An RUI Research Proposal on Minimizing Thermal Noise in Advanced LIGO Test Mass Optics and Exploring Bilinear Noise in Initial LIGO Data

这项研究项目将主要集中在了解和减少熔融二氧化硅的机械损失。我们将探索通过在惰性气体和真空中仔细的退火来降低大型抛光熔融二氧化硅光学元件机械损耗的方法。这项技术已经在小样本上被证明是成功的，预计也会对大样本有所裨益。此外，还将与其他LIGO热噪声研究人员合作，建立熔融二氧化硅机械损耗的理论模型。这样的模型将极大地帮助我们理解基本的损失机制，并可能为如何进一步减少这种损失提供指导。最后，双相干数据监测器的发展将继续下去，这是一种从高斯噪声的大背景中分离双线性噪声、突发事件和线性调频事件的稳健方法。这项关于熔融二氧化硅的研究对高级LIGO具有很大的前景。PI先前已经证明，退火可以将熔融二氧化硅的机械损耗降低到与蓝宝石相同的水平，蓝宝石是建议用于高级LIGO光学器件的另一种材料，比高级LIGO的要求更好。使用二氧化硅的好处包括优异的光学质量和更好的光学材料体验。正如PI之前所显示的，熔融二氧化硅的损失在最小化时完全在表面，至少对于到目前为止测量的几何形状来说是这样。换句话说，损耗随着光学元件尺寸的增大而减小。因此，预计大型光学器件在适当退火时，即使经过抛光，其机械损耗也应低于高级LIGO要求。降低测试质量中的热噪声将增加LIGO在其最敏感频段的天文覆盖范围，并增强探测和研究引力波事件的可能性。

This research project will focus primarily on understanding and reducing the mechanical loss in fused silica. Methods of reducing the mechanical loss in large, polished, fused silica optics through careful annealing in inert gas and vacuum will be explored. This technique has already proven successful on small, flame-drawn samples, and is expected to benefit larger samples as well. In addition, a theoretical model for the mechanical loss in fused silica will be developed in collaboration with other LIGO thermal noise researchers . Such a model would greatly aid our understanding of the fundamental loss mechanisms and may provide guidance as to how this loss might be further reduced. Finally, development will continue on a bicoherence data monitor, which is a robust method for separating bilinear noise, burst events, and chirp events from a large background of Gaussian noise.This research on fused silica holds a great deal of promise for Advanced LIGO. The PI has previously demonstrated that annealing can reduce the mechanical loss in fused silica to a level equal to that of sapphire, the other material proposed for Advanced LIGO optics and better than the requirements for Advanced LIGO. The benefits of using silica include excellent optical qualities and greater experience as an optical material. As the PI has previously shown, the loss in fused silica, when minimized, is entirely in the surface, at least for the geometries measured thus far. In other words, the loss decreases as the size of the optic increases. Therefore it is expected that large optics, when properly annealed, should, despite being polished, have a mechanical loss below the Advanced LIGO requirements. Lowering the thermal noise in the test masses will increase LIGO's astronomical reach in its most sensitive frequency band and enhance the probability for detection and study of gravitational wave events.