MRI: Acquisition of a Cryogenic Testbed for Advancing Gravitational-Wave Observation Technology

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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. By discovering gravitational waves from merging black holes and neutron stars, the NSF-funded Laser Interferometer Gravitational-Wave Observatory (LIGO) has opened a new window on the universe. But today’s observatories are only just sensitive enough to probe the gravitational-wave sky. LIGO Voyager, a potential upgrade to maximize the potential of the LIGO facilities, and Cosmic Explorer, a 40km baseline next-generation US concept, would greatly expand humanity’s access to the gravitational universe and observe all star-sized black hole mergers, by leveraging advanced technologies, chiefly crystalline silicon optics operated at very low (cryogenic) temperatures. Key challenges for the cryogenic operation of these observatories include: fabricating large, pure silicon crystals with excellent optical properties; identifying high-quality optical coatings; and noiselessly holding the optics to stable low temperatures. This project will support the acquisition of a flexible cryogenic testbed to enable researchers at California State University Fullerton to address some of these challenges, particularly those regarding optical properties of the silicon and coatings and temperature and vibration control. This acquisition will provide opportunities for hands-on experience with cryogenic hardware to a generation of students at primarily undergraduate and Hispanic-serving institutions: CSUF and nearby community colleges (through established research programs). Scientific results made possible by this acquisition will expand the discovery space of gravitational-wave science by making essential contributions to the design of Cosmic Explorer while informing potential upgrades to current facilities.LIGO Voyager and Cosmic Explorer would peer deep into the gravitational universe reaching observation rates of tens per hour, signal-to-noise ratios in the thousands, and observing all neutron star and stellar-mass black hole mergers. The use of cryogenic crystalline silicon optics and suspensions to reduce noise is a cornerstone for Voyager and Cosmic Explorer. Silicon has zero thermal expansion at 123 K, eliminating thermoelastic noise and thermal aberrations from light absorption, and the lower temperature reduces thermal vibrations. Key challenges for the cryogenic operation of these optics include: fabricating large, pure silicon crystals with low optical scattering and absorption; identifying optical coatings with excellent optical and material properties; and noiselessly holding the optics to target temperatures. This project will support the acquisition of a flexible cryogenic testbed to enable California State University Fullerton to address these challenges, particularly optical characterization and temperature and vibration control of coated silicon optics. The acquisition will enable research on the material and optical properties of crystalline silicon optics, crystalline AlGaAs/GaAs coatings, and amorphous silicon and silica coatings, each of interest to the optics and materials communities. It will provide opportunities for hands-on experience with cryogenic hardware to a generation of students at primarily undergraduate and Hispanic-serving institutions: CSUF and nearby community colleges (through established research programs). Scientific results made possible by this acquisition will expand the discovery space of gravitational-wave science by making essential contributions to the design of Cosmic Explorer while informing potential upgrades to current facilities.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.