Molecular dynamics simulation on laser ablation of metal and silicon

Ablation phenomena of material induced by laser irradiation are complicated and it is unjustifiable to analyze them theoretically with a continuum model. In this study, atomic behavior of copper, aluminum and silicon during laser ablation is simulated applying molecular dynamics. Variation of atomic array and stress state of atoms during and after laser irradiation are shown visually. Main conclusions obtained are summarized as follows. (1) Thermal shock wave travels to interior of material with laser irradiation. Propagation velocity of thermal shock wave is equal to elastic wave velocity. (2) In ablation process, mam small voids generate in the liquid phase at first. Then they become larger and larger, and adjacent voids combine each other, which develop into a relatively larger void. Finally, the vicinity of surface bounds out forming into relatively large lumps. (3) In metal with laser irradiation of relatively high power density, molten metal whose kinetic energy is too small to evaporate becomes spherical by surface tension and deposit around the hole. On the other hand, in the case of relatively low power density, fusing atoms flow out from the molten pool and deposit around the hole. (4) In silicon, a part of vaporizing atoms deposits around the hole, whose height is smaller than that in metal under the same laser irradiating condition. The surface of generated wall of silicon is rough comparing with metal.