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

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 worldwide research activity on low-noise coatings, with a focus on the results obtained at the Laboratoire des Matériaux Avancés. We report new updated values for the Ta2O5, Ta2O5-TiO2, and SiO2 coatings of the Advanced LIGO, Advanced Virgo, and KAGRA detectors, and new results from sputtered Nb2O5, TiO2-Nb2O5, Ta2O5-ZrO2, MgF2, AlF3, 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 in structural analyses and models.

Mirrors used in the LIGO interferometers for first detection of gravitational waves.

For the first time, direct detection of gravitational waves occurred in the Laser Interferometer Gravitational-wave Observatory (LIGO) interferometers. These advanced detectors require large fused silica mirrors with optical and mechanical properties and have never been reached until now. This paper details the main achievements of these ion beam sputtering coatings.