DFG/NSF: Novel Low Loss Coatings-Enabling the Third Generation of Gravitational-Wave Detectors

一个世纪前，爱因斯坦预言了引力波的存在，引力波是时空曲率中的涟漪。2015年9月14日，LIGO项目的(第二代)探测器进行了第一次直接GW探测。这对基础物理学来说是一个开创性的事件，首次观测到了一个合并成单个黑洞的二元黑洞系统，并为我们打开了一扇通往宇宙的新窗口，让我们能够“倾听”它的引力信号。该奖项支持的项目将使下一代GW探测器的灵敏度和引力天文学的新发现成为可能，并将提高黑洞和中子星合并的探测率。引力波导致LIGO反射镜的间隔发生微小变化，以至于反射镜及其涂层的热振动，即所谓的布朗热噪声，将限制当前和未来探测器的灵敏度。该项目将开发低热噪声的新材料，用于未来的LIGO升级。这项工作是斯坦福大学的Martin Fejer团队和汉堡大学的Jessica Steinlechner团队合作完成的，该奖项支持美国对合作的贡献。这一领域的进展将使更广泛的应用研究界受益，因为除了LIGO外，还有用于低热噪声涂层的应用：原子钟、量子信息系统、精密干涉测量都需要低损耗涂层。这种多学科合作的性质使其成为培养研究生的理想选择。高反射反射镜涂层中的热噪声与涂层厚度、材料的机械损失和镜面温度成正比。为了显著降低涂层的热噪声，未来的GW探测器将采用低温操作。本项目的目标是在对涂层的性能、成分和结构进行研究的基础上，开发用于未来GW探测器的高反射多层涂层，以满足对吸收、反射和机械损耗的苛刻要求。虽然该项目主要针对未来的低温探测器，但在室温探测器下运行的探测器升级的热噪声降低也是拟议研究的一部分。这项工作的一个关键部分是优化表现出较低机械损失水平的涂层材料，如非晶硅和氮化硅；并研究纳米层的使用，事实证明，纳米层可以抑制结晶，从而实现更高的热处理温度，从而降低光学和机械损失。汉堡将拥有利用脉冲激光沉积(PLD)系统沉积涂层的独特能力，该系统具有加热衬底和可变激光脉冲持续时间的功能。斯坦福大学在LSC中发挥了领导作用，开发了表征非晶涂层材料的光学和结构特性的实验方法。这项工作将以涂层性能研究为基础，以了解沉积参数、涂层结构、损耗和吸收之间的联系。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。

A century ago, Einstein predicted the existence of gravitational waves (GWs) which are ripples in the curvature of space-time. On 14th September 2015, the (second-generation) detectors of the LIGO project made the first direct GW detection. This was a ground-breaking event for fundamental physics, observing for the first time a binary black hole system merging to form a single black hole, and has opened a new window into the universe allowing us to 'listen' to its gravitational signatures. The project supported by this award will enable sensitivities envisioned for the next generation GW detectors and new discoveries in gravitational astronomy, as well as an improvement of the detection rates for black hole and neutron star mergers. Gravitational waves cause changes in the separation of LIGO's mirrors so small that the thermal vibration of the mirrors and their coatings, so called Brownian thermal noise, will limit the sensitivity of current and future detectors. This project will develop new materials with low thermal noise to be used in future LIGO upgrades. This work is a collaborative effort between Martin Fejer's group at Stanford University and Jessica Steinlechner's group at Hamburg University, with this award supporting the US contribution to the collaboration. Progress in this area will benefit a broader applied research community, since there are applications beyond LIGO for low thermal noise coatings: atomic clocks, quantum information systems, precision interferometry all demand low-loss coatings. The nature of this multidisciplinary effort makes it ideal for training graduate students.Thermal noise in highly-reflective mirror coatings is directly proportional to the coating thickness, the mechanical loss of the materials and the mirror temperature. To significantly reduce coating thermal noise, future GW detectors will be cryogenically operated. The aim of this project is the development of highly-reflective multilayer coatings for future GW detectors, based on studies of coating properties, composition and structure, to meet the challenging requirements on absorption, reflectivity and mechanical loss. While this project mainly targets future cryogenic detectors, thermal noise reduction for detector upgrades operating at room temperature detectors is also part of the proposed research. A key part of this effort is optimizing coating materials which have demonstrated lower levels of mechanical loss, such as amorphous silicon and silicon nitride; and investigate the use of nano-layers, proven to suppress crystallization enabling higher heat treatment temperatures, which can lead to lower optical and mechanical losses. Hamburg will have a unique ability to deposit coatings using a pulsed laser deposition (PLD) system with heated substrates and variable laser pulse durations. Stanford has had a leading role within the LSC in developing experimental methods to characterize the optical and structural properties of the amorphous coating materials. This work will be underpinned by studies of coating properties to understand links between deposition parameters, coating structure, loss and absorption.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.