Study On Performance Of THz-wave Parametric Oscillator With Short Cavity Based On MgO: LiNbO₃ Crystal

In recent twenty years, THz-wave Technology has obtained some development both in the field of fundamental research and in the field of application research. The key to promoting the development of THz-wave application technology and related interdisciplinarity is the development of THz-wave radiation source technology. To research and develop such THz source that has high power, high energy, high efficiency, room-temperature-operation and wide tunability is the goal of many researchers. THz-wave experimental research and theoretical analysis that produced by optical parametric oscillator based on MgO:LiNbO₃ crystal as the nonlinear optical medium have been demonstrated in this dissertation.Firstly, the newest progress of THz and its classes of research technology including the radiation source of THz, detector and variety of application were introduced. Some basic theories such as the principium of parametric oscillation, oscillation threshold and phase-matching technology, etc. have been discussed too. THz-wave parametric oscillator can produce THz-wave by using the principle of optical parametric oscillation. The micro-mechanism of producing THz-wave has been demonstrated, which mainly included two processes: the optical parametric oscillation and Raman scattering. And the influence of system performance induced by shortening the length of resonant cavity was discussed. In experiment, one way was introduced to improve the experiment device that shortening the length of resonant cavity using one high performance reflecting mirror with SWPF. The good results of decreasing the oscillation threshold, extending the tunable range, keeping stable monochromaticity were obtained by shortening cavity. As the medium of energy exchange between pump beam and parametric beam, LiNbO₃ crystal played an important role in the performance of THz-wave parametric oscillator. The optical performance, the effective nonlinear coefficient, the phase-matching feature and the analysis of angle tunability of LiNbO₃ were discussed. LN crystal doped with 5%mol MgO can decrease photorefractive effect and increase laser-induced damage threshold. The experimental phenomena indicated that SLN and CLN brought different influences to the stability of THz-wave. And the physical mechanisms of the surface damage and body damage of LiNbO₃ crystal emerging in the experiment were discussed. The strong self-focusing effect could bring on serious damage of LiNbO₃ crystal and greatly weakened the output power of THz-wave.