等离子屏蔽效应下飞秒激光照射金箔的分子动力学模拟

Molecular dynamics simulation of femtosecond laser irradiation of gold foil under plasma shielding effect

采用耦合了双温度模型的分子动力学方法对飞秒激光烧蚀金箔的传热过程进行了模拟研究,考虑了非傅里叶效应,探究了不同激光能流密度下等离子体羽流的屏蔽作用.根据密度分布将激光烧蚀过程中的金箔划分为过热液体层、熔融液体层和固体层,并比较了不同激光能量密度下过热液体层表面发生的相爆炸沸腾现象以及表面温度的变化情况.结果表明,随着激光能量密度的增大,等离子体的屏蔽比例几乎呈线性增大.在激光的烧蚀过程中,金箔的上表面最先经历液体层以及过热液体层,并且随着时间的推移,液体层和过热液体层逐渐向金箔底部移动.过热液体层发生体积移除的相爆炸沸腾是金箔烧蚀的主要方式,随着激光能量的增大,爆炸沸腾发生的时间提前,并且结束的时间相应延后,持续时间变长.

A molecular dynamics method coupled with a dual temperature model was used to simulate the heat transfer process of femtosecond laser ablation of gold foil. The non-Fourier effect was considered, and the shielding effect of the plasma plume under different laser energy flow densities was explored. According to the density distribution, the gold foil in the laser ablation process is divided into superheated liquid layer, molten liquid layer and solid layer, and the phase explosive boiling phenomenon and the surface temperature changes on the surface of the superheated liquid layer under different laser energy densities are compared. The results show that as the laser energy density increases, the plasma shielding ratio increases almost linearly. During the laser ablation process, the upper surface of the gold foil first goes through the liquid layer and the superheated liquid layer, and with the passage of time, the liquid layer and the superheated liquid layer gradually move to the bottom of the gold foil. The phase explosive boiling of the volume removal in the superheated liquid layer is the main way of gold foil ablation. With the increase of laser energy, the time of explosive boiling occurs earlier and the time is delayed accordingly, and the duration becomes longer.