This work presents the characterization of the optical and mechanical properties of thin films based on ( T a 2 O 5 ) 1 − x ( S i O 2 ) 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 S i O 2 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.

A novel merit function was constructed using the spectral coefficient average error and standard deviation, which can simultaneously optimize the expectation of spectral coefficient error and the envelope of standard deviation. Thus, a multi-objective optimization strategy based on Non-Dominated Sorting Genetic Algorithm and Sequential quadratic programming was proposed. By comparing result of wideband anti-reflection film, cut-off filter and Infrared dual-band filter designed by the conventional algorithm and the new algorithm, the control effect of the new algorithm on sensitivity of film parameters error was verified. The results show that the novel design method has the characteristics of time-efficient calculations and is capable of effectively improving the production yield of the film system, which has practical significance.