First Generation of Vortex Plasmons via Vortex-Beam End-Fire Coupling

Surface plasmon polaritons (SPPs) carrying an orbital angular momentum were first obtained at a cylindrical brass-ZnS-air interface due to the diffraction of perfect vortex beams at the front end of a cylinder. The beams with a wavelength of 141 µm resulted from the transformation of a Gaussian beam of a free electron laser using a binary axicon and a lens. The propagation of rotating plasmons along an axisymmetric surface over a distance of 70 mm and their diffraction at the rear end of a cylindrical transmission line with conservation of the topological charge of the diffracted free wave were demonstrated.