Multi-Material Coatings with Reduced Thermal Noise

The most sensitive measurements of time and space are made with resonant optical cavities, and these measurements are limited by coating thermal noise. The mechanical and optical performance requirements placed on coating materials, especially for interferometric gravitational wave detectors, have proven extremely difficult to meet despite a lengthy search. In this paper we propose a new approach to high performance coatings; the use of multiple materials at different depths in the coating. To support this we generalize previous work on thermal noise in two-material coatings to an arbitrary multi-material stack, and develop a means of estimating absorption in these multi- material coatings. This new approach will allow for a broadening of the search for high performance coating materials.