Method And Analysis Of Extracting Material Parameters From THz Pulse Wave

THz(1012 Hz) time-domain spectroscopy(TTDS) developed in 1990s is a new technique for spectroscopy measurement. A coherent electromagnetic pulse in the range between the far-infrared and microwave region is used as a detection source. The amplitude of the wave is recorded by electro-optical or photoconductive sampling. After fast Fourier transform, the amplitude and phase of the wave is given, then the complex refractive index standing for the absorption and dispersion of the material in THz region is extracted. Compared with the treatment using Kramers-Kronig relation, TTDS is simpler, more reliable, and more precise. Although TTDS has been developed for more than ten years, commercially available THz spectrometer can only make some qualitatively rather than quantitatively analysis.In this paper, a model developed by T.D.Dorney and D.Duvillaret et al is used to discuss the principle and method for optical constants extracting. The real refractive index and extinction coefficient of materials and the extraction of other material parameters are also discussed. The deviation of the optical constants obtained experimentally from their true values is analyzed using a stimulation method. These stimulation results can be used to direct the experiment and to analyze the experiment data. In experimental study, the dielectric characteristic of some infrared materials is analyzed by the transmission TTDS. The experiment results are valuable to the research of infrared lens, laser window, integrated optical device, the device for blue semiconductor laser, optical detector, nonlinear device, optical waveguide, THz emitter and other devicesThe following is a brief summary of the works conducted in this thesis and the results achieved.1.The principle and method of extracting the optical constants from transmission, reflection, differential, and ellipsometry TTDS are reviewed andanalyzed systematically. The programs using Newton algorithm are developed to solve the equations. The extraction of other material parameters is also discussed in detail.2.Using the simulation method and a lorentzian oscillator model, the influence of the deviation in experimental parameters, including the thickness of samples, the incident angle, the misalignment of the time delay line, the background noise and the laser noise is analyzed. The precision of the optical constants measured by transmission TTDS is evaluated. The stimulation shows that the phase measurement dominates the anti-noise ability of TTDS. On the other hand, the phase will show a 2 n jumping not only in low frequency region but also in resonant,region.3. Using the transmission TTDS, we measured and analyzed the absorption and dispersion of bulk ZnSe(l 10). According to the Drude theory, we obtain the low-frequency and high-frequency dielectric constant of ZnSe. We also observed the absorption caused by multi-phonon processes in ZnSe.4. Using TTDS measurement and analysis, the characteristic of mixed crystal HgCdTe and ZnCdTe in THz region is analyzed. We also observed the absorption by 2TA(X) in HgCdTe and multi-phonon processes by LO(X)-LA(X) in ZnCdTe.