Femtosecond studies of excitonic optical non-linearities in GaAs/Al xGa 1− xAs multiple quantum wells under in-plane uniaxial strain

Abstract

The pump-probe technique was employed in the study of excitonic optical non-linearities at 40 K in a GaAs/Al 0.1Ga 0.9As multiple quantum well under thermally induced in-plane uniaxial strain. We report the first observation of an ultrafast large-angle polarization rotation of the probe light effected by the bleaching of the anisotropic absorption near the heavy hole exciton peak in this material. Dynamic rotations as large as 42° have been measured for a compressive strain of ~ 0.2%. In addition, a dependence of the phase space filling produced by resonantly excited excitons on the orientation of the pump polarization vector has been observed which decays with a time constant of 0.5 ps. This decay is attributed to the ionization of excitons into free electron-hole pairs. The subsequent decline of the probe rotation is governed by the removal of these carriers from the wells.