CN111024622B

CN111024622B - Compact detection system for realizing handheld terahertz reflection spectrum detection

Info

Publication number: CN111024622B
Application number: CN201911195111.1A
Authority: CN
Inventors: 曹恩达; 于勇; 赵一鸣; 宋长波
Original assignee: Beijing Research Institute of Telemetry; Aerospace Long March Launch Vehicle Technology Co Ltd
Current assignee: Beijing Research Institute of Telemetry; Aerospace Long March Launch Vehicle Technology Co Ltd
Priority date: 2019-11-28
Filing date: 2019-11-28
Publication date: 2022-04-22
Anticipated expiration: 2039-11-28
Also published as: CN111024622A

Abstract

A compact detection system for realizing handheld terahertz reflection spectrum detection comprises a terahertz detection head optical subsystem consisting of a collimating lens group, a beam shrinking lens group, a THz deflection optical path, a THz window and a 3D printed detection head structure, a terahertz source subsystem consisting of a femtosecond laser, an optical fiber, a coupler and a THz emitter, and a terahertz detector subsystem consisting of the femtosecond laser, an optical delay line, the optical fiber, the coupler, a THz receiver, an amplifier and a computer; the terahertz detection head optical subsystem uniformly collimates divergent terahertz waves emitted by a terahertz source to be incident on the surface of a detection substance and focuses the reflected terahertz waves to a terahertz detector receiving surface; the terahertz wave emitted by the terahertz source is collimated into uniform parallel light by the collimating lens group, then emitted from the terahertz window through the deflection light path to irradiate the surface of the detection substance, and finally the reflected terahertz wave is focused to the photosensitive surface of the THz receiver through the beam shrinking lens group by the terahertz window and the deflection light path.

Description

Compact detection system for realizing handheld terahertz reflection spectrum detection

Technical Field

The invention relates to a compact detection system for realizing handheld terahertz reflection spectrum detection, which adopts a transmission type light path and is used for solving the problem that the existing terahertz reflection spectrum detection light path for realizing beam expanding, collimating and focusing actions by using a reflector is too huge and cannot realize miniaturized handheld detection. The invention adopts the TPX material which is transparent in THz and visible light wave bands, reduces the difficulty of adjusting the transmission type optical path, and is suitable for a terahertz time-domain spectroscopy detection system (THz-TDS). Through the miniaturized compact design and the vapor-removing airtight design, the invention is ensured to be suitable for any industrial, public place or scientific research environment, and has excellent performance and high flexibility.

Background

As one of the most important new subjects in this century, the terahertz technology has great application value in a plurality of fields such as material analysis identification, material internal defect detection, coating thickness and density evaluation, integrated circuits, superconductor near-field probes and the like.

Because the vibration and rotation transition energy levels of the polar dipoles are in the terahertz photon energy range, many organic molecules have strong absorption and dispersion characteristics in the terahertz frequency range, terahertz spectra of different substances can present different spectral characteristics, even chiral isomeric molecules with the same chemical bond and molecular formula have different terahertz spectral characteristics, and unique identification information (fingerprint spectrum) is provided for the conformation of the molecules. Therefore, the identification of the substance components can be realized through the terahertz time-domain spectroscopy technology.

In 1984, the north american telegraph and telephone company (AT & T), Bell laboratory, and IBM's waters t.j. research center developed Terahertz time-domain spectroscopy (THz-TDS), the most widely studied Terahertz technology AT present. The principle of the THz-TDS technique is to obtain relevant physicochemical information of a material by measuring a pulsed terahertz radiation signal that has passed through or reflected from the surface of the object. By utilizing the THz-TDS technology, the terahertz spectrum of a substance can be obtained, and most of the current terahertz technology is applied based on the THz-TDS technology.

