Dark Plasmon Modes in Symmetric Gold Nanoparticle Dimers Illuminated by Focused Cylindrical Vector Beams

作者：Tian‐Song Deng, J. A. Parker, Yuval Yifat, Nolan Shepherd, Norbert F. Scherer · 发表于：The Journal of Physical Chemistry C · 年份：2018 · DOI：10.1021/acs.jpcc.8b10415 · 被引用次数：55 · 研究领域：Gold and Silver Nanoparticles Synthesis and Applications、Plasmonic and Surface Plasmon Research、Orbital Angular Momentum in Optics

The plasmon hybridization model of electromagnetic coupling between plasmonic nanoparticles predicts the formation of lower energy “bonding” and higher energy “antibonding” modes in analogy with the quantum mechanical description of chemical bonding. For a symmetric metallic nanoparticle dimer excited by linearly polarized light, the hybridization picture predicts that in-phase coupling of the dipole moments is optically allowed, creating bright “modes”, whereas the out-of-phase coupling is dark due to the cancellation of the oppositely oriented dipole moments (in the quasistatic approximation). These bright modes are electric dipolar in nature and readily couple to scalar (i.e., linearly or circularly polarized) beams of light. We show that focused cylindrical vector beams, specifically azimuthally and radially polarized beams, directly excite dark plasmon modes in symmetric gold nanoparticle (AuNP) dimers at normal incidence. We use single-particle spectroscopy and electrodynamics simulations to study the resonance scattering of AuNP dimers illuminated by azimuthally and radially polarized light. The electric field distributions of the focused azimuthal or radial beams are locally polarized perpendicular or parallel to the AuNP dimer axis, but with opposite directions at each particle. Therefore, the associated combinations of single-particle dipole moments are out-of-phase, and the excitation (resonance) is of so-called “dark modes”. In addition, multipole expansion of the...