REFLECTION-REDUCING COATINGS FOR OPTICAL SURFACES.

Abstract : A study of a two-coat reflection-reducing film was made, particularly as regards the method of formation of these films and their properties. The preferred method of application was found to be the addition of portions of Solution no. 157c to glass disks while rotating at 4750 RPM followed by the application of Solution no. 50a (containing 5% butanol) at 2300-2500 RPM with a 15-minute baking at 100-105C after each addition of solution. The films so formed were uniform, clear and hard and very efficient in reducing reflection. A typical disk of 1.525 index glass coated with this system gave a reflection of 0.14% per surface of incident light of 5500 A wave length. The use of various silicon esters for the formation of single-coat films was studied and found to give, at best, films capable of reducing reflection of light from glass of 1.52 index to about 50% of its original value. The films prepared from methyl and ethyl silicates were hard, clear, water-repellent, and were the most effective esters in reducing reflection. Investigation of the use of various silicon compounds (Dow-Corning fluids 400 and 1300, dimethyl silicon dichloride and ethyl silicon trichloride) showed dimethyl silicon dichloride to be the only one capable of giving good nonwetting surfaces without harming the reflection-reducing properties of the films. (Author)