Plasmonic orbital angular momentum manipulation through light control
  Plasmonic vortices (PV) excited by a highly focused radially polarized optical vortex (RPOV) beam on a metal surface are investigated experimentally and theoretically. The proposed method reveals a direct phase singularity and orbital angular momentum (OAM) transfer from an incident structured beam to its counterpart in surface plasmon with dynamic, reconfigurable and high-efficiency advantages. The plasmonic field pattern, phase distributions, Poynting vector and focusing efficiency of PV are studied in detail. Experimental verification further shows that nanoparticles can be confined and manipulated within the region of PV and orbital rotation speed of the trapped particles is altered dynamically by changing the topological charge of the incident light. 
X.-C. Yuan, Z. J. Hu, G. H. Yuan, Z. Shen
physics.optics