Delayed Transition to Coherent Emission in Nanolasers with Extended Gain Media

Abstract

Measurements of the two-photon correlation function ${g}^{(2)}(0)$ provide a means to verify coherent emission in high-$\ensuremath{\beta}$ nanolasers that operate in or close to the thresholdless regime. By deriving an analytic expression for ${g}^{(2)}(0)$, the authors identify lasing regimes in which the onset of coherent emission occurs at significantly higher pumping than is required to reach the intensity jump in the input-output curve. Surprisingly, for extended active media such as quantum wells or monolayer transition-metal dichalcogenides, this coherence threshold is insensitive to the $\ensuremath{\beta}$ factor. This insight is significant for developing efficient nanolasers for ``green photonics''.