Mechanical quality factors of fused silica resonators

We have measured the room temperature resonant quality factors Q for a large set of resonant modes for each of several fused silica blocks and one fused silica cylinder. The modal frequencies ranged from 7.8 to 50 kHz. Our best results were obtained when the samples were suspended in a single loop of fine wire. For every sample tested we have measured at least one mode with Q≥10⁷. Our highest Q for any sample measured was (1.86±0.06)×10⁷ for a block resonating at 26.4 kHz. Our tests included several different types of high purity fused silica, but could not detect any significant differences in mechanical loss. We believe our Q measurements are limited by losses due to our suspensions, as Q depends strongly on the shape of each resonant mode and the proximity of each mode's nodal regions to the wire suspension points.