Polaritonic spectra of optical Mie voids

Abstract: The progress in understanding the optical and microscopic properties of polaritons relies on various optical cavities to confine electromagnetic radiation, which causes a demand for new platforms with higher $Q$-factors and better fabrication robustness. In this context, so called Mie voids -- spherical cavities inside a dielectric medium, where the light confinement occurs due to refractive index contrast at the air-dielectric interface -- present a substantial interest. Here, we theoretically study the resonant characteristics and polaritonic spectra of spherical Mie cavities loaded with resonant media, as well as address the inverted problem, where a Mie void is formed inside a resonant dispersive medium. We establish approximate analytical expressions for the $Q$-factors of Mie void cavities, find the parameter ranges of spherical voids leading to the regimes of weak and strong light-matter coupling and analyze the concomitant effects, such as $Q$-factor enhancement and spatial field localization, from the polaritonic perspective. Our result could be valuable for the design of new polaritonic systems.