Sub-Natural Linewidth Superradiant Lasing with Cold $^{88}$Sr Atoms

TL;DR

This paper demonstrates superradiant lasing with ultracold strontium atoms, achieving a linewidth nearly ten times narrower than the natural linewidth, by extending emission duration and tuning parameters in a bad-cavity regime.

Contribution

It provides experimental evidence of sub-natural linewidth superradiant lasing with cold $^{88}$Sr atoms and explores the conditions for stable, narrow-linewidth emission.

Findings

Lasing linewidth of 820 Hz achieved for 1.1 ms of emission

Extended superradiant emission to several milliseconds

Tuned parameters enable emulation of continuous superradiant laser operation

Abstract

Superradiant lasers operate in the bad-cavity regime, where the phase coherence is stored in the spin state of an atomic medium rather than in the intracavity electric field. Such lasers use collective effects to sustain lasing and could potentially reach considerably lower linewidths than a conventional laser. Here, we investigate the properties of superradiant lasing in an ensemble of ultracold $^{88}$Sr atoms inside an optical cavity. We extend the superradiant emission on the 7.5 kHz wide $^3P_1$ $\rightarrow$ $^1S_0$ intercombination line to several milliseconds, and observe steady parameters suitable for emulating the performance of a continuous superradiant laser by fine tuning the repumping rates. We reach a lasing linewidth of 820 Hz for 1.1 ms of lasing, nearly an order of magnitude lower than the natural linewidth