  In optics, mode conversion is an elegant way to switch between Hermite
Gaussian and Laguerre Gaussian beam profiles and thereby impart orbital angular
momentum onto the beam and to create vortices. In optics such vortex beams can
be produced in a setup consisting of two identical cylinder lenses. In electron
optics, quadrupole lenses can be used for the same purpose. Here we investigate
generalized asymmetric designs of a quadrupole mode converter that may be
realized within the constraints of existing electron microscopes and can steer
the development of dedicated vortex generators for high brilliance electron
vortex probes of atomic scale.
