Investigation of mechanical loss factors of some candidate materials for the test masses of gravitational wave detectors

This Letter describes the results of investigations into the mechanical losses of a selection of crystalline materials with the potential for use as the test masses in advanced gravitational wave detectors. We have measured loss factors of 3.7×10−9 for HEM sapphire, to our knowledge the lowest measured loss factors of sapphire grown by a method suitable to produce test masses of the size and quality needed for use in advanced interferometric detectors. We also present the first measurements of the mechanical loss factors of YAG and Spinel at frequencies of interest for gravitational wave detection.