  We have experimentally demonstrated different operating modes for the front
lenses of the momentum microscopes described in Part I. Measurements at
energies from vacuum UV at a high-harmonic generation (HHG)-based source to the
soft and hard X-ray range at a synchrotron facility validated the results of
theoretical ray-tracing calculations. The key element is a ring electrode
concentric with the extractor electrode, which can tailor the field in the gap.
First, the gap-lens-assisted extractor mode reduces the field strength at the
sample while mitigating image aberrations. This mode gave good results in all
spectral ranges. Secondly, by compensating the field at the sample surface with
a negative voltage at the ring electrode we can operate in zero-field mode,
which is beneficial for operando experiments. Finally, higher negative voltages
establish the repeller mode, which removes all slow electrons below a certain
kinetic energy to eliminate the primary contribution to the space-charge
interaction in pump-probe experiments. The switch from extractor to repeller
mode is associated with a reduction in the k-field-of-view (10-20 % at
hard-X-ray energies, increasing to ~50% at low energies). Real-space imaging
also benefits from the new lens modes as confirmed by ToF-XPEEM imaging with
650 nm resolution.
