Cathode-ray tube having indexing strips on the screen for determining the position of the electron beam

Claim 1

An improved cathode ray tube apparatus comprising: a. an evacuated envelope having a window portion; b. a fluorescent screen located within said envelope at said window portion and comprising a plurality of phosphor strips characterized in that various ones of said strips luminesce in different colors in response to electron impingement, said screen further comprising an electron permeable light reflecting layer disposed over the side of said phosphor strips remote from said window, and a number of discrete indexing strips disposed on said light reflecting layer and emitting radiation in response to electron impingement thereon; c. means for directing a scanning electron beam to said screen; and d. means for indexing said electron beam on said screen, said means comprising a pick-up element responsive to and arranged to receive radiation emitted from said indexing strips, the axis of said pick-up element intersecting said screen at an imaginary point, wherein the improvement comprises: said indexing strips having individual widths increasing with increasing distance from said imaginary point in the direction toward the edge of said screen, the axes of said phosphor strips and said indexing strips being transverse to the scanning direction of said electron beam.