UV irradiation effects on TiO2 thin films

This paper presents the behaviour of a standard optical coat; ing to be used in aerospace applications when exposed to ultraviolet (UV) irradiation. Ellipsometric measurements are carried out in order to monitor the effects produced on the optical properties of the TiO2 film when it is exposed to a 500 W Xenon lamp during the time intervals of l hour, 22 hours and 42 hours. The ellipsometric measurements show that main changes occur in the real part of the refractive index after the first hour of exposure to UV irradiation. To assess a possible relation between the hydrophilicity that the UV irradiation typically induces on the TiO2 thin film, and the variation of the optical properties of the film, the mater contact angle on the TiO2 optical coating was also measured after irradiation under similar conditions.