Laser-excitation of electrons and nonequilibrium energy transfer to phonons in copper

Abstract

After the irradiation of a copper sample with an ultrashort laser pulse, electrons do not follow a Fermi distribution anymore but instead are in a nonequilibrium state. In contrast, the lattice cannot be excited directly by the laser pulse, due to the frequency mismatch. The energy increase in the phononic system only happens due to electron–phonon scattering. We investigate the initial electron dynamics using full Boltzmann-type collision integrals, including material-dependent characteristics by implementing a realistic density of states. We show results on the absorbed energy, details of the electronic nonequilibrium and the resulting electron–phonon coupling parameter in dependence on the photon energy. Our results show a counteracting dependence on the photon energy, which, on the one hand, enables the d-band electrons to absorb high-energy photons and on the other hand, increases the probability of multi-photon absorption.