filter, a mixer, a loop filter and a high voltage amplifier connected in series, the photodetector being connected to the laser, the high voltage amplifier and The piezoelectric ceramic is connected, and a side of the mixer connected to the band pass filter is further connected with a reference signal generator, and the reference signal generator is locked on the chirp clock.
- the dispersion compensation system includes a fiber loop mechanism for adjusting the laser transmission direction, and a first chirped fiber grating and a second chirped fiber for performing dispersion compensation on the laser and having opposite dispersion compensation amounts.
- a grating the fiber optic ring mechanism is provided with an input for connecting to an optical fiber, the optical fiber is for transmitting the laser, and the first chirped fiber grating and the second chirped fiber grating are both annular to the optical fiber The mechanism is connected, and the laser light sequentially passes through the first ⁇ fiber grating and the second ⁇ fiber grating, and exits from the fiber ring mechanism, the first ⁇ fiber grating and the second ⁇ The absolute values of the dispersion compensation amount of the chirped fiber grating are not equal.
- the sample detecting system includes a photoconductive transmitting antenna for generating a terahertz wave, a photoconductive receiving antenna for receiving the terahertz wave, and an optical component for focusing the terahertz wave,
- the photoconductive transmit antenna is coupled to the optical beam splitter
- the photoconductive receive antenna is coupled to the fiber tensioning system
- the photoconductive receive antenna is coupled to the data processing system.
- a fiber delay line is further disposed between the optical beam splitter and the photoconductive transmitting antenna.
- the optical component includes a first lens group for focusing a terahertz wave generated by the photoconductive transmitting antenna on the sample to be detected and a terahertz wave for passing the sample to be detected Focusing on a second lens group of the photoconductive receiving antenna.
- the first lens group includes two polypropylene lenses arranged in sequence along the optical path
- the second lens group includes two polypropylene lenses arranged in sequence along the optical path.
- the optical fiber stretching system includes a telescopic rod, a motor that can drive the telescopic rod to expand and contract, and a telescopic portion for winding the optical fiber, one end of the telescopic rod is connected to the motor, and the telescopic rod is further One end is connected to the telescopic portion and can expand or contract the telescopic portion, and the optical fiber is wound around an outer surface of the telescopic portion.
- phase lock amplification module is further disposed between the photoconductive receiving antenna and the data processing mechanism.
- the phase lock amplification module includes a signal channel for amplifying an input signal, a reference channel for providing a reference signal in phase with the input signal, a phase sensitive detector, and a low pass filter, the signal Both the channel and the reference channel are coupled to the phase sensitive detector, the phase sensitive detector being coupled to the low pass filter.
- the signal path includes a lock-in amplifier connected to the photoconductive receiving antenna, and the lock-in amplifier is connected to the phase sensitive detector;
- the reference channel includes a square wave signal source and a phase shifter that are sequentially connected, and the phase shifter is coupled to the phase sensitive detector.
- the data processing system includes a data processing module and a computer for identifying the sample to be detected, the data processing module is connected to the computer through a network cable, and the data processing module is connected to the lock-in amplification module. .
- terahertz time-domain spectroscopy Due to the use of terahertz waves for detection of samples, terahertz time-domain spectroscopy has the characteristics of non-destructive testing and sample detection, convenient and quick access to material information, and low requirements on external conditions, thus enabling terahertz detection devices. Not only can a variety of substances be identified, but also the application scenarios of the terahertz detection device are expanded.
- the terahertz detection device can automatically identify the samples to be tested without manual identification, thereby greatly improving the efficiency of the security inspection and meeting the needs of different scenarios.
- FIG. 1 is a schematic diagram of a system principle of a terahertz detecting device according to an embodiment of the present invention
- FIG. 2 is a schematic diagram of a laser mode locking principle of a terahertz detecting device according to an embodiment of the present invention
- FIG. 3 is a schematic diagram of a repetition frequency locking mechanism of a terahertz detecting device according to an embodiment of the present invention
- FIG. 4 is a schematic structural diagram of a dispersion compensation system of a terahertz detecting device according to an embodiment of the present invention
- FIG. 5 is another schematic structural diagram of a dispersion compensation system of a terahertz detecting device 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 detecting device according to an embodiment of the present invention
- FIG. 7 is a schematic structural diagram of a positive dispersion chirped fiber grating of a dispersion compensation system of a terahertz detecting device according to an embodiment of the present invention
- FIG. 8 is a schematic structural diagram of a fiber stretching system of a terahertz detecting device according to an embodiment of the present invention.
- FIG. 9 is a schematic structural diagram of a fiber tensioner of a terahertz detecting device according to an embodiment of the present invention.
- FIG. 10 is a schematic structural diagram of a phase lock amplification module of a terahertz detecting device according to an embodiment of the present invention.
- FIG. 11 is a schematic diagram of measuring a beverage by a terahertz detecting device according to an embodiment of the present invention.
- FIG. 12 is a schematic diagram of waveforms of reflected pulses when a terahertz detecting device measures a sample to be detected according to an embodiment of the present invention.
- first and second are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated.
- features defining “first” and “second” may include one or more of the features either explicitly or implicitly.
- the meaning of "a plurality" is two or more unless specifically and specifically defined otherwise.
- a terahertz detecting device includes a laser system for generating laser light, a dispersion compensation system for performing dispersion compensation on a laser beam, an optical beam splitter 3, and a time delay scanning laser.
- a fiber drawing system 4 a sample detecting system 5 for transmitting and receiving terahertz waves and detecting a sample 6 to be inspected, and a data processing system 7 for analyzing test data
- the laser system 1 passes through the optical fiber 10 and the dispersion compensation system 2
- the dispersion compensation system 2 is connected to the optical beam splitter 3 through the optical fiber 10
- the optical beam splitter 3 is simultaneously connected to the optical fiber stretching system 4 and the sample detecting system 5 through the optical fiber 10
- the optical fiber stretching system 4 passes the optical fiber 10 and the sample.
- the detection system 5 is connected while the sample detection system 5 is connected to the data processing system 7.
- the working principle of a terahertz detecting device is as follows: First, the laser light generated by the laser system 1 is transmitted to the dispersion compensation system 2 through the optical fiber 10, and the dispersion compensation is performed in advance through the dispersion compensation system 2; then the laser passes through the optical splitting After the device 3 is divided into two beams, a laser beam reaches the sample detecting system 5 and is used to emit a terahertz wave. After the terahertz wave is irradiated onto the sample to be detected 6, the information of the sample to be detected 6 is carried, and then the sample 6 to be detected is carried.
- the terahertz wave of the information is received by the sample detection system 5; the other laser beam passes through the fiber stretching system 4 and reaches the sample detection system 5, and is coupled with the terahertz wave carrying the information of the sample 6 to be detected to form test data;
- the data is transmitted to the data processing system 7 for processing, and the sample 6 to be detected is identified, thereby realizing the judgment and alarm of the inflammable and explosive materials.
- terahertz time-domain spectroscopy has the following advantages:
- Frequency bandwidth has a bandwidth of approximately 0.1 THz to 5 THz.
- the terahertz time-domain spectroscopy system can achieve a signal-to-noise ratio of up to 10 4 at less than 3 THz, which is much higher than that of Fourier transform infrared spectroscopy and has good stability.
- Non-destructive testing and sample detection can effectively detect various physical information and chemical information of the sample to be detected in the terahertz band, which can be used for qualitative identification of substances. analysis. In addition, due to the safety and penetration of terahertz waves, it is suitable for non-destructive testing of biological tissues. Terahertz time-domain spectroscopy also features high detection sensitivity and stable operation at room temperature, so it can be widely used for sample detection.
- terahertz time-domain spectroscopy technology can easily and quickly acquire a variety of material information, such as the amplitude and phase information of dielectric materials, biomacromolecules and semiconductor materials, and can also directly reflect the conductivity.
- the carrier information in the material at the same time, the coherence of the terahertz time-domain spectrum makes the electric field waveform contain the complete information such as the intensity, phase and time of the terahertz pulse, which can be absorbed by the Fourier transform into the spectrum signal.
- Spectral and dispersive spectroscopy can easily and quickly acquire a variety of material information, such as the amplitude and phase information of dielectric materials, biomacromolecules and semiconductor materials, and can also directly reflect the conductivity.
- the carrier information in the material at the same time, the coherence of the terahertz time-domain spectrum makes the electric field waveform contain the complete information such as the intensity, phase and time of the terahertz pulse, which can be absorbed by the Fourier transform into the spectrum
- the terahertz time-domain spectroscopy system can work at room temperature, eliminating the need for complex refrigeration systems.
- Non-contact measurement Terahertz radiation can directly reflect the information of carriers in the conductive material, so the terahertz time-domain spectroscopy system is more convenient and effective than the non-contact measurement based on the Hall effect.
- terahertz time-domain spectroscopy Due to the use of terahertz waves to detect sample 6, terahertz time-domain spectroscopy has the characteristics of non-destructive testing and sample detection, convenient and quick access to material information, and low requirements on external conditions, thus enabling terahertz detection.
- the device not only recognizes a variety of substances, but also expands the application scenario of the terahertz detection device.
- the terahertz detection device can automatically identify the sample to be tested 6, without manual identification, thereby greatly improving the efficiency of the security inspection and meeting the needs of different scenarios.
- the terahertz detecting device provided in this embodiment is provided with a lithium battery, which can conveniently perform outdoor detection, and can also prevent the detection from being unable to be detected due to the instantaneous power failure, and can protect the device.
- the terahertz detecting device is also provided with a universal wheel at the bottom, so that the terahertz detecting device can be freely moved, so that it can be detected at any position as needed.
- the laser system 1 includes a laser 11 connected in sequence, a saturable absorber 12, an optical coupler 13, a gain fiber 14 and a fiber grating 15, and the optical coupler 13 is connected to the saturable absorber 12.
- a pump source 16 is also connected to the side.
- the laser 11 is a femtosecond laser such that a femtosecond laser pulse can be generated.
- the saturable absorber 12 Since the saturable absorber 12 has a large absorption of weak light and a small absorption of strong light, when the laser intensity generated by the laser 11 is too low, the laser light is absorbed by the saturable absorber 12, and when the laser 11 produces a laser intensity When high, the laser passes through the saturable absorber 12, so that the saturable absorber 12 is used to ensure that the output power of the laser 11 meets the requirements.
