Quantifying surface loss of mechanically polished silica cantilevers

Materials with a high quality factor are used, for the test mass and suspension elements, in interferometric gravitational wave detectors to reduce off resonance thermal displacement noise. An experiment to increase the quality factor of mechanically polished silica cantilevers by etching their surface is described. An estimation of the thickness of the damaged layer due to polishing is found and we estimate how lossy this layer is. This was achieved by repeatedly etching a cantilever in solution and measuring its mechanical loss in each instance. In this way mechanical loss as a function of etch depth can be determined. This layer was estimated to be 0.5 micron deep with a loss of Os=2.98 x 10-8 which is three times higher than the surface loss predicted by the current empirical model. This has important implications as the test mass mirrors used in interferometric gravitational wave detectors are comprised of mechanically polished silica. Measurements of single layer dielectric coatings of silica, tantala and doped tantala for use in interferometric gravitational wave detectors is also described. It was found that the silica coating had the lowest level of measured mechanical loss overall at 3.77 x 10-5. It was also found doped tantala had a lower level of measured loss than tantala, 2.965 x 10-4 in the doped case compared to 4.24 x 10-4