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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.
Starting from the cylindrical heat conduction equation, the transient temperature field distribution of the laser crystal in the Nd: YAG laser diode pumped by a laser diode (LD) was calculated by the finite element method. For single pulse, The influence of the beam waist position and beam waist radius on the single pulse process and the influence factors of the crystal thermal relaxation time were analyzed. According to the ray tracing theory, the temperature distribution in the laser crystal was analyzed After dynamic equilibrium, the time-dependent optical path difference between the center and the edge caused by the temperature gradient shows that when the beam waist is located at the end face of the crystal, the temperature of the end face of the beam with the larger beam waist radius decreases and when the beam waist radius is not changed When the position of the beam is shifted backward, the temperature of the end face of the crystal decreases. The thermal relaxation time can be shortened to some extent by increasing the convective heat transfer coefficient or air flow rate, decreasing the air temperature and decreasing the crystal radius. When the crystal temperature distribution reaches the dynamic equilibrium , The temperature of each point in the crystal changes periodically; the relative optical path length difference (OPD) caused by the crystal radial temperature gradient also changes periodically with time.