Characterization of Ion-Beam-Sputtered <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mrow><mml:mi>Al</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:math> Thin Films for Gravitational-Wave Interferometers

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 (${\mathrm{Al}\mathrm{F}}_{3}$) thin films that have one of the lowest refractive indexes among the known coating materials and we discuss their application in current and future GWDs.