Electron Beam Excited Surface Plasmon Polaritons Carrying Orbital Angular Momentum

A method to generate surface plasmon polaritons (SPP) carrying orbital angular momentum (OAM) is proposed. Here the electrons beam is rotating around the nanowire as well as going along it at the same time. As the trace of the electron beam is chiral, the SPP it generate can be chiral as well, enabling it to carry OAM with specific topological charge, on condition that the speed of electron matches the phase speed of light. When multiple synchronous electron sources exist, electromagnetic modes whose symmetry match that of electron sources can be additionally strengthened, possible increase the suppression ratio to other modes.