Design and test of a lens system for a high energy and high resolution electron spectrometer

We describe the design and the laboratory test of an electrostatic input lens developed for high energy ( > 5 keV ) and high resolution photoelectron spectrometers. The lens is part of a hemispherical electron energy analyzer and is designed to optimize the overall accepted solid angle, taking into account the constraints due to the acceptance of the hemispherical dispersing element. In particular, the lens can be operated with two different polarization schemes enabling to obtain high and constant linear magnification ( M l = 12 and M l = 20 ) in a large interval of retarding factor ranging from an acceleration of 5 to a retardation of 600 (dynamical range of 3000) by the same mechanical layout. These features make such an electrostatic input element a considerable improvement in the technical challenge to perform high quality experiments in high energy photoemission.