Geometric aberrations in cylindrically symmetric electrostatic lenses

Abstract

Using a computer model of a two cylinder electrostatic lens, some novel relationships have been found to exist between the input and output parameters of meridional rays. These relationships have been developed and used to show that, for a wide range of practical lens geometries, it is possible to represent all the third and fifth order aberrations in terms of just two of the normal parameters. Formulae have been derived to describe some of the quantities associated with this type of lens defect and the problems of minimising the aberrations are discussed.