Dielectric function for a model of laser-excited GaAs

Abstract

We consider a model for the ultrashort pulsed-laser excitation of GaAs in which electrons are excited from the top of the valence band to the bottom of the conduction band. The linear optical response of this excited system in the visible and near-UV is calculated by solving a statically screened Bethe-Salpeter equation. Single-particle electron energies and wave functions are taken from ab initio electronic structure calculations. The screened electron-hole interaction W is calculated with a model dielectric function which includes the excited carriers. Though band-gap renormalization is neglected, dramatic changes are observed in the shape of ${\ensuremath{\epsilon}}_{2}(\ensuremath{\omega})$ due to Pauli blocking and the enhanced screening of W. We estimate the error incurred in the static screening approximation by performing static screening calculations with the assumption that the excited carriers respond too slowly to screen W.