- the output power of the laser 11 is higher than 80 mW, and the pulse width of the femtosecond laser pulse is less than 100 fs.
- the pump source 16 is coupled to the laser light passing through the saturable absorber 12 in the optical coupler 13
- the coupled laser light is gained by the gain fiber 14 and filtered by the fiber grating 15 to obtain a laser of a specific wavelength. Meet the requirements for use.
- the laser system 1 further includes a repetition frequency locking mechanism that can be used to lock the frequency of the laser generated by the laser 11; the laser 11 is provided with a piezoelectric ceramic that can be used to adjust the cavity length of the laser cavity thereof.
- the PZT piezoelectric ceramic 111, the PZT piezoelectric ceramic operates under the control of the PZT drive 110; the repetition frequency locking mechanism is coupled to the PZT piezoelectric ceramic 111, and the repeating frequency locking mechanism is coupled to the laser 11.
- a small portion of the laser light generated by the laser is split by the coupler and then enters the repetitive frequency locking mechanism.
- a corresponding high voltage signal is generated, and then the high voltage signal controls the movement of the PZT piezoelectric ceramic 111 through the PZT drive 110.
- the cavity length of the laser cavity is changed, and the frequency of the laser is adjusted to stabilize the repetition frequency of the output laser.
- 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 sequentially connected, and the photodetector 171 is connected to the laser 11, high voltage.
- the amplifier 175 is connected to the PZT piezoelectric ceramic 111, and the side of the mixer 173 connected to the band pass filter 172 is also connected to a reference signal generator 176, which is locked to the cuckold clock 177.
- a small portion of the light generated by the femtosecond laser is split by the coupler and then irradiated onto the photodetector 171 and captured by the photodetector 171.
- the photodetector 171 outputs a signal whose frequency is an integer multiple of the repetition frequency (denoted as N f rep ), and the signal can be filtered by the band pass filter 172 to obtain a signal of a desired frequency (i.e., a signal of N f rep ).
- N is 4, that is, the output frequency of the photodetector 171 is 4 times the repetition frequency, and after passing through the band pass filter 172, the fourth harmonic of the repetition frequency is obtained; of course, higher order harmonics can also be obtained; In fact, the higher the harmonic order of the mixing input, the more sensitive the system is to frequency changes, resulting in higher stability after forming a closed-loop control system.
- the signal after passing through the band pass filter 172 and the reference signal generated by the reference signal generator 176 are mixed into the mixer 173 to obtain a beat signal.
- the reference signal generator 76 is locked on the cuckoo clock 177, and the frequency of the reference signal is set in accordance with the repetition frequency to be locked. In the present embodiment, the frequency of the reference signal is 1000 MHz.
- the compensation control signal is output, and the compensation control signal passes through the high voltage amplifier 175 to obtain a high voltage signal for controlling the PZT drive 110, thereby controlling the PZT piezoelectric ceramic 111, and the tiny through the PZT piezoelectric ceramic 111.
- the displacement changes the cavity length of the laser cavity, thereby suppressing small fluctuations in the repetition frequency, and finally dynamically tracking the upper reference signal (ie, locked to the reference signal), so that the repetition frequency f rep obtains the same stability as the Cuckoo clock 177, ensuring the output laser The repetition frequency is stable.
- the loop controller 174 is the core of the entire repetitive frequency locking mechanism, which not only has the function of low-pass filtering, but also improves the dynamic response characteristics and stability characteristics of the system.
- 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 characteristics of the system, and the DC bias circuit is to find a suitable frequency point before locking.
- the proportional integral controller includes a bandwidth selection section, an integral link section, and a low frequency gain limit (Low) Frequency Gain Limit (abbreviated as LFGL) part; the bandwidth selection part is to select the appropriate bandwidth.
- low-frequency gain limit is used to limit low-frequency gain, prevent integral saturation due to improper conditions at the moment of locking, limit low-frequency gain before locking, find lock point, release after locking Restricted, thus entering the pure integral link.
- the above settings make the operation of the repetition frequency locking process more flexible, which is convenient for quickly finding the locking point and completing the locking efficiently and accurately.
- the repetition rate of the commonly used femtosecond laser is about 20 Hz (ie, the repetition frequency is ⁇ 20 Hz).
- the femtosecond laser repetition frequency can be stabilized at 100. MHz ⁇ 1mHz, which greatly improves the stability of the femtosecond laser.
- the dispersion compensation system 2 includes a fiber loop mechanism for adjusting the laser transmission direction, and a first chirped fiber grating 221 and a second beam for performing dispersion compensation on the laser and having opposite dispersion compensation amounts.
- the fiber grating 222, the 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 light 100, and the first ⁇ fiber grating 221 and the second ⁇ fiber grating 222 are both connected to the fiber ring mechanism, and the laser 100 sequentially passes through the first chirped fiber grating 221 and the second chirped fiber grating 222 and exits from the fiber loop mechanism, and the first chirped fiber grating 221 and the second chirped fiber grating 222 absolutely compensate for the dispersion of the laser light 100.
- the values are not equal.
- the working principle of the dispersion compensation system 2 is as follows: First, the optical fiber 10 transmitting the laser light 100 is connected to the fiber ring mechanism, and the first ⁇ fiber grating 221 and the second ⁇ fiber grating 222 are sequentially connected with the fiber ring mechanism, thereby After the laser 100 enters the fiber loop mechanism through the optical fiber 3, it is sequentially subjected to dispersion compensation by the first chirped fiber grating 221 and the second chirped fiber grating 222, and then exits from the fiber loop mechanism.
- 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 amount of fs/nm (femtosecond/nano). Level, so that the amount of tiny dispersion of the femtosecond laser can be compensated.
- the advantage of such an arrangement is that since the first chirped fiber grating 221 and the second chirped fiber grating 222 for performing dispersion compensation on the laser light 100 and having opposite dispersion compensation are provided, the laser light 100 sequentially passes through the first chirped fiber. After the grating 221 and the second chirped fiber grating 222, the total dispersion compensation amount can reach the order of fs/nm, so that the minute dispersion amount of the femtosecond laser can be compensated, and the reliability of the laser transmission is effectively guaranteed.
- the fiber optic ring mechanism includes a first fiber optic circulator 211, and the first fiber optic circulator 211 includes a first input port 2110, a first port 2111, and a second port disposed along a laser transmission direction. 2112 and a third port 2113, 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 fiber optic circulator 211 is a four port fiber optic circulator.
- the fiber optic ring mechanism includes a second fiber optic circulator 212 and a third fiber circulator 213.
- the second fiber circulator 212 includes a second input port 2120 disposed in the laser transmission direction, and a fourth The port 2121 and the fifth port 2122
- the third fiber circulator 213 includes a third input port 2130, a seventh port 2131, and an eighth port 2132 disposed along the laser transmission direction
- the second input port 2120 is connected to the optical fiber 10
- the fourth port 2121 is connected to the first chirped fiber grating 221
- the fifth port 2122 is connected to the third input port 2130
- the seventh port 2131 is connected to the second chirped fiber grating 222.
- the second fiber circulator 212 is a three port fiber circulator
- the third fiber circulator 213 is a three port fiber circulator
- the second fiber circulator 212 and the third fiber circulator 213 are connected to each other by the optical fiber 103.
- the second fiber circulator 212 and the third fiber circulator 213 can also be other types of fiber circulators, such as a four-port fiber circulator. In use, only three of the ports can be used in sequence. .
- the refractive index change period in the first chirped fiber grating 221 gradually increases along the incident direction of the laser light 100, and the refractive index change period along the second chirped fiber grating 222 The incident direction of the laser light 100 gradually decreases.
- the first chirped fiber grating 221 is a negative dispersion chirped fiber grating, and laser components of different frequencies in the laser 100 are totally reflected at different positions of the negative dispersion chirped fiber grating, wherein the high frequency laser component 1001 is totally reflected.
- the position is deeper than the position at which the low-frequency laser component 1002 is totally reflected, such that the optical path of the high-frequency laser component 1001 is greater than the optical path of the low-frequency laser component 1002, thereby generating a negative dispersion;
- the second chirped fiber grating 222 is a positive-dispersion fiber.
- the grating, the laser components of 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 the optical path of the low frequency laser component 1002, thereby generating positive dispersion.
- the refractive index change period in the first chirped fiber grating 221 gradually decreases along the incident direction of the laser light 100, that is, the first chirped fiber grating 221 is a positive dispersion chirped fiber grating; the second chirped fiber grating
- the refractive index change period in 222 gradually increases along the incident direction of the laser light 100, that is, the second meander fiber grating 222 is a negative dispersion fiber grating.
- the dispersion compensation by the first chirped fiber grating 221 and the second chirped fiber grating 222 is reversed, when the laser 100 passes through the first chirped grating 221 and the second chirped fiber grating 222 in sequence, the first chirped fiber grating
- the sum of the dispersion compensation amount of 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.
- the magnitude of the refractive index change 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 ) AI a t b ( I )
- n eff is the effective refractive index of the fiber and ⁇ is the grating period.
- the small difference ⁇ B of the Bragg reflection wavelength at different positions indicates that at the same position of the ⁇ fiber grating, the wavelength satisfying the reflection condition has a slight difference, or the reflection positions of the two beams of the same frequency in the ⁇ fiber grating have slight differences, and the whole Considering that the amount of dispersion compensation of the chirped fiber grating is slightly different.
- the value of the exposure power density I is set to 450 mW/cm 2
- a fiber grating having a dispersion compensation amount of 14 ps/nm is obtained, and the set value of the exposure power density I is 440 mW/cm 2 .
- the dispersion compensation amount is 13.95 ps/nm fiber grating.
- the two fiber gratings are reversely connected to the fiber circulator, and the total dispersion compensation amount is the sum of the dispersion compensation amounts of the two fiber gratings, that is, 50 fs/nm (ie, 0.05 ps/nm). Therefore, the total dispersion compensation amount can be on the order of fs/nm, so that the minute dispersion amount of the femtosecond laser can be compensated.
- 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 50 fs/nm to 100 fs/nm.
- the absolute value of the total dispersion compensation amount is 50 fs/nm, so that the minute dispersion amount of the femtosecond laser can be compensated, and the reliability of the laser transmission is effectively ensured.
- the sample detecting system 5 includes a photoconductive transmitting antenna 51 for transmitting terahertz waves, a photoconductive receiving antenna 52 for receiving terahertz waves, and an optical component for focusing terahertz waves.
