Atomistic modeling of ultrashort-pulse ultraviolet laser ablation of a thin LiF film

摘要

We study UV-laser-induced melting and ablation of 10nm thick LiF films by UV laser irradiation. Our method combines a molecular dynamics scheme for LiF and a set of equations describing the temporal evolution of the conduction-electron density and temperature due to laser irradiation. We find that with increasing laser fluence, the crystal is heated, then melts, then temporary voids form, until it finally ablates, and even multifragmentation occurs. This sequence of events parallels that found in other materials, such as in metals, with similar values for the relative energization thresholds, if normalized to the cohesive energy of the material or to the melting temperature. The ablation mechanism is shown to be mechanical spallation of the molten crystal due to the high tensile pressure building up after the oscillatory relaxation of the initial high thermoelastic pressure.