脉冲激光二极管端面抽运全固态激光器热效应瞬态过程

从圆柱状晶体热传导方程出发,采用有限元方法,对脉冲激光二极管(LD)端面抽运Nd∶YAG激光器中激光晶体的瞬态温度场分布进行了计算.对单脉冲过程中,晶体升温和降温时端面温度的分布情况进行了计算;分析了束腰位置和束腰半径对单脉冲过程的影响,以及晶体热弛豫时间的影响因素;根据光线追迹理论,分析了激光晶体内温度分布达到动态平衡后,由温度梯度引起的中心与边缘相对光程差时变特性.结果表明,当束腰位于晶体抽运端面时,增大束腰半径晶体端面温度降低;当不改变束腰半径并且后移束腰位置时,晶体端面温度降低;增大冷却液对流换热系数或者空气流速、降低空气温度以及减小晶体半径都可不同程度地缩短热弛豫时间;当晶体温度分布达到动态平衡后,晶体内各点温度呈周期性变化;由晶体径向温度梯度引起的相对光程差(OPD)也随时间作周期性变化.

Transient Thermal Effect in Pulsed Laser Diode End-Pumped Solid-State Laser

Based on the fundamental theory of heat transfer in cylinder, the transient temperature field in the laser crystal of pulsed laser diode (LD) end-pumped Nd∶YAG laser is analyzed by the finite-element method. The temperature distribution of crystal end surface in the process of temperature rise and fall is calculated in a single pulse process. The influences of beam waist width and its location on the temperature distribution and the factors influencing the thermal relaxation time are presented. Based on the theory of ray trace, the time variation of optical path difference at the center and fringe of crystal end surface caused by temperature gradient after the temperature distribution in the crystal reaches a dynamic balance is analyzed. The results show that the increase of beam waist width or rearward shift the beam waist without changing beam waist width will reduce the end surface temperature when the laser beam waist is located on the pumped end surface. Increasing the heat transfer coefficient of cooling liquid or flow velocity of air, reducing the air temperature or the radius of laser crystal can shorten the thermal relaxation time. After the transient temperature distribution reach a dynamic balance, the temperature in crystal and relative optical path difference (OPD) caused by radial temperature gradient will periodically change with time.