Unified theoretical description of out-of-equilibrium electron intraband dynamics in gold induced by femtosecond laser pulses

The modeling of the intraband dynamics of conduction electrons in gold induced by a femtosecond laser pulse is addressed. Current approaches, based on the numerical resolution of the Boltzmann equation, are only able to describe electron excitation or relaxation processes. In the present paper, within a single formalism, our kinetic model accounts quantitatively for both excitation and relaxation processes, i.e., photon absorption, thermal conductivity, and electron-phonon coupling coefficient. We suggest that such an approach can only be built by including Umklapp processes in the description of electron collisions. In addition to normal electronic collisional processes with phonons and other electrons, the present theoretical description further includes these mechanisms: (i) a conduction electron can be scattered in the second Brillouin zone after a collision, contributing significantly to the photon absorption, and (ii) the influence of the discrete and periodic nature of the lattice on electron collisions is considered, enabling in particular the coupling between electron and transverse phonons. A good agreement of predictions of this unified modeling with experimental observations for absorption and energy transfer from electrons to the lattice is obtained. We have investigated the influence of the Umklapp processes on the imaginary part of the dielectric function, the electron-phonon coupling parameter, and the transient shape of the electron energy distribution.