Abstract
High-performance two-electrode electron gun lens designs with lower spherical and chromatic aberration coefficients than the Butler gun are presented. It is shown that the Butler gun is a specific solution to the general class of one-interval polynomial lenses of degree three. It is found that the higher-order (> 3) polynomial lenses have equipotential angles at the saddle points which differ from 54°44′08″. Reductions in aberration disks of 60% are possible using the new lenses instead of the Butler gun. Retarding-mode performance of the lenses is considered for potential application to low voltage microscopy. A simple design of a scanning gun microscope is considered.
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