Approach for simultaneous measurement of two-dimensional angular distribution of charged particles: Spherical aberration correction using an ellipsoidal mesh

An approach for simultaneous measurement of two-dimensional angular distribution of charged particles is proposed. This concerns spherical aberration correction in electrostatic lenses with potential use of a mesh. In an earlier work, an effective use of a spherical mesh has succeeded to obtain a large acceptance angle limited to around 60° (±30°). The present work is aimed at dramatically increasing acceptance angles limited in conventional lenses. For this purpose, spherical aberration behavior of mesh lenses is studied in detail using an analytical approximation and ray tracing, with particular attention paid to the effect of the mesh shape. It is shown here that the lens ability to correct spherical aberration over wide aperture angles can be effectively enhanced by the ellipsoidal deformation of a spherical mesh. We demonstrate that an effective use of an ellipsoidal mesh provides remarkable performance characteristics for electrostatic lenses, which opens new possibilities in surface and materials analysis techniques. Simple examples of ellipsoidal mesh lenses are presented that allow very wide acceptance angles of up to 120°.