METHOD FOR THE PREPARATION OF POROUS SILICA ANTIREFLECTION COATINGS VARYING IN REFRACTIVE-INDEX FROM 1.22 TO 1.44

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 mum with a 10-ns pulse length.