A sample with a quasi-inhomogeneous refractive index profile has been prepared by r.f. magnetron sputtering by mixing very thin layers of SiO2 and Al2O3. It has been proved that the quasi-inhomogeneous profile is, to the accuracy of our experiment, undistinguishable from the smoothly inhomogeneous profile. This effective inhomogeneous profile was then established from the measured ellipsometric data by the new method based on Tikhonov’s regularization technique. As the method uses some a-priori information on the system, the results are rather qualitative but they seem to reveal the depth profiles of the refractive index and extinction coefficient as well as their dispersion.