Re-engineering of optical constants and layer thicknesses from in situ broadband monitoring: an oscillator model approach

We present and discuss an in situ optical characterization methodology for calculating individual film thicknesses and optical constants of a multilayer coating. The method is applied to the plasma-ion assisted evaporation of a titania-silica five-layer stack making use of in situ transmittance measurements. In order to guarantee the Kramers-Kronig consistency of the optical constants, a simplified Lorentzian oscillator model has been applied for describing the dispersion of optical constants. Accompanying measurements of the vacuum-air shift of the coatings verify the porosity of the obtained coatings. We emphasize the significance of the application of this characterization technique in order to obtain reliable information from repeatability experiments, necessary to quantify stochastic deposition errors.