Electron beam characteristics inferred using experimental lens transmission through a pair of apertures

Many spectroscopic applications of electron optics require an experimental verification of the electron beam characteristics under typical experimental conditions. Electron trajectory calculations in the gaussian approximation are not adequate for this purpose. A simple method is presented by which experimentally determined curves of the lens throughput as a function of the lens potentials can be analyzed using electron trajectory calculations which include spherical aberration. Good agreement between the calculated and observed transmission through a double aperture allows the inference of electron beam parameters such as the maximum angle of beam divergence at the exit or entrance of the lens, or the location and size of the image. As an example, the properties of the transport lens used in an LEED electron polarimeter are determined.