Study Of Pulsed THz Time-domain Spectroscopic Imaging And THz Continuous Wave Imaging

Terahertz (THz) imaging is one of the most promising applications in the THz science and technology. The powerful, compact, and tunable emitter, the high sensitivity, low noise , and wide frequency spectrum detector, the quick, efficient data processing method, the optimized optics design are the most important several factors in a imaging system for practical application, such as non-destruction testing, security inspection, biomedical imaging and so on.This thesis mainly focuses on the pulsed THz time-domain imaging technique and continuous THz wave imaging technique for functional imaging and structure imaging. On the one hand, pulsed THz time-domain spectroscopy/imaging system must be established because there is no commercial product at present. Two sets of imaging systems have been built in our Lab. The hardware architectures based on optoelectronic generation and detection of THz radiation are described, and building and optimizing approach has also been summarized. Several efficient data processing methods are introduced. The inner structure of a sun-flower seed can be detected and the concealed explosive materials can be distinguished by using these imaging methods. On the other hand, the applications of continuous THz wave imaging system have also been demonstrated. Ablation of rocket jet-propeller's spout and inner defect of rocket-fuel-tank-insulation-foam have been successful detected by this system. The reason for the generation of interference in the continuous wave system is discussed, which ever puzzled the user of this system. The main results and conclusions are listed as follows.(1) Two sets of THz time-domain spectroscopic imaging systems have been established, which utilize the InAs crystal or photoconductive antenna as emitter and the ZnTe crystal as sensor. Approaches for establishing, optimizing and noise reducing are clearly introduced. The spectrum of terahertz radiation excited from the surface of a <100> InAs crystal pumped by laser pulse with different central wavelength (from 840nm to 770nm) is also investigated.(2) The THz time-domain spectroscopic imaging system is described in detail. Several important factors, including setup, beam measurement, data processing methods, which are very essential to further researches and applications are addressed. THz images obtained by using different data processing method can identify the inner structure of a sun-flower seed and can distinguish the concealed explosive materials. It demonstrates the capacity of THz time-domain spectroscopic imaging system(3) The THz continuous wave imaging system is described. Ablation of rocket...