Progress in the measurement and reduction of thermal noise in optical coatings for gravitational-wave detectors

TL;DR

This review summarizes recent advances in measuring and reducing thermal noise in optical coatings crucial for gravitational-wave detectors, highlighting new materials, techniques, and structural models to enhance sensitivity.

Contribution

It provides updated experimental results and discusses innovative coating materials and structures to lower thermal noise in gravitational-wave detector optics.

Findings

New low-noise coating measurements for LIGO, Virgo, and KAGRA.

Introduction of novel materials like amorphous silicon and crystalline coatings.

Progress in structural analysis and modeling of optical coatings.

Abstract

Coating thermal noise is a fundamental limit for precision experiments based on optical and quantum transducers. In this review, after a brief overview of the techniques for coating thermal noise measurements, we present the latest world-wide research activity on low-noise coatings, with a focus on the results obtained at the Laboratoire des Mat\'{e}riaux Avanc\'{e}s. We report new updated values for the Ta$_2$O$_5$, Ta$_2$O$_5$-TiO$_2$ and SiO$_2$ coatings of the Advanced LIGO, Advanced Virgo and KAGRA detectors, and new results from sputtered Nb$_2$O$_5$, TiO$_2$-Nb$_2$O$_5$, Ta$_2$O$_5$-ZrO$_2$, MgF$_2$, AlF$_3$ and silicon nitride coatings. Amorphous silicon, crystalline coatings, high-temperature deposition, multi-material coatings and composite layers are also briefly discussed, together with the latest developments of structural analyses and models.