Experimental determination of the refractive index profile of rugate filters based on in situ measurements of transmission spectra

We demonstrate the calculation of the refractive index profile (reverse engineering) of an inhomogeneous optical coating based on in situ measured optical transmission spectra. A full triangular algorithm has been applied for refractive index profile calculation. The obtained profile is consistent with deposition rate recordings obtained during film deposition from quartz crystal monitors. The proposed methodology is also applicable for reverse engineering tasks in traditional high-low-stacks. As an additional feature, the method may be utilized for re-calibrating quartz monitors used for deposition control either after or during the deposition experiment.