Ultra-Narrow Linewidth Brillouin Lasers with Nanokelvin Thermometry

TL;DR

This paper demonstrates an ultra-narrow linewidth Brillouin laser with 20 Hz linewidth, achieved through a large mode-volume resonator and SBS nonlinearity, combined with nanokelvin thermometry for precise temperature stabilization.

Contribution

It introduces a compact, highly stable Brillouin laser system with unprecedented linewidth and temperature sensitivity, suitable for field applications.

Findings

Achieved 20 Hz laser linewidth using a large mode-volume resonator and SBS.

Demonstrated nanokelvin-level temperature sensing for resonator stabilization.

Enabled potential for portable, ultra-stable laser sources.

Abstract

Ultrastable lasers serve as the backbone for some of the most advanced scientific experiments today and enable the ability to perform atomic spectroscopy and laser interferometry at the highest levels of precision possible. With the recent and increasing interest in applying these systems outside of the laboratory, it remains an open question as how to realize a laser source that can reach the extraordinary levels of narrow linewidth required and yet still remain sufficiently compact and portable for field use. Critical to the development of this ideal laser source is the necessity for the laser to be insensitive to both short- and long-term fluctuations in temperature, which ultimately broaden the laser linewidth and cause drift in the laser's center frequency. We show here that the use of a large mode-volume optical resonator, which acts to suppress the resonator's fast thermal fluctuations, together with the stimulated Brillouin scattering (SBS) optical nonlinearity presents a powerful combination that enables the ability to lase with an ultra-narrow linewidth of 20 Hz. To address the laser's long-term temperature drift, we apply the narrow Brillouin line as a metrological tool that precisely senses a minute change in the resonator's temperature at the level of 85 nK. The precision afforded by this temperature measurement enables new possibilities for the stabilization of resonators against environmental perturbation.