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.
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