Surface plasmon-polariton study of the optical dielectric function of silver

The optical dielectric function of silver is measured by excitation of surface plasmon-polaritons on a silver-covered silica grating for a range of wavelengths in the visible region of the spectrum. By exciting the surface plasmon-polariton at the grating/silver interface the silver is protected from sulphidization and contamination. Comparison of angle-dependent reflectivities with grating modelling theory gives both the real and imaginary parts of the dielectric function of the silver. The results compare very favourably with those obtained by other workers using more conventional methods for samples held in an ultra-high vacuum or with protected interfaces.