Abstract: An improved electrostatic electron lens for photoelectron emission microscopes is disclosed, having a planar upper surface on its beam entrance electrode highly polished to a mirror finish for light reflection. The lens is positioned between a light source and a specimen holder such that light may be reflected off the planar upper surface of the entrance electrode onto the specimen for causing photoemission of electrons from such specimen. The lens is constructed to enable expansion of the lens electrodes during heating, such as "bake-out" to remove adsorbed gases, without breaking the insulators between such electrodes. An intermediate electrode is disposed in a spaced, insulated relationship between the beam entrance electrode and an exit electrode by two insulator members.