Determination of Noise-Free Optical Constants in the Infrared by Kramers—Kronig Transformation of the Reflectance Ratio in s- and p-Polarization

A method for Kramers–Kronig transformation of the reflectance ratio of s- and p-polarized light is discussed. The method is well suited for the determination of the optical constants of isotropic samples such as pellets prepared from powders. An algorithm is given that performs the transformation, including extrapolation at the data margins and an automated data fitting routine, that can handle very complex spectra of, e.g., biomacromolecules such as cellulose to obtain noise free spectra. Criteria for evaluation of the quality of the obtained data are given, and experimental data for cellulose II and xylane are presented.