Continuous Terahertz Long-range Imaging

The terahertz (THz) radiation, which refers to the spectral region between 0.1 to 10 THz, occupies a large portion of the electromagnetic spectrum between the microwave and infrared bands. THz radiation is able to penetrate through many non-polarized materials that are opaque to visible and infrared light (such as plastics, chinaware, textiles, paper and so on), and THz band covers the fingerprint of many chemical materials, such as explosives, drug, and virus. Because of its'special characteristics, THz imaging technology has huge application potential in fundamental studies, industry applications, biomedication, and national security defenses. With the development of semiconductor technologies, a compact, relatively fast, easily operated, and portable CW imaging system has been realized, showing multiple application prospects in a number of areas.This thesis mainly focuses on the continues wave(CW) THz standoff imaging technology, analyzes a few critical questions from theoretical and experiment aspects, more concerned with the applications of CW THz standoff imaging technology, which are very essential to further research and exploration. The main works are listed as follows:(1)Insulating foam and hidden articles are inspected by utilizing reflection CW THz imaging system. Combining with THz specialty for this material, the images are analyzed. The results show that this new technology can be widely used in non-destructive inspection and security inspection.(2)Improvement of the continuous wave imaging system. The resolution of CW imaging system is prominently improved by increasing the numerical aperture of CW imaging system.(3)Improvement of the continuous wave imaging system. A polyethylene Fresnel lens is used to collimation terahertz wave for standoff propagation. Six aluminum mirrors are employed to increase distance. An Aluminum plate with holes, an airplane model and a toy gun are imaged at 8m , 20m , and 30m from the imaging unit. The results shows the ability of CW THz standoff imaging system.In conclusions, in this paper, we give a detailed investigation and analysis on CW THz standoff imaging technology, including theoretical analysis, experimental system, and some discussions. The results are of important significance to improve CW THz imaging technology.