Nd∶GGG激光晶体热容工作下的热致效应与冷却特性数值模拟

Numerical Simulation of Thermal Induced Effects and Cooling Characteristics of Nd∶GGG Laser Crystal Slabs in the Heat Capacity Operation Mode

基于对称双侧激光二极管(LD)抽运Nd∶GGG(掺钕钆镓石榴石)激光晶体板条,从热传导基本方程出发,以废热等效于内热源模型为前提,利用有限元分析软件ANSYS对Nd∶GGG板条在热容工作下的瞬态温度场及应力场进行了数值模拟,分析了在不同边界条件下温度和应力随时间和空间的变化特性及其热致变形。计算结果表明:在激光发射阶段,边界非绝热使得板条在垂直光轴方向产生温度梯度,由此产生的折射率梯度和应力梯度导致距离光轴最远的板条边缘和光轴处产生约0.2μm的变形量。同时模拟了冷却阶段空气对流冷却、水循环冷却及喷雾冷却条件下的温度变化过程,研究了适用于热容板条固体激光器工作的冷却手段。

Based on the fundamental theory of heat transfer, the mathematical formulas that describing the transient temperature distributions of two-sided laser diode （LD） pumped Nd： GGG （gadolinium gallium garnet） heat capacity slab laser were derived in this paper. By means of finite element analysis by ANSYS, transient temperature fields and stress distribution in the slab medium were simulated with various boundary conditions, while the beam distortions induced by thermal gradients were analyzed briefly. The obtained results could benefit to the primary designing of solid state heat capacity laser （SSHCL）. Numerical analysis proved that under incomplete adiabatic boundary conditions, it would result in temperature gradients perpendicular to the optical axis. About 0.2 μm optical path differences would occur between the edge and optical axis of the slab. In addition, the thermal distributions in the slab during the subsequent cooling stage were mainly studied. The influences of different cooling methods such as air cooling, water cooling and mist cooling were discussed and cooling methods suitable for a SSHCL were briefly studied.