Institute of Information Theories and Applications FOI ITHEA
Determination of the so-called optical constants (complex refractive index N, which is usually a function
of the wavelength, and physical thickness D) of thin films from experimental data is a typical inverse non-linear
problem. It is still a challenge to the scientific community because of the complexity of the problem and its basic
and technological significance in optics. Usually, solutions are looked for models with 3-10 parameters. Best
estimates of these parameters are obtained by minimization procedures. Herein, we discuss the choice of
orthogonal polynomials for the dispersion law of the thin film refractive index. We show the advantage of their
use, compared to the Selmeier, Lorentz or Cauchy models.