At present, the terahertz spectrum detection technology at home and abroad has been developed more mature, and the most typical terahertz spectrum detection technology is as follows: teraview company in England has produced a modularized TPS Spectra 3000 terahertz spectrometer, and can realize the detection of a terahertz probe, a transmission spectrum and a reflection spectrum by switching detection modules; a TeraScan continuous wave terahertz spectrum analysis system and a TeraFlash time domain spectrum analysis platform of Germany Toptica company; the development of a terahertz time-domain spectrometer based on femtosecond laser is developed by national major scientific instruments special for great-minded units, namely Daheng New era science and technology GmbH, and the development of the terahertz time-domain spectrometer is developed; the research institute of Beijing telemetry has completed the development of model machines of the gate-type terahertz time-domain spectrum security check instrument.

The development and the invention are basically based on the THz-TDS theory, but the common problem of the development and the invention is the problem that the miniaturization of an optical system for detecting the reflection spectrum cannot be realized, and the development and the invention cannot be applied to a handheld detection system in the fields of industry, security inspection and the like.

Compared with the transmission spectrum detection means, the reflection spectrum detection has the advantages that both solid matters and polar liquid can be detected, the detection signal to noise ratio is high, and the like. For polar liquid materials which strongly absorb terahertz waves, terahertz electric field change of a detection container wall and a liquid interface can be used for realizing high signal-to-noise ratio detection which cannot be realized by transmission spectrum, and further the application range of terahertz spectrum detection is expanded.

Although the exploration and research of a reflection terahertz spectrum detection system for a long time have been carried out at home and abroad, the products similar to the thought of the invention which can be found at present are not reported yet. The difference between the present invention and the present invention will be described by taking a reflected terahertz spectrum detection system developed by the air force research institute of brux city, texas, 2011 as an example.

According to the current available data, 2011 the united states research institute of brux city air force in texas developed a compact reflective terahertz spectral detection system for detecting optical parameters of biological tissues, and many tests were carried out. The terahertz working wave band of the system is 0.1-2.5THz, broadband THz radiation is generated by using a photoelectric switch technology, and the optical characteristics of ethanol, water, muscle, adipose tissue and skin can be measured in the 0.1-1.6THz wave band.

Disclosure of Invention

The technical problem solved by the invention is as follows: the defects of the prior art are overcome, and the compact detection system for realizing the handheld terahertz reflection spectrum detection is provided and used for realizing the uniform collimation irradiation of terahertz waves and the focusing, receiving and transmitting of diffuse reflection spectrum.

The technical scheme of the invention is as follows: a compact detection system for realizing handheld terahertz reflection spectrum detection comprises a femtosecond laser, an optical fiber, a coupler, a THz emitter, an optical delay line, a THz receiver, an amplifier, a computer, a collimating lens group, a beam shrinking lens group, a THz deflection light path, a THz window and a detection head structure printed in a 3D mode; after the femtosecond laser emits laser pulses and is divided, one path of laser passes through the optical fiber and the crystal of the coupler pumping THz emitter to excite the terahertz waves, the other path of laser passes through the optical delay line controlled by the computer to adjust the laser phase, and the free carriers are excited by the optical fiber and the crystal of the coupler pumping THz receiver photosensitive surface; terahertz waves excited by the THz emitter are shaped into uniform parallel light through the collimating lens group, then the uniform parallel light is emitted from the THz window through the THz deflection light path to irradiate the surface of a detection target, the terahertz waves reflected by the detection target are emitted into the beam shrinking lens group through the THz window and the THz deflection light path, the terahertz waves are uniformly focused on a photosensitive surface of a THz receiver after beam shrinking and shaping, carriers are modulated to move to generate electric signals, and the electric signals are amplified by the amplifier and then input to the computer to reconstruct a terahertz spectrum; and finally, the integrated forming and lightweight design of the optical subsystem of the terahertz detection head are realized through the 3D printed detection head structure, and the dry and sealed design of the detection system is further realized.

The THz source adopts a photoconductive effect, a broadband terahertz wave with the bandwidth reaching 5.5THz is excited by pumping InGaAs crystals by a mode-locked femtosecond fiber laser, the maximum value of the energy of the excited terahertz wave is 20 mu w, and the shortest time of single bandwidth scanning is 0.02 s.