- 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
- the photoconductive receiving antenna 52 is connected to the data processing system 7.
- the optical component 53 includes a first lens group for focusing a terahertz wave generated by the photoconductive transmitting antenna 51 on the sample 6 to be detected and for focusing a terahertz wave passing through the sample 56 to be detected on the photoconductive receiving antenna 52.
- the second lens group is included in the sample detecting system 5
- the second lens group includes a first lens group for focusing a terahertz wave generated by the photoconductive transmitting antenna 51 on the sample 6 to be detected and for focusing a terahertz wave passing through the sample 56 to be detected on the photoconductive receiving antenna 52
- a fiber delay line 54 is further disposed between the optical beam splitter 3 and the photoconductive transmitting antenna 51.
- the delay line of current terahertz time-domain spectrometers is a free-space delay line, most of which uses a mobile platform for delay. Such devices lack stability and are susceptible to vibration and temperature fluctuations leading to delay imbalances.
- the fiber delay line is adopted, which has high stability and is easy to integrate.
- the optical component 53 includes four polyolefin lenses, wherein the first lens group includes two polyolefin lenses, the second lens group includes two other polyolefin lenses, and the polyolefin lens may be an aspherical mirror or a spherical mirror.
- the terahertz wave emitted by the photoconductive transmitting antenna 51 first passes through the two polyolefin lenses of the first lens group and is focused to the surface of the sample 6 to be detected, and carries the information of the sample 6 to be detected after being reflected on the surface of the sample to be detected 6. Then, the terahertz wave passes through the two polyolefin lenses of the second lens group and is received by the photoconductive receiving antenna 52 and converted into a corresponding electrical signal.
- the conventional fiber tensioner uses a piezoelectric ceramic tensile fiber. These piezoelectric bodies are usually driven by a high-power high-voltage source, and the cost of the driver is high. The high-voltage power supply is also likely to cause interference to surrounding circuits, which is disadvantageous for Device integration.
- the fiber drawing system 4 provided in this embodiment includes a first coupler 43 for splitting the laser, two fiber stretchers, a second coupler 44 for combining the lasers, and the light for combining A photodetector 45 that converts the signal into an electrical signal and a display device 46 for converting the electrical signal into a visual pattern.
- display device 46 is an oscilloscope such that electrical signals can be converted into a visual time domain waveform.
- the two fiber stretchers are referred to as a first fiber stretcher 4101 and a second fiber stretcher 4102, respectively.
- the optical beam splitter 3 is connected to the first coupler 43 through the optical fiber 10.
- the first coupler 43 is simultaneously connected to the first optical fiber stretcher 4101 and the second optical fiber stretcher 4102 through the optical fiber 10, and the first optical fiber tensioner 4101
- the second fiber tensioner 4102 is connected to the second coupler 44 through the optical fiber 10
- the second coupler 44 is connected to the photodetector 45 through the optical fiber 10
- the photodetector 45 is connected to the display device 46.
- the optical fiber 10 connected to the first optical fiber tensioner 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 second optical fiber stretcher 4102. surface.
- One end of the first fiber tensioner 4101 is a reference arm, and the end of the second fiber tensioner 102 is used as a signal arm.
- the working principle of the optical fiber stretching system 4 provided in this embodiment is as follows:
- the laser is transmitted through the optical fiber 10 to the first coupler;
- the laser beam is split into two bundles after passing through the first coupler 43, one bundle is transported to the second coupler 44 by the optical fiber 10 wound around the first fiber stretcher 4101, and the other bundle is passed through the second fiber stretcher 4102.
- the optical fiber 10 is transmitted to the second coupler 44;
- the two laser beams reaching the second coupler 44 are merged into a bundle after passing through the second coupler 44, and transmitted to the photosensor 45 through the optical fiber 10;
- the photosensor 45 converts the received optical signal into an electrical signal and transmits the electrical signal to the display device 46;
- Display device 46 converts the electrical signals into visual graphics and displays them.
- the optical path experienced by the two laser beams Similarly, the optical path difference is zero; then, a triangular wave modulation signal is applied to the second fiber stretcher 4102 as a signal arm such that the optical path and the laser light transmitted through the optical fiber 10 at the second fiber stretcher 4102
- the optical path of the laser light transmitted by the optical fiber 10 at the first fiber tensioner 4101 is different, thereby generating an optical path difference; since the two laser beams are transmitted to the second coupler and merged into one bundle, when the combined laser light is transmitted to the photosensor 45 Interference occurs at the time; by analyzing the interference signal, the optical path difference can be obtained, thereby obtaining the tensile length of the optical fiber.
- the first fiber tensioner 4101 is identical to the second fiber tensioner 4102, so that it can be effectively ensured that when the motor is in the initial state, the optical fiber 10 is wound in the same manner in the first fiber tensioner 4101 or the first In the case of the two-fiber stretcher 4102, the optical path difference is zero.
- the end where the first fiber tensioner 4101 is located is used as a reference arm in order to solve the problem that the light effect interference fringe contrast is lowered due to the winding bending.
- the optical fiber tensioner further includes a telescopic rod 411, a motor 412 that can drive the telescopic rod 411 for telescoping, and a telescopic portion 413 for winding the optical fiber 10.
- a telescopic rod 411 One end of the telescopic rod 411 is connected to the motor 412, and the telescopic rod The other end of the 411 is connected to the expansion and contraction portion 413 and can expand or contract the expansion and contraction portion 413.
- the working principle of the optical fiber tensioner is as follows: First, the motor 412 is fixed, and the motor 412 is connected to one end of the telescopic rod 411, and then the other end of the telescopic rod 411 is connected to the expansion and contraction portion 413, and then the optical fiber 10 is wound around the expansion and contraction portion 413.
- the motor 412 is powered on, and the telescopic rod 411 is driven to extend as needed, so that the expansion and contraction portion 413 can be expanded to drive the optical fiber 10 wound around the expansion and contraction portion 413.
- the motor 412 drives the telescopic rod 411 to retract, so that the expansion and contraction portion 413 can be contracted, and the optical fiber 10 wound around the expansion and contraction portion 413 is contracted.
- optical fiber 10 is stretched by driving the telescopic rod 411 by the motor 412 to drive the telescopic rod 413, thereby effectively increasing the tensile length of the optical fiber 10, thereby increasing the laser light in the optical fiber.
- the transmission length in 10 increases the optical path scan range.
- the expansion and contraction portion 413 includes a first expansion and contraction portion 4131 and a second expansion and contraction portion 4132.
- the motor 412 is disposed between the first expansion and contraction portion 4131 and the second expansion and contraction portion 4132, and the motor 412 is fixedly coupled to the first expansion and contraction portion 4131.
- the rod 411 is also disposed between the first elasticized portion 4131 and the second elasticized portion 4132, and the other end of the telescopic rod 411 is connected to the second elasticized portion 4132, and the optical fiber 10 is wound around the first elasticized portion 4131 and the second elasticized portion 4132.
- the outer surface is also disposed between the first elasticized portion 4131 and the second elasticized portion 4132, and the other end of the telescopic rod 411 is connected to the second elasticized portion 4132, and the optical fiber 10 is wound around the first elasticized portion 4131 and the second elasticized portion 4132.
- the motor 412 drives the extension rod 411 to extend, and the extension rod 411 drives the second expansion and contraction portion 4132 to move away from the first expansion and contraction portion 4131, so that the expansion and contraction portion 413 is entirely expanded outward.
- the optical fiber 10 wound around the surface of the first telescopic portion 4131 and the second telescopic portion 4132 is 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 telescopic portion 4132 is oriented
- the expansion-contraction portion 413 is entirely contracted, and the optical fiber 10 wound around the surfaces of the first elastic-contraction portion 4131 and the second elastic-contraction portion 4132 is contracted.
- the telescopic portion 413 includes the first telescopic portion 4131 and the second telescopic portion 4132 that can be used relative to each other, the optical fiber 10 is stretched and contracted by the relative movement of the first telescopic portion 4131 and the second telescopic portion 4132, and the movement mode is simple. It is flexible, and the stretching length of the optical fiber 10 is easy to adjust, and the stretching length of the optical fiber 10 can be effectively increased, and the optical path scanning range is increased.
- first telescopic portion 4131 is a first semi-cylindrical body, the surface of the first semi-cylindrical wound optical fiber 10 is a curved surface; the second telescopic portion 4132 is a second semi-cylindrical body, and the second semi-cylindrical body is wound around the optical fiber 10
- the surface is a curved surface.
- the first elasticized portion 4131 and the second elasticized portion 4132 constitute one cylinder, and the first elasticized portion 4131 and the second elasticized portion 4132 are the same size.
- the optical fiber 10 Since the optical fiber 10 is wound around the curved surfaces of the first semi-cylindrical body and the second semi-cylindrical body, 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 is damaged during stretching and shrinking.
- the material of the first elasticized portion 4131 is metal, and the material of the second elasticized portion 4132 is metal. Therefore, the first elasticized portion 4131 and the second elasticized portion 4132 are rigid in texture, and the optical fiber 10 can be better driven to stretch and contract. It should be understood that the material of the first elastic portion 4131 may also be other materials with firm texture, and the material of the second elastic portion 4132 may also be other hard materials.
- the number of the motors 412 is two, and the number of the telescopic rods 411 is two.
- the two motors 412 are arranged and fixed along the axial direction of the first telescopic portion 4131. Each motor 412 is connected to one telescopic rod 411, two The other end of the telescopic rod 411 is connected to the second telescopic portion 4132.
- the two electrodes 412 are fixedly connected at positions close to both ends of the first telescopic portion 4131, respectively, so that the first telescopic portion 4131 is more stable during the movement, thereby making the stretching and contraction of the optical fiber 10 smoother.
- the motor 412 is connected to the motor driver, and by controlling the motor driver, the movement mode of the motor 412 is controlled, and the fiber tensioner is controlled.
- the fiber stretcher has a maximum stretch of 6 cm for the optical fiber 10 wound around the stretchable portion 413, so that a delay of 200 ps can be achieved.
- a phase lock amplification module 8 is further disposed between the photoconductive receiving antenna 52 and the data processing mechanism 7. Since the energy converted by the photoconductive receiving antenna 52 is low, it needs to be amplified by the current amplifier and then enters the phase-locked amplifying module 8 for secondary amplification, and then transmitted to the data processing system 7 for processing and analysis.
