Kramers - Kronig analysis of non-normal incidence reflection

A method is given for using the Kramers-Kronig dispersion relations to evaluate optical and dielectric parameters of materials from reflectance data measured at 45° incidence. The method requires only a single determination of the reflectance spectrum and is valid for incident light which is either polarized or completely unpolarized. As an example, the real and imaginary parts of the complex dielectric constant, n 2 - k 2 and 2 nk respectively, are evaluated from the 45° reflectance spectrum of a single crystal of magnesium oxide and compared with the values obtained from normal-incidence data.