The THz detector realizes synchronization of single bandwidth scanning time and a THz source through same femtosecond laser pump modulation, a THz electric field is sampled on an LT-InGaAs crystal which is focused by THz waves and grows at a low temperature by adopting a photoconductive sampling principle, the sampling signal is amplified by an amplifier, the dynamic range of the THz detector is larger than or equal to 90dB, and the corresponding detection spectral bandwidth reaches 5.5 THz.

The optical delay line consists of a twice total reflection prism, a motor and a slide rail, the femtosecond laser is coupled into the optical fiber through the total reflection of the twice total reflection prism of the optical delay line, the motor is controlled through a computer, the twice total reflection prism carries out periodic displacement on the slide rail, the periodic change of the optical path between the laser and the optical fiber coupler is realized, the phase of the femtosecond laser in the terahertz detector subsystem is modulated, and the sampling of an electric field for detecting the terahertz spectrum is realized; meanwhile, the femtosecond laser phase modulation rate is regulated and controlled by controlling the rotating speed of the motor, and the spectrum sampling frequency of the system is controlled.

The collimating lens group consists of two 1-inch-caliber TPX material plano-convex lens convex surfaces which are oppositely arranged at intervals of 35mm, and the beam shrinking lens group consists of a 1.5-inch lens and a 1-inch-caliber TPX material lens plano-convex lens convex surface which are oppositely arranged at intervals of 27 mm; the THz conversion optical path consists of two 1.5-inch-diameter terahertz-level gold-plated reflectors; the reflector for turning the terahertz wave of the collimating lens group is an A reflector, and the reflector for turning the terahertz wave of the beam shrinking lens group is a B reflector; the terahertz window is made of a terahertz-level z-cut quartz crystal with the caliber of 2 inches.

The optical axis of the transmitting optical path formed by the collimating lens group and the THz emitter and the optical axis of the receiving optical path formed by the beam reducing lens group and the THz receiver are arranged in parallel, and the optical axis of the transmitting and receiving optical path is arranged in a non-equal height mode relative to the structural substrate of the detecting head for 3D printing; A. b, the two reflectors rotate 15 degrees relatively in the horizontal direction relative to the base of the 3D printed probe structure, so that the distance between the transmitting and receiving optical paths is compressed to the maximum degree, and no position interference between the two reflectors in the THz folding optical path is ensured; the reflector A rotates 45 degrees relative to the direction of the optical axis of the straight mirror group towards the base of the detecting head structure printed in the 3D mode, and therefore the terahertz waves can be emitted from the THz window without being blocked; the B reflector rotates 42 degrees relative to the optical axis of the beam reducing mirror group towards the direction of the base of the detecting head structure printed in a 3D mode, and is placed asymmetrically with the A reflector, so that the terahertz waves reflected by the diffuse reflection detection target are incident into the beam reducing mirror group in parallel, and the THz window is arranged in a same receiving and transmitting mode.

The probe structure for 3D printing adopts photosensitive resin high-precision 3D printing, and the integrated molding of the optical subsystem structure of the terahertz probe is realized; a hollow porous structure is simultaneously designed under the tool structures of the THz emitter and the THz receiver of the 3D printing detection head structure, and a drying agent is placed, so that the anhydrous design of the optical subsystem of the terahertz detection head is realized.

The shell of the 3D printing probe structure is divided into two parts by adopting a nylon material for 3D printing, and the shell part with the functions of protecting the collimating and beam reducing lens group, the THz deflection light path and the THz window is realized; meanwhile, a sealing groove structure is designed, and a sealing rubber ring is arranged, so that the airtight design of the optical subsystem of the terahertz detection head is realized; a butt-joint airtight structure is designed at a shell handle part with a holding function, so that the optical subsystem of the terahertz detection head and data lines of other subsystems and connecting lines of optical fibers realize sealed rubber tube protection, and the airtight design of the connecting line part of each subsystem and the optical subsystem of the terahertz detection head is realized.

