高功率激光倍频过程的热效应分析

在高功率倍频过程中,非线性倍频晶体由于吸收了基波和谐波的功率,造成倍频晶体内温度的变化,破坏了晶体原来的相位匹配条件,从而导致频率变换效率降低、输出谐波功率不稳定等问题,对于高功率高重复频率激光器系统尤其严重.根据热传导方程分析了晶体内部的热分布,利用非线性晶体的折射率方程分析了非线性倍频晶体温度变化时,其相位匹配、允许参量以及光波走离角的变化情况,为实现高功率倍频激光奠定了理论基础.

Thermal effect analysis in the process of high power frequency doubling

In the process of high power frequency-doubling, the temperature inside the nonlinear crystal will become non-uniform because of absorbing the fundamental and second harmonic waves, leading to phase mismatch, conversion efficiency reduce and output power instability. This phenomenon appears severe in the high power high repetition rate laser system. Temperature distribution inside KTP crystal was analyzed by solving thermal conductivity equation. According to temperature distribution of KTP, we have theoretically calculated the optimal phase matching angles, tolerance angles and walk-off angles of type II KTP crystal as function of temperature.