Initial experiences with an electrostatic Ω-monochromator for electrons

An electrostatic electron monochromator has been designed, simulated and built. It consists of four hemispherical condensers providing 180° deflection each and leading to an Ω-shaped optic axis. Due to its high dispersion of 80 μm/eV a final energy width below 0.1 eV should be attainable with a standard slit having a width of some μm. The system is highly symmetric and thus should not introduce limiting aberrations. But the experimental results are not yet satisfactory. Operating the monochromator together with a Schottky emission gun we obtained up to now a reduction of the energy width to only 37%.