Kramers-kronig analysis of relative reflectance spectra measured at an oblique angle.

Relative specular reflectance R is defined as R = R(s)/R(w), where R(s) and R(w) are absolute reflectances of a sample material s and a material w for which the index of refraction n(w) and the extinction coefficient k(w) are known quantities. An algorithm was developed for computing n(s)and k(s) from the sample's R spectrum measured for radiant flux polarized perpendicular to the plane of incidence and reflected at oblique angle theta. Kramers-Kronig analysis of the R spectrum provides DeltaPhi the difference between phase shifts for electromagnetic waves reflected at the surfaces of materials s and w. Real and imaginary parts of a Fresnel equation for relative reflectivity provide equations for computing n(s) and k(s) when theta, DeltaPhi n(w), and k(w) are known quantities. Optical constants for aqueous solutions containing NaCl were computed in this manner; distilled water was the reflectance standard.