Efficient Measurement of the Orbital-Angular-Momentum Spectrum of an Electron Beam via a Dammann Vortex Grating

Orbital angular momentum (OAM) of electrons in free space must be omnipresent, but unfortunately we lack efficient equipment and techniques to measure the OAM state of an electron beam. This work demonstrates that a nanofabricated diffraction grating can be used as a device to address this problem. The authors present a protocol for obtaining an electron beam's OAM spectrum, and experimentally demonstrate how this approach can be used in a variety of applications, including those with magnetic materials. The results will have an impact on a great range of studies of electron OAM, and of other quantum waves, too.