Some properties of symmetrical slit ("cylindrical") electron lenses

Abstract

The focal lengths of a series of symmetrical slit (cylindrical) electrostatic electron lenses are determined as a function of aperture size and applied potential. It is shown that all practical lenses may be represented on a single curve by means of a parameter simply related to potential and geometry. From this it is deduced that lens strength depends more on the size of the central aperture than on that of the outer apertures.