采用结合双温模型的分子动力学方法, 研究了典型脉宽飞秒脉冲激光与镍钛二元形状记忆合金相互作用时能量密度对靶材烧蚀深度的影响。模拟了脉宽为100 fs, 能量密度为0~125 mJ/cm2的单脉冲激光辐照90 nm厚镍钛合金薄膜的过程。模拟结果表明, 飞秒单脉冲激光烧蚀镍钛二元形状记忆合金会产生两种不同的烧蚀相。能量密度较低时, 烧蚀结果呈现弱烧蚀相, 烧蚀深度较低, 并且与光学穿透深度相关; 能量密度较高时, 烧蚀结果呈现强烧蚀相, 烧蚀深度大幅度增大。采用“拼花法”对高斯飞秒脉冲激光辐照镍钛靶材的形貌进行预测, 发现使用能量密度为阈值附近的飞秒激光辐照靶材时, 能够获得底部较为平坦的烧蚀弹坑。

The interaction between femtosecond laser and NiTi binary shape memory alloy is simulated by molecular dynamics method combining with two-temperature model. The effects of femtosecond laser fluence on the ablation depth are investigated. In the simulation, the NiTi shape memory alloy film with the depth of 90 nm is irradiated by the single pulse with the duration of 100 fs and the fluences varying from 0 to 125 mJ/cm2. The simulation results show that two different ablation phases exist for single pulse ablating NiTi shape memory alloy. For lower fluence, the ablating result presents gentle ablation phase, the ablation depth is lower and related with the optical penetration depth. For higher fluence, the ablating result presents strong ablation phase and the ablation depth increases markedly. Predicting the morphology of NiTi target irradiated by the single pulse via mosaic approach shows that more flat ablation craters at the bottom can be obtained by using femtosecond laser fluence near the ablation threshold to irradiate the target.