Delayed Transition to Coherent Emission in Nanolasers with Extended Gain Media

The ongoing miniaturization of semiconductor lasers has enabled ultra-low threshold devices and even provided a path to approach thresholdless lasing with linear input-output characteristics. Such nanoscale lasers have initiated a discourse on the origin of the physical mechanisms involved and their boundaries, such as the required photon number, the importance of optimized light confinement in a resonator, and mode-density enhancement. Here, high-metal-clad coaxial nanolasers, which facilitate thresholdless lasing are investigated. Both the conventional lasing characteristics, as well as the photon statistics of the emitted light at 10 K under continuous wave excitation are experimentally and theoretically investigated. While the former lacks adequate information to determine the threshold to coherent radiation, the latter reveals a finite threshold pump power. The work confirms an important aspect of high-lasers, namely that a thresholdless laser does have a finite threshold pump power and must not be confused with a hypothetical zero-threshold laser. Moreover, the results reveal an excitation power dependent-factor which needs to be taken into account to correctly describe the experimental data. The properties and the terminology of thresholdless lasing have accompanied the development of laser physics in the last decades. More recently, the realization of nanoscale devices

Section: Doi: 101002/lpor202000065mentioning

confidence: 99%

Thresholdless Transition to Coherent Emission at Telecom Wavelengths from Coaxial Nanolasers with Excitation Power Dependent β‐Factors

Kreinberg

Laiho

Lohof

et al. 2020

“…Quieting the spontaneous emission noise requires a more intense photon field in the cavity for the TMD laser than the fewemitter laser, which is why the intracavity photon number at the laser threshold is expected to be two to three orders of magnitude larger than the quantum limit of ≈1. [183] As a result, the transition to coherent emission in the autocorrelation function has been predicted to take place at a significantly higher pump rate, than at which the non-linearity in the input-output curve occurs. While Figure 11.…”

Section: Identifying Lasing Operationmentioning

confidence: 99%

Atomically Thin van der Waals Semiconductors—A Theoretical Perspective

Gies

Steinhoff

2021

2D semiconductors and their heterostructures have developed into a flourishing research field. A more or less simultaneous start of experimental and theoretical developments has led to continuous advancements in both branches of physics that continue to benefit from one another in an exemplary manner. This article gives an overview of the theoretical advancements that have resulted from a decade of research on 2D van der Waals materials and reviews current theoretical methods, focussing on exciton-plasma balance, excited-state optics, and laser physics.

“…Therefore, we shall now turn our attention to the main subject of this study, which is what exactly is the influence of spontaneous emission factor β , Q ‐factor, and the Purcell factor F P on the laser characteristics, most notably, the lasing threshold? The literature is full of mentions that somehow increasing either one of β , [ 40,41 ] Q , [ 42,43 ] and F P , [ 44–48 ] or preferentially, all of them is bound to boost the laser performance. This claim has become unquestionable for many researchers (with some notable exceptions, [ 14,27,49 ] ) even though, to the best of our knowledge, no rigorous proof of it had been given.…”

Section: Introductionmentioning

confidence: 99%

How Do the Purcell Factor, the Q‐Factor, and the Beta Factor Affect the Laser Threshold?

Khurgin

Noginov

2021

As lasers get more and more miniaturized and their dimensions become comparable to the wavelength, two interconnected phenomena take place: the fraction of spontaneous radiation going into a specific laser mode (β‐factor) increases and can ultimately reach unity, while the radiative lifetime gets shortened by the Purcell factor Fp. Often it is assumed that an increase of these two factors, along with the quality factor (Q‐factor), almost invariably causes reduction of the lasing threshold. This assumption is tested on various photonic and plasmonic lasers, demonstrating that, while there is obvious correlation between the aforementioned factors and the laser threshold, the dependence is far from being straightforward and omnipresent. Depending on specific laser material and geometry, the threshold can decrease, increase, or stay unchanged when β‐factor, Q‐factor, and Fp increase. For the most part, the reduction of threshold is achieved simply by reducing the laser volume and this volume reduction can concurrently cause the increase in β‐factor and/or Purcell factor, but it would be imprudent to say that the increase in either of these factors is the cause of the threshold reduction.