Nanophotonic Phenomena in Mesoscale Dielectric Particles*

Nanophotonic phenomena, such as zero optical back scattering, nonradiating anapole states, etc. are related to the excitation of single dipolar modes – hence so far, they have only been observed in the nanoscale regime at the optical frequencies within a few relatively high-index dielectric materials (refractive index, n > 3). Here, we unravel dipolar regime, demonstrate close-to-zero backscattering, and excite optical anapoles in mid-index titanium di-oxide (TiO₂) dielectric spheres (n ~ 2.6) at the mesoscale regime (particle diameter, d ~ incident wavelength, l) under illumination with tightly focused Gaussian beams (TFGBs). We observe successive minima associated with dipolar excitation satisfying the first Kerker condition in the scattering spectra of single TiO₂ spheres with diameters in the micrometer range. Moreover, at specific wavelengths, for example l ~ 590 nm for d ~ 0.78 mm, and l ~ 665 nm for d ~ 0.88 mm, the electric and magnetic dipolar scattering amplitudes simultaneously go close-to-zero leading to the excitation of hybrid optical anapoles with the total scattering intensity ~ 5 times weaker for TFGB illumination with numerical aperture, NA ~ 0.95 vs. 0.1. Our results open up new directions of research for the observation of novel optical phenomena and applications in dielectric particles at mesoscale.