Ultrastable vacuum-gap Fabry-P\'erot cavities operated in air

TL;DR

This paper presents a simple method for creating ultrastable optical cavities that operate in air without vacuum enclosures, maintaining long-term stability and achieving record low phase noise for portable laser applications.

Contribution

The authors introduce a novel optical contact bonding technique that enables vacuum-gap cavities to function in air, simplifying design and enhancing portability while maintaining high stability.

Findings

Long-term cavity stability over 1 year without degradation

Achieved phase noise of -105 dBc/Hz at 10 kHz for 1550 nm laser

Demonstrated microfabricated cavity with high stability and low phase noise

Abstract

We demonstrate a vacuum-gap ultrastable optical reference cavity that does not require a vacuum enclosure. Our simple method of optical contact bonding in a vacuum environment allows for cavity operation in air while maintaining vacuum between the cavity mirrors. Vacuum is maintained long term, with no observed degradation in cavity stability for over 1 year after bonding. For a 1550 nm laser stabilized to a 9.7 mL in-vacuum bonded cavity, the measured Allan deviation is $2.4\times 10^{-14}$ at 1 s and its phase noise is thermal-noise-limited from 0.1 Hz to 10 kHz, reaching about -105 dBc/Hz at 10 kHz offset frequency. This represents the highest stability of any oscillator operated without a vacuum enclosure. Furthermore, we demonstrate a 0.5 mL in-vacuum bonded cavity created using microfabricated mirrors and cavity dicing, with phase noise reaching -95 dBc/Hz at 10 kHz offset frequency. By relieving the need for high-vacuum enclosures, we greatly enhance the portability and utility of low noise, compact cavity-stabilized lasers, with applications ranging from environmental sensing to mobile optical clocks to ultralow noise microwave generation.