Direct Measurement of Coating Thermal Noise in Optical Resonators

TL;DR

This paper reports direct measurements of coating thermal noise in optical resonators, revealing unexpected spectral behavior that impacts high-precision optical measurements like gravitational wave detection.

Contribution

It provides the first direct measurement of coating thermal noise in the audio band and uncovers deviations from expected power-law behavior.

Findings

Measured coating thermal noise spectrum in the audio band

Observed non-standard power spectral behavior

Implications for optical resonator stability and sensitivity

Abstract

The best measurements of space and time currently possible (e.g. gravitational wave detectors and optical reference cavities) rely on optical resonators, and are ultimately limited by thermally induced fluctuations in the reflective coatings which form the resonator. We present measurements of coating thermal noise in the audio band and show that for a standard ion beam sputtered coating, the power spectrum of the noise does not have the expected power-law behavior.