Mesh-based semitransparent photocathodes.

Semitransparent photocathodes consisting of vacuum-deposited layers of CsI on electroformed nickel meshes with 40 and 60 lines/mm spacing have been investigated for applications in vacuum-ultraviolet electronic imaging devices. These photocathodes are found to have about half the quantum yield of an opaque CsI photocathode, but a factor of 2 to 3 greater quantum yield than a conventional semitransparent CsI photocathode. The limitations of window materials on short-wavelength spectral response, and their disadvantages in an energetic charged-particle environment, are eliminated. Unlike conventional opaque photocathodes, the mesh photocathodes can be used interchangeably with conventional semitransparent photocathodes in a wide variety of electronic imaging devices. Tests of mesh photocathodes in laboratory electrographic cameras indicate that best results for most applications are obtained if the output electron image has a somewhat poorer resolution than that corresponding to the mesh spacing.