Electron beam source of narrow energy distribution

Abstract

An electron source is disclosed for generating a flow of electrons of substantially narrow energy distribution. Such a source may be incorporated into a cathode ray tube (CRT) where the beam of narrow energy electrons is modulated, as by a grid or other target element of the CRT; the current control characteristics of the CRT are dependent upon the energy distribution of the electron beam, and as the width of this distribution in the beam or flow of electrons is decreased, the sensitivity of the CRT is increased. In accordance with the teachings of this invention, the electron beam source includes a mirror element for critically absorbing incident electrons whose energy is above a predetermined value. Electrons whose energy is below the critical predetermined value are reflected from the mirror element to form an electron flow of a substantially uniform energy level. In an illustrative embodiment of this invention, the mirror element comprises a support layer upon which there is disposed a material, such as gold black, deposited in a smoke form and having a low secondary electron emission ratio. The critical predetermined value is related to the voltage difference between the cathode element for generating the electrons and the mirror element; this voltage difference is set to determine the energy level of those electrons reflected from the mirror element. Significantly, the electron source of this invention is capable of providing either a narrow or pencil beam of electrons, or a flood beam of electrons of substantially uniform energy.