Second Harmonic Generation Enhancement from Plasmonic Toroidal Resonance in Core-Shell Nanodisk

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.