Radiation effects on sapphire optical fibers were investigated using off-line gamma-ray, neutron and electron beam irradiation and on-line proton irradiation. The optical attenuation of these optical fibers was studied from UV to IR (200 nm -1700 nm). For the in-situ measurements radioluminescence was also investigated as function of the total irradiation dose.1 Introduction Extensive studies were carried out in the last years in the field of the radiation effects on various optical components to be used in plasma diagnostics for ITER (International Thermonuclear Experimental Reactor) like fusion installations. Mirrors, windows and optical fibers were investigated under gamma-ray, neutron or electron beam irradiation. As plasma facing components, windows are supposed to be subjected to high temperature, particle bombardment, and ionizing radiation exposure. Optical fibers will play an important role in optical data links, distributing sensing systems, light-guides for spectroscopy and for the visualization of thermal field distribution [1, 2]. They will be forced to work under high radiation fields (gamma-rays and neutrons) and, in some situations at high temperatures [3].Until now research was carried out in relation to the evaluation of the irradiation effects on silica glass optical fibers over the entire spectral range UV-visible-IR. The results indicated both a decrease of the optical transmission of the optical fibers, and the presence in same cases of a irradiation induced luminescence (radioluminescence) [4]. These effects depend on the optical fiber type, its ingredients, the manufacturing process, and the irradiation conditions (type of radiation, total dose and dose rate, particle fluence, etc.). These phenomena depend strongly on the wavelength; specific spectral bands are affected. For this reason, they can partially distort the signal they carry by attenuating it or by increasing the signal-to-noise ratio. Special pre and post irradiation treatments (i.e. hydrogen loading) can induce a radiation hardening. In some situations, the irradiation produced distortion exhibits a recovery upon hearting the optical fiber (thermal annealing) or after an optical signal of a specific wavelength is launched over the optical fiber (photobleaching).The overall conclusion to these investigations is that silica optical fibers still are sensitive to irradiation, mostly in the UV-visible spectral range, as irradiation induced color centers appear. For this reason we started to investigate how sapphire optical fibers perform under various irradiation conditions, being known the radiation resistance of this material. According to our present knowledge, irradiation test were performed only on bulk sapphire samples (i.e. windows) [5][6][7], no such investigation was done on optical fibers made of sapphire.
Abstract:The focus of the present paper deals, for the first time, with commercial UV optical fibers, characterizing their behaviour as they are subjected to very high flux wiggler generated synchrotron radiation. Five distinct types of UV optical fibers, produced by three manufactures, were exposed to total doses between 5 Gy and 2000 Gy. The exposure to synchrotron radiation was performed in two campaigns. The tests were run off-line and considered the dependence of the radiation induced attenuation (RIA) as function of the total dose. The recovery of the radiation induced colour centres was studied at room temperature and after heating the samples up to 560 K. As a première, we also investigated through THz imaging and spectroscopy the irradiated optical fiber samples. Under these conditions, three of the optical fibers proved to be radiation resistant. The two optical fibers sensitive to synchrotron radiation exhibited a linear variation of the optical absorption at the wavelengths of λ = 229 nm, λ = 248 nm, and λ = 265 nm, for total doses between 60 Gy and 2000 Gy. These two samples showed also an increase of the optical absorption in the UV spectral range when heated to 560 K. The optical fibers sensitive to synchrotron radiation can potentially be used for on-line radiation dosimetry. ©2014 Optical Society of America
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