Color selective filters

Abstract

A color selective filter in the form of a holographic reflector is produced by a method which includes the step of exposing a photosensitive film of gelatine to a monochromatic laser beam. In order to obtain acceptably short exposure times and to enable substantially the whole of the available laser light to be utilized, a relatively narrow laser beam is sequentially scanned across the surface area of the gelatine film in a scanning pattern which consists of a large number of parallel straight lines. The diameter of the laser beam spot is very large as compared with the spacing between adjacent line scans. In this way each point on the gelatine film is scanned a very large number of times. The laser beam 8 is generated by a laser 7 and deflected by two movable mirrors 10 and 11, which are controlled so that the beam scans the whole of the gelatine film 1.

Dependencies are inferred from the claim text.