Radiation Induced Attenuation Kinetics in Pure-Silica-Core Optical Fibers during Successive Irradiations

We present an experimental investigation regarding the 10 keV X-ray radiation induced attenuation (RIA) in the range 2-5 eV (620 - 248 nm) measured on radiation hardened optical fibers. We performed in situ RIA measurements during three irradiation runs having the same dose rate and the same duration. Our data evidence that the radiation induced STH1 and the Cl related defects are mainly responsible for these excess losses in the range 2-3.5 eV during irradiation. This RIA disappears one hour after the irradiation stop. Furthermore, the related RIA kinetic observed during the first irradiation run differs from those observed during the successive runs, these ones being faster during the irradiation and unchanged after it. By contrast, no more differences in the RIA increase were observed in the irradiations successive to the first run. These results indicate that after the first irradiation the initial population and typology of defects, involved in the generation processes, is not restored (irreversible channels). By contrast, the population and typology of the defects present in the fiber after the first transmission recovery is activated by new irradiation and reformed at end of each ones giving rise to reversible channels.