Thermal noise measurements on micro-cantilevers coated with dielectric materials

In recent years an increasing number of devices and experiments are shown to be limited by mechanical thermal noise. In particular sub-Hertz laser frequency stabilization and gravitational wave detectors, that are able to measure fluctuations of 10^-18 m/√(Hz) or less, are being limited by thermal noise in the dielectric coatings deposited on mirrors. We present a novel technique of structural relaxation analysis based on the direct thermal noise measurements on micro-cantilevers and we compare it with the results obtained from the mechanical loss measurements. The dielectric coatings are deposited by ion beam sputtering. The results presented here give a loss angle of annealed tantala and as-deposited silica coatings of (3.9 ± 0.4)·10^-4 and (5.8 ± 1.0)·10^-4 respectively, from 10 Hz to 20 kHz.