基于1560 nm 激光单次通过PPLN 晶体倍频到780 nm 激光的实验，分析了准相位匹配倍频过程中非线性转换系数与温度之间的关系。详细计算了考虑晶体极化周期的热膨胀时，晶体非线性转换系数和匹配温度的变化。采用有限元的方法，计算了激光穿过PPLN 晶体时，整个晶体和出射端面的温度场分布，并由此给出了出射面的非线性转换系数的分布情况，重点分析了晶体尺寸、光功率及散热方式对热效应的影响。仿真结果表明：增加晶体的宽度、采用导热性能好的材料作散热材料，并采用四面包围的散热方式有利于晶体的散热。

Based on the frequency doubling mechanism of a continuous wave 1560 nm laser single-passing a PPLN crystal, the dependence of nonlinear conversion efficiency on temperature is investigated. The effects of thermal expansion of the crystal′s polarization period on the nonlinear conversion efficiency and matching temperature have been studied in detail. By using finite element method, the temperature fields in the whole crystal and on the output facet are numerically calculated, and the nonlinear conversion efficiency is extracted when the laser passes through the crystal. The dependences of the crystal size, input laser power, and the strategy of heat dissipation on the temperature field are also presented, respectively. It is demonstrated that the performance of the PPLN crystal on frequency doubling can be improved by a wider crystal and the materials with good heat conductivity surrounding the crystal.