利用分步快速傅里叶变换和四阶龙格-库塔法,对具有一定温升分布的倍频晶体的二次谐波转换过程进行了研究。综合考虑了谐波转换过程中的离散、衍射、二阶、三阶非线性等效应,着重讨论了倍频晶体吸收光能后,晶体内温升分布对晶体内o光和e光的折射率分布的影响,定量分析了温度分布引起的相位失配量、输出光场分布、二次谐波转换效率随倍频晶体温度分布变化的规律。结果表明:在高功率倍频系统中,倍频晶体温升分布引起基频光、倍频光的相位失配,相位失配导致输出光场光强分布的变化以及谐波转换效率的降低。

Second-harmonic generation(SHG) of high-intensity laser with an SHG crystal for typeIangle phase matching has been studied by the use of a split-step algorithm based on the fast Fourier transform and a fourth-order Runge-Kutta(R-K) integrator. The transverse walk-off effect,diffraction,the second-order and the third-order nonlinear effects have been taken into consideration. Influences of a temperature rise distribution of the SHG crystal on the refractive indices of ordinary wave and extraordinary wave have been discussed. The rules of phase mismatching quantity,intensity distribution of output beam and frequency conversion efficiency varying with the temperature rise distribution of the SHG crystal have been analyzed quantitatively. The calculated results indicate that in a high power frequency conversion system,the temperature rise distribution of SHG crystal would result in the phase mismatching of fundamental and harmonic waves,leading to the variation of intensity distribution of the output beam and the decrease of the conversion efficiency.