Intrinsic losses in various kinds of fused silica

We systematically measured the intrinsic mechanical quality factors of 13 kinds of bulk fused silica from four companies using a nodal support system. Some of them have actually been adopted as mirror substrates in interferometric gravitational wave detectors. The measured quality factors widely ranged from 7 x 10(5) to 4 X 10(7). They turned out to be independent of one specific property, such as the amount of OH content, suggesting that the loss mechanism has several origins. We found that many of the samples showed smaller losses at lower frequency. From the viewpoint of the mirror thermal noise, it would be fortunate if the loss continued to decrease with decreasing frequency, We also found that an annealing process increases their quality factors.