High-resolution nonlinear laser spectroscopy of heavy-hole excitons in GaAs/AlGaAs quantum-well structures: A direct measure of the exciton line shape

We report high-resolution nonlinear laser-spectroscopy studies of the n=1 heavy-hole exciton in GaAs multiple quantum wells. Using a new method of cw frequency-domain four-wave mixing, we first show that the excitation relaxation consists of both fast and slow components. We then show that the contribution of well-width fluctuations to inhomogeneous broadening can be elimiated enabling us to obtain a direct measure of the intrinsic exciton line shape. Under certain conditions, this line shape is non-Lorentzian and cannot be explained on the basis of simple excited-state relaxation dynamics.