Resonant excitation and manipulation of high-index dielectric nanostructures (such as Silicon, Germanium) provide great opportunities for engineering novel optical phenomena and applications. Here, we report selective excitation and enhancement of multipolar resonances, and non-radiating optical anapoles in silicon nanospheres using cylindrical vector beams (CVBs). Our approach can be used as a spectroscopy tool to enhance and identify multipolar resonances as well as a straightforward alternate route to excite electrodynamic anapoles at the optical frequencies.
Nonradiating anapoles are superposition of internal modes that can act as an energy reservoir by reducing the far-field scattering. We report experimental excitation of the electrodynamic anapole mode in isotropic silicon nanospheres at the optical frequencies using radially polarized beam illumination. The superposition of equal and out-of-phase amplitudes of the Cartesian electric and toroidal dipoles produces by a pronounced dip in the scattering spectra with the scattering intensity almost reaching zero – a signature of anapole excitation. The total scattering intensity associated with the anapole excitation is found to be more than 10 times weaker, and the internal energy is found to be 6 times greater for illumination with radially vs. linearly polarized beams. Our approach provides a simple, straightforward alternative path to realize electrodynamic anapole mode at the optical frequencies.
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