- the phase-locked amplification module 8 has the characteristics of strong anti-interference ability and high signal accuracy when extracting weak signals in strong noise, and can acquire changes in the size and direction of the measured signal, and thus can be widely applied to signal detection.
- the phase lock amplification module 8 includes a signal path, a reference channel, a phase sensitive detector 84 (abbreviated as PSD), and a low pass filter 85.
- the signal path includes a lock-in amplifier 81 coupled to the photoconductive receiving antenna 52. The function of the signal is to first amplify the input signal with the same frequency modulated by the reference signal with noise, and initially reduce the noise by selecting.
- the reference channel includes a square wave signal source 82 and a phase shifter 83 connected in series 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 both connected to the phase sensitive detector 84.
- the phase sensitive detector 84 functions to mix the input signal and the reference signal, and output the sum frequency signal and the beat frequency signal.
- the phase sensitive detector 84 is coupled to a low pass filter 85 which functions to filter out the sum frequency signal, leaving only the difference frequency signal.
- the reserved difference frequency signal is amplified and output.
- a balanced modem is used for phase-locked amplification to extract a weak terahertz signal that is submerged by noise, and its dynamic range is wide, reaching 100. dB, can detect the signal of pA level.
- 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 via a network cable, and the data processing module 71 is connected to the lock-in amplification module 8.
- the data processing module 71 also has a control function to control the operating states of the various systems of the terahertz detecting device. Specifically, the data processing module 71 can control the operating state of the laser system 1 to control whether the laser system 1 starts to operate. The data processing module 71 can control the motion state of the motor 412 by the motor driver, thereby controlling the operating state of the fiber stretching system 4. The data processing module 71 can control the operational state of the photoconductive transmitting antenna 51 to control whether the photoconductive transmitting antenna 51 emits a terahertz wave. At the same time, the data processing module 71 can also control the working state of the lock-in amplification module 8.
- the data processing module 71 extracts the time domain electric field signal by using the equivalent sampling method, and changes the time delay between the two laser pulses through the fiber stretching system 4, and converts the high frequency and fast signals into low frequency and slow signals for processing, thereby Accurate reconstruction of terahertz waveforms for efficient acquisition and analysis of terahertz signals and noise suppression.
- the terahertz time domain signal is on the order of picoseconds (ps) or even shorter, the current response time rises along the basic subcutaneous In the order of seconds, it is difficult to detect this signal by ordinary current detectors, so it is necessary to extract the terahertz time domain electric field signal by using equivalent time sampling technique.
- the laser pulse is a femtosecond laser pulse, its duration is much shorter than the duration of the terahertz pulse. By changing the time delay between the two laser pulses, the high frequency and fast signals can be converted into low frequency and slow signal processing.
- Each cycle of the repeated signal or one cycle is taken as a sample, and each sampling point is taken from a different position of each input signal waveform, and several sampling points form a cycle, which can be composed of a cycle similar to the original signal.
- Waveforms in turn, can extract terahertz waveforms.
- the flammable and explosive item recognition algorithm employed by the computer 72 is a recognition algorithm of a reflective terahertz time domain spectroscopy system (abbreviated as a THz-TDS system).
- THz-TDS systems can be divided into two categories: transmissive and reflective.
- Transmissive THz-TDS technology is used to identify substances by measuring the transmission spectra of various substances and extracting optical parameters.
- transmissive THz-TDS technology requires contact with both ends of the material.
- transmissive THz-TDS technology is practical and versatile. There is a huge bottleneck.
- the reflective THz-TDS technique is employed, since the terahertz wave acts only on the inner wall interface of the container and does not need to be transmitted through the liquid, it exhibits superiority in the problem of strong liquid absorption.
- the reflective THz-TDS technology is used to identify and detect different liquids.
- the time domain signal needs to be converted to the frequency domain.
