热阻塞效应对激光辐照靶材烧蚀过程的影响分析

研究了百兆瓦级激光烧蚀碳/碳复合材料靶材产生的等离子体吸收激光束能量引起的热阻塞效应。首先，基于逆轫致吸收理论，建立了激光在烧蚀靶材产生的等离子体中的传播模型；然后，基于磁流体理论，得到了等离子体在百兆瓦级激光形成的电磁场中的波动方程，建立了等离子体吸收激光能量引起热阻塞效应的模型。最后，对烧蚀过程中粒子的总密度、吸收系数、靶材表面等效热流随激光持续时间的变化规律以及是否考虑热阻塞效应时，靶面垂直方向的温度场进行了数值模拟。结果表明：等离子体的形成，对激光形成了明显的热阻塞效应，削弱了激光对靶材的烧蚀作用，使粒子总密度、吸收系数、靶材表面等效热流以及靶面垂直方向温度场的变化均呈现为非线性。

Analysis of influence of thermal blockage on process of laser irradiation

The thermal blockage effect caused by plasma (produced by mega-watt laser ablation of C/C composite target) absorption laser beam energy is studied in this paper. First, based on the inverse bremsstrahlung absorption theory, a propagation model of laser through plasma generated by ablating the target is built. Then, based on the theory of magnetic fluid, wave equations of plasma in the form of electromagnetic caused by mega-watt laser and thermal blockage effect model caused by the plasma absorption laser energy are introduced. Finally, numerical simulation gives the total density of particles in the ablation process, absorption coefficient, changes of target surface equivalent heat flux and whether thermal blockage effect is taken into account, the differences of the temperature field curve along the vertical direction of the target surface. The results show that because of the plasma formation, the thermal blockage effect is obvious to the laser. It weakens the burning effect of laser on the target, and makes the total particle density, the absorption coefficient, the equivalent heat flow on target surface and temperature field vertical to target surface all change nonlinearly.