Toward a theoretically limited SPP propagation length above two hundred microns on an ultra-smooth silver surface [Invited]

We demonstrate the optical medium for surface plasmon-polariton wave (SPP) propagation with ultra low losses corresponding to the theoretically limited values. The unique element of the optical medium is an atomically-flat single-crystalline silver thin film that provides extremely low losses. The SPP excited on the surface of such thin films (λ = 780 nm) is characterized by a SPP propagation length equal to 200 µm, which is twice longer than previously reported experimental results and corresponds to theoretically limited values for silver films.