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Antireflective graded index silica coating, method for making

  • US 4,535,026 A
  • Filed: 06/29/1983
  • Issued: 08/13/1985
  • Est. Priority Date: 06/29/1983
  • Status: Expired due to Fees
First Claim
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1. A radiation-transmitting non-porous vitreous substrate of predetermined refractive index having coated on at least one surface thereof a substantially non-reflecting coating which functions effectively over a predetermined wide band of radiations, said non-reflecting coating comprising:

  • a single silica layer overcoated on said non-porous substrate and having an exposed surface, the thickness of said silica layer as measured between the exposed surface thereof and the silica layer-substrate interface being generally uniform and in the range of from about 150 nm to about 600 nm with the silica layer displaying throughout its thickness at least ome degree of porosity, and the porosity of said overcoated silica layer together with the non-porous nature of said substrate forming a defined interface therebetween;

    all of said silica layer consisting essentially of silica except for other glass-forming constituents which may diffuse from said substrate and into said silica layer proximate said layer-substrate interface during the forming-processing of said silica layer on said substrate;

    that portion of said silica layer which is immediately proximate the exposed surface thereof displaying the highest degree of porosity and the porosity of said silica layer gradually decreasing from the exposed surface thereof to a depth which is at least about one-quarter of the longest wavelength of said predetermined wide band of radiations to provide a graded degree of porosity which decreases as the distace from the exposed surface thereof increases;

    that portion of said silica layer which is immediately proximate the exposed surface thereof having an index of refraction which approaches unity, and that portion of said silica layer which is immediately proximate the interface between said silica layer and said substrate having an index of refraction which approaches that of said substrate; and

    the size of the individual pores in said silica layer being sufficiently small that radiations impinging upon the exposed surface of said silica layer are transmitted therethrough without being significantly scattered.

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