Toroidal multipoles, together with electric and magnetic multipoles, provide a complete description of electromagnetic responses of matter. The fundamental toroidal resonance has been extensively achieved and investigated in nanooptics, showing great ability to increase light absorption and light force. In this paper, we obtained plasmonic toroidal dipole resonance in core-shell (dielectric-core/gold-shell) nanodisk and demonstrated an enhanced second harmonic generation (SHG) from this resonance. It was shown that the toroidal dipole resonance based SHG depends on the refractive index of dielectric-core. For large refractive index cases, head-to-tail magnetic dipole pairs form a close loop, which is a signature of toroidal dipole and results in the enhancement of SHG. In addition, the frequency of this SHG red shifts as the refractive index of dielectric-core increases. We also investigated the cases in which the dielectric-core is filled with several common materials. Moreover, the toroidal resonance based SHG depends on both inner and outer radius of the core-shell nanodisk. Such results may serve for the developments of nonlinear nanooptics and their applications.

中文翻译：

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核壳纳米盘中等离子体环形谐振的二次谐波产生增强


环形多极子与电和磁多极子一起提供了物质电磁响应的完整描述。基本环形共振已在纳米光学中得到广泛实现和研究，显示出增加光吸收和光力的巨大能力。在本文中，我们在核壳（电介质核/金壳）纳米盘中获得了等离子体环形偶极子共振，并证明了该共振增强的二次谐波产生（SHG）。结果表明，基于二次谐波的环形偶极子谐振取决于介质芯的折射率。对于大折射率的情况，头尾磁偶极子对形成闭环，这是环形偶极子的特征，并导致倍频增强。此外，随着介质芯折射率的增加，SHG 的频率会发生红移。我们还研究了电介质芯填充几种常见材料的情况。此外，基于环形谐振的二次谐波取决于核壳纳米盘的内半径和外半径。这些结果可能有助于非线性纳米光学及其应用的发展。