# Lasing on a narrow transition in a cold thermal strontium ensemble

## TL;DR

This paper demonstrates lasing on a narrow, forbidden transition in a thermal strontium ensemble at mK temperatures, revealing collective effects and coherence in a high-temperature atomic system.

## Contribution

It introduces a simple thermal ensemble system that achieves lasing on a forbidden transition, combining experimental and theoretical analysis of threshold, dynamics, and decoherence effects.

## Key findings

- Lasing observed on a forbidden $^1$S$_0
ightarrow ^3$P$_1$ transition.
- Strong collective coupling and high atomic coherence achieved in a thermal ensemble.
- Theoretical modeling using a Tavis-Cummings framework matches experimental results.

## Abstract

Highly stable laser sources based on narrow atomic transitions provide a promising platform for direct generation of stable and accurate optical frequencies. Here we investigate a simple system operating in the high-temperature regime of cold atoms. The interaction between a thermal ensemble of $^{88}$Sr at mK temperatures and a medium-finesse cavity produces strong collective coupling and facilitates high atomic coherence which causes lasing on the dipole forbidden $^1$S$_0 \leftrightarrow ^3$P$_1$ transition. We experimentally and theoretically characterize the lasing threshold and evolution of such a system, and investigate decoherence effects in an unconfined ensemble. We model the system using a Tavis-Cummings model, and characterize velocity-dependent dynamics of the atoms as well as the dependency on the cavity-detuning.