Response of GaAs to fast intense laser pulses

Motivated by recent experiments, we have performed simulations which show in detail how the electrons and ions in GaAs respond to fast intense laser pulses (with durations of order 100 fs and intensities of order $1-10\hspace{0.5em}{\mathrm{T}\mathrm{W}/\mathrm{c}\mathrm{m}}^2).\mathrm{}$ The method of tight-binding electron-ion dynamics is used, in which an arbitrarily strong radiation field is included through a time-dependent Peierls substitution. The population of excited electrons, the atomic displacements, the atomic pair-correlation function, the band structure, and the imaginary part of the dielectric function are all calculated as functions of time, during and after application of each pulse. Above a threshold intensity, which results in promotion of about 10% of the electrons to the conduction band, the lattice is destabilized and the band gap collapses to zero. This is most clearly revealed in the dielectric function $\epsilon \left(\omega \right),$ which exhibits metallic behavior and loses its structural features after 100–200 fs.