Heat Transfer in Femtosecond Laser Processing of Metal

The short time scales and high intensities obtained during femtosecond laser irradiation of metals require that heat transfer calculations take into account the nonequilibrium that exists between electrons and the lattice during the initial laser heating period. Thus, two temperature fields are necessary to describe the process--the electron temperature and the lattice temperature. In this work, a simplified one-dimensional, parabolic, two-step model is solved numerically to predict heating, melting, and evaporation of metal under femtosecond laser irradiation. Kinetic relations at the phase-change interfaces are included in the model. The numerical results show close agreement with experimental melting threshold fluence data. Further, it is predicted that the solid phase has a large amount of superheating and that a distinct melt phase develops with duration of the order of nanoseconds.