Compared with the prior art, the invention has the advantages that:

(1) the terahertz detection system is different from the existing imaging terahertz detection system, and obtains substance information by obtaining the reflection spectrum of the surface and the shallow layer of a detected object to perform detection and identification, so that the working wavelength range of the terahertz detection system is expanded; meanwhile, the terahertz transmission spectrum detection system is different from a complex terahertz reflection spectrum detection system consisting of a conventional linear long optical system light path and a multi-reflection parabolic mirror, and a THz deflection light path is introduced, so that the light path of the linear transmission spectrum detection system with a longer size is folded into a parallel transmitting and receiving light path, and the illuminating light path is folded to a vertical downward direction, so that the miniaturization of a transceiving co-location and optical system is realized, meanwhile, the introduction of a semi-transparent semi-reflective mirror is avoided, the high signal-to-noise ratio of the system is ensured, and the terahertz transmission spectrum detection system can be applied to a handheld terahertz spectrum detection system.

(2) The invention adopts the lightest organic polymer TPX at present as the optical material of the THz lens, can better realize the lightweight design of the detection system, because the material is transparent in the full wave band from visible light to terahertz, and the refractive index hardly changes along with the wavelength, can place the He-Ne laser at the position of the THz emitter during the installation and adjustment, as the reference during the installation and adjustment, in order to reduce the installation and adjustment difficulty and period.

(3) The terahertz wave detector has the characteristic of miniaturization of a transmission spectrum detection light path and the characteristic of uniqueness of a reflection spectrum when detecting polar material components such as liquid and the like which strongly absorb terahertz waves, and can also consider the miniaturization of a system and the universality in the aspect of detection application.

(4) Under the condition of realizing system compactness, the invention further designs a smart drying agent storage box and an airtight design of the system, can ensure that the dry atmosphere in the detection system reduces the absorption interference of water vapor, can exert the characteristic of the system for rapidly scanning spectrum under the fixation of the supporting cover of the shell structure, rapidly and repeatedly detects the same surface, and improves the signal-to-noise ratio through data processing.

Drawings

FIG. 1 is a schematic diagram of the working principle of the present invention;

FIG. 2 is a terahertz optical performance evaluation diagram of the key position of the optical system according to the invention;

Detailed Description

The composition schematic diagram of the compact detection system for realizing the handheld terahertz reflection spectrum detection is shown in the attached figure 1. The terahertz detector comprises an A terahertz source subsystem, a B terahertz detector subsystem, a C terahertz detector optical subsystem and a THz window, wherein the A terahertz source subsystem comprises a femtosecond laser, an optical fiber coupler and a THz emitter, the B terahertz detector subsystem comprises an optical delay line, an optical fiber coupler, a THz receiver, an amplifier and a computer, and the C terahertz detector optical subsystem comprises a THz collimating lens group, a THz beam shrinking lens group, a THz turning light path and a THz window.

The working principle of the A terahertz source subsystem is that an all-fiber femtosecond laser emits femtosecond laser pulses with 1550nm wave bands, after beam splitting, one path of laser for exciting terahertz waves is directly coupled and transmitted through a fiber coupler, and InGaAs crystals of a pumping THz emitter excite the terahertz waves.

The all-fiber femtosecond laser has the characteristics of small volume, high reliability and simple mode locking operation, and the volume and the weight of the terahertz source subsystem can be effectively reduced by adopting the laser; the InGaAs crystal is irradiated by ultrashort laser pulse of femtosecond laser to generate photoconductive effect, electron holes are excited to photo carriers, transient drift current with rapidly enhanced intensity is generated under the action of an external electric field, electrons jump from a valence band to a conduction band, and radiation generates coherent terahertz pulse, and compared with a metal-based semiconductor material, the InGaAs semiconductor can achieve the working bandwidth of 5.5 THz.

