Fig. 3. Cathodoluminescence signature of plasmonic vortex.

a, b Finite-difference time-domain (FDTD) simulations of the electric-field amplitude a and phase b of a plasmonic vortex generated from a single dipole excitation at the origin of a spiral channel at a wavelength of 660 nm. c FDTD simulated far-field response of a plasmonic vortex transmitted through a plane 200 nm above the surface of the spiral for the same wavelength as in a and b showing the characteristic annular profile of a vortex beam. d The rastered and integrated far-field profile of the plasmonic vortex calculated via the far-field intensity profile from a dipole excitation is calculated for every position in a 40 × 40 array covering a 1 µm × 1 µm area around the origin of the spiral (closest direct analog to CL). e The CL response of the plasmonic vortex at 660 nm. In both the simulated d and experimental e rastered images, the pattern of concentric spiral arms emanating from the origin can be observed. Scale bar = 500 nm