Equipment for advanced optical coatings and materials research, characterisation and development for gravitational wave detectors and beyond

爱因斯坦的广义相对论预言，处于强引力场中的动力系统会以引力辐射的形式释放出大量的能量。引力波是时空结构中的涟漪，以光速从源头传播，携带着有关引力波发射的物理过程的信息，这是其他任何方式都无法获得的。2105年6月14日，两个黑洞（BHs）碰撞产生的引力波（GWs）被探测到，这为爱因斯坦的理论提供了惊人的验证。在穿过地球和探测器之前，信号已经传播了440mpc（约15亿光年）。它打开了一扇观察宇宙的新窗口，就像使用第一批射电望远镜或第一批x射线望远镜一样。在我们的GW探测器的情况下，它们对大约10赫兹到几千赫的频率范围内的GW敏感。自第一次探测以来，又观测到5次双黑洞碰撞或合并。2017年8月17日，LIGO和处女座探测器观测到两个太阳质量致密体（中子星或黑洞）合并的信号。1.7秒后，费米卫星上的伽马射线探测器观测到伽马射线暴（GRB）。伽马射线暴已经被观测了40多年，尽管它们的起源还不清楚，但人们推测它们一定是两颗中子星碰撞的结果。结合GW信号和GRB信号，以及进一步的电磁波谱观测，表明该事件是中子星-中子星碰撞，导致了短时间的GRB和随后的千新星。由于所有这些探测，发表的新物理学和天体物理学的财富是非凡的。干涉探测器的全球网络包括德国-英国的GEO600，法国-意大利的Virgo，美国的激光干涉引力波天文台（LIGO），以及正在建设中的新探测器——日本的KAGRA。LIGO和Virgo正在提高它们的灵敏度，目标是在两年内达到设计目标。不同项目之间的合作可以实现对大部分天空中各种来源和现象的持续数据采集。这项设备提案将支持由我们的“重力辐射研究”综合拨款[ST/N005422/1]支持的探测器研究和开发实验计划。我们的目标是改进检测器，增加我们可以检测到的信号数量。如果我们能将灵敏度提高10倍，那么我们就能“看到”10倍远的信号，或者1000倍大的空间。这将使检出率提高1000倍。探测器的灵敏度主要受限于与反射镜衬底、反射涂层和悬浮元件相关的热噪声，以及用于感应GW的激光的量子性质所产生的噪声。我们的这一部分研究的目标是在低热噪声、硅衬底、低温悬浮液和改进干涉仪拓扑以对抗量子噪声的镜面涂层领域进行创新改进。所要求的设备将使我们能够大大增加对材料的测量，这些测量可能有助于我们减少探测器中的噪音。

Einstein's General Theory of Relativity (GR) predicts that dynamical systems in strong gravitational fields will release vast amounts of energy in the form of gravitational radiation. Gravitational waves are ripples in the fabric of spacetime and travel from their sources at the speed of light, carrying information about physical processes responsible for their emission, obtainable in no other way. The detection of gravitational waves (GWs) from the collision between two black holes (BHs) on 14th of June 2105 provided a spectacular validation of Einstein's theory. The signal had travelled 440 Mpc or around 1.5 billion light years before passing through the Earth and the detectors. It has opened a new window on the Universe, similar in that respect to when the first radio telescopes or the first X-ray telescopes were used. In the case of our GW detectors, they are sensitive to GWs in the frequency range of approximately 10 Hz to a few kHz. Since that first detection, 5 more binary black hole collisions, or coalescences, have been observed and on August the 17th 2017, LIGO and Virgo detectors observed the signal from the coalescence of two solar mass compact bodies, either neutron stars or black holes. 1.7 seconds later a gamma-ray detector on a satellite called "Fermi" observed a gamma ray burst (GRB). GRBs have been seen for over 40 years and although their origin was not strictly known, it had been speculated that them must be from the result of the collision of two neutron stars. The combination of the GW signal and the GRB signal, along with further follow-up observations across the electromagnetic spectrum, showed that this event had been a neutron star- neutron star collision, leading to a short duration GRB and subsequent kilonova. The wealth of new physics and astrophysics that have been published as a result of all these detections has been extraordinary.The worldwide network of interferometric detectors includes the German-UK GEO600, the French-Italian Virgo, the American Laser Interferometer Gravitational-Wave Observatory (LIGO) and is being enhanced with a new detector under construction - KAGRA in Japan. The LIGO and Virgo are improving their sensitivities and aim to meet their design goal within 2 years. Cooperation amongst different projects enables continuous data acquisition, with sensitivity to a wide range of sources and phenomena, over most of the sky. This proposal for equipment will support the experimental programme of detector research and development supported by our Consolidated Grant 'Investigations in Gravitational Radiation' [ST/N005422/1]. Our aim is to improve the detectors and increase the number of signals we can detect. If we can increase sensitivity by a factor of ten, then we "see" signals from ten times further away, or a volume of space 1,00 times larger. This would increase detection rates also by a factor of 1,000. Detector sensitivity is mainly limited by thermal noise associated with the substrates of the mirrors, their reflective coatings, and their suspension elements, as well as by noise resulting from the quantum nature of the laser light used to sense the GW. This part of our research is targeted towards making innovative improvements in the areas of mirror coatings for low thermal noise, silicon substrates, cryogenic suspensions and improved interferometer topologies to combat quantum noise. The equipment requested will enable us to greatly increase the measurements we can make on materials that can potentially help us reduce the noise in our detectors.