Laser emission from semiconductor microcavities: Transition from nonperturbative to perturbative regimes

We have demonstrated laser emission at densities below the saturation exciton density in a semiconductor microcavity by tuning the cavity resonance to the low-energy side of the inhomogeneously broadened exciton distribution. Laser emission in this regime arises from population inversion of localized excitons at the low-energy tail of the inhomogeneous distribution. Distinct spectral line shapes of laser emission and especially a large and abrupt change in the lasing threshold are observed when the composite system undergoes a transition from the nonperturbative to the perturbative regimes. The abrupt threshold change is attributed to ionization of excitons occurring in the transition region.