LASER-EMISSION FROM SEMICONDUCTOR MICROCAVITIES - THE ROLE OF CAVITY POLARITONS

We present an experimental study on the role of cavity polaritons in l aser emissions from a GaAs quantum-well microcavity. We show that cavi ty polaritons play no role in the laser emission process when the cavi ty is nearly resonant with the excitons. The laser emissions emerge fr om the bare cavity mode instead of from a cavity-polariton branch and the threshold density is much higher than the saturation density at wh ich cavity polaritons vanish. We also show that the presence of emissi on doublers near the lasing threshold, which was previously taken as a n evidence for laser emission from cavity polaritons, is primarily the result of spatial and/or temporal variations of exciton densities wit hin the excitation volume.