Advancing Faraday Isolators and Optical Modeling for Future Gravitational-Wave Detectors

NSF's Laser Interferometer Gravitational-wave Observatory (LIGO) confirmed Einstein’s 100-year-old prediction with the first detection of gravitational waves from two merging black holes. It set the stage for gravitational-wave astronomy as a powerful science tool for observing the invisible side of the universe in new unprecedented ways. Many other detections followed at an accelerating rate - from violent black-hole mergers to neutron star collisions, and detections revealing unexpected objects of uncertain nature. Technological upgrades of the instruments continue to improve detection sensitivity, helping shed more light on our understanding of the dense nature of the universe, the formation of black holes throughout cosmic time, or that of the universe. The Voyager technologies aim to reduce the quantum noise by cryogenically cooling the mirrors to lower thermal fluctuations. Cosmic Explorer is proposing much larger scale facilities (40 km long) with unique features and technologies that would improve the sensitivity by one order of magnitude. Faraday isolators are key devices that help prevent scatter light from resonating inside the interferometer, and their performance is essential in determining the gravitational-wave detector’s sensitivity. Also, planning and designing these uncommon large-scale facilities requires well-developed optical design tools and reliable optical models. The projects supported by this award address research to advance the development of low-loss Faraday isolators for future upgrades and the next generation of gravitational-wave detectors, and for developing optical design models for the Cosmic Explorer optical layout, and optimizations for future LIGO upgrades. These projects will continue to offer research opportunities to undergraduate students at Montclair State University, who will gain valuable practical skills beneficial for future professions in industry or academia and inspire young scientists to consider careers in gravitational-wave astrophysics. The research work supported by this award has two components: First, an experimental component that aims at advancing the development of Faraday isolators to satisfy stringent low-loss and high-performance requirements for the next generation of gravitational-wave detectors. Particularly, losses in these components are widely recognized as limiting factors in the effectiveness of squeezing, and therefore improving the losses has immediate consequences on the detection sensitivity. In high-power areas such as the input optics, laser absorption in the magneto-optical elements makes these isolators susceptible to thermal effects due to the temperature dependence of their optical parameters. Research will be carried out at two wavelengths of interest – 1 um and 2 um. The experimental component also researches new promising low-absorption magneto-optical materials and their thermo-optic properties and includes broadband and cryogenic studies of these materials. The second component addresses 3-dimensional modeling of optical layouts in Cosmic Explorer and post A+, positioning of optical components, optimizing interfacing with other systems, and placement of baffles for minimizing the effects of scattering.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.