The working principle of the B terahertz detector subsystem is that the all-fiber femtosecond laser emits femtosecond laser pulses with 1550nm wave bands, after beam splitting, one path of laser of a modulation phase is emitted by the laser, and enters the optical fiber coupler after being folded by the twice total reflection prisms of the optical delay line. Firstly, the laser is modulated by a delay line, a twice total reflection prism in an optical delay line is driven by a motor controlled by a computer to perform periodic displacement on a slide rail, so that the periodic change of the optical path between a laser and an optical fiber coupler is realized, the phase of femtosecond laser in a terahertz detector subsystem is modulated, and the sampling of an electric field for detecting a terahertz spectrum is realized; meanwhile, the femtosecond laser phase modulation rate is regulated and controlled by controlling the rotating speed of the motor so as to control the spectrum acquisition rate of the system and realize that the maximum acquisition rate reaches 50 Hz; the femtosecond laser excites free carriers through an LT-InGaAs crystal of a photosensitive surface of the THz receiver pumped by the optical coupler, the carriers are pulled to move by a received photoelectric field of the terahertz echo, current signals are generated, and the current signals are input into a computer after being amplified by an amplifier and rebuild terahertz detection spectrum signals.

The terahertz spectrum reconstruction is completed once every time the prism of the optical delay line moves for one period, the average repeated sampling time can be set by adjusting the motor parameter to control the motion state of the prism, the spectrum is reconstructed by sampling for many times, and the performance of the system background noise in the spectrum is reduced; the LT-InGaAs crystal is an InGaAs semiconductor material grown at low temperature, and has a superlattice structure period which is similar to the wavelength of a terahertz wave, so that the enhancement of a nonlinear optical process is realized, higher working temperature is realized while higher quantum efficiency is kept, the background noise of a system is reduced, the dynamic range reaches 90dB, and the application at room temperature is facilitated; in the terahertz detection echo signal sampling, an electric field of an ether Hertz echo signal pulse is used as a deflection electric field, free current carriers in an LT-InGaAs crystal pumped by femtosecond laser move to generate current with the intensity changing along with the terahertz electric field, the current carriers have very short service life, only when ultrashort femtosecond laser sampling pulses and terahertz pulses irradiate simultaneously, current pulses can be generated in a detector, the size of the current passing through the detector is in direct proportion to the transient terahertz electric field, the waveform of the whole terahertz spectrum can be reconstructed through scanning fitting, and the terahertz electric field can be directly recovered.

The working principle of the optical subsystem of the terahertz detection head C is that divergent terahertz waves output by the THz emitter are corrected by the THz collimating lens group, then parallel terahertz light with uniform energy distribution is output, the parallel terahertz light is refracted by the THz turning light path and then is emitted from the THz window, the surface of a detection target is illuminated, terahertz waves reflected by the detection target are incident to the optical subsystem of the terahertz detection head through the THz window, the terahertz waves are refracted by the THz turning light path and then are input into the THz beam shrinking lens group, and the terahertz light spots converged by the THz receiver photosensitive surface are uniformly covered by the corrected output energy.

TPX material and 4-methylpentene polymer adopted by the lenses of the collimating mirror group and the beam shrinking mirror group are unique crystalline polymers in the prior high-transparency resin, have obvious melting point and good injection molding uniformity, can realize good material uniformity, simultaneously have the advantages of high temperature resistance, hydrophobicity and small shrinkage rate, and can not generate surface fog phenomenon through hundreds of high-temperature cooking experiments, thereby meeting the requirements of stricter material quality in the design of an illumination scanning objective lens, and compared with the most common high-resistance silicon (HRFZ-Si) in the traditional terahertz element, the TPX material has the characteristics of ultraviolet, visible and terahertz full-band transparency, the transmittance exceeds 80 percent and is more than 90 percent in the terahertz band, and the terahertz wave transmittance of the HRFZ-Si is only 50-54 percent; TPX is used as a material with the minimum density in the organic polymer, and compared with HRFZ-Si, the TPX can more effectively realize the light weight of the probe; the THz refraction optical path adopts a double-reflector refraction optical path, and compared with the common-window placement of a receiving and transmitting optical path realized by a beam splitter, 75% of energy loss caused by the fact that the THz wave is transmitted and received twice by the beam splitter is avoided; the aperture of a THz window of the detecting head reaches 2 inches, the aperture of an emergent terahertz light spot is more than or equal to 40mm, a Z-cut quartz crystal material is adopted, in a wave band of more than 50 mu m, the Z-cut quartz crystal is an excellent material, and is transparent in visible, infrared and terahertz wave bands, and the problem of different light refractive indexes of o-ray and e-ray can be solved by adopting the Z-cut quartz crystal as the quartz crystal is a double-refraction crystal; considering that the quartz material has large dispersion, the invention only uses the quartz material as the THz window material to avoid the deviation of the system focus and the focus of the actual terahertz working wave band when the He-Ne laser is used for adjustment.

