INFLUENCE OF SMALL INHOMOGENEITIES ON THE SPECTRAL CHARACTERISTICS OFSINGLE THIN-FILMS

It is well known that the spectral transmittance and reflectance of a thin film can be influenced by even small inhomogeneities or variation s in its complex refractive-index profile. Formulas are derived that d escribe the theoretical variation of the spectral characteristics for small changes in the refractive index and the extinction coefficient o f a homogeneous thin film. These formulas, accurate to the first order in the change in the complex refractive index, are compared with exac t calculations for a number of different types of inhomogeneities. It is shown that specific qualitative features in the refractive-index pr o file of a nearly homogeneous thin film frequently can be determined from an examination of the change in the spectral transmittance and re flectance at normal incidence. (C) 1997 Optical Society of America.