Research On Key Technology Of High-Resolution Terahertz Time-domain Spectroscopy Detection

With the continuous increase of industrial demand,it is the general trend that researching on THz-TDS system which is compact,miniaturized,high-resolution and fast and real-time monitoring.Among them,providing an optical delay device with long delay and good stability is a key technology to realize a high-resolution THz-TDS system.In this paper,in order to further improve the detection speed and spectral resolution of THz signals,a fast-rotating curved reflector optical delay line is designed,and related experiments are carried out to test its performance.The main research tasks are as follows:Firstly,the THz wave and THz-TDS technology,the application,composition and working principle of THz-TDS technology are introduced;and the working principle of the key technology optical delay line is explained;the existing delay line types at home and abroad are organized and summarized.The above proves that it is the important role that the delay line device provides a longer delay time to quickly detect and improve of spectral resolution.Secondly,the working principle of the curve reflector delay line is studied;and the mathematical model of the basic geometric parameters and delay time of the delay line is established.Zemax optical design software is used to simulate optical path for verifying the feasibility of the delay line;and a collimating and a focusing lens is added to optimize the "defocus" effect brought by the curved reflective surface.The eccentricity of light and the change of RMS radius at different rotation angles are analyzed.At the same time,the influence of errors such as drive motor vibration error,assembly and adjustment error and processing error are analyzed.The simulation results show that the maximum deviation of the center of mass after optimization does not exceed 41?m,and the maximum RMS radius does not exceed 30?m,which can meet the use conditions of most photoconductive antennas to radiate terahertz waves.In order to select a suitable drive motor,the shaft and delay line blades are limited Meta-modal analysis to avoid deformation caused by resonance.The designed optical delay line of the curved reflector is processed;and a Michelson interferometer is built to test the delay distance,linearity and stability of the delay line.The test results show that the maximum delay time of a single blade is 102.401ps;the delay time of one rotation can reach 409.604 ps and the delay distance of 12.28cm;the linearity is about97.3%;and the stability is good when the scanning frequency is 30 Hz.The time-domain waveforms are compared between slow scanning of the traditional delay line and fast scanning of the curve reflector delay line,which found that the peak and valley positions of the waveform are relatively more obvious during the fast scanning;and the time-domain waveform integrity is better.And the time domain signal during fast scanning is more stable,which meets the requirements of fast high-resolution THz-TDS system.