The terahertz detection head optical subsystem of the system is optimally designed based on the non-sequence mode of ZEMAX, and an obtained performance evaluation graph is shown in an attached figure 2. The main performance indexes of the system obtained by the present invention according to the above embodiments are shown in table 1 below.

TABLE 1 Main Performance index of the invention

Compared with a compact reflection terahertz spectrum detection system for detecting optical parameters of biological tissues developed by the air force research institute of Brukes City, Texas, the terahertz spectrum detection system for detecting optical parameters of biological tissues uses the InGaAs material as the terahertz excitation antenna of the THz source, and compared with the metal-based semiconductor material, the terahertz excitation antenna for detecting optical parameters of biological tissues realizes the THz working bandwidth as high as 5.5, the effective working waveband is 0.1-5.5THz, and the working bandwidth is almost doubled. Compared with the detection system which realizes the receiving and transmitting co-location by the vertical distribution of the receiving and transmitting light paths of the beam splitter, the optical system of the invention adopts the asymmetric reflection light paths, not only realizes the receiving and transmitting co-location by the parallel distribution of the receiving and transmitting light paths, effectively reduces the volume of an optical subsystem, but also avoids the inevitable 75% energy loss caused by the two times of transmission and reception of terahertz waves through the beam splitter, and effectively improves the signal-to-noise ratio of the system.

The compact detection system for realizing the handheld terahertz reflection spectrum detection is designed aiming at the detection and identification requirements of flammable, explosive, toxic and harmful dangerous goods in the security inspection field and the requirements of detecting the content of food and industrial raw material substances by using spectrum data, and the like, and the final implementation scheme of the compact detection system for realizing the handheld terahertz reflection spectrum detection is determined by comprehensively considering the international advanced terahertz spectrum detection technology.

The technical problem of the invention is solved: according to the requirement of the security inspection field for identifying and detecting dangerous goods for the portable terahertz reflection spectrum detection system, a compact detection system for realizing handheld terahertz reflection spectrum detection is designed, and the compact detection system is used for realizing the simultaneous arrangement of uniform collimation irradiation of terahertz waves and focusing, receiving and sending of diffuse reflection spectrum.

One of the technical solutions of the present invention: wide operating bandwidth, high signal-to-noise ratio spectral scanning. The method is characterized in that: the broadband terahertz wave excitation unit consists of a 1550nm all-fiber femtosecond laser, an InGaAs terahertz excitation antenna and a metal electrode, and the quick response receiver unit consists of an LT-InGaAs crystal photosensitive surface and a femtosecond laser optical delay line.

The principle of the scheme is as follows: when the detection system works, the terahertz excitation unit emits 1550nm laser by an all-fiber femtosecond laser and passes through a beam splitter, one path of laser irradiates the InGaAs terahertz excitation antenna to excite an electron-hole pair, and photo-carriers generate transient drift current under the action of an external electric field of a metal electrode to radiate coherent terahertz pulses; and the other path of laser irradiates an LT-InGaAs crystal photosurface through modulation of an optical delay line to excite electron-hole pairs, detected terahertz pulses are focused on the crystal photosurface, a terahertz electric field is used as a deflection electric field to promote free carriers in the crystal to move, current with the intensity changing along with the terahertz electric field is generated, and the terahertz electric field is reconstructed to obtain terahertz scanning spectra through sampling and processing current signals.

