The angluar reflectance of single-layer gradient refractive-index films

Abstract

Normal incidence measurements of single-layer gradient refractive-index antireflection films, produced by a chemical etch-leach process on glass sensitized by a phase-separating heat treatment, indicate very low reflection over a broad wavelength regime, 0.35–2.5 μm. First-surface measurements of the reflectance of the gradient index films have now been made, in the visible regime, at off-normal incidence (to 70°) using polarized light. These measurements show that significant reflection reduction is obtained even at high angles of incidence—5.7% reflectance from the filmed glass at 70° compared to 16.4% for the unfilmed glass. Furthermore, although the films exhibit a weak wavelength dependence at high angles, they continue to be effective over a broad spectral region. The optical properties observed are in good agreement with computations based on a gradient refractive-index film with a step at the air-film interface. The optical properties of the film offer considerable advantage over conventional interference films in many applications.