Continuous Terahertz Tomography Experimental Research

The electromagnetic wave whose frequency lies in the range from 0.1 THz to 10THz is known as terahertz wave,which is surrounded by microwave and infrared region and has the properties of both microwave and optical. As the microwave and optical can be used for imaging, it also can be used for the radition source in imaging applications. In the terahertz imaging systems, pepole can easily draw the imaging modalities for microwave and optical imaging into the terahertz range, and this new imaging systems can be effective supplement for other imaging systems. Because of the strong penetrating property for non polar of terahertz, one can use it to obtain the internal structure and composition of the sample. Computer Tomography (CT) technique which is a three dimentional imaging technique and widely used in various medical imaging can detect the internal structure ans material distribution of objects. The imaging method can be applied to terahertz imaging technology due to the penetration performance for non-polar of terahertz wave. And because the photon energy is low to 4meV which is much smaller than the X-Ray's,the terahertz imaging systerm will not cause the ionization damage to sample.In this paper terahertz CT imaging technology is studied by using the CO2 laser pump methanol gases terahertz laser which produced by Edinburgh company and Pyrocom III type pyroelectric camera. And combined with other exiting equipment to build a set of terahertz tomography system. This imaging system consists of two parts: the first part is the data collection system, and the other part is the Matlab code for cross section images reconstruction. At last,the terahertz CT experiment of sevrial samples is taken out, and cross section images are reconstructed successfully.Also three dimension images of object are obtained with different cross section images.The following results have been achieved in this thesis:First,the theory of terahertz CT imaging is studied, the relevant formula is deduced, and the image reconstruction methods also is studied. According to the principle of filtered back projection, the Matlab code for the terahertz Tomography imaging reconstruction is programed. And then Phantom head model is used for simulation. Second, The theory of diffraction tomography has been studied.NUFFT reconstruction method wich is learned from ultrasonic tomography is emploied instead of using filtered back-propagation for imaging reconstruction for its time-consuming.Also Phantom head model is used for simulation.Third, three-dimensional display method in Matlab platform is studied. And three dimension images is builded using the cross section images obtained from ecperiment.Fourth, terahertz CT system is build employed the existing equipment. And a one-dimensional and three-dimensional tomography data acquisition control code is designed in the Labview programming environment, and success achieved acquisition of projection terahertz continuous wave on the different angles.Finally, the experiment of several objects is carried out using this terahertz CT imaging system.At last the cross section images are obtained and the three dimesion lamges.