Abstract
Both the theoretic elements of an interferometric method for the refractive index determination based on a Fabry-Perot etalon and the procedure of the Fabry-Perot cell obtaining are described in this paper. The results obtained by this method for PVA isotropic foils and for PVA foils including small amounts of potassium iodide are given here. Keywords: PVA, FPE, refractive index, isotropic materials