Nonlinear optics in semiconductors and multiple quantum wells

The confinement of electrons and holes in quantum wells allows the fabrication of structures exhibiting enhanced nonlinear optical effects associated with excitonic transitions. By applying femtosecond spectroscopy, it has become possible to study the coherent and incoherent properties of these systems with high temporal resolution, thus gaining a detailed insight into the processes involved in the interactions of photons, electrons and the crystal lattice on a subpicosecond time scale. We present investigations of the nonlinear optical behaviour governed by the relaxation and thermalization dynamics in multiple quantum wells and in low-temperature grown GaAs. Experiments with high temporal and energetic resolution provide a detailed insight into the inter-valence-band thermalization in quantum wells and the influence of shallow bound defect levels in low-temperature grown GaAs.