Detection of Hybrid Optical Anapoles in Dielectric Microspheres

Abstract

Nonradiating optical anapoles are special configurations of charge-current distributions that do not radiate. It was theoretically predicted that, for microspheres, electric and magnetic dipolar coefficients can simultaneously vanish by engineering the incident light, leading to the excitation of nonradiating hybrid optical anapoles. In this work, the experimental detection of hybrid optical anapoles in dielectric microspheres (TiO₂) is reported using dual detection optical spectroscopy, developed to enable sequential measurement of forward and backward scattering under tightly-focused Gaussian beam (TFGB) illumination. The results show that the excitation of TiO₂ microspheres (diameter, d ≈1 µm) under TFGB illumination leads to the appearance of scattering minima in both the forward and backward directions within specific wavelength ranges. These scattering minima are found to be due to vanishing electric and magnetic dipolar coefficients associated with hybrid optical anapoles. The ability to confine electromagnetic fields associated with hybrid optical anapoles can give rise to several novel optical phenomena and applications.