Characterization of transparent thin films by low-coherent diffractometry

We introduce a method to determine the refractive index (RI) and thickness of transparent thin films (TTF) simultaneously. The method is based on Fresnel diffraction from a phase step in the transmission mode. The average visibility of the three central fringes in the Fresnel diffraction pattern depends on the incident beam angle, RI, and thickness of TTF. By analyzing the visibility versus the angle of incidence, the RI and the thickness of TTF are determined simultaneously. Experimental outcomes and the theoretical model are in perfect agreement. The results show that the error in the thickness measurement is about 0.04 m, and the uncertainty of the obtained RI is Δ N = 0.002 . Owing to its very simple setup and reliable results, the method can provide an alternative to conventional methods, e.g. interferometry.