GB574056A - Improvements in electron lenses - Google Patents

Abstract

574,056. Electron lenses. KLEMPERER, O. E. H. April 8, 1942, No. 4628. [Class 39 (i)] An electron lens which has a line focus is formed of two tubular electrodes, the end of one electrode having a pair of projecting portions which extend further along the electron stream than the parts between them. The second electrode may have a complementary shaped end contiguous to the first electrode, or may be of larger diameter so as to surround the end of the first electrode. The cross-section of the tubes may be elongated, square or circular. Apertured electrodes in curved diaphragms may also be used. In one form, two box-like electrodes A, B, Fig. 1, have their opposed edges 3, 4 and 7, 8 curved semicircularly. The other edges 1, 2 and 5, 6 may be straight or curved reversely, as at A<1>, Fig. 7. In a modification, the opposing electrodes may be cylindrical, as at A<11>, Fig. 6. The developed view of the edge of one electrode may show a series of alternately arranged semicircles or smaller arcs of circles, or alternate straight and circular arcs ; the edge of the other electrode showing a complementary curve. The curves of opposing edges may, however, be of different radii. To reduce spherical aberration, the curves may not be arcs of circles, but may have a greater curvature at the centre than at the ends. In the forms shown in Figs. 6, 7, a single curved edge electrode A<1> or A<11> is inserted into a larger cylinder C, shielding being completed by shields 25. The lens may produce a diverging effect so that one or both of the focal lines are virtual. In Fig. 8, a shield electrode D is closed by a curved diaphragm 28 in which is a slot 29 ; the further electrode may have a complementary diaphragm. A parallel beam passing through the slot is focused to a line perpendicular to the longer edges of the slot. Specifications 458,599, 553,466 and 573,901 are referred to.