CHARACTERIZATION OF RADIATIVE SURFACE-MODES AND ANISOTROPY IN AG/SIO2 MULTILAYERS, BY VISIBLE AND IR ELLIPSOMETRY

Ellipsometric measurements in the visible (1.- 5.4 eV) and the IR (0.03-0.5 eV) have been performed on metal/dielectric (Ag/SiO2) periodic multilayers prepared by magnetron sputtering. The results are discussed in terms of radiative modes occurring at the plasma frequency of the metal (3.78 eV) and the longitudinal optical (0.154 eV) and transverse optical (0.133 eV) frequencies of the dielectric. A strong anisotropy is observed near these resonances. It is shown to be due to coupling effects in the multilayer in the visible range and to a classical Berreman effect in the first dielectric layer in the IR range. These effects have potential applications to optical coatings for the IR and for optical communications.