Angle-Resolved Cathodoluminescence Interferometry of Plasmonic and Dielectric Scatterers

We demonstrate angle-resolved cathodoluminescence (CL) interferometry from electron-beam-excited plasmonic and dielectric nanostructures placed above a Au-coated substrate. We use 20-30 keV electrons to coherently excite plasmon-mediated radiation, which interferes with its mirror image, providing a method to determine the particle-substrate spacing. In an aloof excitation geometry, transition radiation emitted from the Au substrate adds to the interferogram and provides a means to probe the electron traveling time. The measured CL interferograms are in excellent agreement with a scattering and interferometry model in which a single electron coherently launches plasmons at two separate locations. Polarization-resolved CL measurements confirm the interferometric scattering model. Electron-excited Si Mie scatterers show interferograms modulated with resonantly enhanced emission. CL interferometry enables accurate measurement of critical distances in nanoscale geometries, in particular along the electron-beam direction, which are not easily accessible in electron microscopy, while offering a platform for studying optical interference in complex geometries.