The effect of UV irradiation on uracil thin layer measured by optical waveguide lightmode spectroscopy.

The polycrystalline uracil thin-layer dosimeter is a well-established method to monitor the biological effects of the environmental ultraviolet (UV) radiation. It is based on the optical density (OD) decrease of the uracil layer in the UV absorption band due to photodimerization of the crystal caused by UV irradiation. In the present study, we report measurements made with optical waveguide lightmode spectroscopy (OWLS) to characterize the changes in the optogeometrical parameters of the uracil layer caused by an artificial UV source. It is shown that UV irradiation causes a decrease in the refractive index and an increase of the optical anisotropy. The determined kinetic parameters of the UV dose-sensor response curves correlate well with results of OD measurements, but the sensitivity of OWLS is about ten times higher. The results show that OWLS is capable of analyzing the UV response of the uracil layer and opens the way for dosimetrical applications.