Continuous Terahertz Imaging Technology

Terahertz (THz,1012Hz) 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 CW THz imaging for actually application by introducing the Reflecting and Transmission-type set respectively. The main research works are listed as follows:(1) Non-destructive detection of insulating foam defects utilizing reflecting Continuous wave THz imaging system is described in detail。However,this recognition is based on human eyes. The defects of space shuttle insulating foam can be discerned automatically using the imaging processing algorithm and Back-Propagation(BP) neural network, which shows an effective way for Non-destructive detection.(2) The feasibility of the Computed tomography technology of CW 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 tomography imaging is deduced based on the Born and Rytov approximation.(3) The transmisson-type CW THz imaging system is debuged. 90 pictures at different angles are obtained utlizing the above system.Associative with the mathematic model of THz computed tomography technology, THz computed tomography imaging is finally achieved and the resolution of the image is discussed. THz computed tomography technology will provide a more effective method for non-destructive detection and security inspection.