Anapole arising from a Mie scatterer with dipole excitation

Abstract

We examine theoretically that an electric dipole close to a subwavelength sphere can yield an anapole (the dipole-sphere system is a nonradiating source). Physically, the anapole arises when the dipole induced by the source inside the sphere cancels out with the dipole contribution of the source with respect to the center of the sphere. The condition for the anapole is established and this state can be achieved with either a dielectric sphere with a high refractive index or a metallic sphere. Since there is a residual radiation (much smaller than the radiated power of the dipole in the absence of the scatterer) originating from high-order multipoles, the anapole is almost ideal. However, we show that the residual radiated power can be reduced even more by placing two electric dipoles on opposite sides of the spherical scatterer. This paper might have implications for controlling radiative properties of emitters and implementing applications related to molecular localization and sensing.