NSF Award
2320711
This award supports research in relativity and relativistic astrophysics, and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. "Gravitational wave astrophysics is one of the most exciting frontiers in science.” states the National Academy of Sciences Decadal Survey (2020). This award will help achieve a key advancement in sensitivity for gravitational wave detectors and help resolve a noise source that has limited the field for the past two decades. Since 2015, the Laser Interferometer Gravitational-wave Observatory (LIGO) has detected over 90 events, including the inspiral and coalescence of binary neutron star and binary black hole systems. The most recent improvements to the detector promise new observations on a weekly basis. Nevertheless, LIGO’s sensitivity remains limited by coating thermal noise (CTN). The research funded by this award will enable the development of crystalline mirror coatings, which could reduce CTN by a factor of 10 compared to the current mirror coatings. This significant advancement in sensitivity will allow the detection of many more events at much higher sensitivity. Gravitational wave observations have informed and inspired a broad range of astronomers, physicists, students, and the general public. Many people are intrigued by black hole and neutron star observations and their fascination helps raise the public’s scientific awareness. This award will train undergraduate and graduate students with skills that can be applied to research and to technical areas in the broader economy. The team will continue to work hard providing these opportunities to groups that have been historically disenfranchised. Finally, the knowledge gained in this research will advance the areas of gravitational wave astrophysics, precision optics, and the materials science of low-dissipation materials.<br/><br/>Mirror coating thermal noise (CTN) limits the sensitivity of current interferometric gravitational wave detectors in the central frequency band <br/> (the region of highest sensitivity). The current mirror coating technology of ion beam sputtered (IBS) amorphous oxides, which is used on all current gravitational wave detectors has, over the past 15 years, seen only modest gains in reducing the elastic loss that generates CTN. Fortunately, crystalline GaAs/AlGaAs coatings (hereafter AlGaAs coatings) meet LIGO’s stringent optical requirements and have a CTN estimated to be 10 times lower than the current Advanced LIGO coatings. This gain in sensitivity will generate a dramatic jump in event rate, which increases as the cube of the sensitivity range. It will also allow nearby events to be observed with very high signal-to-noise ratio, which may provide insights into the structure of neutron stars and additional tests of general relativity. Finally, crystalline coatings exceed the requirements for all planned future gravitational wave detectors. Thus, this award funds an advancement in instrumentation that will benefit the field for decades. However, challenges remain as AlGaAs coatings are birefringent, experience crystal defects, and have only been made in small diameters. This award will fund the LOCCCI instrument that will enable the development of low-noise, large-diameter, crystalline coatings for gravitational wave detectors. The LOCCCI instrument will be initially used to test these coatings at large diameters (20 cm) for birefringence noise, crystal defect densities, and surface uniformity. This investigation will then inform manufacturing improvements and ultimately justify the development of the 30 cm coatings that will be deployed in the detectors. This instrument will also test that the production coatings conform to design specifications.<br/><br/>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.
