Optical properties of liquid mercury

Interest in the optical properties of liquid Hg has resulted in numerous studies over the past quarter of a century. Consistent differences have been observed between the optical properties of liquid Hg deduced from reflectance and from ellipsometric spectra, and several models have been proposed which have attempted to explain these differences by the introduction of an inhomogeneous and/or anisotropic surface region. However, a systematic analysis of the previously existing and new ellipsometric data for liquid Hg fails to demonstrate the existence of a surface transition zone having inhomogeneous and/or anisotropic properties. It is further shown that the contradiction between the optical constants obtained from ellipsometric and from reflectance measurements is not real and that the former are representative of liquid Hg while the latter contain large uncertainties because of insufficient sensitivity. The observed deviations of the optical constants of liquid Hg from ''Drude'' behavior still require theoretical explanation.