Optical coatings for gravitational-wave detection

Einstein's General Theory of Relativity predicts waves in spacetime caused by oscillating masses. Such waves, known as gravitational waves, are predicted to be created by binary black hole or neutron star inspirais, supernova, or other catastrophic astronomical events. Even with such large masses moving so rapidly, the expected size of the waves is extremely small, typically of order 10 -21 in unitless strain as seen on Earth. LIGO, the Laser Interferometer Gravitational Wave Observatory, is a basic physics experiments designed to detect and study these waves. The next generation interferometers, known as Advanced LIGO, are currently being designed. Thermal noise from mechanical loss in the optical coatings of the mirrors is expected to be an important limiting noise source. Reducing this noise by developing lower mechanical loss coatings, while preserving optical and thermal properties needed in the interferometer, is an area of active research.