Molecular Dynamics Simulations of Femtosecond Laser Ablation and Spallation of Gold

The behavior of micron-sized gold films irradiated by a femtosecond laser is investigated via molecular dynamics simulations. The ultrafast laser heating induces a stress-confined state near the surface of the film. For sufficient laser fluences, decomposition of the stress-confined state leads to ablation of molten material in the frontal and spallation of crystalline solid at the rear sides of the sample. Simulations for thick films (>0.5 μm) give distinct fluence thresholds for ablation and spallation of 137 and 193 mJ/cm2, respectively, whereas for thin films only a single fracture process is observed. For thin films, it is shown that absorbed fluence at fracture threshold is a function of foil thickness. As foil thickness is decreased to the limit of very thin foils, the stress-confinement picture becomes increasingly less valid.