Theory of Reflectance

Abstract

The accurate measurement of the refractive index of transparent liquids is possible using conventional devices such as Abbe-refractometer or an interferometer. The problems of estimation of the real refractive index arise when the liquid is optically very thick i.e. absorbing but non-scattering, or the liquid is turbid which usually means relatively strong scattering of light and sometimes simultaneous absorption of light. Fortunately, reflection spectroscopy can be applied to such difficult tasks that require the estimation of the complex refractive index of turbid liquids. In addition reflection spectroscopy can provide means for adsorption studies [50] such as for example contamination of probe window. There are sources that describe thoroughly the exploitation of reflection spectroscopy in material research [51, 52] and industrial measurement applications [53]. However, there has been recent progress both in technology for reflection spectroscopy and spectra analysis, which give new light to the physical phenomena behind the measured data related to reflection measurements. In this chapter we will describe the theory of the oblique incidence light reflection from absorbing or turbid liquids.