Determination of the Complex Refractive Index Profile of the Thin Gradient Layer by Surface Plasmon Resonance

The algorithm for determining the refractive index profile and extinction coefficient by depth for thin gradient-index metal and dielectric films is presented. To reconstruct the in-depth profile of optical constants of a gradient-index thin film the angular scanning data at several wavelengths under surface plasmon resonance conditions are used. The gradient-index layer profile is approximated by the pchip function over a several number of points. The coordinates of these points are found by minimizing the discrepancy function using BOBYQA iterative algorithm.