在脉冲激光二极管(LD)端面抽运固体激光器中,存在热效应瞬态过程,即晶体的温度分布具有时变性,晶体温度的时变过程受到热弛豫时间的影响。从热传导方程出发,采用解析法和数值法分别对晶体降温过程中温度的时变性进行计算; 采用有限元方法,对晶体热弛豫时间及其影响因素进行数值计算,分析了晶体直径、密度、热传导系数和比热等热物性参数对热弛豫时间的影响; 采用流体流动换热理论,充分考虑了冷却水流温度和速度对晶体温度分布的影响。结果表明,通过调整晶体尺寸、冷却系统可以实现对热弛豫时间的控制。根据有限元软件ANSYS的计算结果,分析了晶体抽运端面上径向温度的时变分布,晶体边缘与中心的温差和光程差; 初步计算了晶体热透镜不同径向位置处的焦距差。结果表明,晶体冷却过程中,不同径向位置与中心的温差和相对光程差具有时变性,晶体热透镜的聚焦特性也是随时间变化的。

The process of transient thermal effect exists in pulsed laser diode (LD) end pumped solid state laser, which means that temperature distribution in laser crystal is changing with time. The process of time-varying temperature is influenced by thermal relaxation time. Based on the heat conduction equation, the characteristic of time-varying temperature in temperature declining process is calculated by analysis and numerical method. Based on the finite element method, the thermal relaxation time and its influencing factors are presented. The diameter, thermal parameters of crystal such as density, coefficient of heat conduction and specific heat are analyzed. Based on the theory of flow and heat transfer of water, influences of crystal temperature distribution such as temperature and velocity of cooling water are considered. The results show that thermal relaxation time can be controlled by changing diameter or cooling system. Based on the solution of ANSYS, time-varying temperature distribution, temperature difference and relative optical path difference between center and edge in pumped surface of crystal are analyzed. Focal length difference at different radii of the thermal lens is analyzed simply. The results indicate that in cooling process, temperature difference and relative optical path difference between center and other different radial positions are all changed with time; focus property of crystal thermal lens is also changed with time.