Theory of Electron-Ion Energy Transfer Applied to Laser Ablation

Electron-ion temperature equilibration will be considered for states of matter typically occurring during laser ablation that is for strongly heated electrons and densities similar and lower than the one in the solid. The focus will be on fluid systems after the melt of the lattice as these dominate the hydrodynamic phase of the ablation process. It is shown that simple expressions derived for dilute gases and plasmas become highly questionable for solid-density fluids whereas the electron-phonon picture is inapplicable as well. Instead, one has to consider the collective behavior of electrons and ions in the strongly coupled fluid. The strong inter-ionic forces also strongly affect the heat capacities applied in a two-temperature model. The results presented here are based on a quantum-statistical approach applying nonequilibrium Green's functions.