- the reference signal and the detection signal are separated. Very close, making data processing difficult, so the method is not practical enough to adapt to containers or packages of different thicknesses.
- the terahertz detecting device utilizes different refractive indexes of different substances, thereby causing characteristics of different amplitudes and shapes of the detecting signal light pulses, and for detecting signals light pulses in the time domain, using a pattern recognition method for the container or the packaging The ingredients in the items are discriminated.
- the artificial intelligence algorithm for example, linear discriminant analysis or support vector machine algorithm design
- the artificial intelligence algorithm can be used to discriminate whether the item is safe or not.
- a method for detecting dangerous goods using the terahertz time domain spectroscopy technique is described by taking the beverage component as an example.
- the terahertz pulse 611 propagates in the air, liquid bottle 602, and liquid 601, two reflections occur at the point where the air contacts the outer wall 603 of the bottle, and the inner wall 604 of the bottle contacts the liquid 601, respectively.
- the Fresnel formula for reflectivity is:
- n 1 and n 2 are the refractive indices of the two materials in contact, and the angle ⁇ is the incident angle.
- Different liquids 601 are reflecting different shapes of terahertz pulses. Principal component analysis was performed on the shape of the reflected pulse of different liquids, and the cumulative variance value was calculated.
- the cumulative variance formula is as follows:
- N is the number of samples in the calibration sample set
- Y i r is the ith reference value of the sample
- Y i p is the ith predicted value of the sample. Threshold judgment is made on the cumulative variance value, and the dangerous value is exceeded when the threshold is exceeded.
Abstract
一种太赫兹检测装置，包括用于产生激光的激光系统、用于对激光进行色散补偿的色散补偿系统、光分束器、用于对激光进行延时扫描的光纤拉伸系统、用于产生和接收太赫兹波并对待检测样品进行检测的样品检测系统和用于对测试数据进行分析的数据处理系统，激光系统通过光纤与色散补偿系统连接，色散补偿系统通过光纤与光分束器连接，光分束器通过光纤同时与光纤拉伸系统、样品检测系统连接，光纤拉伸系统通过光纤与样品检测系统连接，同时样品检测系统通过光纤与数据处理系统连接；不仅可以对多种物质进行识别，而且可以自动识别待检测样品，从而大大提高了安全检查的效率，满足不同场景的使用需求。
Description
本发明涉及安全检查技术领域，更具体地说，是涉及一种太赫兹检测装置。
易燃、易爆物品的检测关乎公共场所的安全，因此在人流量较为密集的场所，例如机场、地铁、汽车站等，通常需要进行安全检查，以便排除隐患。液态危险品在常温下通常呈液态，具有组分均匀、流动性好、运输方便、易于制造和伪装、隐蔽性强等特点；此外，液态危险品的原材料可以分开运输，或者可以与多种化合物混合，从而增加了安全检查工作的难度。
目前，排除易燃、易爆物品的通常做法是：液体类，让携带者喝一口，以示没有危害，然而这种做法不仅效率低，而且容易引发旅客的抵触情绪；固体类，在安检区提供的安检机，需要工作人员仅凭借其外型信息来简单判定是否是违禁品。目前国内外的安检设备中，虽然有针对炸药、爆炸物、毒品等重大危险物质的自动识别系统，但技术尚不完善，而且价格昂贵。此外，面对人们日常生活中大量的常见危险品，却没有哪一种安检产品能够达到自动识别，都需要对其进行半人工识别，甚至是开包检查人工识别。
现有的安全检测设备包含的技术有X射线、拉曼光谱技术、介电常数探测技术等。但是，X射线对生物体损害强，对于那些不容易挥发的液态危险品，尤其是密闭容器中的液态危险品，基本上无法检测，对于金属检测则很容易受到金属杂物的干扰而增大误报率；激光拉曼光谱采用低功率激光光源，激光光束可以穿透透明瓶装液体，其对非透明容器却无能无力；介电常数技术作用范围有限，通常是用于探测容器内的液态物品，需要贴近样品探测，且穿透能力有限。
以上不足，有待改进。
本发明实施例的目的在于提供一种太赫兹检测装置，以解决现有技术中存在的安全检查效率低下、且检测的危险品种类有限的技术问题。
为解决上述技术问题，本发明实施例采用的技术方案是：提供一种太赫兹检测装置，包括用于产生激光的激光系统、用于对所述激光进行色散补偿的色散补偿系统、光分束器、用于对所述激光进行延时扫描的光纤拉伸系统、用于产生和接收太赫兹波并对待检测样品进行检测的样品检测系统和用于对测试数据进行分析的数据处理系统，所述激光系统通过光纤与所述色散补偿系统连接，所述色散补偿系统通过光纤与所述光分束器连接，所述光分束器通过光纤同时与所述光纤拉伸系统、所述样品检测系统连接，所述光纤拉伸系统通过光纤与所述样品检测系统连接，同时所述样品检测系统与所述数据处理系统连接。
进一步地，所述激光系统包括依次连接的激光器、可饱和吸收体、光耦合器、增益光纤和光纤光栅，所述光耦合器与所述可饱和吸收体连接的一侧还连接有泵浦源。
进一步地，所述激光系统还包括重复频率锁定机构，所述重复频率锁定机构用于锁定所述激光器产生的激光的频率，所述激光器设有可用于调节其激光腔的腔长的压电陶瓷，所述重复频率锁定机构与所述压电陶瓷连接，同时所述重复频率锁定机构与所述激光器连接。
进一步地，所述重复频率锁定机构包括依次连接的光电探测器、带通滤波器、混频器、环路滤波器和高压放大器，所述光电探测器与所述激光器相连，所述高压放大器与所述压电陶瓷连接，所述混频器连接所述带通滤波器的一侧还连接有基准信号发生器，所述基准信号发生器锁定在铷钟上。
进一步地，所述色散补偿系统包括用于调整所述激光传输方向的光纤环形机构，用于对所述激光进行色散补偿、且色散补偿量相反的第一啁啾光纤光栅和第二啁啾光纤光栅，所述光纤环形机构设有用于与光纤连接的输入端，所述光纤用于传输所述激光，所述第一啁啾光纤光栅和所述第二啁啾光纤光栅均与所述光纤环形机构连接，且所述激光依次通过所述第一啁啾光纤光栅和所述第二啁啾光纤光栅后从所述光纤环形机构中出射，所述第一啁啾光纤光栅和所述第二啁啾光纤光栅的色散补偿量的绝对值不相等。
进一步地，所述样品检测系统包括用于产生太赫兹波的光电导发射天线、用于接收所述太赫兹波的光电导接收天线和用于对所述太赫兹波进行聚焦的光学组件，所述光电导发射天线与所述光分束器连接，所述光电导接收天线与所述光纤拉伸系统连接且所述光电导接收天线与所述数据处理系统连接。
进一步地，所述光分束器与所述光电导发射天线之间还设有光纤延时线。
进一步地，所述光学组件包括用于将所述光电导发射天线产生的太赫兹波聚焦在所述待检测样品上的第一透镜组和用于将经过所述待检测样品后的太赫兹波聚焦在所述光电导接收天线的第二透镜组。
进一步地，所述第一透镜组包括两个沿光路依次设置的聚丙烯透镜，所述第二透镜组包括两个沿光路依次设置的聚丙烯透镜。
进一步地，所述光纤拉伸系统包括伸缩杆、可驱动所述伸缩杆进行伸缩的电机和用于缠绕光纤的伸缩部，所述伸缩杆的一端与所述电机连接，所述伸缩杆的另一端与所述伸缩部连接并可带动所述伸缩部扩张或收缩，所述光纤缠绕在所述伸缩部的外表面。
进一步地，所述光电导接收天线与所述数据处理机构之间还设有锁相放大模块。
进一步地，所述锁相放大模块包括用于将输入信号放大的信号通道、用于提供与所述输入信号同相位的参考信号的参考通道、相敏检波器以及低通滤波器，所述信号通道和所述参考通道均与所述相敏检波器连接，所述相敏检波器与所述低通滤波器连接。
进一步地，所述信号通道包括与所述光电导接收天线连接的锁相放大器，所述锁相放大器与所述相敏检波器连接；
所述参考通道包括依次连接的方波信号源和移相器，所述移相器与所述相敏检波器连接。
进一步地，所述数据处理系统包括数据处理模块和对所述待检测样品进行识别的计算机，所述数据处理模块通过网线与所述计算机连接，所述数据处理模块与所述锁相放大模块连接。
本发明实施例提供的一种太赫兹检测装置的有益效果在于：
（1）由于采用了太赫兹波对待检测样品进行检测，太赫兹时域光谱技术具有可进行无损检测及样品探测、获取物质信息方便快捷、对外界条件要求低等特点，从而使得太赫兹检测装置不仅可以对多种物质进行识别，而且拓展了太赫兹检测装置的应用场景。
（2）太赫兹检测装置可以对待检测样品进行自动识别，而不需要人工进行辅助识别，从而大大提高了安全检查的效率，满足不同场景的使用需求。
为了更清楚地说明本发明实施例中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本发明实施例提供的太赫兹检测装置的系统原理示意图；
图2为本发明实施例提供的太赫兹检测装置的激光锁模原理示意图；
图3为本发明实施例提供的太赫兹检测装置的重复频率锁定机构示意图；
图4为本发明实施例提供的太赫兹检测装置的色散补偿系统的一种结构示意图；
图5为本发明实施例提供的太赫兹检测装置的色散补偿系统的另一种结构示意图；
