GB611440A - Method and apparatus for producing low reflection coatings on optical elements - Google Patents

Abstract

611,440. Low reflection coatings. KODAK, Ltd., and ORD, P. R. April 29, 1946, No. 12851. [Class 97 (i)] [Also in Group XL (a)] In a method of forming a low reflection coating on a glass surface, the chamber, in which the glass is placed, is evacuated and a hightension discharge is produced therein to start a low-tension discharge of longer path, whereby the glass surface is cleaned and the coating material is simultaneously, or subsequently, thermally evaporated on the said surface. Apparatus for carrying out this method comprises an evacuable chamber enclosing two pairs of electrodes, one of said pairs being connected across a condenser and a low-tension supply, while the other pair is connected to a very high-tension supply, means also being provided for vaporizing the coating material. One electrode may be common to both of said pairs. As shown, a support 11 for a bell jar 10 has an opening 12 leading to pumps for the evacuation of the chamber, which encloses lenses 13 to be coated as by magnesium fluoride, which is carried by a strip 25 connected with terminals 26, 27 leading to an electric supply. Separate from this supply is a low-tension supply which consists of a transformer 15 and a condenser 16 across the terminals of which are connected aluminium rods 17, 18, with tungsten inserts 19, 20 forming the low-tension electrodes. The high-tension electrodes 23 are enclosed in an evacuated casing 24 connected with a transformer 21 energized by A.C. Thus, the pressure in the chamber having been reduced to less than 0.005 mm. Hg., the intermittent high voltage spark across electrodes 23 is brought into operation to ionise the space between electrodes 19, 20 and allow of the intermittent discharge of the condenser, whereby the lens surfaces are electronically bombarded. Strip 25 may be heated to vaporize the magnesium fluoride during or after the electric discharge.