Polynomial Profile Reconstruction of Gradient-Index thin Films by Surface Plasmon Microscopy Based on Acousto-Optical Tunable Filter

The present study proposes a method to reconstruct the approximate form of the optical profile of thin gradient films using polynomial functions. The approach relies on experimental spectral and angular measurements of reflected quasimonochromatic p-polarized light, which is filtered by an acoustooptic tunable filter. The measurements are conducted through surface plasmon resonance on a thin gold film coated with a gradient-index dielectric on a prism in Kretschmann geometry. The wavelength dispersion of the resonance angle is established to select the appropriate polynomial sequence representing the type of optical profile. To determine the type of polynomial that best approximates the true optical profile, an additional measurement is proposed when the thin film surface is in contact with a non-reactive liquid (e.g. alcohol). The proposed optical characterization method of thin gradient films has the potential for nondestructive control of thin films, including real-time production of thin films.