图6为本发明实施例提供的太赫兹检测装置的色散补偿系统的负色散啁啾光纤光栅的结构示意图；
图7为本发明实施例提供的太赫兹检测装置的色散补偿系统的正色散啁啾光纤光栅的结构示意图；
图8为本发明实施例提供的太赫兹检测装置的光纤拉伸系统的结构示意图；
图9为本发明实施例提供的太赫兹检测装置的光纤拉伸器的结构示意图；
图10为本发明实施例提供的太赫兹检测装置的锁相放大模块的结构示意图；
图11为本发明实施例提供的太赫兹检测装置测量饮料示意图；
图12为本发明实施例提供的太赫兹检测装置测量待检测样品时的反射脉冲的波形示意图。
为了使本发明所要解决的技术问题、技术方案及有益效果更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅用以解释本发明，并不用于限定本发明。
需要说明的是，当元件被称为“设置于”另一个元件，它可以直接在另一个元件上或者间接在该另一个元件上。当一个元件被称为是“连接于”另一个元件，它可以是直接连接到另一个元件或间接连接至该另一个元件上。此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括一个或者更多个该特征。在本发明的描述中，“多个”的含义是两个或两个以上，除非另有明确具体的限定。
请参阅图1，一种太赫兹检测装置，包括用于产生激光的激光系统1、用于对激光进行色散补偿的色散补偿系统2、光分束器3、用于对激光进行延时扫描的光纤拉伸系统4、用于发射和接收太赫兹波并对待检测样品6进行检测的样品检测系统5和用于对测试数据进行分析的数据处理系统7，激光系统1通过光纤10与色散补偿系统2连接，色散补偿系统2通过光纤10与光分束器3连接，光分束器3通过光纤10同时与光纤拉伸系统4、样品检测系统5连接，光纤拉伸系统4通过光纤10与样品检测系统5连接，同时样品检测系统5与数据处理系统7连接。
本实施例提供的一种太赫兹检测装置的工作原理如下：首先激光系统1产生的激光通过光纤10传输到色散补偿系统2，并通过色散补偿系统2预先进行色散补偿；然后激光通过光分束器3后分成两束，一束激光到达样品检测系统5后用于发射太赫兹波，太赫兹波照射到待检测样品6上后会携带待检测样品6的信息，然后携带待检测样品6的信息的太赫兹波被样品检测系统5接收；另一束激光通过光纤拉伸系统4后到达样品检测系统5，并与携带待检测样品6的信息的太赫兹波进行耦合形成测试数据；然后测试数据传输到数据处理系统7进行处理，对待检测样品6进行识别，从而实现对易燃易爆物品的判断及报警。
其中，由于太赫兹波的独特性质，太赫兹时域光谱技术具有以下优点：
（1）频带宽：具有大约从0.1THz ~ 5THz的频带宽度。
（2）信噪比高：太赫兹时域光谱系统在小于3THz时信噪比可高达10
4，远高于傅里叶变换红外光谱技术，且具有较好的稳定性。
（3）可进行无损检测及样品探测：利用太赫兹时域光谱技术可以有效探测待检测样品反映于太赫兹波段的各种物理信息和化学信息等方面的信息，从而可用于进行物质的定性鉴别分析。此外，由于太赫兹波的安全性和穿透性，使其适合用来对生物组织进行无损检测。太赫兹时域光谱技术还具有探测灵敏度高以及能在室温下稳定工作等特点，因此可以广泛应用于样品的探测。
（4）获取介质信息方便快捷：利用太赫兹时域光谱技术能够方便、迅速地获取多种材料信息，如电介质材料、生物大分子以及半导体材料等的振幅和相位信息，也可以直接反映出导电材料中的载流子信息；同时，太赫兹时域光谱的相干性使电场波形包含了太赫兹脉冲的强度、相位、时间等完整信息，通过傅立叶变换使其转换为频谱信号，便可得到吸收光谱与色散光谱。
（5）对外界条件要求低：太赫兹时域光谱系统可在室温下工作，省去了复杂的制冷系统。
（6）非接触测量：太赫兹辐射能够直接反映导电材料中载流子的信息，因而太赫兹时域光谱系统比基于霍尔（Hall）效应的非接触性测量更为方便、有效。
（7）安全无害：太赫兹波的单光子能量低，1THz对应4.1meV的能量，检测物质时不会破坏被检测物质的成分，且对操作人员也是安全的。
本实施例提供的一种太赫兹检测装置的有益效果在于：
（1）由于采用了太赫兹波对待检测样品6进行检测，太赫兹时域光谱技术具有可进行无损检测及样品探测、获取物质信息方便快捷、对外界条件要求低等特点，从而使得太赫兹检测装置不仅可以对多种物质进行识别，而且拓展了太赫兹检测装置的应用场景。
（2）太赫兹检测装置可以对待检测样品6进行自动识别，而不需要人工进行辅助识别，从而大大提高了安全检查的效率，满足不同场景的使用需求。
本实施例提供的太赫兹检测装置内设有锂电池，可方便进行户外检测，同时也可以防止由于瞬间断电而无法进行检测，以及可以对设备进行保护。太赫兹检测装置的底部还设有万向轮，从而使得太赫兹检测装置可以随意移动，从而可以根据需要在任何位置进行检测。
请参阅图2，进一步地，激光系统1包括依次连接的激光器11、可饱和吸收体12、光耦合器13、增益光纤14和光纤光栅15，光耦合器13与可饱和吸收体12连接的一侧还连接有泵浦源16。优选地，激光器11为飞秒激光器，从而可以产生飞秒激光脉冲。
由于可饱和吸收体12对弱光吸收大，而对强光吸收少，因此当激光器11产生的激光强度太低时，激光会被可饱和吸收体12吸收，而当激光器11产生的激光强度变高时，激光才会透过可饱和吸收体12，因此采用可饱和吸收体12，可保证激光器11的输出功率满足要求。在本实施例中，激光器11的输出功率高于80 mW，飞秒激光脉冲的脉冲宽度小于100 fs。
由于泵浦源16与经过可饱和吸收体12的激光在光耦合器13中进行耦合，耦合后的激光经过增益光纤14进行增益，并经过光纤光栅15进行滤波，从而可以获得特定波长的激光，满足使用要求。
请参阅图3，进一步地，激光系统1还包括重复频率锁定机构，重复频率锁定机构可用于锁定激光器11产生的激光的频率；激光器11设有可用于调节其激光腔的腔长的压电陶瓷，优选为PZT压电陶瓷111，PZT压电陶瓷在PZT驱动110的控制下工作；重复频率锁定机构与PZT压电陶瓷111连接，同时重复频率锁定机构与激光器11连接。激光器产生的激光的一小部分光通过耦合器分光后进入到重复频率锁定机构中，经过重复频率锁定机构后产生相应的高压信号，然后高压信号通过PZT驱动110控制PZT压电陶瓷111运动，从而改变激光腔的腔长，进而对激光的频率进行调节，使得输出激光的重复频率稳定。
在本实施例中，重复频率锁定机构包括依次连接的光电探测器171、带通滤波器172、混频器173、环路滤波器174和高压放大器175，光电探测器171与激光器11相连，高压放大器175与PZT压电陶瓷111连接，混频器173连接带通滤波器172的一侧还连接有基准信号发生器176，基准信号发生器176锁定在铷钟177上。
飞秒激光器产生的激光中有一小部分光通过耦合器分光后照射在光电探测器171上，并被光电探测器171捕获。光电探测器171输出频率为重复频率整数倍（记为N
f
rep
）的信号，该信号通过带通滤波器172可以进行滤波，从而获得需要频率的信号（即N
f
rep
的信号）。优选地，N为4，即光电探测器171输出频率为4倍重复频率，经过带通滤波器172后获得的是重复频率的四次谐波；当然，也可以获得更高次的谐波；事实上，混频输入的谐波次数越高，系统对频率的变化越敏感，从而形成闭环控制系统后可以获得更高的稳定度。
经过带通滤波器172后的信号与基准信号发生器176产生的基准信号进入混频器173进行混频，从而可得到差频信号。基准信号发生器76锁定在铷钟177上，并且根据待锁定的重复频率设定基准信号的频率，在本实施例中，基准信号的频率为1000
MHz。差频信号进入环路控制器174后输出补偿控制信号，补偿控制信号通过高压放大器175后得到高压信号，用于控制PZT驱动110，从而控制PZT压电陶瓷111，通过PZT压电陶瓷111的微小位移改变激光腔的腔长，从而可以抑制重复频率的微小波动，最终动态跟踪上基准信号（即锁定至基准信号），从而使得重复频率
f
rep
获得和铷钟177同样的稳定度，确保输出激光的重复频率稳定。
其中环路控制器174是整个重复频率锁定机构的核心，不仅具有低通滤波的作用，而且还可以改善系统的动态响应特性和稳定特性。
进一步地，环路控制器174包括比例积分控制器和直流偏置电路，其中比例积分控制器的功能是改善系统的动态响应特性，而直流偏置电路是为了在锁定前寻找合适的频率点，为实现快速锁定做准备。比例积分控制器包括带宽选择部分、积分环节部分和低频增益限制（Low
Frequency Gain Limit，简写为LFGL）部分；其中带宽选择部分是为了选择合适的带宽，在未锁定时，将环路切换到宽带的位置，便于快速扫频，当锁定时再把环路切换到窄带的位置，减小误差，提高锁定性能；低频增益限制部分用于限制低频增益，防止在锁定的瞬间由于条件不合适而发生积分饱和，在锁定前限制低频增益，寻找锁定点，待锁定后解除限制，从而进入纯积分环节。上述设置使得重复频率锁定过程的操作更加灵活，有利于快速找到锁定点，高效准确地完成锁定。常用的飞秒激光器的重复频率的稳定性在20 Hz左右（即重复频率±20 Hz），在本实施例中，飞秒激光重复频率可稳定在100
MHz±1mHz，从而极大提高了飞秒激光器的稳定性。
请参阅图4，进一步地，色散补偿系统2包括用于调整激光传输方向的光纤环形机构，用于对激光进行色散补偿、且色散补偿量相反的第一啁啾光纤光栅221和第二啁啾光纤光栅222，光纤环形机构设有用于与光纤10连接的输入端，光纤10用于传输激光100，第一啁啾光纤光栅221和第二啁啾光纤光栅222均与光纤环形机构连接，且激光100依次通过第一啁啾光纤光栅221和第二啁啾光纤光栅222后从光纤环形机构中出射，第一啁啾光纤光栅221和第二啁啾光纤光栅222对激光100的色散补偿量的绝对值不相等。
色散补偿系统2的工作原理如下：首先将传输激光100的光纤10与光纤环形机构连接，同时将第一啁啾光纤光栅221、第二啁啾光纤光栅222与光纤环形机构顺次连接，从而使得激光100通过光纤3进入到光纤环形机构中后，依次通过第一啁啾光纤光栅221和第二啁啾光纤光栅222进行色散补偿，然后从光纤环形机构中出射。由于第一啁啾光纤光栅221和第二啁啾光纤光栅222的色散补偿相反且色散补偿量不相等，因此当激光100依次通过第一啁啾光纤光栅221和第二啁啾光纤光栅222后，其总色散补偿量为第一啁啾光纤光栅221的色散补偿量和第二啁啾光纤光栅222的色散补偿量之和，且总色散补偿量可以达到fs/nm（飞秒/纳米）的量级，从而可以对飞秒激光的微小色散量进行补偿。
这样设置的有益效果在于：由于设置有用于对激光100进行色散补偿、且色散补偿相反的第一啁啾光纤光栅221和第二啁啾光纤光栅222，因此当激光100依次通过第一啁啾光纤光栅221和第二啁啾光纤光栅222后，总色散补偿量可以达到fs/nm的量级，从而可以对飞秒激光的微小色散量进行补偿，有效保障激光传输的可靠性。
请参阅图,4，在一个实施例中，光纤环形机构包括第一光纤环形器211，第一光纤环形器211包括沿激光传输方向设置的第一输入端口2110、第一端口2111、第二端口2112和第三端口2113，第一输入端口2110与光纤10连接，第一端口2111与第一啁啾光纤光栅221连接，第二端口2112与第二啁啾光纤光栅222连接。通过第一光纤环形器211将第一啁啾光纤光栅221和第二啁啾光纤光栅222连接，不仅可以实现对激光100的微小色散补偿，而且结构紧凑，安装方便。优选地，第一光纤环形器211为四端口光纤环形器。
