Technology Of Terahertz Source And Detection Based On Femtosecond Lase Exciting Semiconductor Material

The technology of terahertz (THz) source and detection is the most significant part in the area of terahertz research. Specially, the terahertz source and detection systerms based on the method of exciting the semiconductor with an ultrafast pulse have attracted more attention because of important value of research and application. This manuscript focused on physical mechanisms in the process of terahertz radiation from the excited semiconductor. We obtained amplitude expressions of terahertz electric field using analytic and numerical computation. We discussed the generation efficiency and detection sensitivity of terahertz systerms and found physical factors which affected them strongly. Finally we demonstrated the optimal combination of those factors to optimize the working efficiency of terahertz generation & detection systerms. The details of my work are listed in the following:(1) By employing the Drude-Lorentz model to analy the motion of photogenearted carriers in the semiconductor surface under the influence of both external magnetic field and built-in electric field, we obtained amplitude expressions of terahertz electric field. Then the effects on enhanceing terahertz radiation, of laser incident angle, intensity and direction of the external magnetic field, and the semiconductor's features were under discussion. We clarified the optimal orientation of external magnetic to maximize the output power of terahertz radiation.(2) We studied the terahertz generation based on optical rectification and present a set of equations describing the terahertz generation in the zincblende crystals. Moreover, the dependence of terahertz emission efficiency on the polarization and incident angle of pump beam, the crystal-orientation, the azimuth angle is discussed. We also discussed the THz generation under the normal incidence and the oblique incidence of incident beam. Figures generated by MATLAB have been compared and analized to find the optimal combination of physical factors refered above.(3) We introduced the terahertz detection of electro-optic sanpling and calculated the detected signal by the method of balance-detection. We show the dependence detection of THz field on the crystal-orientation and the polarization of probe beam. Since the orientation and polarization are chosen arbitrarily, the equations supplied by us are valid in general cases. For the experimental setup with transceiver which transmits and detects terahertz radiation in the same crystal, we have demonstrated the optimal combination of both parameters above to optimize the working efficiency.(4) We studied the effect of phase mismatch in the nonlinear process generated inside the crystals, the optical dispersion in the electro-optic crystal affects the THz pulse detection. We found the transverse optical (TO) phonon resonance frequency limit the abilitivity of detection. We presented both the frequency spectrum of THz generation and the THz detection. The distribution of frequency spectrum is affected by the crystal materials, the thickness of crystal and the duration of incident pulse. According to the relevant physics formulas, We make a program by Matlab to simulate the changes of both the generated THz pulse and detecteded THz pulse with different parameters, we obtained some conclusion about the choices of crystal materials and the thickness, which make a great significant for THz source and detection systerm.