Controlling the gain contribution of background emitters in few-quantum-dot microlasers

TL;DR

This study experimentally and theoretically investigates how background gain from off-resonant quantum dots influences single-emitter lasing in microlasers, demonstrating the possibility to control and analyze individual quantum dot contributions.

Contribution

It introduces a two-color excitation method to tune background gain and distinguish between resonant and off-resonant quantum dot contributions in microlaser lasing.

Findings

Single-QD gain alone cannot induce lasing in the studied microlaser.

Off-resonant QDs can contribute up to 70% of emission.

Background gain from off-resonant QDs is essential for lasing transition.

Abstract

We provide experimental and theoretical insight into single-emitter lasing effects in a quantum dot (QD)-microlaser under controlled variation of background gain provided by off-resonant discrete gain centers. For that purpose, we apply an advanced two-color excitation concept where the background gain contribution of off-resonant QDs can be continuously tuned by precisely balancing the relative excitation power of two lasers emitting at different wavelengths. In this way, by selectively exciting a single resonant QD and off-resonant QDs, we identify distinct single-QD signatures in the lasing characteristics and distinguish between gain contributions of a single resonant emitter and a countable number of off-resonant background emitters to the optical output of the microlaser. We address the important question whether single-QD lasing is feasible in experimentally accessible systems and show that, for the investigated microlaser, the single-QD gain needs to be supported by the background gain contribution of off-resonant QDs to reach the transition to lasing. Interestingly, while a single QD cannot drive the investigated micropillar into lasing, its relative contribution to the emission can be as high as 70% and it dominates the statistics of emitted photons in the intermediate excitation regime below threshold.