ULTRAFAST NONLINEAR OPTICS IN GAAS ALGAAS QUANTUM-WELLS/

By degenerate four-wave mixing experiments in a two-beam geometry, we have investigated the initial coherence and dephasing of quasi two-dim ensional excitons and biexcitons in GaAs multiple quantum wells. The d ephasing has contributions from phonon scattering, interface-roughness scattering and exciton-exciton scattering. Inhomogeneous broadening a nd generation of coherent wavepackets play a significant role in the c oherent exciton dynamics. The incoherent exciton dynamics, diffusion a nd recombination, is studied by three-beam transient grating experimen ts. A significant difference in the interface roughness scattering of coherent and incoherent (thermalized) excitons is observed.