Collaborative Research: Stanford-Florida Program in Support of LIGO on Coatings and Core Optics

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年对聚结黑洞引力波的探测，开启了引力波天文学领域。与Advanced LIGO相比，灵敏度提高两倍的引力波探测器将使黑洞聚合的探测率提高数量级，并能够探测到双星中子星等较暗的物体，从而大大提高它们在多信使天文学中的价值。未来探测器的所有升级和概念都依赖于开发新的镜面涂层材料来降低热噪声，这是斯坦福大学的Martin Fejer团队和佛罗里达大学的Hai-Ping Cheng团队合作的这个项目的核心研究重点。减少这种噪声源需要减少测试质量块上的镜面涂层的机械损耗。该项目的目标是开发符合机械和光学要求的镜面涂层，以便在未来几代LIGO中实施。要实现室温探测器的这一目标，需要解决非晶态材料物理学中的一个长期存在的问题：了解非晶态金属氧化物的性质并找到减少非晶态金属氧化物中低能激发的方法。在更长的时间尺度上，拟议的3G探测器的低温操作扩大了低噪声镜面材料的可能选择，包括非晶态或晶体半导体。Advanced LIGO探测器的中频灵敏度受到镜面涂层机械损耗引起的热噪声的限制，包括Advanced LIGO Plus在内的未来升级将寻求将这一噪声源降低两倍或更多。斯坦福大学和佛罗里达大学的合作伙伴与LSC涂料研究中心(CCR)的合作伙伴已经确定了与室温和低温机械损失相关的不同结构基元，这导致了Germania(GeO2)薄膜的合成，从而产生了除二氧化硅之外损耗最低的非晶态氧化物薄膜。展望未来，这一基于电子和X射线散射原子结构数据的结构指南将成为开发具有较低弹性损失的高折射率非晶涂层的范例。涂层弹性损失的原子模拟与涂层沉积过程的模拟相结合，将为候选材料的选择提供指导，帮助解释实验结构数据，并最终有助于合成实验的设计。斯坦福大学的另一项长期工作是测量低光学损耗材料在亚ppm/cm级别的吸收，这可以追溯到初始LIGO测试质量中二氧化硅和蓝宝石之间的向下选择。这些小组将继续使用为这些研究开发的干涉工具来表征单晶硅样品的低温损失，以评估它们是否适合在旅行者号技术演示器和未来的低温探测器中实施。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 detection of gravitational waves from coalescing black holes in 2015 launched the field of gravitational wave astronomy. Gravitational-wave detectors with a two-fold increase in sensitivity over Advanced LIGO would yield an order of magnitude increase in detection rate for black hole coalescences, and enable detection of fainter objects like binary neutron stars, greatly increasing their value for multi-messenger astronomy. All future detector upgrades and concepts rely on the development of new mirror coating materials to reduce thermal noise, which is the core research focus this collaborative project between Martin Fejer's group at Stanford University and Hai-Ping Cheng's group at the University of Florida. Reducing this noise source requires reducing the mechanical loss in the mirror coatings on the test masses. The goal of this project is to develop mirror coatings consistent with the mechanical and optical requirements for implementation in future generations of LIGO. Meeting this goal for room temperature detectors requires a solution of a longstanding problem in the physics of amorphous materials: understanding the nature of and finding means to reduce the low-energy excitations in amorphous metal oxides. On a longer time-scale, the proposed 3G detectors' cryogenic operation broadens the possible choice of low-noise mirror materials to include amorphous or crystalline semiconductors.The mid-band sensitivity of the Advanced LIGO detectors is limited by thermal noise resulting from mechanical loss in the mirror coatings, and future upgrades including Advanced LIGO Plus will seek to reduce this source of noise by a factor of two or more. The Stanford-Florida partnership, alongside collaborators in the LSC Center for Coatings Research (CCR), has identified different structural motifs associated with room-temperature vs cryogenic mechanical losses, which led to synthesis of germania (GeO2) films, giving rise to the lowest-loss amorphous oxide film other than silica. Going forward, this structural guide, based on electron and x-ray scattering atomic structure data, will serve as a paradigm informing the development of high-refractive-index amorphous coatings with lower elastic loss. Atomic modeling of coating elastic loss combined with simulations of the coating deposition process will provide guidance for the selection of candidate materials, assist in interpretation of experimental structure data, and will ultimately assist in the design of synthesis experiments. Another long-standing effort at Stanford has been measurements of the absorption of low-optical-loss materials at the sub-ppm/cm level, dating back to the down select between silica and sapphire for initial LIGO test masses. The groups will continue to use the interferometric tool developed for those studies to characterize cryogenic losses in single-crystal silicon samples to evaluate their suitability for implementation in the Voyager technology demonstrator and future cryogenic 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.