An optical method for in situ diagnostics of atomic layer deposition, hosed on the measuring of the reflectivity of a F-polarized light in fully transparent systems, is proposed and analyzed by using a classical four-phase approximation. The method is applied to the monitoring of TiO2 growth. It is shown;hot the sensitivity of the method is high if one uses the angles of incidence close to the Brewster angle of the substrate. The method is called incremental dielectric reflection.