Characterization of ion-beam-sputtered AlF$_3$ thin films for gravitational-wave interferometers

TL;DR

This paper investigates ion-beam-sputtered AlF$_3$ thin films, highlighting their low refractive index and potential to reduce thermal noise in gravitational-wave detector mirrors.

Contribution

It provides detailed optical and mechanical characterization of AlF$_3$ coatings, proposing their use in advanced gravitational-wave interferometers.

Findings

AlF$_3$ films exhibit low refractive index and suitable optical properties.

Mechanical properties suggest low thermal noise contribution.

Potential application in next-generation gravitational-wave detectors.

Abstract

Thermal noise in amorphous coatings is a limitation for a wide range of precision experiments such as gravitational-wave detectors (GWDs). Mirrors for GWDs are composed of multiple thin layers of dielectric materials deposited on a substrate: the stack is made of layers with a high refractive index interleaved with layers of a low refractive index. The goal is to obtain high reflectivity and low thermal noise. In this paper we report on the optical and mechanical properties of ion-beam-sputtered aluminium fluoride (AlF$_3$) thin films which have one of the lowest refractive index among the known coating materials and we discuss their application in current and future GWDs.