Selective excitation and enhancement of multipolar resonances in dielectric nanospheres using cylindrical vector beams
Selective excitation and enhancement of multipolar resonances in dielectric nanospheres using cylindrical vector beams
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DOI：
10.1063/1.5132791
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发表时间：
2020-01-21
影响因子：
3.2
通讯作者：
Fujii, Minoru
中科院分区：
文献类型：
--
作者：
Manna, Uttam;Sugimoto, Hiroshi;Fujii, Minoru
高折射率介电纳米结构中两个或多个共振之间的复杂相互作用的共振激发和操纵为工程新的光学现象和应用提供了巨大的机会。然而，困难往往出现时，解释所观察到的光谱，因为重叠的宽共振贡献的许多因素，如颗粒的大小，形状和背景指数。因此，选择性激发光谱上相互重叠的共振提供了一个通往更好地理解复杂相互作用的途径。在这里，我们展示了选择性激发和增强的多极共振的硅纳米球使用圆柱矢量光束（CVB）与不同直径的纳米球和数值孔径（NA）的激发。通过结合单粒子光谱和电动力学模拟，我们表明，径向偏振光束可以选择性地激发电多极子，而方位角偏振光束可以选择性地激发磁多极子，即使多极共振卷积在一起，由于其光谱重叠。此外，聚焦具有高NA的CVB可以导致电场或磁场的主导纵向极化。我们发现，增强的纵向极化与增加NA的径向和方位偏振光束可以选择性地增强电和磁多极共振，分别。我们的方法可以用作光谱学工具，以增强和识别多极共振，从而更好地了解其他电介质纳米结构中的光-物质相互作用，以及作为第一步，通过打破纳米结构的对称性，激发电介质低聚物中的暗模式和Fano共振。由AIP Publishing授权出版。
Resonant excitation and manipulation of complex interactions among two or more resonances in high-index dielectric nanostructures provide great opportunities for engineering novel optical phenomena and applications. However, difficulties often arise when interpreting the observed spectra because of the overlap of the broad resonances contributed by many factors such as particle size, shape, and background index. Therefore, selective excitation of resonances that spectrally overlap with each other provides a gateway towards an improved understanding of the complex interactions. Here, we demonstrate selective excitation and enhancement of multipolar resonances of silicon nanospheres using cylindrical vector beams (CVBs) with different diameters of nanospheres and numerical apertures (NAs) of the excitations. By combining single particle spectroscopy and electrodynamic simulations, we show that the radially polarized beam can selectively excite the electric multipoles, whereas the azimuthally polarized beam can selectively excite the magnetic multipoles even though multipolar resonances are convoluted together due to their spectral overlap. Moreover, focusing the CVBs with high NA can lead to a dominant longitudinal polarization of the electric or magnetic field. We show that the enhanced longitudinal polarization with increasing NA of the radially and azimuthally polarized beams can selectively enhance the electric and magnetic multipolar resonances, respectively. Our approach can be used as a spectroscopy tool to enhance and identify multipolar resonances leading to a better understanding of light-matter interactions in other dielectric nanostructures as well as serve as a first step toward excitation of dark mode and Fano resonances in dielectric oligomers by breaking the symmetry of the nanostructures. Published under license by AIP Publishing.