New experimental setup to use ellipsometry to study liquid-liquid and liquid-solid interfaces

Different types of optical light guides were constructed and tested to enable convenient multiple angle of incidence ellipsometry, on solid and liquid interfaces in liquid solutions. Two light guides are needed on an ellipsometer, one to guide the incoming light and one to guide the light that is reflected at the test surface, and therefore one light guide was mounted on the laser arm and one on the detector arm of the ellipsometer. With this arrangement the optical windows automatically adjust to always be perpendicular to the direction of the light independent of the angle of incidence. The purpose with these light guides is to facilitate the passage of light through the air/solution interface. A thorough theoretical and experimental analysis of optical errors introduced by such light guides is presented. This discussion includes the effect of multiple reflections between and within the windows of the light guides' On the basis of this analysis a new ellipsometry setup with light guides, consisting of glass tube's with glued end windows, was developed. This setup makes it possible to perform accurate measurements in almost any type of measuring cell at any angle of incidence