Excitation of optical anapoles in dielectric nanospheres

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.