SPECTRAL SIGNATURES OF EXCITONIC 4-WAVE-MIXING SIGNALS IN GAAS MULTIPLE-QUANTUM WELLS

We investigate the spectral properties of the excitonic nonlinear resp onse in a GaAs quantum-well sample containing wells of different thick nesses. We observe both the heavy-hole biexciton and the light-hole bi exciton in the transient four-wave mixing spectrum and estimate their binding energy dependence on well width. For moderate excitation densi ties the signal for negative delay at the heavy-hole exciton and biexc iton resonances is due to two-photon transitions to the biexciton stat es through the exciton states. The temporal behavior of the transient four-wave mixing signal from the heavy-hole exciton resonance is stron gly dependent on the spectral position of the laser. We show that this effect is due to interference phenomena and to excitation-induced dep hasing. (C) 1996 Optical Society of America.