p- and s-polarized FTIR reflectance spectroscopy at oblique incidence by Kramers-Kronig transformation

A computational procedure has been developed for deriving dielectric functions of solids from reflectance spectra at off-normal incidence and p- or s-polarization. Based on the generalized Kramers-Kronig relations, the whole set of additional phase corrections-'Blaschke factors'-caused by singularities have been derived. This analysis may be used to omit those regions of measurement parameters (angle of incidence and polarization) which contribute to frequency-dependent phase corrections, because they are hardly accessible for unknown materials. Error estimation, including the angle dependence of typical sources of error, has shown the advantages of measurements at angles of incidence ranging from 60 degrees to 80 degrees in comparison with those at normal incidence. These benefits have been verified by the transformation of experimental spectra.