Time-resolved four-wave mixing in GaAs/AlAs quantum well structures.

Femtosecond nonlinear laser spectroscopy is applied to study the dynamics of coherent optical excitations in semiconductors. In particular, excitonic excitations in quantum wells and superlattice structures are considered. Two examples demonstrate that four-wave mixing experiments with time-resolved detection of the nonlinear signal are able to distinguish between quantum beats and polarization interference.