Study of the Interaction of Light with Rough Metal Surfaces. I. Experiment

Abstract

This paper describes measurements of the reflectivity, scattering, and transmission of light by metals with rough surfaces. For surfaces whose roughness is very short ranged, the ratio of rough-surface reflectivity to smooth-surface reflectivity varies exponentially as ${\ensuremath{\lambda}}^{\ensuremath{-}2}$ both above the plasmon frequency and in regions where ${\ensuremath{\epsilon}}_{2}\ensuremath{\gg}|{\ensuremath{\epsilon}}_{1}|$. In the latter regions for these rough surfaces, the scattered intensity follows a ${\ensuremath{\lambda}}^{\ensuremath{-}4}$ wavelength variation. For surfaces which are more wavy, the reflectivity and scattered light vary less rapidly with wavelength. Well below the plasmon frequency, additional fields not present on smooth surfaces, but coming from induced extra currents and dipoles on rough surfaces, add coherently to the specular beam, with a resonant wavelength variation. Near the plasmon frequency there is extra absorption. We have studied the angular variation of the scattered light, and have observed additional incoherent light associated with these extra dipoles and currents. We compare the experimental results with the scalar scattering theory and make some general comments about the properties of surface dipoles and currents.