A sorter for electrons based on magnetic elements

The orbital angular momentum (OAM) sorter is an electron optical device for the measurement
of an electron's OAM. It is based on two phase elements, which are referred to as an \unwrapper"
and a \corrector"and are located in Fourier conjugate planes. The simplest implementation
of the sorter is based on the use of electrostatic phase elements, such as a charged needle for
the unwrapper and electrodes with alternating charges or potentials for the corrector. Here,
we use a formal analogy between phase shifts introduced by charges and vertical currents to
propose alternative designs for the sorter elements, which are based on phase shifts introduced
by magnetic elds. We use this concept to provide a general guide for phase element design,
which promises to provide improved reliability of phase control in electron optics.