γ-radiation-induced absorption in pure-silica-core fibers in the visible spectral region: the effect of H2-loading

γ-radiation-induced absorption in the visible spectral region is studied in H₂-loaded and untreated optical fibers with high-OH low-Cl KU core and low-OH low-Cl KS-4V core. H₂-loading is found to suppress the low-dosage transient absorption band centered at 670 nm in KS-4V fibers. After irradiation to 1.7 MGy(Si), H₂-loaded fibers show losses many times lower than the untreated fibers. H₂-loaded and irradiated fibers are found to retain very high radiation resistance under subsequent irradiations even in the absence of molecular hydrogen. It is concluded that H₂-loading followed by pre-irradiation can be used as an efficient radiation hardening technique for pure-silica optical fibers