Tantalum oxynitride (TaOxNy) thin films have been deposited by reactive ion beam-assisted ac double magnetron sputtering. Thin films deposited by this method are known to have high mechanical durability and adhesion. A controlled variation of the refractive index of these optical coatings has been achieved through a systematic control of the oxygen and nitrogen gases present in the chamber during the film deposition. This method offers a rapid and economical way of fabricating interference and gradient index coatings used in many optical applications. To show the potential of this deposition method, a Bragg mirror stack was made with twenty alternating layers of oxygen-rich (high x) and nitrogen-rich (high y) TaOxNy thin films. (C) 2016 Published by Elsevier B.V.