Photobleaching of Radiation-Induced Color Centers in a Germania-Doped Glass Fiber

Experiments have been performed to measure the effects of photobleaching on radiation-induced absorption in a Corning germania-doped graded-index fiber (type 1506) held at 77 K. Fiber segments 4.6 m long were exposed to radiation pulses of approximately 280 rads(Si) and 24-ns pulsewidth while suspended in a liquid nitrogen bath. Wavelength-dependent absorption measurements and photobleaching were also carried out on the fiber in situ. The measurements showed a broad radiation-induced absorption band peaking between 5000 and 6000 Ã…. It was partially photobleached with light in the wavelength range of 6556 to 9556 Ã…, and was almost entirely photobleached with light at 4556 and 5556 Ã… wavelengths. This absorption band was readily removed with a room-temperature thermal anneal and is thus identified as the source of transient darkening in germania-doped fibers irradiated at higher temperatures.