Thickness and model optimization in characterization of optical interference films by using discontinuities of n(lambda) solutions

The characterization of inhomogeneous thin film has been a widely studied topic. In the present work an inhomogeneous film model where the real part of the refractive index has a parabolic profile through the film thickness is supposed and a procedure for the unequivocal determination of the model parameters from normal incidence spectro-photometric measurements of T(lambda), R(lambda) and R'(lambda) is outlined. The parabolic model can be useful in the initial stage of investigation on a film material, which is suspected of being inhomogenous, as the model parameters, the gradient and curvature of the n parabolic profile, provide a quantitative evaluation of the film inhomogeneity even when the parabolic model is not realistic.