Continuous Terahertz Imaging System Applied Research

Terahertz (THz) radiation, which occupies a large portion of the electromagnetic spectrum between the infrared and microwave bands, can be used as the source of the illumination just like X-rays and the visible light which are helpful to the research region. It also plays an important role in the areas such as security-inspection, testing of aerospace materials aspects, non-destructive detection for materials. THz wave can be distincted as the pulsed and continuous wave(CW), depending on the method on how to generate and detect THz wave. Based on the visible characteristics of many biologic and chemical media in THz range, and special imaging advantages of pulsed imaging, pulsed imaging has become an important choice in many applied fields. But with the development of semiconductor technologies, a compact, relative fast, easily operated and portable CW imaging system has been realized, showing its'practicability increasingly in many applied fields. It become another important choice apart from pulsed imaging, promoting development of THz imaging technologies together.The thesis mainly focuses on the continuous wave THz imaging for actually application by introducing the 0.2 THz CW Reflecting and 0.71 THz BWO (Backward Wave Oscillator) Transmission-type and Reflecting set respectively. The main research works are listed as follows:(1) Non-destructive detection of insulating foam defects utilizing reflecting 0.2 THz Continuous wave THz imaging system is described in detail。For example, void. And we evaluate the result of the imaging.(2) The feasibility of the Computed imaging technology of continuous wave THz wave has been proved. Combining with the THz basic wave equation, we assume that : 1)The target is smaller than Rayleigh rang of THz beam. 2) The beam can be well described by a planar Gaussian beam with the Rayleigh range. The mathematic model of THz computed imaging is deduced based on the Born and Rytov approximation.(3) The 0.2 THz Reflecting-type CW THz imaging system is debuged. We use this system test the foam of the aerospace materials. We analyze the influence of the size of the defects.(4) We presents a terahertz (THz) imaging system with a Backward Wave Oscillator (BWO) (include Reflecting and Transmission-type). BWO Continuous-Wave THz imaging is a new approach to non-destructive testing. This system is build by ourselves. A number of potential imaging applications are demonstrated using the 0.71 THz radiation, including nondestructive real-time testing for plastic bus fare card, campus debit card and various articles contained in an envelop. The same time, we present the results of Reflecting and Transmission about the sample surface and the foam. This work shows that a BWO THz imaging system is very practical and effective in nondestructive identification and security inspections applications in the future.