Aluminum Gallium Arsenide Coatings to Improve LIGO Sensitivity

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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.