Reducing the effect of thermal noise in optical cavities

TL;DR

This paper presents two innovative methods to reduce thermal noise in optical cavities, aiming to enhance the stability of optical frequency standards by operating near instability or increasing cavity length.

Contribution

It introduces and analyzes two novel schemes—near-instability operation and longer cavities—to significantly lower thermal noise effects in optical frequency references.

Findings

A 10 cm cavity can reach low 10^(-16) instability levels.

A 39.5 cm cavity can achieve below 10^(-16) fractional frequency instability.

Reduced sensitivity to vibrations (<10^(-10)/g) in all directions.

Abstract

Thermal noise in optical cavities imposes a severe limitation in the stability of the most advanced frequency standards at a level of a few 10^(-16) (s/t)^(1/2) for long averaging times t. In this paper we describe two schemes for reducing the effect of thermal noise in a reference cavity. In the first approach, we investigate the potential and limitations of operating the cavity close to instability, where the beam diameter on the mirrors becomes large. Our analysis shows that even a 10 cm short cavity can achieve a thermal noise limited fractional frequency instability in the low 10^(-16) regime. In the second approach, we increase the length of the optical cavity. We show that a 39.5 cm long cavity has the potential for a fractional frequency instability even below 10^(-16), while it seems feasible to achieve a reduced sensitivity of <10^(-10)/g for vibration-induced fractional length changes in all three directions.