The second technical solution of the invention is as follows: lightweight compact transmission-type terahertz optical system. The method is characterized in that: the terahertz polarization beam splitter comprises four parts, namely a collimating mirror, a terahertz window, a beam shrinking mirror and a reflection and refraction optical path.

The principle of the scheme is as follows: the terahertz lens of the system abandons the high-resistance silicon crystal material with high density which is widely adopted at present, and uses a novel organic polymer terahertz optical material TPX with low density to realize lightweight design; the design of a terahertz transceiving common window is adopted, divergent terahertz waves emitted by a terahertz source are uniformly collimated by a collimating mirror and then are incident on the surface of a detection substance, the deflection angle of a reflecting mirror is designed to meet the requirement of maximum receiving of reflected light, and the reflected terahertz waves are focused on the photosensitive surface of a terahertz detector through a beam shrinking mirror; the terahertz collimating mirror group and the beam shrinking mirror group are designed by parallel optical axis branches, and the terahertz reflecting mirror is used for deflecting a light path to realize the receiving and sending of a total terahertz window, so that the system volume is reduced.

The third technical solution of the invention is as follows: 3D prints detecting head optics subsystem structure, its characterized in that: the detecting head optical subsystem structure consists of an optical system tool structure for high-precision photosensitive resin 3D printing and a detecting head optical subsystem protective shell structure for high-strength nylon 3D printing.

The principle of the scheme is as follows: aiming at the characteristic that the traditional machining is difficult to process of the tool structure designed by the optical system, the photosensitive resin material capable of being printed in a high-precision 3D mode is adopted for integral forming processing, so that the structural precision of the tool is guaranteed, and meanwhile, the rapid integral forming processing is realized; the overall cost requirement and the strength requirement of the system are considered, in the processing of the system shell structure, the nylon material with lower processing precision and higher material strength is adopted for 3D printing processing, and the system cost and the strength requirement are considered, so that the system can realize all-weather stable operation in various environments at lower cost.

The invention has not been described in detail in part of the common general knowledge of those skilled in the art.

Claims

1. The utility model provides a realize compact detecting system of hand-held type terahertz reflection spectrum detection which characterized in that: the system comprises a femtosecond laser, an optical fiber and coupler, a THz emitter, an optical delay line, a THz receiver, an amplifier, a computer, a collimating lens group, a beam shrinking lens group, a THz deflection light path, a THz window and a detecting head structure for 3D printing; after the femtosecond laser emits laser pulses and is divided, one path of laser passes through the optical fiber and the crystal of the coupler pumping THz emitter to excite the terahertz waves, the other path of laser passes through the optical delay line controlled by the computer to adjust the laser phase, and the free carriers are excited by the optical fiber and the crystal of the coupler pumping THz receiver photosensitive surface; terahertz waves excited by the THz emitter are shaped into uniform parallel light through the collimating lens group, then the uniform parallel light is emitted from the THz window through the THz deflection light path to irradiate the surface of a detection target, the terahertz waves reflected by the detection target are emitted into the beam shrinking lens group through the THz window and the THz deflection light path, the terahertz waves are uniformly focused on a photosensitive surface of a THz receiver after beam shrinking and shaping, carriers are modulated to move to generate electric signals, and the electric signals are amplified by the amplifier and then input to the computer to reconstruct a terahertz spectrum; finally, the integrated forming and lightweight design of the optical subsystem of the terahertz detection head are realized through the 3D printed detection head structure, and the dry and sealed design of the detection system is further realized;

2. The compact detection system for realizing handheld terahertz reflection spectrum detection according to patent claim 1 is characterized in that: the THz source adopts a photoconductive effect, a broadband terahertz wave with the bandwidth reaching 5.5THz is excited by pumping InGaAs crystals by a mode-locked femtosecond fiber laser, the maximum value of the energy of the excited terahertz wave is 20 mu w, and the shortest time of single bandwidth scanning is 0.02 s.

