Multi-material two-temperature model for simulation of ultra-short laser ablation

We investigate the interaction of 100 fs laser pulses with metal targets at moderate intensities (1012 to 5 1013 W/cm2). To take into account effects of laser energy absorption and relaxation we develop a multi-material two-temperature model based on a combination of different approaches. The backbone of the numerical model is a high-order multi-material Godunov method in a purely Eulerian form. This formulation includes an interface-tracking algorithm and treats spallation at high strain rates and negative pressures. The model consistently describes the hydrodynamic motion of a two-temperature plasma and accounts for laser energy absorption, electron–phonon/ions coupling and electron heat conductivity. In particular, phase transitions are accurately taken into account by means of a wide-range two-temperature multi-phase equation of state in a tabular form. The dynamics of the phase transitions and the evolution of the heat-affected zone are modeled and analyzed.We have found that a careful treatment of the transport coefficients, as well as consideration of phase transitions is of a great importance in obtaining reliable numerical results. Calculation results are furthermore compared for two metals with different electron–phonon coupling parameters (Au and Al). We have found that the main part of ablated material results from fragmentation of melted phase caused by tensile stresses. A homogeneous nucleation mechanism alone does not explain experimentally observed ablation depth.