Interaction with Metals

Abstract

In contrast to dielectric materials, metals are characterized by a high density of quasi-free electrons causing strong absorption of laser light from the beginning of the ultrashort laser pulse without the need of nonlinear absorption effects like multiphoton absorption. In a femtosecond timescale the energy transfer to the electrons can therefore be regarded as instantaneous. Their thermalization and movement is fast enough to occur during a typical femtosecond pulse duration. The transfer of energy from the electronic system to the lattice, however, needss relaxation times of the order of some picoseconds. The heating process of the lattice is for subpicosecond pulses no longer determined by the pulse duration but by the material-dependent relaxation time. This circumstance limits the reduction of heat load and explains recast occurring even when using ultrashort pulses.