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

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. Our work addresses the important question whether single-QD lasing is feasible in experimentally accessible systems and shows 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.

Delayed Transition to Coherent Emission in Nanolasers with Extended Gain Media

“…To do so, all given values of β are evaluated at P = P th . While nonconstant β factors have been investigated in different contexts [21][22][23], this approximate treatment fully serves the purpose in this work. For β approaching unity, the intensity jump goes to zero, reflecting the concept of thresholdless lasing often referred to in the literature [12][13][14].…”

“…To do so, all given values of β are evaluated at P = P th . While nonconstant β factors have been investigated in different contexts [21][22][23], this approximate treatment fully serves the purpose in this work.…”

Physics and Applications of High‐β Micro‐ and Nanolasers

“…In this bad‐cavity limit, it has been shown that although the optical amplification in single‐QD lasers was provided dominantly by a resonant emitter, the gain contribution from further non‐resonant QDs is necessary to enter the lasing regime. [ 133 ] For a real single‐QD laser, the question arises as to whether it can (only) function in the regime of strong cQED coupling and how lasing and the climbing the Jaynes–Cummings ladder differ. In the area of high‐β single‐QD lasers, deterministic fabrication technologies are interesting, since they permit a precise control of the position and number of the QDs in the laser's active area.…”

Quantum dot micropillar lasers

“…In the following we consider a micropillar laser with embedded InGaAs QDs that were grown with a moderate density of 10 10 cm −2 . Details are found in [144]. The QDs feature a large oscillator strength, which in combination with the low mode-volume micropillar ensures pronounced lightmatter interaction.…”

“…Using this insight, we formulate a laser model that is based on the microscopic approach introduced in section 3 for a two-component gain medium [144]. We consider the single resonant emitter and N BG background emitters, each with coupling and loss parameters that are obtained from matching the data shown in figure 22.…”