Biexcitons in semiconductor microcavities

The properties of a planar semiconductor microcavity in the strong coupling regime have been studied by spectrally resolved degenerate four-wave-mixin g using fs laser pulses. In addition to the conventional cavity polaritons new spectral features, which are of biexcitonic origin can be resolved. The coupling of these states to the light field of the resonator has been stud ied by investigating their cavity detuning dependence. The observed dispers ion agrees with a bipolariton model, where the exciton to biexciton transit ion is strongly coupled to the electro-magnetic field in the cavity.