Electron vortex beams for chirality probing at the nanoscale

Abstract: In this work we propose a method for probing the chirality of nanoscale electromagnetic near fields utilizing the properties of a coherent superposition of free-electron vortex states in electron microscopes. Electron beams optically modulated into vortices carry orbital angular momentum, thanks to which they are sensitive to the spatial phase distribution and topology of the investigated field. The sense of chirality of the studied specimen can be extracted from the spectra of the electron beam with nanoscale precision owing to the short picometer de Broglie wavelength of the electron beam. We present a detailed case study of the interaction of a coherent superposition of electron vortex states and the optical near field of a golden nanosphere illuminated by circularly polarized light as an example, and we examine the chirality sensitivity of electron vortex beams on intrinsically chiral plasmonic nanoantennae.