Detection of Hybrid Optical Anapoles in Dielectric Microspheres

TL;DR

This paper reports the experimental detection of hybrid optical anapoles in dielectric TiO2 microspheres, revealing scattering minima due to vanishing dipolar coefficients, which could enable new optical phenomena and applications.

Contribution

First experimental demonstration of hybrid optical anapoles in dielectric microspheres using dual detection spectroscopy under focused Gaussian illumination.

Findings

Scattering minima observed in forward and backward directions

Vanishing electric and magnetic dipolar coefficients identified

Potential for novel optical phenomena and applications

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 approx. 1 um) 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.