3. The compact detection system for realizing handheld terahertz reflection spectrum detection according to claim 1, wherein: the THz detector realizes synchronization of single bandwidth scanning time and a THz source through same femtosecond laser pump modulation, a THz electric field is sampled on an LT-InGaAs crystal which is focused by THz waves and grows at a low temperature by adopting a photoconductive sampling principle, the sampling signal is amplified by an amplifier, the dynamic range of the THz detector is larger than or equal to 90dB, and the corresponding detection spectral bandwidth reaches 5.5 THz.

4. The compact detection system for realizing handheld terahertz reflection spectrum detection according to patent claim 1 is characterized in that: the collimating lens group consists of two 1-inch-caliber TPX material plano-convex lens convex surfaces which are oppositely arranged at intervals of 35mm, and the beam shrinking lens group consists of a 1.5-inch lens and a 1-inch-caliber TPX material lens plano-convex lens convex surface which are oppositely arranged at intervals of 27 mm; the THz conversion optical path consists of two 1.5-inch-diameter terahertz-level gold-plated reflectors; the reflector for turning the terahertz wave of the collimating lens group is an A reflector, and the reflector for turning the terahertz wave of the beam shrinking lens group is a B reflector; the terahertz window is made of a terahertz-level z-cut quartz crystal with the caliber of 2 inches.

5. The compact detection system for realizing handheld terahertz reflection spectrum detection according to claim 4, wherein: the optical axis of the transmitting optical path formed by the collimating lens group and the THz emitter and the optical axis of the receiving optical path formed by the beam reducing lens group and the THz receiver are arranged in parallel, and the optical axis of the transmitting and receiving optical path is arranged in a non-equal height mode relative to the structural substrate of the detecting head for 3D printing; A. b, the two reflectors rotate 15 degrees relatively in the horizontal direction relative to the base of the 3D printed probe structure, so that the distance between the transmitting and receiving optical paths is compressed to the maximum degree, and no position interference between the two reflectors in the THz folding optical path is ensured; the reflector A rotates 45 degrees relative to the direction of the optical axis of the straight mirror group towards the base of the detecting head structure printed in the 3D mode, and therefore the terahertz waves can be emitted from the THz window without being blocked; the B reflector rotates 42 degrees relative to the optical axis of the beam reducing mirror group towards the direction of the base of the detecting head structure printed in a 3D mode, and is placed asymmetrically with the A reflector, so that the terahertz waves reflected by the diffuse reflection detection target are incident into the beam reducing mirror group in parallel, and the THz window is arranged in a same receiving and transmitting mode.

6. The compact detection system for realizing handheld terahertz reflection spectrum detection according to claim 1, wherein: the probe structure for 3D printing adopts photosensitive resin high-precision 3D printing, and the integrated molding of the optical subsystem structure of the terahertz probe is realized; a hollow porous structure is simultaneously designed under the tool structures of the THz emitter and the THz receiver of the 3D printing detection head structure, and a drying agent is placed, so that the anhydrous design of the optical subsystem of the terahertz detection head is realized.

7. The compact detection system for realizing handheld terahertz reflection spectrum detection according to claim 1, wherein: the shell of the 3D printing probe structure is divided into two parts by adopting a nylon material for 3D printing, and the shell part with the functions of protecting the collimating and beam reducing lens group, the THz deflection light path and the THz window is realized; meanwhile, a sealing groove structure is designed, and a sealing rubber ring is arranged, so that the airtight design of the optical subsystem of the terahertz detection head is realized; a butt-joint airtight structure is designed at a shell handle part with a holding function, so that the optical subsystem of the terahertz detection head and data lines of other subsystems and connecting lines of optical fibers realize sealed rubber tube protection, and the airtight design of the connecting line part of each subsystem and the optical subsystem of the terahertz detection head is realized.