Collaborative Research: LSC Center for Coatings Research

2015年对合并黑洞引力波的探测启动了引力波天文学领域。NSF资助的Advanced LIGO的“A+”升级旨在实现黑洞合并检测率的数量级提高，并能够检测到像双中子星这样的较暗物体，大大增加它们对多信使天文学的价值。A+升级和所有第三代探测器设计都依赖于低涂层热噪声反射镜的开发。涂层热噪声主要通过降低反射镜材料的机械（弹性）损耗来降低。LIGO科学合作（LSC）涂层研究中心（CCR）的核心研究重点是开发用于A+和第三代探测器的低机械和光学损耗的镜面涂层。CCR的研究使命包括：了解和减少非晶金属氧化物的机械损耗，这是反射镜涂层中最广泛使用的材料;开发和测试晶体（AlGaAs）涂层，这已被证明是小型反射镜的低损耗。在更长的时间尺度上，CCR正在开发与拟议的3G探测器的低温操作兼容的反射镜。Advanced LIGO首次记录的黑洞合并的时域引力波形中可见的残余噪声主要是由于光的量子噪声和由于镜面涂层引起的热噪声。自从第一次发现以来，在减少量子噪声和地震、散射和抖动噪声的耦合方面取得了很大进展，使涂层热噪声成为限制最敏感观测波段引力波天文学的主要障碍。为未来几代探测器减少这种噪声源需要减少测试质量上的镜面涂层中的机械耗散，这是CCR的主要目标。CCR结合了计算建模、涂层沉积、原子结构表征和宏观材料特性的工作组。这些组成部分通常由四个不同的社区执行，这些社区彼此相对孤立。CCR的力量及其加速发现的承诺来自于这些社区的密切整合，这些社区专注于统一的研究目标。在其运行的头两年，CCR的研究已经确定了与室温与低温机械损耗相关的不同结构图案，这导致了氧化锗（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氧化物薄膜。展望未来，这一结构指南将作为一个范例，通知高折射率非晶涂层的发展具有较低的弹性损耗。此外，热光学优化的AlGaAs晶体涂层已经证明涂层热噪声远低于A+的要求，CCR已经制定了一个开发计划，将这些涂层扩展到LIGO反射镜尺寸，并将继续研究这些材料。其他研究路径包括：探索沉积技术，使用非晶金属氧化物生产"超稳定玻璃";稳定非晶涂层，防止结晶，以便通过高温退火，使用纳米层或不同的掺杂材料减少弹性损失。该奖项反映了NSF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。

The detections of gravitational waves from coalescing black holes in 2015 launched the field of gravitational wave astronomy. The NSF-funded “A+” upgrade to Advanced LIGO is designed to achieve 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. The A+ upgrade and all 3rd generation detector designs depend on the development of mirrors with low coating thermal noise. The coating thermal noise is reduced, primarily, by lowering the mechanical (elastic) loss of the mirror materials. The core research focus of the LIGO Scientific Collaboration (LSC) Center for Coatings Research (CCR) is the development of mirror coatings with low mechanical and optical losses for use in A+ and 3rd generation detectors. The research mission of the CCR includes: understanding and reducing mechanical loss in amorphous metal-oxides, the most widely-used materials in mirror coatings; and developing and testing crystalline (AlGaAs) coatings, which have demonstrated low losses for small mirrors. On a longer time-scale, the CCR is developing mirrors compatible with the proposed 3G detectors’ cryogenic operation. The residual noise visible in the time-domain gravitational waveforms of black hole mergers first recorded by Advanced LIGO is mostly due to quantum noise of the light and thermal noise due to the mirror coatings. Since that first discovery much progress has been made in reducing quantum noise and the coupling from seismic, scatter and jitter noise, leaving coating thermal noise as the dominant barrier limiting gravitational-wave astronomy in the most sensitive observation band. Reducing this noise source for future generations of detectors requires reducing the mechanical dissipation in the mirror coatings on the test masses, and forms the main goal of the CCR. The CCR combines groups working on computational modeling, coating deposition, and characterization of atomic structure and macroscopic material properties. These components are often performed by four diverse communities that work in relative isolation from each other. The strength of the CCR and its promise of accelerating discoveries arises from close integration of these communities focused on a unified research goal. In its first two years of operation, research in the 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 will serve as a paradigm informing the development of high-refractive index amorphous coatings with lower elastic loss. In addition, thermo-optically-optimized AlGaAs crystalline coatings have demonstrated a coating thermal noise well below the requirements for A+, and the CCR has generated a development schedule to scale up these coatings to LIGO mirror sizes and will continue investigations into these materials. Other research paths include: exploring deposition techniques to produce “ultrastable glasses” using amorphous metal-oxides; and stabilizing amorphous coatings against crystallization in order to allow elastic loss reduction via high temperature annealing either with nano-layering or with different doping materials.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.