Emission characteristics, photon statistics and coherence properties of high-β semiconductor micropillar lasers

We report on complementary experiment-theory investigations regarding the photon emission statistics and coherence properties of quantum dot-based semiconductor micropillar lasers with high P factors, i.e., a large,coupling of spontaneous emission into the lasing mode. In terms of power-dependent first- and secondorder photon correlation measurements, our results consistently reveal a smooth transition between the regimes of spontaneous and mainly stimulated emission. The gradual onset of lasing is accompanied by strong photon number fluctuations and distinct changes of the field coherence length. In particular, the regime of stabilized coherent emission is found to establish at significantly increased excitation levels above the lasing onsets. As was verified by detailed semiconductor-theoretical calculations on the characteristics of these type of resonator devices, the smooth transition from thermal to coherent emission should indeed become increasingly harder to determine with beta -> 1.