Fitting of transmission data for determining the optical constants and thicknesses of optical films

A multiparameter, nonlinear-curve fitting method is used to determine the refractive indices, absorption coefficients, and thicknesses of mixed yttria-silica films from transmittance spectra. Both homogeneous and inhomogeneous models of refractive index in the films are used for the data analysis. Results suggest that inhomogeneity in the films should be considered when investigating the optical properties of thin films. However, care must be taken when computing a refractive index gradient in an absorbing film as both absorption and index gradients can affect the optical transmittance in a similar manner.