Interaction of electron vortices and optical vortices with matter and processes of orbital angular momentum exchange

摘要

The quantum processes involved in the interaction of matter with, separately, an electron vortex (EV) and annoptical vortex (OV) are described, with matter modeled in terms of a neutral two-particle atomic system, allowingnfor both the internal (electronic-type) motion and the gross (center-of-mass-type) motion of matter to be takenninto account. The coupling of the atomic system to the EV is dominated by Coulomb forces, while that of the OVnis taken in the p · A canonical form which couples A, the transverse vector potential of the optical vortex, to thenlinear momenta of the two-particle system. An analysis of the dipole active transition matrix element is carriednout in each case. The electron vortex is found to be capable of exchanging its orbital angular momentum (OAM)nwith both the electronic and the center-of-mass motions of the atomic system in an electric dipole transition. Inncontrast, for electric dipole transitions the optical vortex is found to be capable of exchanging OAM only withnthe center of mass. The predictions are discussed with reference to recent experiments on electron-energy-lossnspectroscopy using EVs traversing magnetized iron thin-film samples and those involving OVs interacting withnchiral molecules.