用二维辐射流体程序Flash模拟了小焦斑纳秒激光与铝平面靶的相互作用过程,其中入射激光的聚焦半径为25 μm,峰值强度约为1013 W/cm2,波长为532 nm。模拟发现激光通道上的等离子体出现了密度排空的现象,激光焦斑外侧出现环状的射流结构。激光通道上密度排空现象对电子热输运的计算较为敏感,对比干涉实验测量的密度分布,确定了模拟中限流因子的取值为0.08。通过考察辐射致冷与电子横向热输运对等离子体膨胀运动的影响,对环状射流结构的形成原因给出了物理解释,并在模拟上验证了辐射冷却在其形成过程中的主导作用。

With the help of radiation hydrodynamic code Flash, we simulated the ablation process of a small focal-spot nanosecond laser irradiation on an aluminum planar target. The irradiating laser has a focal spot radius of 25 μm and maximum intensity of about 1013 W/cm2 with wavelength of 532 nm. In our simulations, it is observed that electron density in the laser channel is relatively lower than the ambient one in some coronal region. This phenomenon is found to be sensitive to the electron heat conduction model. By comparing simulation results with our experimental electron density profiles, flux limit factor of 0.08 is then determined in our simulation. The annular jet also occurs in our simulations and experiments. The mechanism of annular jet formation is analyzed and discussed, which is mainly related to the radiative cooling.