  Control of the angular momentum of light is a key technology for
next-generation nano-optical devices and optical communications, including
quantum communication and encoding. We propose an approach to controllably
generate circularly polarized light from a circular hole in a metal film using
an electron beam by coherently exciting transition radiation and light
scattering from the hole through surface plasmon polaritons. The circularly
polarized light generation is confirmed by fully polarimetric four-dimensional
cathodoluminescence mapping where angle-resolved spectra are simultaneously
obtained. The obtained intensity and Stokes maps show clear interference
fringes as well as almost fully circularly polarized light generation with
controllable parities by electron beam position. By applying this approach to a
metal film with three holes, a vortex field with a phase singularity is
visualized in the middle of the holes.
