Heat transport analysis for femtosecond laser ablation with molecular dynamics-two temperature model method

Abstract

The phenomena of femtosecond (fs) laser ablation, such as heat transfer mechanism and shock wave propagation, are investigated by using modified molecular dynamics (MMD). In MMD, conventional molecular dynamics and the two-temperature model, which can describe both electron heat conduction and thermal non-equilibrium state between electron and atom, are coupled by employing the relationship between atom kinetic energy and lattice temperature. For TTM, the heat capacity and thermal conductivity of electrons are dependent on atom and electron temperatures. Two boundary conditions are prepared in order to investigate the effect. In case A, a heat bath is expanded to macro-scale by using a finite difference method whose governing equation is a two-temperature model. In case B, a normal heat bath is set at the bottom of the MD region, resulting in relaxation time with a reasonable value and speed of thermal shock wave equal to elastic wave. Finally, we conclude that the dominant heat transport mechanism is electron heat conduction within several picoseconds, after which thermal shock wave and ordinary heat conduction becomes dominant.