Towards Ultrastable Amorphous Coatings for LIGO

2015年，路易斯安那州利文斯顿和华盛顿州汉福德的双激光干涉仪引力波天文台(LIGO)探测器首次探测到两个大质量黑洞碰撞产生的引力波，这不仅证实了爱因斯坦关于引力波存在的预测，也证实了多年来发展引力波探测器(GWD)的努力。引力波探测器是一种干涉仪，在这种干涉仪中，强烈的激光束在两组相互垂直的反射镜之间反弹。引力波导致两个干涉仪臂之间的激光路径长度不同，从而产生了不同的干涉图案，当分析时，该干涉图案确定了产生它们的事件。GWD的探测灵敏度由多种噪声源决定，其中干涉仪镜面镀膜的热噪声是主要噪声源。干涉仪反射镜的高反射率非晶氧化物涂层中的热噪声会导致路径长度差异，从而屏蔽引力波的信号。为了提高目前GWD的灵敏度，满足未来GWD的要求，必须共同努力了解和控制非晶态氧化物涂层中产生热噪声的机理。这项工作将成为这一努力的一部分。该奖项支持旨在展示非晶态氧化物涂层的研究，这些涂层具有显著降低的热噪声和卓越的光学性能，将使最先进的GWD的灵敏度提高约10倍。这项研究工作有两个具体目标：1)通过对用于生长单层薄膜的沉积条件进行系统的参数研究，通过离子束溅射实现降低热噪声的非晶态金属氧化物薄膜；以及2)设计使用这些材料的多层介质涂层，与最先进的材料相比，降低机械损耗。协同的表征工作将支持材料的增长。特别是，CSU的研究人员将与加州理工大学的研究人员合作，评估单层和多层介质涂层的机械损耗。这项研究将以不同的方式支持LIGO计划。通过对无定形氧化物的基础研究，它将使研究在影响热噪声方面发挥作用的物理机制成为可能。它还将提供机会寻求新的涂层设计，以提高先进的LIGO和下一代GWD的灵敏度。与LIGO科学协作(LSC)涂层集团的协同合作计划一致地推动基础材料科学和涂层工程的努力。

The first detection of gravitational waves from the collision of two massive black holes by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in Livingston, Louisiana, and Hanford, Washington in 2015 not only confirmed Einstein's predictions of the existence of gravitational waves but also ratified years of efforts in the development of gravitational wave detectors (GWD). Gravitational wave detectors are interferometers in which an intense laser beam bounces between two sets of mirrors in orthogonal arms. Gravitational waves cause differences in the path length of the laser beam between the two interferometer arms, giving rise to a distinct interference pattern that when analyzed identifies the event that created them. The detection sensitivity of GWD is determined by various noise sources, among which, thermal noise of the coatings in the mirrors of the interferometer is a main component. Thermal noise in the high reflectance amorphous oxide coatings in the interferometer's mirrors causes path length differences that can mask the signals from gravitational waves. To increase the sensitivity of present GWD and meet the demands of future GWD, a concerted effort to understand and control the mechanisms that give rise to thermal noise in amorphous oxide coatings is imperative. This work will form part of that effort. This award supports research aimed at demonstrating amorphous oxide coatings with significantly reduced thermal noise and superior optical properties that will enable an approximate 10x increase in sensitivity of state-of-the-art GWD. The research effort has two specific aims: 1) to realize amorphous metal oxide thin films by ion beam sputtering with reduced thermal noise through a systematic parametric study of the deposition conditions used to grow single films; and 2) to engineer multilayer dielectric coatings using these materials with reduced mechanical loss compared to state-of-the-art. A synergistic characterization effort will support the materials' growth. In particular the CSU researchers will collaborate with Caltech researchers to assess mechanical loss in single and multilayer dielectric coatings. This research will support the LIGO program in different ways. Through fundamental studies in amorphous oxides it will enable investigations of the physical mechanisms that come into play in affecting thermal noise. It will also offer the opportunity to seek for new coating designs that will increase sensitivity of advanced LIGO and of the next generation GWD. Synergistic collaborations with the LIGO Scientific Collaboration (LSC) Coatings Group are planned to congruently advance the fundamental material science and coatings engineering efforts.