Research On High Power Terahertz Detection And Imaging

In this paper,the high power terahertz detection and imaging based on 0.22THz TE₀₃ gyrotron oscillator is investigated.A quasi-optical mode converter for gyrotron is designed,which consisting of a Vlasov launcher,an elliptical reflector and a parabolic reflector is proposed to convert TE₀₃ cylindrical waveguide mode to a Gaussian-like beam.The quasi-optical system is optimized by a numerical code using MATLAB software.The simulation results show that the power transmission efficiency of the operating cavity mode to a fundamental Gaussian distribution is 80.82%,and the scalar Gaussian mode content is 98.2%.A cold test experiment platform is built up to verify the design based on numerical calculation.In experiment,the scalar Gaussian mode content of 98.6%is measured,which shows a good agreement with numerical calculation.An in-line digital holography system based on 0.22THz high power pulse gyrotron is designed,and the digital hologram simulation image is obtained based on the angular spectrum theory and phase recovery algorithm;the amplitude distribution and the phase distribution are obtained based on the angular spectrum theory and phase recovery algorithm;the 3D multi-layer holographic reconstruction is obtained based on the compressed sensing algorithm.The simulation results show that the system can be used as a tool to analyze and study the phase of samples,and also can be used in material analysis,biomedicine and nondestructive testing in the future.All these works will play a positive role in the establishment of digital holography system based on 0.22THz gyrotron.A stepped frequency imaging radar based on 0.22THz high power frequency tunable gyrotron oscillator is designed.The dual Cassegrain antenna with separated transceiver and receiver is used for transmitting stepped frequency pulse signal.Frequency tuning of gyrotron oscillator is achieved by adjusting gytrotron electron beam voltage or superconducting magnet strength.The radar can be used for investigations on target recognition of small objects such as UAV which can take concealed weapons and threat material.A dual frequency terahertz pulse radar is designed which based on the dual frequency terahertz gyrotron.The targets echo model including micro Doppler information is established for the vibration,rotation and rolling targets.The simulation results show that the 0.11THz radar and 0.22THz radar both have centimeter level detection ability for micro-motion feature extraction of vibration,rotation and roll.Under the condition of strong noise,the self-power spectrum time-frequency analysis can suppress the noise and improve the detection ability of micro-motion feature extraction.Through the cross-power spectrum time-frequency analysis of 0.11THz and0.22THz radar echo base-band signals,the micro-motion feature extraction of the same frequency will be enhanced,and the noise will be suppressed,which is conducive to extract micro-motion feature information.