Nonlinear optical processes of excitons in semiconductor microcavity structures

We investigated the nonlinear optical responses of excitons in a GaAs single quantum well (SQW) embedded in a 1/2 λ planar microcavity in the weak, intermediate and strong coupling regime. We performed frequency selective degenerate four-wave mixing (DFWM) experiments using tunable picosecond laser pulses as well as time domain DFWM with subpicosecond pulses. In the intermediate coupling regime, the enhancement of the nonlinear signal does not coincide with the normal mode resonance observed in linear reflection spectra. This indicates that the formation of ‘cavity polaritons’ is not yet complete even if a clear splitting appears in the linear spectrum. This is in contrast to the strong coupling regime where strong signal appears at the normal mode resonance. With these results, the criteria of strong coupling regime are discussed.