Simple method for measuring bilayer system optical parameters

A simple method for measuring bilayer system refractive indexes and thicknesses in the low absorbing part of spectra is demonstrated. The method is based on application of Savitzky - Golay smoothing filters and interference fringe separation in the reflected or transmitted spectra of the bilayer system. The refractive indexes and thicknesses are extracted from the wavelengths corresponding to extreme points in the spectrum. Due to the fact that wavelength difference of extreme points in the analyzed spectrum is defined by the product of both, the layer thickness and refractive index, one must generate an appropriate initial guess of these parameters. For refractive index approximation two different methods have been used - point by point and Sellmeier dispersion relation. The final optimization procedure is based on a priori assumption that the thickness calculated from permutations of all extreme points in the spectrum should be the same. Thus the optimal penalty parameter for finding the solution is the standard deviation of calculated thicknesses. In order to demonstrate the effectiveness of this simple method, results of thin organic film thicknesses and refractive indexes are presented.