Exclusive and efficient excitation of plasmonic breathing modes of a metallic nanodisc with the radially polarized optical beams

The plasmonic breathing modes of a metallic nanodisc are dark plasmonic modes and thus also have the advantage of much smaller radiation loss. These modes emerged previously in electron energy loss spectroscopy experiments and were then pursued with optical excitation methods. In this paper, through the finite element method type numerical simulations, we show evidence of the pure excitation of these modes under the illumination of two counter-propagating, radially-polarized optical beams. The obtained near-field spectrum of a single Au or Ag nanodisc shows the plasmonic resonant peaks at which the electric field distributions, as well as the plasmonic dispersion relationship both clearly exhibit the characteristics of the plasmonic breathing modes. We expect that the method that we have proposed, due to operating conveniently in the manner of far field excitation, will open many possibilities in practical applications based on the interaction between a single metal nanodisc with the radially polarized optical beam or between a metal nanodisc array with the beam array.