CAREER: Integrated Research and Education on Gravitational Wave Detector Optics

American University, Washington DC

Investigators

Abstract

This CAREER grant supports work on optics research to improve the sensitivity of gravitational wave detectors and other precision optical measurements as well as using expertise in optics to organize and host a day of fun competition, the Optics Olympiad, for Washington DC high school students. Gravitational waves come from Einstein's theory of gravity, and are one of the few specific predictions of Einstein's theory that can be experimentally checked against other theories of gravity (like Isaac Newton's). Determining if Einstein's, Newton's, or perhaps some other theory of gravity correctly describes our universe is necessary to developing a complete understanding of the laws of nature. This experiment is being performed by the Laser Interferometer Gravitational-wave Observatory (LIGO) with two large, four kilometer long detectors in Louisiana and Washington state. Once gravitational waves are detected by LIGO, these detections will serve as another method of studying the universe, complementary but different from optical, radio, and other conventional telescopes. With gravitational wave detections, we expect to learn more about black holes, neutron stars, supernova, the origins of the universe, and other high energy astronomical events. Unfortunately, the effect of gravitational waves on the LIGO detectors is very small, and noise from other phenomenon can easily overwhelm the gravitational signal. This grant supports work to better understand and reduce coating thermal noise, a critical noise source that limits our ability to detect gravitational waves. The related education and outreach project is to pass on the excitement about optics we develop working on LIGO to high school students through a fun and educational competition, the Optics Olympiad. In addition to individuals and teams competing on knowledge and understanding of optics, there will be panel discussions, a guest lecturer, and tours of science laboratories at American University. Thermal noise in the coatings of the LIGO optics is caused by mechanical loss, as shown by the Fluctuation Dissipation theorem. We will reduce this thermal noise by developing Aluminum-Gallium-Arsenide (AlGaAs) crystals and silicon nitride for use as LIGO coatings. AlGaAs has already shown lower thermal noise in other precision optics experiments under different conditions. Preliminary results with AlGaAs under LIGO conditions indicate some improvement in mechanical loss compared to current coatings, but not as much as expected. This may be due to surface conditions on the substrate, which will be explored using various chemical and mechanical surface treatments. The effects of these treatments on AlGaAs mechanical loss will be explored using normal mode quality factor, or Q, measurements. We will also better characterize and understand thermal noise from AlGaAs using the complete description of mechanical loss as the imaginary part of the stiffness tensor. This may allow for ways to improve thermal noise through the layer design of the coating beyond improvements from better materials. The Optic Olympiad will include a formative assessment to determine what elements of the Olympiad are helping to reach the goals of increasing students understanding of physics and optics as well as improving their impression of STEM careers. Results of this assessment and the Olympiad in general will be presented to the physics education research community, likely as a journal article or conference presentation.