LIGO Document G0900600-v1

Exploring Coating Thermal Noise via Loss in Fused Silica Coatings

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Thermal noise in the test mass mirror coatings is a leading noise source for advanced interferometer gravity wave detectors. Reducing this noise should result in a significant gain in both the sensitivity and the estimated count rate. The coating thermal noise arises from the mechanical loss (dissipation) in the coating materials, predominantly the high-index material. The mirror coating currently planned for Advanced LIGO is a multilayer dielectric consisting of silica (low-index) and titania-doped tantala (high index). We will present our results on the use of annealing to substantially lower the excess mechanical loss in the silica coating layers and compare this coating loss with the predicted loss for bulk fused silica. We will also discuss the applicability of this process to multilayer coatings and the results of annealing a multilayer niobia/silica coating. Finally we will explore how these results might inform near-term coating research directions and the design of future coatings.
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