Analysis of surface plasmon polariton nanofocusing by asymmetric metal-coated dielectric probe: Partial metal-coating

For the purpose of developing the probe using surface plasmon polariton (SPP) nanofocusing that is valid for incident linearly polarized (LP) wave, the partially metal-coated dielectric conical probe is investigated numerically by the volume integral equation. It is found that it possible to perform SPP nanofocusing using this probe for incident LP Gaussian beam in addition to incident radially polarized (RP) beam. The basic characteristics of the strongly localized and enhanced optical near-fields on the tip of the probe and optical intensities inside the probe are investigated. For the incident LP beams, it is found that the optimum structure of the partially metal-coated dielectric probe exists. For the case of incident RP beam, partial metal-coating of the probe degrades the characteristic of nanofocusing, i.e., fully metal-coated conventional probe is the optimum shape for incident RP beam.