Coatings for Next Generation Gravitational Wave Interferometers

该奖项支持相对论和相对论天体物理学的研究，并阐述了美国国家科学基金会“宇宙之窗”宏伟构想的优先领域。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。这些项目将为不同的研究生群体提供深入了解影响非晶态材料内耗的物理机制的机会，同时获得光学科学方面的宝贵专业知识。这一跨学科研究项目将培养具有宝贵技能的学生，为学术、国家实验室和工业环境中的先进科学技术做出贡献。PI的团队最近取得了突破性成果。他们已经确定了二氧化钛和二氧化锗的混合物，它们的内部耗散水平为0.0001。与最先进的材料相比，这种低水平的机械损失可以提供几乎两倍于布朗噪声水平的改善。这些结果将使生产满足高级LIGO探测器升级计划的热噪声要求的反射镜成为可能。该团队将研究二氧化钛掺杂GeO2导致如此低的机械损失的基本机制，并实施进一步降低机械损失的策略。它还将研究薄膜的光学特性，以满足先进LIGO探测器涂层的严格吸收损耗要求。基于这些优化材料的多层介质涂层将通过离子束溅射沉积，并以其布朗噪声进行表征，布朗噪声的降低极大地影响了引力波探测器的灵敏度。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award supports research in relativity and relativistic astrophysics and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. 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. The projects will offer a diverse group of graduate students opportunities to gain in-depth understanding of the physical mechanisms that affect internal friction in amorphous materials and at the same time gain valuable expertise in optical sciences. This interdisciplinary research project will train students with valuable skills to contribute to advance science and technology in academic, national laboratory and industrial settings.The PI's team has recently achieved a breakthrough result. They have identified mixtures of titanium dioxide and germanium dioxide that show internal dissipations at a level of 0.0001. Such a low level of mechanical loss can provide for an almost a factor of two improvement on the level of Brownian noise with respect to the state-of-the-art materials. These results will make it possible to produce the mirrors that will meet the thermal noise requirements for the planned upgrades of the Advanced LIGO detectors. The team will investigate the fundamental mechanisms in TiO2 doped GeO2 that lead to such low mechanical loss and implement strategies to further reduce it. It will also investigate the optical properties of thin films to meet the stringent absorption loss requirements of the coatings for Advanced LIGO detectors. Multilayer dielectric coatings based on these optimized materials will be deposited by ion beam sputtering and characterized for their Brownian noise, which reduction greatly impacts the sensitivity of gravitational wave detectors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.