Narrow plasmon-polaritons resonances in metal-dielectric microspheres

The properties of plasmon-polaritons (PP) in a coated microsphere with alternating metal-dielectric layers are numerically studied. The eigenfrequencies spectrum f0 as well the electromagnetic field spatial distribution depending on the type of metals is investigated. It is found that the eigenfrequencies of PP depend considerably on the value of radius of the bottom dielectric microsphere r1. If r1⪡λ0 (e.g. for gold) the well-known quasi-stationary relation between of frequencies of PP and plasma frequency ω=ωp/3 is satisfied closely. In opposite case (e.g. for aluminium) such a relation is broken.