Tantalum oxide and silicon oxide mixture coatings deposited using microwave plasma assisted co-sputtering for optical mirror coatings in gravitational wave detectors

This work presents the characterization of the optical and mechanical properties of thin films based on ( Ta₂O5)_1−x(SiO₂)_x mixed oxides deposited by microwave plasma assisted co-sputtering, including post-annealing treatments. The deposition of low mechanical loss materials (3 × 10⁻⁵) with a high refractive index (1.93) while maintaining low processing costs was achieved and the following trends were demonstrated: The energy band gap increased as the SiO₂ concentration was increased in the mixture, and the disorder constant decreased when the annealing temperatures increased. Annealing of the mixtures also showed positive effects to reduce the mechanical losses and the optical absorption. This demonstrates their potential as an alternative high-index material for optical coatings in gravitational wave detectors using a low-cost process.