Crossover from exciton to biexciton cavity polaritons

Summary form only given. We exploit a high-quality semiconductor microcavity for the creation of an exciton gas near the optical saturation density. The sample is excited by short laser pulses that are resonant with both the cavity mode and the exciton transition. The microcavity provides a narrow spectral filter that strongly inhibits the photoexcitation of dissociated electron-hole pairs. On the other hand, as a result of the fast scattering processes, also the exciton states not directly coupled with light are populated (which can re-radiate only through scattering back into the few optically active states near k=0) giving rise to a reservoir of excitons lasting several tens of ps. This physical system is therefore ideal for isolating and studying the interactions between excitons. We report novel oscillator strength transfer phenomena induced by the exciton-exciton correlation.