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，并解决了NSF“宇宙之窗”大构想的优先领域。2015年探测到来自合并黑洞的引力波开启了引力波天文学领域。与先进的LIGO相比，引力波探测器的灵敏度提高了两倍，对黑洞合并的探测率将提高一个数量级，并能探测到双中子星等较暗的物体，极大地提高了它们在多信使天文学中的价值。所有未来探测器的升级和概念都依赖于新的镜面涂层材料的发展，以减少热噪声，这是斯坦福大学马丁·费杰（Martin Fejer）的团队和佛罗里达大学程海平（Hai-Ping Cheng）团队合作项目的核心研究重点。减少这种噪声源需要减少测试质量上反射镜涂层的机械损耗。该项目的目标是开发符合未来几代LIGO实施的机械和光学要求的镜面涂层。为了实现室温探测器的这一目标，需要解决非晶材料物理学中一个长期存在的问题：了解非晶金属氧化物的性质并找到减少低能量激发的方法。在更长的时间尺度上，提出的3G探测器的低温操作拓宽了低噪声反射材料的选择范围，包括非晶或晶体半导体。先进的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，未来的升级包括先进的LIGO Plus将寻求通过两倍或更多的因素来减少这种噪声源。斯坦福大学-佛罗里达大学的合作伙伴关系，以及LSC涂层研究中心（CCR）的合作者，已经确定了与室温和低温机械损耗相关的不同结构基元，从而合成了锗（GeO2）薄膜，从而产生了除二氧化硅以外损耗最低的非晶态氧化膜。展望未来，基于电子和x射线散射原子结构数据的结构指南将为开发具有低弹性损失的高折射率非晶涂层提供范例。涂层弹性损失的原子建模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，并最终帮助设计合成实验。斯坦福大学的另一项长期努力是测量亚ppm/cm水平下低光损耗材料的吸收，这可以追溯到LIGO初始测试质量中二氧化硅和蓝宝石之间的选择。这些小组将继续使用为这些研究开发的干涉测量工具来表征单晶硅样品的低温损失，以评估其在旅行者号技术演示器和未来低温探测器中实施的适用性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.