Transition from a microcavity exciton polariton to a photon laser

In a previous paper [Phys. Rev. A 54, R1789 (1996)], we reported the observation of a laserlike transition in a single GaAs quantum well microcavity and gave the interpretation as spontaneous buildup of coherent exciton-polariton population via stimulated polariton-phonon emission. In this Brief Report, we present new experimental data and correct our previous interpretation for the microcavity polariton system at high density. We observe a continuous transition from a microcavity polariton emission to a bare photon laser. This conclusion is based on the measurements of the angular resolved photoluminescence, linewidth, and intensity of the lasing line as well as the reflection spectrum under cw pumping.