Photon-number correlations near the threshold of microcavity lasers in the weak-coupling regime

The quantum-noise properties near the threshold of microcavity lasers are studied theoretically and experimentally in the weak-coupling regime. Computations based on two-level quantum theory show that the microlasers exhibit a high degree of second-order coherence compared with conventional lasers as a result of the suppression of spontaneous emission into nonlasing modes, and that there always exists a finite threshold for these lasers defined by the peak of the photon-number correlation function corresponding to the spontaneous-to-stimulated transition.