title: Plasmonic lens made of multiple concentric metallic rings under radially polarized illumination.
abstract: Optimal plasmonic focusing can be achieved through matching the rotational symmetry of the plasmonic lens to the polarization symmetry of a radially polarized illumination. In this letter, we report the experimental confirmation of the focusing properties and field enhancement effect of plasmonic lens made of multiple concentric annular rings using a collection mode near field scanning optical microscope. Surface plasmons excited at all azimuthal directions propagate toward the geometric center and constructively interfere at the focus to create a strongly enhanced evanescent optical "needle" field that is substantially polarized vertically to the plasmonic lens surface. The field enhancement factor can be improved through adding more rings while maintaining the plasmonic focal spot size. Strategy for optimizing the field enhancement factor is studied with both analytical and numerical methods.
authors.affiliation: Electro-Optics Graduate Program, University of Dayton, 300 College Park, Dayton Ohio 45469, USA.
authors.forename: Weibin
authors.initials: W
authors.lastname: Chen
authors.forename: Don C
authors.initials: DC
authors.lastname: Abeysinghe
authors.forename: Robert L
authors.initials: RL
authors.lastname: Nelson
authors.forename: Qiwen
authors.initials: Q
authors.lastname: Zhan
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D007909:Lenses; D008029:Lighting / Q000295:instrumentation*; D008670:Metals / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology / Q000295:instrumentation*; D012031:Refractometry / Q000295:instrumentation*; D020349:Surface Plasmon Resonance / Q000295:instrumentation* / Q000379:methods
chemical_list: D008670:Metals