Investigation of excitonic saturation by time-resolved circular dichroism in GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells

Time- and wavelength-resolved circular dichroism of the excitonic saturation in GaAs-${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells at room temperature is investigated using a degenerate excite-probe method. For moderate excitation, the effects of photogenerated carriers on the heavy-hole exciton resonance are separately identified as the contributions of phase-space filling and Coulombic effects (screening and line-shape broadening). These contributions are observed to be of a similar magnitude. The induced circular dichroism of the exciton saturation was observed to decay with a time constant of 50 ps, which is attributable to electron spin relaxation.