Silver dielectric stack with near-zero epsilon at a visible wavelength

Measurements from reflection and transmission from a glass slab with a plasmonic thin film coating are presented. The coating consists of nano-metric silver layers separated by nano-metric layers of polyimide. Maxwell Garnett calculation of the effective dielectric function of the coating for the light propagating normal to the coating predicts a zero crossing of the real part of this function at a visible wavelength. The measured behavior of the reflectivity as a function of the wavelength is in agreement with the behavior of the reflectivity of a glass slab coated with a material with the Maxwell Garnett effective dielectric function. The concurrence of the experimental and theoretical results demonstrates that filter properties of the stack may be tuned by varying the stack geometry.