Influence of the energy transport of electrons by optical phonon emission on the superluminescence and reversible bleaching of a thin GaAs layer excited by a strong picosecond light pulse

Abstract

The dependence of the superluminescence and optical bleaching of GaAs during the interband absorption of a strong picosecond light pulse on the photon energy ℏωex of the exciting pulse is investigated experimentally. The bleaching (transmission enhancement, i.e., greater transparency) mainly reflects the density of the photogenerated electron-hole plasma. Several events are observed when the distance between the energy level at which electrons are generated and the level from which they undergo stimulated recombination is a multiple of the longitudinal optical phonon energy. These events are: 1) amplification of recombination superluminescence; 2) slowing of the increase in optical bleaching as ℏωex is increased; and 3) an increase in the shift of the edge of the emission spectrum toward longer wavelengths. These phenomena are qualitatively attributed to an increase in the fraction of transitions involving the emission of LO phonons in the energy transport of electrons toward the bottom of the conduction band and to the influence of this process on the heating of the electron-hole plasma and the density of nonequilibrium LO phonons.