Next generation optical coatings to fully open the window on the gravitational Universe

一百多年前，爱因斯坦预言了引力波（GWs）的存在--由两个黑洞合并等剧烈事件引起的时空涟漪。这些引力波会弯曲空间，从而改变物体之间的距离，然而即使是最大和最猛烈的天体物理事件也只会导致千米尺度的距离改变原子半径的一小部分。观测GWs需要前所未有的测量精度，这推动了包括量子动力学和材料工程在内的众多研究领域的技术极限。经过几十年的探测器开发，2015年9月14日，Advanced LIGO证实了与两个黑洞碰撞有关的GW（GW 150914）的首次探测。LIGO仪器依赖于通过激光干涉测量法测量大型悬挂镜的位置，这些悬挂镜保持在真空下，相距4公里。与光学望远镜的进步类似，需要扩展GW探测器的天体物理学，以便观察整个引力宇宙。这将开辟一个全新的多信使天文学时代，除了观察光学望远镜无法观察的事件之外。这可能对我们理解宇宙的影响首次出现在GW170817的探测中-这是两颗中子星碰撞的第一次观测。来自GW信号和电磁（光学）对应物和余辉的集体信息有助于回答关键问题，包括元素的起源。目前和未来GW观测站的灵敏度预计将受到限制，在最敏感的频带，与高反射率所需的涂层相关的反射镜的热驱动运动。除此之外，操作第二代GW探测器的经验表明，这些涂层中的光学缺陷（引起激光吸收和散射的点缺陷和纳米气泡）也对扩展其天体物理范围造成了根本性的障碍。因此，迫切需要超越最先进的激光反射镜镀膜技术，让引力宇宙完全开放，并了解宇宙的极端。反射镜的设计是通过使用以特定方式堆叠的介电材料薄层来实现高反射率。近年来的研究已经确定了几种显示较低热噪声水平的材料，并可能改善当前的探测器。然而，如上所述，国际社会面临着几个需要解决的主要挑战，特别是涂层中纳米尺寸气泡的存在，这些气泡会导致激光吸收/散射增加。在该项目中，这些挑战将通过利用世界领先的专业知识和英国最先进的STFC资助设施来解决。我将采用下一代仪器来处理涂层，并优化沉积过程，以减少不必要的功能。数据科学技术将被用来帮助研究，可能会提供更快的结果周转，从而显着推进该领域。近年来，我对这些材料进行了广泛的研究，并在提供解决方案和改进途径方面取得了重大成功。随着我们继续将我们的触角延伸到宇宙的奥秘，现在有了GW探测器等工具，英国的优先事项是继续推动这些仪器的研究创新，使我们能够完全打开引力宇宙的窗口。

More than a hundred years ago, Einstein predicted the existence of gravitational waves (GWs) - ripples in space-time caused by violent events such as the merger of two black holes. These GWs curve space and therefore change the distance between objects, however even the largest and most violent astrophysical events will only cause km-scale distances to change by a fraction of an atomic radius. Observing GWs requires an unprecedented level of measurement accuracy, that pushes the very limits of technology across numerous fields of research including quantum dynamics and materials engineering. After decades of detector development, the first detection of GWs (GW150914) was confirmed by Advanced LIGO on the 14th September 2015, associated with the collision of two black holes. The LIGO instrument relies on measuring the position of large suspended mirrors, held under vacuum and separated by 4 km, by laser interferometry. Similar to the advancement in optical telescopes, there is a need to extend the astrophysical of GW detectors in order to observe the entire gravitational Universe. This would open up an entirely new era of multimessager astronomy, in addition to observing events that are otherwise invisible to optical telescopes. The impact that this can have on our understanding of the Universe was first seen in the detection of GW170817 - the first observation of two neutron stars colliding. The collective information from the GW signal and electromagnetic (optical) counterpart and afterglow helped answer key questions including the origin of elements.The sensitivity of current and future GW observatories is expected to be limited, at the most sensitive frequency band, by thermally-driven motion of the mirrors associated with the coatings required for high-reflectivity. In addition to this, experience of operating the second generation of GW detectors has shown that optical imperfections in these coatings (point defects and nanobubbles that induce absorption and scatter of the laser light) is also creating a fundamental barrier to extending their astrophysical reach. There is therefore an immediate need to push beyond the state-of-the-art in laser mirror coating technology, to allow the gravitational Universe to be fully opened, and understand the extremes of the Universe.The mirrors are designed to have high-reflectivity by use of thin layers of dielectric materials stacked in a specific way. Research over recent years has identified several materials that display lower levels of thermal noise and could potentially improve current detectors. However, as mentioned, the international community are faced by several major challenge that need to be solved particularly the presence of nanometer sized bubbles in the coatings that cause increased laser absorption/scatter. Within this project, these challenges will be addressed through leveraging world-leading expertise and the state-of-the-art STFC-funded facilities in the UK. I will employ next-generation instrumentation to characterise the coatings and optimise the deposition process to mitigate unwanted features. Data science techniques will be employed to aid the research, potentially providing faster turnaround of results that significantly advance the field. Over recent years, I have researched extensively these materials and demonstrated significant success in providing solutions and pathways for improvements.As we continue to extend our reach into the mysteries of the Universe, now with tools such as GW detectors, it is a priority for the UK to continue to drive research innovations for these instruments, allowing us to fully open the window on the gravitational Universe.