Aluminum Gallium Arsenide Coatings to Improve LIGO Sensitivity

LIGO和Virgo探测器对来自天文源的引力波的直接探测为宇宙开辟了一种新的研究类型：引力天文学。引力天文学依赖于使用激光精确测量镜子的位置，镜子中的任何噪声源都代表着我们观察引力现象的能力的限制，例如黑洞，中子启动，超新星和大爆炸。覆盖反射镜表面的光学涂层中原子的热运动足够大，足以成为LIGO灵敏度的重要限制。砷化铝镓（AlGaAs）反射镜已在其他需要精确测量反射镜位置的应用中用作低噪声涂层，包括最精确的时钟和非常精确的激光器。该项目探索在更大的LIGO光学器件上使用AlGaAs反射镜，以确保在引力天文学中实现低噪声优势，就像在其他精密测量应用中一样。该项目使用本科生作为实验室研究人员，本科生接触高端研究既提高了他们的职业生涯，也使他们具备了在21世纪世纪技术工作场所竞争的技能。大型AlGaAs反射镜的开发也可以在其他应用中受益，例如计算机芯片制造和国防直接能源应用。该项目还将继续每年的光学奥林匹克竞赛，该竞赛将一百多名华盛顿特区的中学生带到大学校园。中学生参加光学演示，与大学生以及专业科学家和工程师进行讨论，并参加游戏节目式的比赛。在LIGO中使用AlGaAs反射镜的主要挑战是按比例放大这些涂层的尺寸。该小组将与供应商合作，以增加可以生长和粘合到二氧化硅衬底上的涂层的直径。他们还将进一步研究AlGaAs的材料特性，特别是作为热噪声来源的内部摩擦，以确保AlGaAs在更大尺寸下仍然是一种有吸引力的涂层材料。他们将使用已建立的正常模式品质因数测量和有限元建模技术研究AlGaAs的内部摩擦。他们还将与LIGO光学工作组的其他成员分享AlGaAs样品，以测量光学和其他特性。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The direct detection of gravitational waves from astronomical sources by the LIGO and Virgo detectors has opened the universe to a new type of investigation: gravitational astronomy. Gravitational astronomy relies on precise measurement of the position of mirrors using a laser, and any source of noise in the mirrors represents a limitation to our ability to observe gravitational phenomenon such as black holes, neutron starts, supernova, and the Big Bang. The thermal motions of atoms in the optical coatings that cover the surface of the mirrors is large enough to be a significant limitation on LIGO sensitivity. Aluminum gallium arsenide (AlGaAs) mirrors have been used as low noise coatings in other applications that require precision measurement of mirror positions, including the most accurate clocks and very precise lasers. This project explores using AlGaAs mirrors on the much larger LIGO optics to make sure the low noise benefits can be realized in gravitational astronomy as have been in other precision measurement applications. This project does this using undergraduate students as the laboratory researchers, and exposure of undergraduate students to high end research both enhances their careers and equips them with the skills to compete in the technical workplace of the 21st century. Development of large AlGaAs mirrors can also have benefits in other applications such as computer chip manufacturing and direct energy applications to national defense. This project will also continue the annual Optics Olympiad that brings over a hundred Washington DC middle school students to the university campus. The middle school students participate in optics demonstrations, discussions with university students as well as professional scientists and engineers, and compete in a game show style tournament.The primary challenge in using AlGaAs mirrors in LIGO is to scale up the size of these coatings. The group will work with vendors to increase the diameters of the coatings that can be grown and bonded onto silica substrates. They will also further study the material properties of AlGaAS, and especially the internal friction that is the source of thermal noise, to make sure AlGaAs will still be an attractive coating material at larger sizes. They will research AlGaAs internal friction using the established technique of normal mode quality factor measurements and finite element modeling. They will also share the AlGaAs samples with other members of the LIGO Optics Working Group for measurements of optical and other properties.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.