Laser Ablation of Aluminium: Drops and Voids

In [RTTS11] we have presented a general introduction to the process of laser ablation, its simulation by the molecular dynamics method, and results for aluminium and a complex metallic alloy. Here we will concentrate on how drops or clusters and voids can be simulated which form during laser ablation. Laser ablation is a process where material is removed from the surface of a solid or liquid by very intense laser radiation. We are especially interested in femtosecond pulses on metals where the direct interaction of the laser beam with the conduction electrons plays an important role and must in general be described by a two-temperature model with separate temperatures for the electrons and the atoms. For details on the two-temperature model and the implementation in conjunction with molecular dynamics see [RTTS11]. We will not apply this model here for reaseons explained later. To actually drill a hole with femtosecond pulses requires of the order of ten thousand pulses and time frames up to seconds. This is way beyond the scope of atomistic simulations. But we can treat each laser pulse separately since the time between two pulses is so large that the material cools down. The only difference are modified surfaces. Here we report on large scale ablation simulations and the analysis of the size and angular distribution of single atoms forming a gas phase together with a fraction of droplets. A second part includes the formation of voids in the irradiated region and its temporal evolution.