Charged particle energy analyzers

A charged particle energy analyzer comprising two electrodes, said two electrodes defining a gap therebetween, means for producing a substantially inverse square electric field in said gap between said two electrodes such that the analyzer acts as a spherical mirror analyzer, an object plane of the analyser located in a substantially field free region closer to the center of curvature of the equipotentials of the inverse square electric field than said gap between the two electrodes, and means for producing a charged particle image of a sample on to said object plane, wherein the analyzer includes a baffle means disposed in said gap between the electrodes, such that the baffle means restricts the energies of the charged particles transmitted by the analyzer, at least part of the baffle means being positioned so as to reduce the dependence of the energies of the charged particles transmitted by the baffle means on the position of the particles within the image, and a detector means effective to detect charged particles at least partially transmitted through the analyser.