In-Situ Characterization of Oxide Films on Liquid Alkali Metals Using Second Harmonic Generation (SHG)

ABSTRACTThe experiments described in this paper clearly show that Second Harmonic Generation (SHG) may be used as a sensitive tool for detecting oxide impurities at interfaces not accessible for usual surface characterization methods. As a striking feature, one peak in the temperature dependent SH intensity is observed for liquid potassium and five peaks for liquid cesium. The occurrence of these peaks cannot be understood in terms of the nonlinear optical properties of the pure metal. By varying the oxygen content present in the melt it can be shown that these peaks must be attributed to the presence of oxide impurities segregating at the interface. In addition it is shown that the presence of oxides at the interface inert sapphire - molten alkali metal significantly alters the structure of the sapphire surface finally leading to corrosion visible even by the eye.