Stabilizing an optical cavity containing a bulk diamond crystal at millikelvin temperatures in a cryogen-free dilution refrigerator

TL;DR

This paper demonstrates the stabilization of a high-finesse optical cavity with a diamond crystal at millikelvin temperatures inside a cryogen-free dilution refrigerator, achieving cavity locking to a laser and analyzing stability limits.

Contribution

First demonstration of laser-locking an optical cavity with a bulk diamond crystal at millikelvin temperatures in a cryogen-free setup.

Findings

Cavity stabilization up to a finesse of 1.2×10^4 without diamond.

Finesse limited to 5.8×10^3 with a diamond crystal due to absorption.

Potential for further stabilization based on cavity length fluctuation measurements.

Abstract

We successfully stabilized a Fabry-P\'erot optical cavity incorporating a bulk diamond crystal at millikelvin temperatures in a cryogen-free dilution refrigerator with the pulse-tube cryocooler running. In stark contrast to previous demonstrations where lasers were locked to the cavities, our setup locks the cavity to a laser. Our measurements of cavity length fluctuation suggest that the setup could stabilize a cavity up to a finesse of $1.2\times 10^4$ without the diamond and $5.8 \times10^3$ with the diamond crystal. The finesse with a diamond crystal of approximately 90 is primarily limited by the absorption loss inside the diamond.