Optical properties and radiative modes in Ag/SiO2 multilayers

Optical photometric measurements in the visible range (1.4–5.4 eV) under oblique incidence have been performed on Ag/SiO2 periodic multilayers prepared by magnetron sputtering. The results are discussed in terms of radiative virtual modes due to the Ag layers. The fundamental radiative mode is observed around the plasma frequency of Ag (3.78 eV). A Brewster mode is observed around 3.87 eV. These two radiative modes are weakly influenced by the SiO2 thickness. Below 3.78 eV, strong coupling effects between surface modes at Ag/SiO2 interfaces generate a transparency window with low reflectance whose width is well described within the effective medium approximation.