Visible and infrared optical properties of Ag/SiO₂multilayers: radiative virtual modes and coupling effects

Abstract

Optical measurements (photometry and ellipsometry) were performed under oblique incidence from 0.03 eV to 6 eV on silver/silica (Ag/SiO2) multilayers prepared by magnetron sputtering. Around 3.79 eV, the plasma frequency of Ag, and 0.154 eV and 0.133 eV, the longitudinal and transverse optical frequencies of SiO2, resonances are observed, characteristic of the Ferrell and Berreman modes in single Ag and SiO2 layers. These modes and a Brewster mode observed around 3.87 eV are weakly influenced by the SiO2 thickness in the multilayers. Below 3.78 eV, strong coupling effects between surface plasmon modes at the metal/dielectric interfaces generate a transparency window with low reflectance, whose width is well described within the effective medium approximation.