Relaxation oscillations, stability, and cavity feedback in a superradiant Raman laser

TL;DR

This paper experimentally investigates the relaxation oscillations and stability of a superradiant Raman laser operating in the bad-cavity regime, providing insights into cavity feedback and atomic population dynamics to guide future ultranarrow linewidth laser development.

Contribution

It offers the first detailed experimental analysis of relaxation oscillations and stability in a superradiant Raman laser deep in the bad-cavity regime, including the effects of repumping states and cavity feedback.

Findings

Cavity feedback can stabilize or enhance relaxation oscillations.

Intermediate repumping states influence the oscillator's stability.

The results guide future superradiant laser development.

Abstract

We experimentally study the relaxation oscillations and amplitude stability properties of an optical laser operating deep into the bad-cavity regime using a laser-cooled $^{87}$Rb Raman laser. By combining measurements of the laser light field with nondemolition measurements of the atomic populations, we infer the response of the gain medium represented by a collective atomic Bloch vector. The results are qualitatively explained with a simple model. Measurements and theory are extended to include the effect of intermediate repumping states on the closed-loop stability of the oscillator and the role of cavity feedback on stabilizing or enhancing relaxation oscillations. This experimental study of the stability of an optical laser operating deep into the bad-cavity regime will guide future development of superradiant lasers with ultranarrow linewidths.