Method for the preparation of porous silica antireflection coatings varying in refractive index from 122 to 144

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Abstract
Coatings of refractive index that vary between 1.22 and 1.44 were prepared from combinations of a colloidal silica suspension and a polysiloxane solution. The polysiloxane acted both as a binder and a filler for the colloidal silica particles. Increasing ratios gave coatings of lower porosity, hence higher refractive index, and better abrasion resistance. This variation in refractive index allowed high-efficiency quarter-wave antireflection coatings to be prepared on substrates whose index varied from 1.45 to 2.1. The laser damage thresholds of all the coatings were > 50 J/cm2 at a wavelength of 1.06 μm with a 10-ns pulse length.