Collaborative Research: Center for Coatings Research

A decade after the first detection of gravitational waves, this new form of observational astrophysics is booming. New observations of mergers of neutron stars and black holes were publicly announced weekly during the fourth observing run (O4) of NSF’s Advanced LIGO detectors. The next revolution in gravitational-wave observation, the proposed third generation (3G) detectors, notably the 40-km Cosmic Explorer (CE) in the U.S., will extend the observational reach across cosmic time to high redshifts, enabling observations of the coalescence of remnants of the first stars. These will be the only instruments able to observe stellar-size events at distances where even the James Webb space telescope can only resolve entire galaxies. The Center for Coatings Research (CCR) focuses on the development of advanced mirror coatings for these 3G detectors. CE’s ambitious goals require 1.5 MW of optical power in the detector’s arms. Supporting these enormous optical powers requires mirror coatings with unprecedentedly low optical absorption while meeting myriad other strict requirements, notably thermal noise from internal friction in the coatings. The project has broader scientific impacts on precision measurement technology, benefiting areas like precision timing, quantum information, low noise interferometry, and the search for deviations in the gravitational inverse-square law. The outcomes of this research can also have technological implications for the semiconductor, laser, and quantum computing communities, as correlations between optical and mechanical loss and other loss mechanisms are explored. Additionally, this collaboration between materials science and gravitational wave communities provides research opportunities for students at different education levels. This project aims to develop mirror coatings that meet the optical and mechanical requirements for implementation in CE. The CCR combines groups working on coating deposition, characterization of atomic structure and macroscopic material properties, and computational modeling. These components are often performed by three diverse communities that work in relative isolation from each other. The strength of the CCR and its success in accelerating discoveries arises from the close integration of these communities, focusing on a unified research goal. Since the formation of the CCR in 2017, the collaboration has become a knowledge repository for gravitational wave detector coatings research, making significant progress on all the proposed research directions, including uncovering atomic structural motifs associated with room temperature vs cryogenic mechanical losses, using that understanding to develop Ti:GeO2 coatings that can meet the requirements for Advanced LIGO + (A+), and identifying mechanisms responsible for a major part of the optical absorption in these new materials. The outcomes of this research can also have implications for the semiconductor, laser, and quantum computing communities, essentially any field sensitive to extremely low levels of dissipation. Additionally, this collaboration between materials synthesis, modeling, and characterization groups with the broader gravitational wave community provides a rich multi-disciplinary environment for the preparation of students and post-docs to work in the increasingly complex environments characteristic of contemporary STEM fields. 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.