Investigations in Gravitational Radiation

爱因斯坦的广义相对论（GR）预测，强引力场中的动力系统将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，以光速从其源头传播，携带着关于其发射的物理过程的信息，这是无法通过其他方式获得的。它们是来自宇宙最深处的最难以捉摸的信号之一。全球的干涉探测器网络包括德国-英国GEO 600、法国-意大利Virgo、美国激光干涉仪引力波天文台（LIGO），并正在加强一个正在建造的新探测器--日本的KAGRA。以前的探测器都达到了接近其设计目标的灵敏度，并获得了迄今为止最敏感的数据。不同项目之间的合作使我们能够在大部分天空中连续采集数据，对广泛的来源和现象具有敏感性。来自GEO，LIGO和Virgo的数据已经增加了我们对天文现象的理解。在154次伽马射线爆发时对引力波的搜索已经允许了有史以来最好的排除距离，并为银河系外的软伽马中继源提供了证据。在最近的运行中，双黑洞的距离达到300 Mpc，速率上限现在非常接近一些天体物理模型的预期。对船帆座脉冲星引力波的研究为辐射强度设定了一个上限，这个上限明显低于从观测到的脉冲星自旋下降速率所预期的上限，对应于星星椭圆率的千分之一的极限。虽然最近和当前的观测可能会产生探测，但不能保证。然而，人们非常有信心，目前正在建造的先进探测器将定期观测引力波。先进的LIGO探测器基于英国为GEO 600开发的准单片二氧化硅悬浮概念和我们的德国同事在GEO 600中开发的高功率激光器。先进的处女座探测器还使用了二氧化硅悬浮技术的变体。卡迪夫和格拉斯哥小组已经发起并领导了对天文来源的搜索，这要归功于自八年前第一次数据采集运行开始以来一直支持的算法和分析工作。我们提出了一个计划，导致充分利用先进的LIGO（aLIGO）的数据，建立在持续运作的GEO 600和分析的数据，在最近的LIGO/处女座科学运行。特别是，我们将建立双黑洞合并模型，并对 * 合并的中子星，中子星-黑洞双星和黑洞双星进行深入搜索 * 可能起源于超新星的引力波爆发，* 来自恒星和其他旋转中子星的连续信号，* 通过互相关方法检测到的引力波，包括宇宙学背景。我们建议进行探测器的研究和开发。检测器的灵敏度主要受到与反射镜的基板、反射涂层和悬挂元件相关的热噪声的限制，也受到传感中所用光的量子性质所产生的噪声的限制。我们的研究目标是在这些领域进行创新性改进。我们主要负责aLIGO中的二氧化硅悬浮液，以及aLIGO探测器的增强和升级，包括用于低热噪声的镜面涂层，硅衬底，低温悬浮液和改进的干涉仪拓扑结构以对抗量子噪声。

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. They are among the most elusive signals from the deepest reaches in the Universe. Experiments aimed at detecting them have been in development for several decades, and are now reaching sensitivity levels where detection is expected within a few years.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 former detectors have all reached sensitivities close to their design goals and have taken the most sensitive data to date. Cooperation amongst different projects enables continuous data acquisition, with sensitivity to a wide range of sources and phenomena, over most of the sky.Data from GEO, LIGO and Virgo, have already increased our understanding of astronomical phenomena. Search for gravitational waves at the times of 154 gamma-ray bursts has allowed the best ever exclusion distances and provided evidence for extra-Galactic sources of soft-gamma repeaters. The distance reach for binary black holes in the most recent runs is 300 Mpc and the rate upper limits are now very close to that expected in some of the astrophysical models. The search for gravitational waves from the Vela pulsar has set an upper bound on the strength of radiation that is significantly below that expected from the observed spin down rate of the pulsar, corresponding to a limit on the star's ellipticity of a part in a thousand.While recent and current observations may produce detections, there can be no guarantees. However, there is great confidence that the advanced detectors currently in construction will routinely observe gravitational waves. The advanced LIGO detectors are based on the quasi-monolithic silica suspension concept developed in the UK for GEO 600 and on the high power lasers developed by our German colleagues in GEO 600. The Advanced Virgo detector also uses a variant of the silica suspension technology. The Cardiff and Glasgow groups have initiated and led searches for astronomical sources, thanks to the algorithmic and analysis effort that has been supported since the first data taking runs began eight years ago. We propose a programme that leads to full exploitation of data from Advanced LIGO (aLIGO), building on both continuing operation of GEO600 and analysis of data taken in the most recent LIGO/Virgo science runs. In particular we will model binary black hole mergers and carry outdeep searches for* coalescing binary neutron stars, neutron star-black hole binaries, and black hole binaries* bursts of gravitational waves that may originate from supernovae, * continuous signals from pulsars and other rotating neutron stars,* gravitational waves detected by cross-correlation methods, including a cosmological background.In parallel, we propose detector research and development. 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 light used in sensing. Our research is targeted towards making innovative improvements in these areas. We have major responsibilities for the silica suspensions in aLIGO, and in the development of enhancements and upgrades to the aLIGO detectors, in the areas of mirror coatings for low thermal noise, silicon substrates, cryogenic suspensions and improved interferometer topologies to combat quantum noise.