Experimental measurements of coating mechanical loss factors

All current gravitational wave detectors use test masses coated with alternating layers of two different dielectric materials to form highly reflective mirrors. The thermal noise from mechanical dissipation associated with such coatings may be significant for future detectors such as advanced LIGO. We have measured the mechanical dissipation of a number of types of coatings formed from SiO2 (silica) and Ta2 O5 (tantala). The frequency dependence of the dissipation has been determined, taking into account the contribution of thermoelastic loss.