Temporal and spectral dynamics in multiquantum-well semiconductor saturable absorbers

Performing femtosecond pump-probe measurements on multiquantum-well (MQW) semiconductor saturable absorbers we find a strong spectral dependence of the absorption dynamics on a picosecond time scale. While for long wavelengths a pump pulse induced reduction of the absorption is observed, at short wavelengths the absorption increases due to the pump. We explain this behavior on the basis of a model including photo-induced field screening.