RUI: Advancing Gravitational-Wave Optics to Further Explore the Cosmos

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This award supports research in relativity and relativistic astrophysics, and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. Albert Einstein predicted gravitational waves as a consequence of general relativity in 1916. A century later, the NSF-funded Laser Interferometer Gravitational-Wave Observatory (LIGO) opened a new window on the universe by observing gravitational waves from merging black holes. LIGO and its international partners Virgo and Kagra have since detected gravitational waves from nearly 100 systems. Work is underway to extend the reach of LIGO through the Advanced LIGO+ (A+) upgrades and a potential cryogenic silicon detector, Voyager. A next-generation US observatory, Cosmic Explorer, is also being developed. These detectors will use optical technology to peer deeply into the universe’s dark side and open a wide discovery aperture to the novel and unknown. This project will engage students and faculty at California State University, Fullerton (CSUF) in experimental research aimed at advancing optical technology to further explore the cosmos with gravitational waves. Students and the PI will characterize and develop techniques to reduce the amount of laser light scattered by optical coatings. They will measure the optical scattering of silicon at cryogenic temperatures and estimate its effects on gravitational-wave detector performance. They will map the laser light loss due to birefringence of silicon, at the wavelength and temperature planned for Voyager and possible cryogenic realizations of Cosmic Explorer, for the first time. These studies will help A+ to double the rate of gravitational-wave observations and Voyager and Cosmic Explorer to observe black hole and neutron star collisions to the era of the first stars. This work will additionally contribute to the field of optics and potentially lead to improvements in commercial optics. Conducting this research at CSUF will have a disproportionately positive impact on students from groups traditionally underrepresented in physics.This project will engage students and faculty at California State University, Fullerton (CSUF) in experimental research aimed at advancing optical technology to further explore the cosmos with gravitational waves. To achieve their goals, A+ and Cosmic Explorer require room-temperature optical coatings for 1-micron-wavelength laser light that have improved thermal noise, with still excellent optical properties, including optical scatter. Heat treatment (annealing) of coatings has been shown to decrease both their thermal noise and optical scatter. Students and the PI will employ an annealing scatterometer and an angle-resolved scatterometer to characterize and develop techniques to reduce scattering from the most promising coatings. Voyager technology could extend the reach of LIGO and Cosmic Explorer by reducing thermal noise and thermal aberrations using crystalline silicon optics operated at cryogenic temperatures (123 K, a zero crossing of silicon’s thermal expansion coefficient). The PI and students will use a cryogenic testbed to measure the surface, bulk, and coated optical scattering for high-purity crystalline silicon at cryogenic temperatures and estimate its effects on gravitational-wave detector performance. Optical losses due to birefringence in these transparent crystalline silicon optics could also decrease the astrophysical reach of future detectors. The PI and students will map the birefringence of crystalline silicon at 2-micron-wavelength and 123 K for the first time, using an optical cavity. These studies will help A+ to double the rate of gravitational-wave observations and Voyager and possible cryogenic realizations of Cosmic Explorer to observe black hole and neutron star collisions to the era of the first stars.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.