  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 gravitational-wave
detectors.
