Optical nonlinearities due to long-lived electron/hole plasmas

By choice of appropriate layer thicknesses it is possible to produce GaAs/AlAs quantum well structures in which the lowest energy electron and hole wavefunctions are localized in spatially separate layers. As the low temperature radiative lifetime of such a structure is long (μs) it is possible to observe cw optical nonlinearities at relatively low power densities. In this paper results of optical pump/probe experiments will be presented from a range of standard type II structures along with results from a new type of structure that enhances the spatial separation of the electron/hole population