请参阅图5，在一个实施例中，光纤环形机构包括第二光纤环形器212和第三光纤环形器213，第二光纤环形器212包括沿激光传输方向设置的第二输入端口2120、第四端口2121和第五端口2122，第三光纤环形器213包括沿激光传输方向设置的第三输入端口2130、第七端口2131和第八端口2132，第二输入端口2120与光纤10连接，第四端口2121与第一啁啾光纤光栅221连接，第五端口2122与第三输入端口2130连接，第七端口2131与第二啁啾光纤光栅222连接。优选地，第二光纤环形器212为三端口光纤环形器，第三光纤环形器213为三端口光纤环形器，第二光纤环形器212和第三光纤环形器213通过光纤103相互连接。通过两个光纤环形器分别连接第一啁啾光纤光栅221和第二啁啾光纤光栅222，不仅可以实现对激光100的微小色散补偿，而且可以根据需要进行连接，安装更加灵活。
应当理解的是，第二光纤环形器212和第三光纤环形器213也可为其它类型的光纤环形器，例如四端口光纤环形器，在使用时，仅顺次使用其中的三个端口即可。
请参阅图6和图7，在一个实施例中，第一啁啾光纤光栅221内的折射率变化周期沿激光100入射方向逐渐增大，第二啁啾光纤光栅222内的折射率变化周期沿激光100入射方向逐渐减小。具体地，第一啁啾光纤光栅221为负色散啁啾光纤光栅，激光100中的不同频率的激光分量在负色散啁啾光纤光栅的不同位置发生全反射，其中高频激光分量1001发生全反射的位置比低频激光分量1002发生全反射的位置更深，使得高频激光分量1001的光程大于低频激光分量1002的光程，从而产生负色散；第二啁啾光纤光栅222为正色散啁啾光纤光栅，激光100中的不同频率的激光分量在正色散啁啾光纤光栅的不同位置发生全反射，其中高频激光分量1001发生全反射的位置比低频激光分量1002发生全反射的位置更浅，使得高频激光分量1001的光程小于低频激光分量1002的光程，从而产生正色散。事实上，在实际使用时，只需要将负色散啁啾光纤光栅反向与光纤环形器连接，即可得到正色散啁啾光纤光栅。
在一个实施例中，第一啁啾光纤光栅221内的折射率变化周期沿激光100入射方向逐渐减小，即第一啁啾光纤光栅221为正色散啁啾光纤光栅；第二啁啾光纤光栅222内的折射率变化周期沿激光100入射方向逐渐增大，即第二啁啾光纤光栅222为负色散啁啾光纤光栅。
由于第一啁啾光纤光栅221和第二啁啾光纤光栅222产生的色散补偿相反，因此当激光100依次经过第一啁啾光栅221和第二啁啾光纤光栅222后，第一啁啾光纤光栅221的色散补偿量和第二啁啾光纤光栅222的色散补偿量之和为激光100实际获得的色散补偿量。
在本实施例中，可以通过改变曝光功率密度
I和曝光时间
t的方式来控制啁啾光纤光栅中的折射率变化幅度。折射率
n(
I,t)与曝光功率密度
I和曝光时间
t具有如下关系：
n(
I,t)
=AI
at
b
(
I)
其中
A为3.6×10
-7，为常数；
a为0.78，为常数；
b为曝光强度依赖系数，
b(
I)=0.165+0.028exp(-
I×1×10
-5)。
由上述公式可知，在曝光时间
t相同的情况下，当曝光功率密度
I的范围为0~600mW/cm
2时，折射率
n(
I,t)的变化和曝光功率密度
I的变化近似为线性，因此改变曝光功率密度
I可以很好地控制光纤的折射率
n(
I,t)的变化。得到光纤光栅中折射率
n(
I,t)微小差异后，即可得到光纤光栅中不同位置布拉格反射波长
λ
B的微小差异，其关系满足：
λ B=2
n
eff
Λ
其中
n
eff
为光纤有效折射率，
Λ为光栅周期。
不同位置布拉格反射波长微小差异
λ
B，表示在啁啾光纤光栅的同一位置，满足反射条件的波长具有微小差异，或者相同频率的两束光在啁啾光纤光栅中的反射位置具有微小差异，整体考虑即为啁啾光纤光栅的色散补偿量具有微小差异。
将曝光功率密度
I的值设定为450 mW/cm
2时可得到色散补偿量为14 ps/nm色散量的光纤光栅，而曝光功率密度
I的设定值为440 mW/cm
2时可得到色散补偿量为13.95 ps/nm光纤光栅。在实际使用时，将上述两个光纤光栅与光纤环形器反向连接，其总色散补偿量为两个光纤光栅的色散补偿量之和，即为50 fs/nm（即0.05 ps/nm），因此总色散补偿量可以达到fs/nm的量级，从而可以对飞秒激光的微小色散量进行补偿。
进一步地，第一啁啾光纤光栅21和第二啁啾光纤光栅22的总色散补偿量的绝对值的范围为50 fs/nm~100 fs/nm。优选地，总色散补偿量的绝对值为50 fs/nm，从而可对飞秒激光的微小色散量进行补偿，有效保障激光传输的可靠性。
请参阅图1，进一步地，样品检测系统5包括用于发射太赫兹波的光电导发射天线51、用于接收太赫兹波的光电导接收天线52和用于对太赫兹波进行聚焦的光学组件52，光电导发射天线51与光分束器3连接，光电导接收天线52与光纤拉伸系统4连接且光电导接收天线52与数据处理系统7连接。光学组件53包括用于将光电导发射天线51产生的太赫兹波聚焦在待检测样品6上的第一透镜组和用于将经过待检测样品56后的太赫兹波聚焦在光电导接收天线52的第二透镜组。
优选地，光分束器3与光电导发射天线51之间还设有光纤延时线54。目前的太赫兹时域光谱仪的延迟线是自由空间延迟线，其中大部分使用移动平台进行延时。这样的设备缺乏稳定性且容易受到振动和温度波动而导致延迟失调。而本实施例中采用光纤延时线，稳定性高，且易于集成。
在本实施例中，光学组件53包括四个聚烯烃透镜，其中第一透镜组包括两个聚烯烃透镜，第二透镜组包括另外两个聚烯烃透镜，聚烯烃透镜可以是非球面镜或球面镜，用于对太赫兹波进行准直聚焦。光电导发射天线51发射的太赫兹波首先经过第一透镜组的两个聚烯烃透镜后聚焦至待检测样品6的表面，并在待检测样品6的表面反射后携带了待检测样品6的信息，然后太赫兹波经过第二透镜组的两个聚烯烃透镜后被光电导接收天线52接收，并转化为相应的电信号。
请参阅图8和图9，传统的光纤拉伸器使用压电陶瓷拉伸光纤，这些压电体通常由大功率高压源驱动，驱动器成本高，高压电源也容易对周围电路造成干扰，不利于设备集成。本实施例提供的光纤拉伸系统4包括用于对激光进行分束的第一耦合器43、两个光纤拉伸器、用于对激光进行合束的第二耦合器44、用于将光信号转换为电信号的光电探测器45和用于将电信号转化为可视化图形的显示装置46。优选地，显示装置46为示波器，从而可以将电信号转化为可视化的时域波形。
为了便于描述，两个光纤拉伸器分别记为第一光纤拉伸器4101和第二光纤拉伸器4102。光分束器3通过光纤10与第一耦合器43连接，第一耦合器43通过光纤10同时与第一光纤拉伸器4101、第二光纤拉伸器4102连接，第一光纤拉伸器4101、第二光纤拉伸器4102通过光纤10均与第二耦合器44连接，第二耦合器44通过光纤10与光电探测器45连接，光电探测器45与显示装置46连接。
其中，与第一光纤拉伸器4101连接的光纤10缠绕在第一光纤拉伸器4101的外表面，与第二光纤拉伸器4102连接的光纤10缠绕在第二光纤拉伸器4102的外表面。第一光纤拉伸器4101所在的一端为参考臂，第二光纤拉伸器102所在的一端则作为信号臂。
本实施例提供的光纤拉伸系统4的工作原理如下：
激光经过光纤10传输到第一耦合器处；
激光经过第一耦合器43后分成两束，一束通过缠绕在第一光纤拉伸器4101的光纤10传输到第二耦合器44处，另一束通过缠绕在第二光纤拉伸器4102的光纤10传输到第二耦合器44处；
两束到达第二耦合器44的激光经过第二耦合器44后合并成一束，并通过光纤10传输到光电传感器45处；
光电传感器45将接收到的光信号转变为电信号，并将电信号传递到显示装置46处；
显示装置46将电信号转换为可视化图形并进行显示。
具体地，当作为参考臂的第一光纤拉伸器4101处的光纤10和作为信号臂的第二光纤拉伸器4102处的光纤10的拉伸长度一致时，两束激光所经历的光程一样，因此光程差为零；然后，对作为信号臂的第二光纤拉伸器4102施加三角波调制信号，从而使得经过第二光纤拉伸器4102处的光纤10传输的激光的光程与经过第一光纤拉伸器4101处的光纤10传输的激光的光程不同，从而产生光程差；由于两束激光传递到第二耦合器后合并成一束，当合并后的激光传输到光电传感器45处时会发生干涉；通过对干涉信号进行分析，即可获得光程差，从而获得光纤的拉伸长度。
应当理解的是，第一光纤拉伸器4101与第二光纤拉伸器4102完全相同，从而可有效保证当电机处于初始状态、光纤10以相同的方式缠绕在第一光纤拉伸器4101或第二光纤拉伸器4102时，其光程差为零。将第一光纤拉伸器4101所在的一端作为参考臂，目的是为了解决因绕接弯曲而造成的光效应干涉条纹对比度降低的问题。
请参阅图9，进一步地，光纤拉伸器包括伸缩杆411、可驱动伸缩杆411进行伸缩的电机412和用于缠绕光纤10的伸缩部413，伸缩杆411的一端与电机412连接，伸缩杆411的另一端与伸缩部413连接并可带动伸缩部413扩张或收缩。
光纤拉伸器的工作原理如下：首先将电机412固定，并将电机412与伸缩杆411的一端连接，然后将伸缩杆411的另一端与伸缩部413连接，然后将光纤10缠绕在伸缩部413上；当需要对光纤10进行拉伸时，电机412接通电源，并根据需要驱动伸缩杆411伸长，从而可带动伸缩部413进行扩张，进而可带动缠绕在伸缩部413上的光纤10进行拉伸；当不需要对光纤10进行拉伸时，电机412驱动伸缩杆411回缩，从而可带动伸缩部413进行收缩，进而使得缠绕在伸缩部413上的光纤10收缩。
这样设置的有益效果在于：由于采用电机412驱动伸缩杆411运动、进而带动伸缩部413运动的方式对光纤10进行拉伸，从而可有效增大光纤10的拉伸长度，进而可增加激光在光纤10中的传输长度，从而增大了光程扫描范围。
进一步地，伸缩部413包括第一伸缩部4131和第二伸缩部4132，电机412设于第一伸缩部4131和第二伸缩部4132之间，且电机412与第一伸缩部4131固定连接，伸缩杆411也设于第一伸缩部4131和第二伸缩部4132之间，且伸缩杆的411另一端与第二伸缩部4132连接，光纤10缠绕在第一伸缩部4131和第二伸缩部4132的外表面。
当需要对光纤10进行拉伸时，电机412驱动伸缩杆411伸长，伸缩杆411带动第二伸缩部4132向远离第一伸缩部4131的方向运动，从而使得伸缩部413整体向外扩张，进而带动缠绕在第一伸缩部4131和第二伸缩部4132表面的光纤10进行拉伸；当不需要对光纤10进行拉伸时，电机412驱动伸缩杆411回缩，从而使得第二伸缩部4132向靠近第一伸缩部4131的方向运动，从而伸缩部413整体收缩，进而带动缠绕在第一伸缩部4131和第二伸缩部4132表面的光纤10收缩。
由于伸缩部413包括可相对运用的第一伸缩部4131和第二伸缩部4132，从而通过第一伸缩部4131和第二伸缩部4132的相对运动带动光纤10进行拉伸和收缩，不仅运动方式简单灵活，而且光纤10的拉伸长度容易调节，且可有效增大光纤10的拉伸长度，增大了光程扫描范围。
进一步地，第一伸缩部4131为第一半圆柱体，第一半圆柱体缠绕光纤10的表面为曲面；第二伸缩部4132为第二半圆柱体，第二伸半圆柱体缠绕光纤10的表面为曲面。优选地，第一伸缩部4131和第二伸缩部4132构成一个圆柱体，且第一伸缩部4131和第二伸缩部4132尺寸相同。由于光纤10缠绕在第一半圆柱体和第二半圆柱体的曲面上，因此光纤10在拉伸和收缩时更加平滑，从而使得光纤10的拉伸和收缩更加自然和精确，也防止了光纤10在拉伸和收缩过程中被损坏。
优选地，第一伸缩部4131的材料为金属，第二伸缩部4132的材料为金属。因此第一伸缩部4131和第二伸缩部4132质地坚硬，能更好地带动光纤10进行拉伸和收缩。应当理解的是，第一伸缩部4131的材料也可为其它质地坚定的材料，第二伸缩部4132的材料也可为其它质地坚硬的材料。
