Coatings for Next Generation Gravitational Wave Interferometers

This award supports research in relativity and relativistic astrophysics, and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. Since 2015, when the twin NSF's LIGO gravitational wave detectors (GWD) in the United States detected the first signals originating from the coalescence of two massive black holes, there have been multiple detections at a pace of about one a week. Presently in the LIGO-Virgo-KAGRA fourth observation campaign, detections are revealing new mergers with unexpected results. Key to these remarkable achievements has been the improvements in the sensitivity of GWD, among which the reduction in the coating thermal noise (CTN) of the test masses of the interferometer has had a large impact. The projected 2x reduction in CTN with respect to the current LIGO coatings and beyond for third-generation (3G) GWD is pushing the scientific and engineering boundaries in dielectric coatings to understand and control the fundamental mechanisms in amorphous oxides that contribute to mechanical loss. The project aims to demonstrate next-generation multilayer dielectric coatings that reduce the thermal noise by a factor of two and pave the way to identify strategies to further reduce CTN for 3G GWDs. Toward this goal, new amorphous oxide mixtures will be investigated for their potential to reduce CTN when incorporated into mirror coating stacks. The proposed research on amorphous thin films by ion beam sputtering supports the projected development of GWDs. The fundamental materials and coating design aspects of the project will have a broad impact as near-infrared dielectric coatings are ubiquitous in ultra-stable optical cavities and other laser systems. The know-how to be developed is translational, as the deposition method and equipment we will use are standard in the coatings industry. The proposed research will offer a diverse group of students at all levels multiple opportunities to gain an in-depth understanding of the physical mechanisms that affect internal friction in amorphous materials that are the backbone of interference coatings for ultra-high finesse optical cavities and at the same time gain valuable expertise in optical sciences. This interdisciplinary research project will train students in STEM areas, to contribute to advancing science and technology in academic, national laboratory, and industrial settings. 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.