Mechanical Loss in Tantala/Silica Dielectric Mirror Coatings

TL;DR

This paper investigates the sources of mechanical loss in Ta2O5/SiO2 dielectric mirror coatings used in gravitational wave detectors, finding that Ta2O5 contributes significantly to the overall loss, which may affect detector sensitivity.

Contribution

It identifies the primary source of mechanical loss in the coatings as the bulk Ta2O5 material, providing insights for improving mirror coating performance.

Findings

Loss is mainly due to bulk coating materials.

Ta2O5 has substantially higher loss than SiO2.

Loss at interfaces is less significant.

Abstract

Current interferometric gravitational wave detectors use test masses with mirror coatings formed from multiple layers of dielectric materials, most commonly alternating layers of SiO2 (silica) and Ta2O5 (tantala). However, mechanical loss in the Ta2O5/SiO2 coatings may limit the design sensitivity for advanced detectors. We have investigated sources of mechanical loss in the Ta2O5/SiO2 coatings, including loss associated with the coating-substrate interface, with the coating-layer interfaces, and with the bulk material. Our results indicate that the loss is associated with the bulk coating materials and that the loss of Ta2O5 is substantially larger than that of SiO2.