Collaborative Research: LSC Center for Coatings Research

LIGO科学合作（LSC）涂层研究中心（CCR）由NSF资助，并计划由戈登和贝蒂摩尔基金会共同资助，旨在通过解决限制其性能的主要噪声源来扩展下一代引力波探测器的范围，即干涉仪反射镜中的热噪声。这种噪声减少了来自天文源的可观测引力波信号的数量。它产生于LIGO探测器光学系统中反射镜振动模式的热激发。随着反射镜的机械品质因数（Q）的增加，这些激励的影响减小。由于反射镜的Q值受到沉积在其表面上的反射涂层的限制，因此更低的噪声需要开发更好的涂层。CCR结合了来自美国10个机构的团队，致力于非晶材料的计算建模，涂层的沉积以及其原子结构和宏观特性的表征。这些组成部分通常由三个不同的社区执行，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三个社区的紧密结合，专注于统一的研究目标。涂层热噪声也是精密计时、量子信息、低噪声干涉测量和精密测量领域的限制因素，如寻找引力平方反比定律的偏差。根据该计划开发的在机械和光学性能方面改进现有技术的涂层也适用于这些社区。在教育的更广泛的影响，本科院校与精英研究生课程的混合提供了在所有教育水平的研究机会，并建立了明确的晋升途径，为学生谁希望追求在物理科学的职业生涯。此外，CCR还致力于提高妇女和代表性不足的少数民族的地位，并将继续通过所有主要的公共和社交媒体渠道开展参与者在教育和公共宣传方面的活动。计划于2021年推出的A+ LIGO探测器将通过压缩光注入来降低量子噪声，使热噪声在探测器的中波段占主导地位。 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。该项目的目标是开发符合A+ LIGO机械和光学要求的镜面涂层。实现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：非晶氧化物中低能激发的性质和控制。在更长的时间尺度上，为低温LIGO Voyager探测器开发镜面涂层拓宽了包括非晶或晶体半导体的可能性。主要的研究重点是找到条件下，无定形金属氧化物涂层可以沉积为“超稳定的玻璃”，它具有低密度的结构图案，形成两个层次的系统，弹性耗散的来源。第二个研究轨道寻求在高温退火期间稳定涂层防止结晶的方法，这是另一种已知的减少室温弹性损失的方法。对于LIGO Voyager应用的长期研究，该小组将研究非氧化物涂层，如单晶半导体AlGaAs和AlGaP，它们在小几何形状下表现出较低的机械损耗，但其规模达到LIGO光学器件的尺寸是具有挑战性的;还有非晶硅和氮化硅，它们具有有吸引力的机械性能，但其光学性能必须得到改善。

The LIGO Scientific Collaboration (LSC) Center for Coatings Research (CCR), funded by the NSF and with planned co-funding by the Gordon and Betty Moore Foundation, seeks to extend the reach of the next generation of gravitational wave detectors by addressing the dominant noise source limiting their performance, thermal noise in the interferometer mirrors. This noise reduces the number of observable gravitational wave signals from astronomical sources. It arises from thermal excitation of the vibrational modes of the mirrors in the LIGO detector optics. The effect of these excitations is reduced as the mechanical quality factor (Q) of the mirrors is increased. Since the Q of the mirrors is limited by the reflective coatings deposited on their surfaces, lower noise requires development of better coatings. The CCR combines groups from 10 institutions in the US working on computational modeling of amorphous materials, deposition of coatings, and characterization of their atomic structure and macroscopic properties. These components are often performed by three 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 three communities focused on a unified research goal. Coating thermal noise is also a limiting factor in the fields of precision timing, quantum information, low noise interferometry, and precision measurements like the search for deviations in the gravitational inverse-square law. Coatings improving on the state of the art in mechanical and optical properties developed under this program would be applicable to these communities as well. On broader impacts in education, the mixture of undergraduate institutions with elite graduate programs provides research opportunities at all education levels and establishes clear avenues of advancement for students who wish to pursue a career within the physical sciences. In addition, the CCR has a strong commitment to the advancement of women and underrepresented minorities; and will also continue its participants' activities in issues of education and public outreach through all major channels of public and social media.The A+ LIGO detector, planned for 2021, will reduce quantum noise with squeezed light injection, leaving thermal noise dominant in the mid-band of the detector. Reducing this noise source requires reducing the mechanical dissipation in the mirror coatings on the test masses. The goal of this project is to develop mirror coatings consistent with A+ LIGO's mechanical and optical requirements. Meeting this goal requires solution of a longstanding problem in the physics of amorphous materials: the nature and control of the low-energy excitations in amorphous oxides. On a longer time scale, developing mirror coatings for the cryogenic LIGO Voyager detector broadens the possibilities to include amorphous or crystalline semiconductors. The primary research focus is to find conditions under which amorphous metal-oxide coatings can be deposited as "ultrastable glasses", which have a low density of the structural motifs that form two-level systems, the source of elastic dissipation. A second research track seeks methods to stabilize coatings against crystallization during high temperature annealing, another method known to reduce room temperature elastic losses. For the longer term research towards LIGO Voyager applications, the group will investigate non-oxide coatings such as single-crystal semiconductors AlGaAs and AlGaP, which have shown low mechanical loss for small geometries but whose scale up to the size of LIGO optics is challenging; and also amorphous silicon and silicon nitride, which have attractive mechanical properties but whose optical properties must be improved.