Slow Light Frequency Reference Cavities -- Proof of Concept for Reducing the Frequency Sensitivity Due to Length Fluctuations

TL;DR

This paper proposes a novel laser-frequency stabilization method using a slow-light effect in an optical cavity to significantly reduce frequency sensitivity to length fluctuations, demonstrated with a rare-earth doped crystalline spacer.

Contribution

It introduces a new stabilization technique leveraging slow-light effects to suppress cavity length noise, with experimental validation showing four orders of magnitude improvement.

Findings

Achieved four orders of magnitude reduction in frequency sensitivity.

Demonstrated control of dispersive properties via spectral tailoring.

Validated the slow-light stabilization concept experimentally.

Abstract

Length changes due to thermo-mechanical noise originating from, for example, Brownian motion are a key limiting factor of present day state-of-the-art laser frequency stabilization using Fabry-P\'erot cavities. We present a laser-frequency stabilization concept using an optical cavity with a strong slow-light effect to reduce the impact of cavity length changes on the frequency stability. The resulting noise-reduction factor is proportional to the ratio between the light phase and group velocities in the highly dispersive cavity spacer. We experimentally demonstrate a proof-of-principle implementation of this laser-frequency stabilization technique using a rare-earth doped crystalline cavity spacer in conjunction with semi-permanent spectral tailoring to achieve precise control of the dispersive properties of the cavity. Compared to the same setup in the absence of the slow-light effect a reduction in frequency sensitivity of four orders of magnitude was achieved.