Introduction

Transparent dielectric oxide thin films such as SiO₂, HfO₂, TiO₂, and Ta₂O₅ are in wide use as optical coatings. They are often used in multilayer configurations consisting of alternating layers of high and low index of refraction material with each layer being typically an optical quarter wave thick or some integer multiple thereof. Typical functional designs include anti-reflective (AR) coatings, high reflectance coatings (e.g. low loss laser mirrors), narrow-band pass filters, and short and long wave pass filters for a wide variety of consumer, instrumentation, and telecommunication applications. SiO₂ is considered a low index material with a typical refractive index of 1.45, while HfO₂, TiO₂, and Ta₂O₅ are high-index materials with typical refractive indices in the range 2.0-2.4.