Mirror Coating Thermal Noise Mitigation Using Multi-Spatial Mode Cavity Readout

TL;DR

This paper introduces a method to reduce coating thermal noise in optical cavities by employing multiple spatial modes for laser readout, achieving significant noise reduction comparable to cooling mirrors to cryogenic temperatures.

Contribution

It proposes a novel multi-spatial mode readout technique that enhances thermal noise mitigation in optical cavities, with experimental validation demonstrating substantial noise reduction.

Findings

Thermal noise improvement factor of 1.57 with optimal mode weighting.

Achieved a 1.61 times improvement over fundamental mode in a 0.1 m cavity.

Equivalent to cooling mirrors to 120 K from room temperature.

Abstract

We present an approach to mitigate coating thermal noise in optical cavities by using multiple TEM spatial modes to readout and stabilize laser frequency. With optimal weightings we synthesize a wider sampling of the mirror surface, improving averaging of Brownian thermal fluctuation. We show thermal noise improvement factors of 1.57, comparable to a MESA beam of a nominal 12 m prototype cavity, and a factor 1.61 improvement over the $\textrm{TEM}_{00}$ using three modes in a 0.1 m cavity for a practical laboratory experiment: equivalent to cooling mirrors to 120 K from room temperature.