Principle and basic design of omnidirectional photoelectron acceptance lens

Abstract

Abstract We propose a ±90°-acceptance spherical aberration-corrected electrostatic lens based on the cathode lens technique used in photoemission electron microscopy. This lens, which we call “omnidirectional photoelectron acceptance lens (OPAL)”, is aimed at realizing 2π-steradian photoelectron spectroscopy in a wide energy range. For this lens, modifications of a simple cathode lens were studied in detail by ray-tracing calculations. Then, modified cathode lenses were combined with a decelerating mesh lens in order to achieve a focusing lens with a full acceptance angle of ±90°. Some basic designs of the lens are presented. These designs allow for 2π-steradian photoelectron spectroscopy not only in the UPS regime, but also in the XPS regime, which may open new horizons in photoelectron spectroscopy.