KENBIKYO Vol.51▶No.3 2016
â– Lectures

On the Design of Electron Lenses 1

Shin Fujita and Yoichi Ose

Abstract: A survey on electron lens designing methods is presented in two consecutive articles. The present article comprises the first part and discusses the optics aspect of the lens design. In electron optics the electromagnetic potential plays the role of refractive index in ordinary light optics. The electron optics design is to construct an appropriate potential distribution under a strong constraint that it must satisfy the Laplace equation. The basic strategy to realize good lenses has been to have as short a focal length as possible in order to suppress inevitable aberration effects. We explain the designing principles for achieving short focal lengths. An efficient lens design method that combines the optical parameters obtained from the paraxial trajectory calculation and the emittance diagram representation is presented as well. The sequel article will give example designs of short focal length lenses together with the engineering techniques for their implementations.

Key words: Electromagnetic potential, refractive index, optical parameters, emittance diagram, focal length