Refractive index determination using reflectance extrema

Contours of n and k vs the reflectance and transmittance of a thin film on a glass (n = 1.5) substrate are presented. These contours provide a unique value of (n - ik) and the film thickness, given the normal incidence R and T values at a reflectance extremum, wavelength, and the interference order of the extremum. The results are corrected for the reflectance of the rear of the substrate, and for the wavelength shifts of the extrema, and cover the range n = 1.6-4, k = 0-1. A simple model of strongly scattering films is used to provide n and k contours vs the total reflectance and transmittance of scattering layers: n and k appear to retain their usefulness in this situation.