Research On Extracting Accurate Material's Parameters Based On Terahertz Time-domain Technology

In the past two decades,with the rapid development of terahertz sciences and technology, the interaction between terahertz pulse and material has attracted much more scientific interest owing to particularity of the terahertz wave band and its premium properties, and has been widely applied in the flied of industrial production and science research. Measuring and extracting the material's optical characteristics of terahertz wave band based on terahertz time-domain spectroscopy technique is the tool of further studies of the interaction between terahertz pulse and material, also is the most elementary, common, crucial part of the terahertz science and technology among worldwide researchers. In this paper,principle and application of measuring by terahertz time-domain spectroscopy system have been studied firstly. A novel method is proposed to solve the definition of solid parallel sample.The main contents and innovations in this paper are given below:Part one, the terahertz time-domain spectroscopy system, three types extracting mode, the research situation at home and abroad in detail by terahertz time-domain spectroscopy system.Part two, we improve the measuring method proposed by Duvillaret and Dorney.Theoretical analysing the different optical path method probability in improving accuracy of material's refractive index and absorption confident in the terahertz wave regime, and showing experimental studies to prove the different optical path method.The refractive index and the absorption coefficient from 0.5-2.5THz of high density polyethylene were obtained. And the results show that the measurement precious of refractive index and the absorption coefficient are quite different. The different optical path method can reveal the absorption peak of the materials which can't be revealed by the regular method,and provide a more precious measurement of material optical parameters.Part three, to study the optical characteristics of hemei A, hemei B, GuiZhou yanmei and lignohumic acid by the regular and the different optical path method respectively. Then the paper shows the optical characteristics of hemei A, hemei B,GuiZhou yanmei and lignohumic acid at the range of 0.5-1.5THz, including absorption confident, refractive index, the real part and the imaginary part of permittivity.The mainly innovation is proposing a novel method,the different optical path method, to extract the optical coefficient of martial based on the transmission-type terahertz time-domain spectroscopy, the different optical path method replaces the air reference signal in the regular method with the different thickness material as the reference terahertz signal. Comparing the regular and the different optical path method,we can see that the different optical path method is more accurate, straightforward than the regular method. It is hopeful that the different optical path method improving the definition among the terahertz database of martial spectral signatures in the range of terahertz wave regime.