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

100年前，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计划的(第二代)探测器首次探测到引力波。这是基础物理学的一个开创性事件，首次观测到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进入宇宙的新窗口，允许我们‘聆听’它的引力特征，揭示以前隐藏的物体。这个项目的成功成果将使下一代引力波探测器的灵敏度和引力天文学的新发现成为可能，例如探测新的源，提高源的总体研究的探测率，并且能够看到更暗更远的源。引力波引起&lt；1E-19M的分光镜，形成干涉探测器。这是一个如此微小的位移，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在探测器最灵敏的频率上的灵敏度，在这些频率上，许多有趣的源有望被探测到，如合并的中子星和自旋的脉冲。在这个项目中，我们将开发低热噪声的新材料，这涉及到了解材料中的原子过程，以使干涉引力波探测器的灵敏度提高。高反射镜膜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，未来的引力波探测器将进行低温操作。低温探测器在反射镜中需要较低的光吸收，以最大限度地减少来自激光束的热量，从而保持低温工作温度。该项目的目的是在涂层性能、成分和结构研究的基础上开发高反射多层涂层，以满足对吸收、反射率和机械损耗的挑战性要求。虽然该提案主要针对未来的低温探测器，但对在室温下工作的探测器(如Advanced LIGO和Virgo)的升级降低热噪声也将是拟议研究的一部分。

100 years ago, Einstein predicted the existence of gravitational waves which are ripples in the curvature of space-time. On 14th September 2015, the (second-generation) detectors of the LIGO project made the first gravitational-wave 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, revealing previously hidden objects.A successful outcome of this project would enable sensitivities envisioned for the next generation gravitational-wave detectors and new discoveries in gravitational astronomy, e.g. the detection of new sources, an improvement of the detection rates for population studies of sources, and enable to see fainter and more distant sources.Gravitational waves cause changes of < 1e-19m in the separation of mirrors forming an interferometric detector. This is a displacement 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 at the detectors’ most sensitive frequencies, where the detection of many interesting sources is expected such as merging neutron stars and spinning pulsars.In this project we will develop new materials with low thermal noise, which involves understanding the atomic processes in the materials, to enable sensitivity improvements of interferometric gravitational wave detectors.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 gravitational wave detectors will be cryogenically operated. Cryogenic detectors require low optical absorption in the mirrors to minimize heating from the laser beam, and therefore maintain the cryogenic operation temperature. The aim of this project is the development of highly-reflective multilayer coatings based on studies of coating properties, composition and structure, to meet the challenging requirements on absorption, reflectivity and mechanical loss.While the proposal is mainly targeted at future cryogenic detectors, thermal noise reduction for upgrades of detectors operating at room temperature (such as Advanced LIGO and VIRGO) will also be part of the proposed research.