Measuring Plasmonic Dichroism with Electron Vortex Beams

Plasmonic circular dichroism has been demonstrated in clusters of metallic nanoparticles with chiral structure by measuring the difference in absorption spectra between right and left circularly polarized light, but is limited in the energy scales it can probe and spatial resolution it can achieve. Electron vortex beams, which carry quantized amounts of orbital angular momentum, can be realized in transmission electron microscopes. These vortex beams can probe excitation energies ranging from meV to keV and can achieve atomic resolution. Recently, simulations have shown that metallic nanoparticles with a chiral structure can exhibit a dichroic signal resolvable with electron energy loss spectroscopy when excited with right- and left-handed electron vortex beams analogous to the circular dichroism displayed with optical spectroscopies using polarized light. Here we present initial experimental results and further simulations showing intrinsic and extrinsic dichroism in chiral nanoparticle structures and their dependence on the amount of orbital angular momentum being transferred from electron vortex beams to plasmon modes.