Nanofocusing of Surface Plasmon Polaritons by the Tapered Metallic Plasmonic Waveguide: Optimal Angle Near the Apex

Abstract

Conditions for the optimal concentration of electromagnetic energy of the optical frequency at the apex of the sharp tapered metallic tips used as the surface plasmon polariton waveguide are considered. It is theoretically predicted that nanofocusing of the surface wave is optimal when singularity of the electric field of the focusing wave exists at the ideally sharp apex of the tip. For a given angle near the apex of the conical tip the frequency range, in which singularity of focused electric field exists in the vicinity of geometrically ideal apex, is found. The character of this singularity is analyzed. Analogously, for a given frequency of the surface plasmon polaritons the range of angles for which singularity of electric field exists at the tip’s apex is found.