COHERENT TRANSIENT SPECTROSCOPY OF EXCITONS IN GAAS-ALGAAS QUANTUM-WELLS

Coherent transient optical spectroscopy techniques provide a means of studying the relaxation of electronic excitations in solids. Using these techniques we examine the relaxation of excitons in GaAs-AlGaAs multiple quantum wells at low temperature. Localization of excitons due to interface disorder results in inhomogeneous broadening of the absorption spectrum and relaxation due to migration between localization sites. The temperature and energy dependence of the relaxation indicate the presence of complex scattering mechanisms. The dependence of the optical response on the polarization of the incident excitation fields is shown to result in a dramatic change of the dephasing and broadening characteristics of the optical response. This response is interpreted in terms of the presence of both localized and delocalized excitons. Mechanisms for the polarization dependence are discussed.