COMPUTATION OF OPTICAL-PROPERTIES OFF THE GAUSSIAN PLANE FOR ELECTRON-BEAM SYSTEMS

A new method has been developed for computing the electron-optical pro perties on and off the Gaussian image plane for an electron optical sy stem comprising any combination of magnetic and electrostatic lenses a nd deflectors. Formulae, with which the electron beam size and profile can be modelled in any image plane, have been derived to compute the general electron trajectories based on the third-order geometrical abe rrations and first-order chromatic aberration. The shapes and position s of the crossover in the object plane and of the final aperture are u sed as the initial conditions to define the electron beam, which enabl es estimation of the effects of the misalignments of the source and th e aperture. The electron distribution at the source has been taken int o account to calculate the images. Computer programs using the new for mulae have been developed. Some examples and discussions are presented in this paper.