# Thresholdless transition to coherent emission at telecom wavelengths from coaxial nanolasers

## TL;DR

This paper investigates coaxial nanolasers at telecom wavelengths, demonstrating that they exhibit thresholdless lasing with a finite pump power, clarifying misconceptions about zero-threshold lasers.

## Contribution

It provides both experimental and theoretical insights into the photon statistics of high-beta coaxial nanolasers, emphasizing the finite threshold pump power despite thresholdless emission.

## Key findings

- Photon statistics reveal a finite threshold pump power.
- High-beta nanolasers can exhibit thresholdless emission with a finite pump.
- Clarifies the distinction between thresholdless and zero-threshold lasers.

## Abstract

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, we investigate high-$\beta$ metal-clad coaxial nanolasers, which facilitate thresholdless lasing. We experimentally and theoretically investigate both the conventional lasing characteristics, as well as the photon statistics of the emitted light. While the former lacks adequate information to determine the threshold to coherent radiation, the latter reveals a finite threshold pump power. Our work clearly highlights an important and often misunderstood aspect of high-$\beta$ lasers, namely that a thresholdless laser does have a finite threshold pump power and must not be confused with a hypothetical zero threshold laser.