Delayed transition to coherent emission in nanolasers with extended gain media

TL;DR

This paper investigates the complex behavior of nanolasers with extended gain media, revealing that coherence can be achieved at higher pump powers than the traditional threshold, challenging existing perceptions about high-$eta$ lasers.

Contribution

It introduces a new understanding of laser threshold in cavity-QED nanolasers, highlighting regimes where coherence and intensity thresholds diverge, especially in high-$Q$ nanolasers with extended gain.

Findings

Coherence can occur at higher pump powers than the intensity threshold.

High-$eta$ factors do not necessarily reduce power consumption in these nanolasers.

Stimulated emission is essential to suppress spontaneous emission noise.

Abstract

The realization of high-$\beta$ lasers is one of the prime applications of cavity-QED promising ultra-low thresholds, integrability and reduced power consumption in the field of \textit{green photonics}. In such nanolasers spontaneous emission can play a central role even above the threshold. By going beyond rate-equation approaches, we revisit the definition of a laser threshold in terms of the input-output characteristics and the degree of coherence of the emission. We demonstrate that there are new regimes of cavity-QED lasing, realized e.g. in high-$Q$ nanolasers with extended gain material, for which the two can differ significantly such that coherence is reached at much higher pump powers than required to observe the thresholdlike intensity jump. Against the common perception, such devices do not benefit from high-$\beta$ factors in terms of power reduction, as a significant amount of stimulated emission is required to quieten the spontaneous emission noise.