高重复频率水冷Nd:YAG激活镜放大器的温度特性

为解决高重复频率大能量激光放大器的热管理问题,采用数值模拟与实验分析的方法,对背面水冷Nd:YAG激活镜放大器的流体散热进行了研究.基于低雷诺数k-ε湍流模型,建立了流-固共轭传热多物理场藕合分析模型,对比分析了近壁面处理方法对流体流动、对流扩散和热传导过程及温度分布的影响,分析研究了不同冷却液流量和泵浦参数对流场特性、激光介质温度和波前分布的影响.数值模拟表明:激光介质的温度分布与固液边界层内的黏性作用密切相关,且冷却液的热扩散主要发生在100μm范围内;激光介质的热沉积分布中心对称,而温度分布沿水流方向不对称,最大温升位于出水口端且基本保持不变;增益介质前表面的温度分布与介质的波前分布随冷却液流量非线性变化,而随泵浦参数线性变化;实验结果与数值模拟符合较好.

Temperature characteristics of high repetition rate watercooled Nd:YAG active mirror amplifier

In order to deal with the thermal management problem of high-energy high-repetition rate laser amplifiers,the efficient heat removal in water-cooled Nd:YAG active mirror amplifiers is investigated in detail through numerical modeling and experimental analysis.According to the low Reynolds number k-ε turbulence model,a full fluid-solid conjugate heat transfer model is established to give a comprehensive model of flow and thermal characteristics in three dimensions.The thermal distributions obtained from the model are then used to calculate all mechanical stresses in the laser medium and thermally-induced wavefront distortions.In comparison with the standard k-ε turbulence model,the influences of the near-wall treatments of the above model on the process of fluid flow,convection diffusion and heat conduction,and temperature distributions are analyzed.Meanwhile,the effects of coolant flow rate and pump parameter on the flow field characteristics,temperature and wavefront distributions of the YAG disk are also studied.Numerical simulation results reveal that the temperature distribution of the laser medium is closely related to the viscous effect in the solid-liquid boundary layer.Although the heat deposition distribution of the laser medium is symmetrical,the temperature profile is asymmetrical as a result of the increasing water temperature along the water flow.The maximum temperature rise of the disk is at the outlet end,and the position remains almost unchanged.The front-surface temperature distributions and wavefront profiles of Nd:YAG vary nonlinearly with the coolant flow rates,but linearly with the pump parameter.Model predictions show that when the laser amplifier operates at a repetition rate of 50 Hz,the thermal diffusion of the coolant mainly occurs in a range of 100μm,and the maximum temperature difference of the coolant reaches up to 10.85℃.Correspondingly,the maximum temperature variation over the front-surface active region is less than 4℃.with an average temperature of 49.62℃,which leads to a total peak-to-valley wave front distortion of 7.27λ.The experimentally measured temperature distributions are in reasonable agreement with numerical simulations.The research results are beneficial to designing and optimizing the high-energy,high-repetition rate water-cooled Nd:YAG active mirror amplifiers.