Directionally scattered surface plasmon polaritons (SPPs) promote the efficiency of plasmonic devices by limiting the energy within a given spatial domain, which is one of the key issues to plasmonic devices. Benefitting from the magnetic response induced in high-index dielectric nanoparticles, unidirectionally scattered SPPs have been achieved via interference between electric and magnetic resonances excited in the particles. Yet, as the magnetic response in low-index dielectric nanoparticles is too weak, the directionally scattered SPPs are hard to detect. In this work, we demonstrate forward scattered SPPs in single low-index polystyrene (PS) nanospheres. We numerically illustrate the excitation mechanism of plasmonic induced electric and magnetic multipole modes, as well as their contributions to forward SPP scattering of single PS nanospheres. We also simulate the SPP scattering field distribution obtaining a forward-to-backward scattering intensity ratio of 50.26:1 with 1 μm PS particle. Then the forward scattered SPPs are experimentally visualized by Fourier transforming the real-space plasmonic imaging to k$k$-space imaging. The forward scattered SPPs from low-index dielectric nanoparticles pave the way for SPP direction manipulation by all types of nanomaterials.

中文翻译：

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单个低折射率介电纳米粒子的定向表面等离子体激元散射：模拟和实验

定向散射表面等离子体激元 (SPP) 通过限制给定空间域内的能量来提高等离子体器件的效率，这是等离子体器件的关键问题之一。受益于在高折射率介电纳米粒子中引起的磁响应，单向散射的 SPP 已经通过粒子中激发的电共振和磁共振之间的干涉实现。然而，由于低折射率介电纳米粒子的磁响应太弱，定向散射的 SPP 很难检测到。在这项工作中，我们展示了单个低折射率聚苯乙烯 (PS) 纳米球中的前向散射 SPP。我们用数值说明了等离子体诱导的电和磁多极模式的激发机制，以及它们对单个 PS 纳米球正向 SPP 散射的贡献。我们还模拟了 SPP 散射场分布，使用 1 μm PS 颗粒获得了 50.26:1 的前后散射强度比。然后通过傅立叶将真实空间等离子体成像变换为k$k$空间成像。来自低折射率介电纳米粒子的前向散射 SPP 为所有类型纳米材料的 SPP 方向操纵铺平了道路。