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”大理念的优先领域。2015年对黑洞合并引力波的探测开启了引力波天文学领域。引力波探测器的灵敏度比先进的LIGO提高了两倍，这将使黑洞合并的探测率提高一个数量级，并能够探测到像双中子星这样的微弱物体，大大增加了它们对多信使天文学的价值。所有未来的探测器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费耶尔小组和佛罗里达的Hai-Ping Cheng小组之间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的反射镜涂层中的机械损失。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。实现室温探测器的这一目标需要解决非晶材料物理学中的一个长期问题：理解非晶金属氧化物的性质并找到减少非晶金属氧化物中低能激发的方法。在更长的时间尺度上，拟议中的3G探测器的低温操作拓宽了低噪声镜材料的可能选择，包括非晶或晶体半导体。Advanced LIGO探测器的中波段灵敏度受到镜涂层中机械损耗引起的热噪声的限制，未来的升级包括Advanced LIGO Plus将寻求将这种噪声源降低两倍或更多。斯坦福-佛罗里达州的合作伙伴关系，以及LSC涂料研究中心（CCR）的合作者，已经确定了与室温与低温机械损耗相关的不同结构基序，这导致了氧化锗（GeO 2）薄膜的合成，从而产生了除二氧化硅之外损耗最低的非晶氧化物薄膜。展望未来，这种基于电子和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耗的高折射率非晶涂层的范例。结合涂层沉积过程的模拟，涂层弹性损失的原子建模将为候选材料的选择提供指导，有助于解释实验结构数据，并最终有助于合成实验的设计。斯坦福大学的另一项长期努力是在亚ppm/cm水平上测量低光损耗材料的吸收，这可以追溯到最初LIGO测试质量的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中的低温损失，以评估其在旅行者技术演示器和未来低温探测器中的适用性。该奖项反映了NSF的法定使命，并被认为值得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来支持。

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.