Delayed formation of coherence in the emission dynamics of high-Q nanolasers

In the realization of ultrasmall semiconductor lasers, cavity-QED effects are used to enhance spontaneous emission and enable the lasing threshold to be crossed with gain contributions from only a few solid-state emitters. Operation in this regime fosters correlation effects that leave their fingerprint especially in the emission dynamics of nanolasers. Using time-resolved photon-correlation spectroscopy, we show that in a quantum-dot photonic-crystal nanolaser emitting in the telecom band, second-order coherence associated with lasing is established on a different timescale than the emission itself. By combining measurements with a microscopic semiconductor laser theory, we attribute the origin to carrier-photon correlations that give rise to non-Markovian effects in the emission dynamics that are not captured by laser rate-equation theories. Our results have direct implications with respect to the modulation response, repetition rate, noise characteristics, and coherence properties of nanolasers for device applications.