超短激光蚀除金属机制的分子动力学研究

 采用耦合电子热传导方程的分子动力学方法，研究了飞秒激光辐照下金属Ni的熔化及蚀除动力学。分析了靶材内部温度分布特征及蚀除产物的构成，主要包含单个原子及大团簇。确定了断裂位置和蚀除开始的标志，即该处温度分布出现小的峰值，且粒子数密度急剧下降。模拟结果表明：强烈的蒸发及靶材内部所产生的拉应力分别是单个原子及大团簇喷射的机制。同时，深入探讨了激光诱导压力波的传播规律，预测了压力波的波速，约为4.97 km/s。将不同脉冲能量密度下的蚀除速率同实验数据加以对比，结果相差16%~20%。预测了熔深随时间的变化规律，基本随时间的延续而呈上升的趋势。发现过热现象的存在。

Molecular dynamics of the mechanism of ultrashort laser ablation of metals

By means of combining a heat conduction equation for electron with molecular dynamics method, the dynamics of melting and ablation processes at Ni surfaces under femtosecond laser irradiation is studied. The temperature distribution of lattice and the components of ablation products are analyzed, single atoms and clusters constitute the ablation products. The location where ablation occurs and the time when ablation sets in are marked by a strong increase in temperature as well as a sharp decrease in density. Simulation results show that intense evaporation and tensile stresses generated in the target are responsible for the ejection of single atoms and big clusters. The propagation of laser-induced stress wave is also further investigated, and the velocity of stress wave is predicted to be nearly 4.97 km/s simultaneously. The rates of ablation predicted are close to experimental data. A trend of increase with time for the depth of molten zone is predicted. Superheating phenomenon is also discovered.