Plasmonic Particle-on-Film Nanocavity in Tightly Focused Vector Beam: a Full-Wave Theoretical Analysis from Near-Field Enhancement to Far-Field Radiation

摘要: Based on the local electric field enhancement of gap-mode surface plasmon resonance, plasmonic particle-on-film nanocavity (PPoFN) can realize Raman signal multiple orders magnitude, even single molecule detection. The tightly focused radially polarized (Bessel-Gaussian) beam (TFRPB), containing a cylindrical symmetry longitudinal component, is superior excitation source for PPoFN to generate more intriguing electromagnetic hot spot in gap. For optical response TFRPB, some theoretical and experimental studies at certain wavelength have been reported, but full-wave analysis about near- far-field properties still lacking because it difficult achieve dispersion-free confocal light experiment. In this paper, we analyze TFRPB by using numerical simulation with finite element method (FEM). comparison, linearly (Gaussian) (TFLPB) also implemented. comprehensive results enhancement, nanofocusing property, radiation, found that strongest toroidal dipole (TD) mode good performance Importantly, result will provide reference application vector beam.