ENERGY-FILTERED IMAGING WITH ELECTROSTATIC OPTICS FOR PHOTOELECTRON MICROSCOPY

A simple first-order theory shows that energy-filtered imaging can be accomplished using spherical-sector capacitors without a restriction on the deflection angle of the sector. The geometrical requirements for placement of coupling lenses to achieve this result are derived using a virtual-image concept and are illustrated for the 90° and 180° sector cases. The dispersion of the sector capacitor introduces aberrations which affect the image quality. These aberrations are discussed analytically and with the aid of ray-tracings. It is found that these aberrations can be made small enough to be negligible in the practical operation of an energy-filtered photoelectron microscope. © 1990.