Radiation resistance of optical materials against synchrotron radiation

Radiation resistance of optical materials against synchrotron radiation is important, if optical components for the high energetic regime should be produced. In the framework of the European project EUFELE, which deals with the development of optical coatings for the free electron laser at ELETTRA (Trieste), a set of C aF2 substrates was irradiated with synchrotron radiation. The synchrotron radiation was varied by wavelength, dose, and high energetic background. Before and after irradiation, the CaF2 substrates were investigated spectrophotometrically in the VUV, VIS and IR range. The surface structure was characterised by microscope methods. Structure investigations were done with XRD measurements. CaF2 shows different types of degradation like colour centre formation, surface modification, and increased VUV absorption bands. Defect formation will be presented in dependence of synchrotron irradiation conditions.