Single-layer, gradient refractive index antireflection films effective from 035 to 25 μ

TLDR

The broadband antireflection film is a single, porous, silica‑rich skeletal layer. The study proposes using these films in applications such as solar energy devices. The films are fabricated by chemically etching/leaching phase‑separated glasses, with optical properties tuned by the temperature and time of both the heat treatment and the etch/leach step. The films achieve reflectance below 0.5 % across 0.35–2.5 µm, and steeper refractive index gradients—and thus lower reflectance—are obtained when phase separation and etch/leach are performed at higher temperatures.

Abstract

Gradient refractive index antireflection films are produced by a chemical etch/leach process applied to glasses sensitized by a phase-separating heat treatment. The reflectance (two surfaces) is effectively reduced from ~ 8% to < 1/2% in the wavelength regime 0.35–2.5 μ. The broadband antireflection film consists of a single, porous, skeletal layer made up largely of silica. The optical properties of the film are shown to depend on the time, temperature parameters of the phase-separating heat treatment, as well as the time, temperature parameter of the film-forming etch/leach treatment. The properties of films produced under different process conditions are correlated in a fashion that suggests that progressively steeper refractive index gradients are obtained for samples phase separated and formed at higher temperatures. A number of applications for these films are suggested, including solar energy devices.