A TANDEM 4-ELEMENT LENS SYSTEM FOR SURFACE ELECTRON-SPECTROSCOPY

Electron ray tracing studies and experimental tests of a tandem four-element lens system are presented. The lens system operates over a 0-400-eV energy range and is suited for applications such as angle-resolved photoemission spectroscopy and inelastic electron scattering spectroscopy requiring high energy and angular resolution. Each four-element lens of the tandem lens system can be operated in a zoom lens mode in which both the position and linear magnification of the image remain constant over a wide range of deceleration ratios. Performance characteristics including lens transmission, angular acceptance properties as a function of deceleration ratio, and operating voltages for the lens elements are evaluated analytically and by electron ray tracing analysis. Empirical tests of the lens system incorporated into an inelastic electron scattering spectrometer are compared with predicted performance. Comparison of four-element lens properties with corresponding properties of three-element lenses are also presented.