Development of coating materials and jointing techniques for future gravitational wave detectors

This project will focus on the development and characterisation of novel optical coating materials for gravitational wave detectors. Optical mirror coatings are core components of these detectors, and thermal noise arising from the internal friction in the coatings is a critical limit to the sensitivity to astrophysical sources of gravitational waves that can be achieved. In addition to having low thermal noise, these coatings must have ultra-low optical absorption, to prevent heating and thermal distortion of the mirror. This project will investigate new coating materials and new types of coating design, aiming to develop the required coating solutions to allow planned detectors like the Einstein Telescope and Cosmic Explorer to meet their sensitivity goals. In particular, so-called 'multimaterial coatings' will be investigated. These are novel coating designs using several materials in which the position of each material in the coating stack is optimised to ensure the most desirable properties of the entire coating can be achieved.
The student will use a variety of techniques for measuring the internal friction of coating materials at room temperature and at cryogenic temperatures. Photo-thermal common-path interferometry will be used to study the optical absorption of the coatings and a wide-range of other chemical, optical and structural characterisation techniques will be used e.g. Raman spectroscopy, ellipsometry, optical stress measurements. Coating materials and designs will be developed in collaboration with colleagues at the University of Strathclyde, and the work is embedded in the world-wide collaborative effort to solve the coating thermal noise problem for future gravitational wave detectors. Many of the techniques used to study coatings are also applicable to study novel methods of jointing materials together to construct the suspended mirrors used in gravitational wave detectors. It is therefore planned to extend some of these studies to developing jointing methods involving thin metallic coatings suitable for use with the crystalline materials proposed for use in future detectors, with the internal friction of the bonds being a crucial parameter.