Light scattering from liquid surfaces: Ellipsometric coefficient

In this paper we discuss a theory of light reflection from a liquid in equilibrium with its vapor. We take into account the fluctuations of the Gibbs surface between the two phases and generalize the planar formula given by Drude for the ellipsometric coefficient. At the same time, by considering a finite width of the metastable region, we go beyond the capillary-wave model which assumes a sharp step discontinuity between the two phases. The two effects cannot be treated separately since they give rise to a strong interference. We show also that the capillary-wave model is inadequate to explain light measurements and leads to wrong conclusions. Throughout the paper we focus on recent experimental measurements of the coefficient of ellipticity, which constitute the motivation of the present work.