Information Based On The Polarization Of Terahertz Imaging

Terahertz wave (THz) is a novel radiate source which has many unique advantages. The spectra of materials in the THz band always contain abundant information in both physics and chemistry realms. Recently, THz technology is growing up quickly and attracting more and more attentions. One of most important applications of the THz technology is imaging. There are many methods have been invented for THz imaging. However, most of the THz imaging techniques achieve only one component of the THz electric field vector and impute the decrease of signal to the absorption and scattering of the sample. In fact, a rotation of the electric field vector induced by birefringence of the sample can also cause such a decrease. Besides the birefringence, the polarization of a THz pulse can also be changed by various other effects, such as not-normal-incidence reflection and multiple scattering. Therefore, the rotation of THz polarization which is an important factor should be considered. In this thesis, the character of THz polarization, the method of using different detect crystals to detect the polarization of THz, and the reason of variety of polarization have be discussed. The main results are listed as fellows:1. Detections of THz in different crystals are analyzed and used to test the terahertz polarization of the system. In this thesis, <110> and <111> types ZnTe crystals were used to detect terahertz wave. An available detecting method which could measure two orthogonal components of the THz field had been found, which is a foundation work for next step.2. By imaging both two orthogonal components of the THz field, the rotation of THz field which induced by the sample can be analyzed. Two different types of ZnTe crystals were used in imaging. After analyses, it is found that the diffraction and scattering at the edge of samples, not birefringence, cause the change of the THz polarization.3. In order to better interpret the rotation and variety of the THz electric field vector, the birefringence model and polarizer model Jones matrixes have been employed to describe the polarization information and to exhibit the image of the sample.