Heat Transport Analysis of Femtosecond Laser Ablation with Full Lagrangian Modified Molecular Dynamics

The purpose of this study is to analyze the heat transport mechanism of femtosecond laser ablation. Under the condition that laser pulse duration is on the order of femtoseconds, a thermal nonequilibrium state between an electron and atom exists and must be taken into account. In order to describe physical phenomena such as heat transport under a nonequilibrium state, a new method, modified molecular dynamics in which molecular dynamics (MD) couples with the two-temperature model (TTM) in a particle- based method, is proposed. In this method, MD simulates the motion of an atom and TTM simulates both electron heat conduction and energy exchange through electron-atom iInteractions. This approach yields the use of laser iIntensity as a parameter. For nonequilibrium heat transport, electron heat conduction transports most of the absorbed laser energy and becomes the dominant heat transport mechanism. At thermal equilibrium, above the ablation threshold fluence, electron heat conduction and thermal waves are dominant, while below the ablation threshold fluence, only electron heat conduction is dominant.