Radiation-induced attenuation (RIA) of light is studied in a pure-silica-core Panda fiber under γ-irradiation in the dose range 1-106 Gy at the dose rates in the range 0.015-5 Gy/s. A 5-mW erbium fiber superluminescent source or a white-light lamp (integral power of <0.5 μW) are used as the probe light source. Both RIA dose dependences at separate wavelengths in the near-IR range and RIA spectra in the near-IR and visible ranges at fixed doses are investigated. The spectra are Gaussian deconvolved and analyzed. 1.55-μm light (500 μW) is found to produce photobleaching not only of the 0.95- and 1.12-eV RIA bands, the effect observed previously, but also of the 2.6- and 1.63-eV RIA bands associated with inherent and strain-assisted self-trapped holes (STHs), respectively. RIA at λ=1.55 μm is found not to depend on dose rate at those below 0.15 Gy/s, which opens up the possibility to simply estimate the upper bound of RIA gained by the end of space mission. In particular, the RIA upper bound at λ=1.55 μm of ~1.5 dB/km is predicted for a 1-kGy space mission. RIA at λ=1.55 μm in pure-silica-core Pandas is also found to cease to depend on dose rate and probe light power at high doses (~105 Gy). The reason is that all the short-lived RCCs sensitive to the former parameters completely disappear at high doses, whereas RIA at λ=1.55 μm becomes wholly determined by the long-wavelength RIA band peaking at λ<1.7 μm and known to be dose-rate-independent and photobleaching-insensitive.
Radiation-induced absorption (RIA) of light in the visible spectral region is studied in three differently coated puresilica- core, F-doped-silica cladding optical fibers ("pure-silica fibers", PSFs) drawn from the same preform under γ-irradiation up to 1 kGy, the irradiation temperature being varied in the range ±60 °C. The coating types include aluminum, copper and polyimide. It is found out that the extremum of the temperature dependence of RIA due to strainassisted self-trapped holes (STHs) in Al- and polyimide-coated PSFs is shifted towards higher temperatures (≥+60 °C) as compared to acrylate-coated PSFs, of which the extremum temperature was previously found to be around 0 °C. Additional heat treatment in the process of application of the above coatings is argued not to the main factor influencing RIA, which increases primarily to the very presence of a metal layer on the silica surface. The latter, in turn, increases strain in the silica network and the STH population. Photobleaching of the STH-associated bands and UV-tail produced by the probe white-light halogen lamp under γ-irradiation at a dose of ~1 kGy and dose rate of 1.31 Gy/s is assessed quantitatively to be in the range from 20% to 90%.
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