Speaker
Description
Coating thermal noise (CTN) is one of the main limitations to enhancing the sensitivity of interferometric gravitational wave detectors, especially in room temperature detectors in the critical frequency 100 Hz region. These coatings, fabricated by ion beam sputtering as Bragg reflectors alternating high- and low-refractive-index layers, undergo a post-deposition annealing to reduce internal stresses while keeping the layer amorphous. Partial crystallization of the coating layer might have beneficial effects on CTN, as it originates from the amorphous nature of the coating. However the crystallization kinetics must be engineered to keep optical losses low.
The present study aims to determine the crystallization kinetics in high refractive index coating materials as a function of annealing temperature and duration. Tantalum oxide is used as model system to develop a protocol to investigate crystallization properties, with perspective applications to other coating materials such as Ti:Ta2O5, Ti:GeO2, Ti:SiO2. Identifying the parameters that govern the transition from the amorphous to the polycrystalline phase will enable the development of optimized, material specific annealing procedures.