  We propose a method for sorting electrons by orbital angular momentum (OAM).
Several methods now exist to prepare electron wavefunctions in OAM states, but
no technique has been developed for efficient, parallel measurement of pure and
mixed electron OAM states. The proposed technique draws inspiration from the
recent demonstration of the sorting of OAM through modal transformation. We
show that the same transformation can be performed with electrostatic electron
optical elements. Specifically, we show that a charged needle and an array of
electrodes perform the transformation and phase correction necessary to sort
orbital angular momentum states. This device may enable the analysis of the
spatial mode distribution of inelastically scattered electrons.

Instrumentation and Detectors;Optics;Quantum Physics