Mechanical loss in state-of-the-art amorphous optical coatings

TL;DR

This study investigates mechanical dissipation in advanced amorphous optical coatings, revealing higher-than-expected losses in multi-layer stacks that impact gravitational-wave detector sensitivity.

Contribution

It provides new experimental data on mechanical loss in ion-beam-sputtered coatings and links dissipation to stress conditions, informing noise reduction strategies.

Findings

Measured dissipation exceeds expectations in multi-layer stacks

Dissipation correlates with stress in the coatings

Implications for gravitational-wave detector noise budgets

Abstract

We present the results of mechanical characterizations of many different high-quality optical coatings made of ion-beam-sputtered titania-doped tantala and silica, developed originally for interferometric gravitational-wave detectors. Our data show that in multi-layer stacks (like high-reflection Bragg mirrors, for example) the measured coating dissipation is systematically higher than the expectation and is correlated with the stress condition in the sample. This has a particular relevance for the noise budget of current advanced gravitational-wave interferometers, and, more generally, for any experiment involving thermal-noise limited optical cavities.