CO_2激光差频GaSe晶体产生太赫兹波的数值计算

Simulation on THz radiation via difference frequency mixing of CO_2 laser in GaSe crystal

以可调谐CO2激光差频非线性GaSe晶体为例，在共线相位匹配方式下，计算了oe—e和oe—o两种相位匹配方式下的角度调谐特性、有效非线性系数、走离角和允许角。结果表明：GaSe晶体可产生73．84～3000μm的太赫兹波，且有效非线性系数为4l-54pm／V；走离角在1．771°～10．63°之间；所允许的最大发散角为13．95～94．7μm·rad，对入射光的方向性要求较高。对于500μm以上的太赫兹波，两种匹配方式除有效非线性系数外没有大的区别。模拟结果对于开展基于激光差频技术产生太赫兹的研究具有重要的指导意义。

The process that Q switched tunable CO2 laser pumps nonlinear GaSe crystal was studied. Based on the collinear phase match type, the phase matching angle, effective nonlinear coefficient, walk- off angle and acceptant angle were calculated. The results are as follow： THz wave between 73.84 and 3 000 Izm can be generated using DFG based on GaSe crystal which has high effective nonlinear coefficient of 41-54 pm/V. The walk off angle is big, which is between 1.771° and 10.63°. With the small acceptant angle 13.95-94.7 μm.rad, the requirement in directional property is strict. When the THz wavelength is above 500 μm, the two phase matching types, oe-e and oe-o, are very similar except the effective nonlinear coefficient. In experiments, it was up to the experiment conditions to decide which type to choose. The simulation result can guide the experiments about DFG in GaSe crystal.