  We compare polariton lasing with photon lasing of a planar GaAs/GaAlAs
microcavity with zero detuning between the bare cavity mode and the bare
exciton mode. For the emission from the lower energy-momentum dispersion branch
we find a two-threshold behavior of the ground state in the input-output curve
where each transition is accompanied by characteristic changes of the in-plane
mode dispersion. In particular, we show that the thresholds are unambiguously
evidenced in the photon statistics of the emission based on the second-order
correlation function. Moreover, the distinct two-threshold behavior is
confirmed in the evolution of the emission pulse duration.
