Research On Key Technologies Of Compact Terahertz Spectrum Detection System

Terahertz spectrum detection can detect the characteristic absorption spectrum of a substance in real time and perceive the presence of dangerous goods;terahertz radiation is non-ionizing and safe to the human body;the use of software to analyze the spectral characteristics does not require imaging,to avoid the image information detected by manual operation,leading to privacy leakage problem.This makes it important to study the key technology of terahertz spectrum detection.This paper studies the terahertz time-domain spectral detection technology from the perspective of applied optics,and adopts the method of time-domain spectral transformation to extract the optical parameters such as the refractive index and absorption coefficient of the sample.The research content of this article mainly has the following aspects: 1?The molecular terahertz spectroscopy characteristics were studied.In this paper,the spectral range of molecular energy transitions is analyzed from a simplified model of molecular motion,and the principle of terahertz spectrum detection technology is studied for this spectral range.The handheld terahertz spectroscopy detection system was studied from the perspective of applied optics.A compact handheld terahertz optical system was simulated and designed to solve the difficulties of handheld terahertz spectrum detection technology.2?The influence of atmospheric absorption on the detection of terahertz spectrum is analysed.In this paper,the method of spectral subtraction and mean smoothing is proposed to suppress the influence of atmospheric absorption,and simulate and experimentally verify the suppression technology of atmospheric absorption interference.Firstly,after the time-domain spectral subtraction,the spectrum is average filtered to achieve the suppression of atmospheric absorption interference,and the suppression algorithm is simulated and verified for the terahertz water vapor absorption line J_Ka,Kc=2₁₁-2₀₂ at 0.752 THz.According to the temperature and humidity conditions in different indoor environments,atmospheric absorption background suppression experiments are carried out in several relative humidity environments,and the inhibition rates are all over 95%.In the environment of more than 40% relative humidity,terahertz spectroscopy is carried out on a variety of samples,and the spectra are compared experimentally before and after processing using the atmospheric absorption interference suppression algorithm,and the inhibition rates are all over 90%.Through spectral subtraction,the background spectrum of atmospheric absorption interference is eliminated,and the averaged filter is used to smooth the spectrum in the processed spectrum to weaken the remaining spectrum of the atmosphere.The key technical difficulties of atmospheric absorption interference suppression is solved.3?Using the Fabry-Perot effect,the terahertz transmission characteristics of three different terahertz spectral detection methods are analyzed,and the optical parameters such as the refractive index and absorption coefficient of the inversion samples are studied.Four decision models of terahertz spectrum attenuation rate trend,characteristic absorption line position,refractive index spectrum distribution and absorption coefficient spectrum information are established to solve the key technical difficulties of identifying the substances under the covering shielding.4?Three practical application scenarios are classified to identify common wrapping materials and test samples and to analyze available experimental alternatives.The THz time domain spectra of the transmission and reflection modes are obtained.By analyzing the time domain spectra of transmission,the terahertz attenuation characteristics of wrappings are obtained,and the work of Liu et al.is extended by analyzing the characteristics of atmospheric spectrum,providing a reference for the commercial application of THz-TDS.The consistency between the transmission and reflection spectrum is verified.Through analysis of 5 kinds of liquid for reflection spectra,the reliability of detection model of polar liquid is verified.And analyzing the liquid sample absorption line spectra distribution characteristics,summered the set 1.3THz as threshold of sectrum,can quickly and effectively distinguish between liquid dangerous goods and security.Finally,according to the three typical application scenarios,the substance recognition models are analyzed,and different comprehensive dicision methods are used for different application scenarios to ensure the accuracy of the substance recognition.