GB573901A - Improvements in electron lens systems - Google Patents

Abstract

573,901. Electron lenses. KLEMPERER, O. E. H. March 24, 1942, No. 3922. [Class 39 (i)] An electron lens for focusing a beam, preferably ribbon-shaped, into a straight line, comprises a pair of electrodes on opposite sides of the beam, the opposed edges of which define a passage of elongated cross-section for the beam, and the separation of the edges diminishes towards their ends. By appropriate choice of the shape of the edges it is possible to focus into a straight line a flat beam which approaches within a distance of the ends of the edges which is less than the maximum separation of the edges. The electrodes may co-operate with another similarly shaped pair of electrodes spaced axially therefrom. The edges 11, 12, Fig. 4, may be joined to form a single closed tubular member giving complete shielding of the beam. The shape of these edges is found empirically by passing beams at different distances x1, x2, x3 from the centre x0 of a box-shaped electrode 19, determining the focal length and the ratio of this focal length to the focal length of a central beam, and diminishing the separations in the same ratio to the values yl, y2, y3. The ends 16 may be cut off by flat sides. The edges may also form the edges of an aperture in a diaphragm 20, Fig. 6, on the end of a shielding tube, the shape being obtained by strips 25 welded across the corners to give an empirically determined correction at two distances from x0. The shape thus determined would be punched out for massproduction. Reference has been directed, by the Comptroller to U.S.A. Specification 2,058,482.