A new separator design for aberration corrected photoemission electron microscopes

Aberration correction of photoemission electron microscopes (PEEM) by electron mirrors requires use of a magnetic beam separator. Due to the stringent requirement on aberrations, such a device is a complex integrated magnetic system. The one that has been installed at BESSY II is essentially fixed in its optical properties hence very susceptible to problems caused by mechanical or magnetic imperfections. Here we present a separate function design that is simple to construct and fully adjustable, which allows more relaxed tolerances on alignment errors and power supply ripples. The simulation with realistic lenses shows that this design gives as good, if not better, a performance as the existing design.