Methods are developed for the successive determination of the refractive index, thickness, and extinction coefficient of a slightly absorbing thin film situated on a slightly absorbing or transparent substrate. The refractive index is found from a measurement of the Brewster angle for the film-substrate interface. This Brewster angle, termed the second-surface Brewster angle, is shown to be highly insensitive to small values of the extinction coefficient. The film thickness is deduced from measurements of the angles at which maxima and minima occur in the measured distribution of reflectance vs angle of incidence. Thus, neither the refractive index nor the thickness determinations requires the magnitude of the reflectance as input. On the other hand, the extinction coefficient is deduced from the value of the reflectance at a maximum point in the distribution of reflectance vs incidence angle.
M. RUIZ-URBIETA and E. M. SPARROW, "Refractive Index, Thickness, and Extinction Coefficient of Slightly Absorbing Thin Films," J. Opt. Soc. Am. 62, 931-937 (1972)