Experimental Detection of Kerker Anapoles in Mid-Index Dielectric Microspheres

It has been hypothesized that in the case of Mie scattering, the emergence of pure electric or magnetic scattering regimes at Kerker conditions under dipolar excitation can give rise to zero total scattering efficiency at the optical regime, known as Kerker anapole. To detect this, we illuminated spherical titanium dioxide (TiO­­₂) with an average size of ~ 1.1 microns using tightly focused Gaussian beams (TFGBs) that mimic the scattering properties of dipolar fields. We measured the scattering spectra of the single particles in both the forward and backward directions and found that there are several dips associated with the 1^st and 2^nd Kerker conditions. Moreover, the scattering minima of the backscattered spectra nearly coincide with the scattering minima of the forward scattering spectra under illumination TFGBs, which is a signature of Kerker anapole. The detection of optical anapole can potentially overcome the limitations of current optical devices in terms of non-efficient coupling and directionality of light.