Principle and basic design of omnidirectional photoelectron acceptance lens

We propose a +/- 90 degrees-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 2 pi-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 degrees. Some basic designs of the lens are presented. These designs allow for 2 pi-steradian photoelectron spectroscopy not only in the UPS regime, but also in the XPS regime, which may open new horizons in photoelectron spectroscopy. (C) 2020 The Japan Society of Applied Physics