Analysis of electrostatic small-angle deflection

Electron beam aberrations resulting from deflection by two sets of similar, mutally perpendicular electrostatic deflectors have been studied. The analysis is applicable to the cases where the beam can be treated as a collection of noninteracting individual electrons deflected through a small angle by spatially smooth fields. The analysis shows that, with the types of electrostatic deflectors commonly used, anastigmatism cannot be achieved unless external corrections are employed.