  The microscopic mechanism of metal ablation induced by ultrashort laser pulse
irradiation is investigated. A two-temperature model scheme combined with
molecular dynamics (TTM-MD) is developed to incorporate electronic entropy
effects into the simulation of metal ablation while satisfying the energy
conservation law. Simulation with the TTM-MD scheme reveals that ultrashort
laser pulse irradiation near the ablation threshold causes high-energy ion
emission and sub-nanometer depth ablation, as observed experimentally, due to
the electronic entropy effect. It is also shown that the electronic entropy
effect is also significant in spallation.
