Electron emitter with focussing arrangement

Claim 1

An electron emitter including: a body of material which has a plurality of projections forming field emitter zones, which zones are separated by regions having no substantial projections and are thus not field emissive; a foraminous extractor electrode arrangement adjacent the body for receiving an extractor potential to apply an electron extraction field to the projections to draw electrons from the projections; and a foraminous focus electrode arrangement for receiving a further potential and positioned on that side of the extractor arrangement remote from the body; means for applying the potentials to the electrode arrangements; the potential applying means being so arranged and the electrode arrangements being so positioned relative to one another and to the zones, that the electrode arrangements electrically interact to form a plurality of electric focussing fields to cause electrons drawn from respective ones of the zones to converge onto predetermined paths, each zone being aligned with corresponding openings in both the electrode arrangements and each said region being aligned with corresponding material portions of the electrode arrangements.