Projection cathode ray tube

Abstract

A high-quality projection cathode ray tube is for projecting the image, displayed on a fluorescent surface, as an enlarged image on a screen in front of the fluorescent surface through a projection lens disposed at a given distance ahead. On the inner surface of a face panel, a multilayer optical interference film including optical thin film layers of alternately superimposed high refractive and low refracte index material is provided. The outermost surface of the multilayer optical interference film is coated with a film of an inorganic material such as silicon dioxide which is optically transparent and stable with respect to the impact of an electron beam. The thickness of the transparent film is not less than 1.0 .mu.m. Even an electron beam having a high energy which has passed through the gaps of the phosphor layer loses the energy in this protective film. Thus, the projection cathode ray tube is capable of reducing the deterioration of the light output with time, by suppressing the browning phenomenon of the glass surface of the face panel and the multilayer optical interference film.

Dependencies are inferred from the claim text.