进一步地，电机412的数量为两个，伸缩杆411的数量相应为两个，两个电机412沿第一伸缩部4131的轴向排列固定，每个电机412均连接一个伸缩杆411，两个伸缩杆411的另一端均与第二伸缩部4132连接。优选地，两个电极412分别固定连接在靠近第一伸缩部4131的两端的位置，从而使得第一伸缩部4131在运动过程中更加平稳，进而使得光纤10的拉伸和收缩更加平稳。
在本实施例中，电机412连接有电机驱动器，通过对电机驱动器进行控制，从而实现对电机412的运动方式的控制，进而对光纤拉伸器进行控制。光纤拉伸器对缠绕在伸缩部413上的光纤10的最大拉伸量为6 cm,从而可以实现延时200 ps。
请参阅图10，进一步地，光电导接收天线52与数据处理机构7之间还设有锁相放大模块8。由于经过光电导接收天线52转化的电信号能量较低，因此需要通过电流放大器放大后进入锁相放大模块8二次放大，然后再传输到数据处理系统7进行处理和分析。
为了压缩噪声的带宽，并提高信噪比，需要对信号进行放大和去噪声处理。锁相放大模块8在提取强噪声中的微弱信号时具有抗干扰能力强、信号精确度高等特点，并且能获取被测量信号的大小和方向的变化，因而可广泛应用于信号检测。
锁相放大模块8包括信号通道、参考通道、相敏检波器84（简写为PSD）和低通滤波器85。信号通道包括与光电导接收天线52连接的锁相放大器81，其作用是先把伴有噪声的被以参考信号相同频率调制的输入信号放大，并经选放初步减小噪声。参考通道包括依次连接的方波信号源82和移相器83，其作用是提供一个与输入信号同相位的参考信号，参考信号为方波信号。移相器83和锁相放大器81均与相敏检波器84相连，相敏检波器84的作用是对输入信号和参考信号进行混频，输出和频信号和差频信号。相敏检波器84与低通滤波器85相连，低通滤波器85的作用是将和频信号滤除，仅保留差频信号。保留的差频信号进行放大处理后输出。在本实施例中，为实现低成本小体积的锁相放大器，采用平衡调制解调器进行锁相放大，以提取被噪声淹没的微弱太赫兹信号，其动态范围宽，达到100
dB，能检测pＡ级的信号。
进一步地，数据处理系统7包括数据处理模块71和对待检测样品6进行识别的计算机72，数据处理模块71通过网线与计算机72连接，数据处理模块71与锁相放大模块8连接。
进一步地，数据处理模块71也具有控制作用，可以控制太赫兹检测装置的各个系统的工作状态。具体地，数据处理模块71可以对激光系统1的工作状态进行控制，从而控制激光系统1是否开始工作。数据处理模块71可以通过电机驱动器控制电机412的运动状态，从而控制光纤拉伸系统4的工作状态。数据处理模块71可以对光电导发射天线51的工作状态进行控制，从而控制光电导发射天线51是否发射太赫兹波。同时数据处理模块71也可以对锁相放大模块8的工作状态进行控制。
数据处理模块71采用等效采样方法提取时域电场信号，并通过光纤拉伸系统4改变两个激光脉冲之间的时间延迟，将高频、快速信号转变为低频、慢速信号进行处理，从而准确重建太赫兹波形，实现太赫兹信号的有效采集及分析及噪声抑制。
虽然利用光电导探测技术可以得到一个正比于太赫兹辐射场的瞬变电流，但由于太赫兹时域信号大约在皮秒（ps）量级甚至更短，电流响应时间上升沿基本都在亚皮秒量级，普通的电流探测器很难测到该信号，因此需要利用等效时间采样技术提取太赫兹时域电场信号。由于激光脉冲为飞秒激光脉冲，其持续时间远小于太赫兹脉冲的持续时间，通过改变两个激光脉冲之间的时间延迟，可以把高频、快速信号转变为低频、慢速信号处理，在重复信号的每个周期或相隔几个周期取一个样，而每个取样点分别取自每个输入信号波形不同的位置上，若干个取样点组成一个周期，可以组成类似于原信号一个周期的波形，进而可以提取出太赫兹波形。
进一步地，计算机72采用的易燃易爆物品识别算法为反射式太赫兹时域光谱系统（简写为THz-TDS系统）的识别算法。
常见的THz-TDS系统可分为两类：透射式和反射式。利用透射式THz-TDS技术通过测量各类物质的透射谱，提取光学参数，从而对物质进行识别。然而采用透射式THz-TDS技术进行测量时需要和物质的两端接触，对液体、特别是在太赫兹波段具有很强吸收性的液体，透射式THz-TDS技术在实用性和通用性上都有极大的瓶颈。相对而言，采用反射式THz-TDS技术时，由于太赫兹波仅在容器内壁界面上和液体作用、而不需要透射过液体，因此在液体强吸收性的问题上展现出了优越性。
传统利用反射式THz-TDS技术对不同液体进行识别检测时，在数据处理的过程中需要把时域信号转换到频域；然而在实际应用中由于容器壁往往很薄，参考信号和检测信号相距很近，使得数据处理困难，因此该方法实用程度不高，不能适应不同厚度的容器或包装。
本实施例提供的太赫兹检测装置利用不同物质的折射率不同、从而导致检测信号光脉冲的振幅和形状不相同的特性，针对时域的检测信号光脉冲，利用模式识别的方法对容器或包装内的物品成分进行判别。
本实施例提供的太赫兹检测装置的易燃易爆物品识别算法的过程为：
首先利用主成分分析进行数据降维，实现数据的特征提取；
利用人工智能算法（例如可采用线性判别分析或支持向量机算法设计），对物品安全与否进行判别。
由于无需进行傅里叶变换转换到频域再分析，因而可以减少物质判别的时间。
请参阅图11和图12，以检测饮料成分为例，说明本实施例利用太赫兹时域光谱技术危险品识别的方法。太赫兹脉冲611在空气、液体瓶602和液体601中传播时，分别在空气与瓶外壁603接触处、瓶内壁604与液体601接触处发生两次反射。反射率的菲涅尔公式为：
r = (
n 2 cos θ-
n 1 cos θ)/(
n 2 cos θ+
n 1 cos θ)
其中
n
1、
n
2为相接触的两种材料的折射率，
θ角为入射角。
第一次测量太赫兹脉冲611在空气、液体瓶602和空气界面上传播，可以获得第一反射脉冲612，从而可以测量出液体瓶602的材料的介电常数和厚度；当得到液体瓶602的材料参数后，再进行一次在空气、液体瓶602的瓶内壁604和液体601界面的测量，可以获得第二反射脉冲613，通过数据处理后可以得到液体601的介电常数。
不同的液体601在反射不同形状的太赫兹脉冲。对不同液体的反射脉冲形状进行主成分分析，计算得到其累积方差值，累积方差公式如下：
R=[∑(
Y
i
r
-
Y
i
p
)
2]/
N
其中，
N为校准样品集中样品的数量，
Y
i
r
是样品的第i个参考值，
Y
i
p
是样品的第i个预测值。对累积方差值进行阈值判断，超过阈值则为危险品。
以上所述仅为本发明的实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。
Claims (15)
- 一种太赫兹检测装置，其特征在于：包括用于产生激光的激光系统、用于对所述激光进行色散补偿的色散补偿系统、光分束器、用于对所述激光进行延时扫描的光纤拉伸系统、用于产生和接收太赫兹波并对待检测样品进行检测的样品检测系统和用于对测试数据进行分析的数据处理系统，所述激光系统通过光纤与所述色散补偿系统连接，所述色散补偿系统通过光纤与所述光分束器连接，所述光分束器通过光纤同时与所述光纤拉伸系统、所述样品检测系统连接，所述光纤拉伸系统通过光纤与所述样品检测系统连接，同时所述样品检测系统与所述数据处理系统连接。
- 如权利要求1所述的太赫兹检测装置，其特征在于：所述激光系统包括依次连接的激光器、可饱和吸收体、光耦合器、增益光纤和光纤光栅，所述光耦合器与所述可饱和吸收体连接的一侧还连接有泵浦源。
- 如权利要求2所述的太赫兹检测装置，其特征在于：所述激光系统还包括重复频率锁定机构，所述重复频率锁定机构用于锁定所述激光器产生的激光的频率，所述激光器设有可用于调节其激光腔的腔长的压电陶瓷，所述重复频率锁定机构与所述压电陶瓷连接，同时所述重复频率锁定机构与所述激光器连接。
- 如权利要求3所述的太赫兹检测装置，其特征在于：所述重复频率锁定机构包括依次连接的光电探测器、带通滤波器、混频器、环路滤波器和高压放大器，所述光电探测器与所述激光器相连，所述高压放大器与所述压电陶瓷连接，所述混频器连接所述带通滤波器的一侧还连接有基准信号发生器，所述基准信号发生器锁定在铷钟上。
- 如权利要求1所述的太赫兹检测装置，其特征在于：所述色散补偿系统包括用于调整所述激光传输方向的光纤环形机构，用于对所述激光进行色散补偿、且色散补偿量相反的第一啁啾光纤光栅和第二啁啾光纤光栅，所述光纤环形机构设有用于与光纤连接的输入端，所述光纤用于传输所述激光，所述第一啁啾光纤光栅和所述第二啁啾光纤光栅均与所述光纤环形机构连接，且所述激光依次通过所述第一啁啾光纤光栅和所述第二啁啾光纤光栅后从所述光纤环形机构中出射，所述第一啁啾光纤光栅和所述第二啁啾光纤光栅的色散补偿量的绝对值不相等。
- 如权利要求1所述的太赫兹检测装置，其特征在于：所述样品检测系统包括用于产生太赫兹波的光电导发射天线、用于接收所述太赫兹波的光电导接收天线和用于对所述太赫兹波进行聚焦的光学组件，所述光电导发射天线与所述光分束器连接，所述光电导接收天线与所述光纤拉伸系统连接且所述光电导接收天线与所述数据处理系统连接。
- 如权利要求6所述的太赫兹检测装置，其特征在于：所述光分束器与所述光电导发射天线之间还设有光纤延时线。
- 如权利要求6所述的太赫兹检测装置，其特征在于：所述光学组件包括用于将所述光电导发射天线产生的太赫兹波聚焦在所述待检测样品上的第一透镜组和用于将经过所述待检测样品后的太赫兹波聚焦在所述光电导接收天线的第二透镜组。
- 如权利要求8所述的太赫兹检测装置，其特征在于：所述第一透镜组包括两个沿光路依次设置的聚丙烯透镜，所述第二透镜组包括两个沿光路依次设置的聚丙烯透镜。
- 如权利要求6所述的太赫兹检测装置，其特征在于：所述光纤拉伸系统包括用于对激光进行分束的第一耦合器、两个光纤拉伸器、用于对激光进行合束的第二耦合器、用于将光信号转换为电信号的光电探测器和用于将电信号转化为可视化图形的显示装置，所述光分束器与所述第一耦合器通过光纤连接，所述第一耦合器同时与两个所述光纤拉伸器通过光纤连接，两个所述光纤拉伸器均与所述第二耦合器通过光纤连接，所述第二耦合器与所述光电探测器通过光纤连接，所述光电探测器与所述显示装置连接。
- 如权利要求10所述的太赫兹检测装置，其特征在于：所述光纤拉伸器包括伸缩杆、可驱动所述伸缩杆进行伸缩的电机和用于缠绕光纤的伸缩部，所述伸缩杆的一端与所述电机连接，所述伸缩杆的另一端与所述伸缩部连接并可带动所述伸缩部扩张或收缩，所述光纤缠绕在所述伸缩部的外表面。
- 如权利要求6所述的太赫兹检测装置，其特征在于：所述光电导接收天线与所述数据处理机构之间还设有锁相放大模块。
- 如权利要求12所述的太赫兹检测装置，其特征在于：所述锁相放大模块包括用于将输入信号放大的信号通道、用于提供与所述输入信号同相位的参考信号的参考通道、相敏检波器以及低通滤波器，所述信号通道和所述参考通道均与所述相敏检波器连接，所述相敏检波器与所述低通滤波器连接。
- 如权利要求13所述的太赫兹检测装置，其特征在于：所述信号通道包括与所述光电导接收天线连接的锁相放大器，所述锁相放大器与所述相敏检波器连接；所述参考通道包括依次连接的方波信号源和移相器，所述移相器与所述相敏检波器连接。
- 如权利要求12所述的太赫兹检测装置，其特征在于：所述数据处理系统包括数据处理模块和对所述待检测样品进行识别的计算机，所述数据处理模块通过网线与所述计算机连接，所述数据处理模块与所述锁相放大模块连接。
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