Optical and mechanical properties of ion-beam-sputtered MgF$_2$ thin films for gravitational-wave interferometers

Abstract

Brownian thermal noise associated with highly reflective coatings is a fundamental limit for several precision experiments, including gravitational-wave detectors. Research is currently ongoing to find coatings with low thermal noise that also fulfill strict optical requirements such as low absorption and scatter. We report on the optical and mechanical properties of ion-beam-sputtered magnesium fluoride thin films, and we discuss the application of such coatings in current and future gravitationalwave detectors.

Measurement and simulation of mechanical and optical properties of sputtered amorphous SiC coatings

“…By definition, the measured dilution factor D of Eq. ( 3) is very sensitive to variations of frequencies and masses [32], so we took special care to prevent the curvature of the disks induced by the presence of the coating layers by performing a double-deposition on both the substrate faces, as explained in section 2, and monitored the temperature of the disks during the ring-down measurements. Indeed, the frequency ratio in Eq.…”

“…where η ∼ 9.5 × 10 −3 K −1 and q ∼ 1.9 × 10 −5 are coefficients we previously measured on nominally identical fused-silica disks. This correction is critical, whenever mode frequencies are measured in a system where temperature may drift [32]. Further details about our GeNS systems are available elsewhere [29,33].…”