Calibration in the Visible and Infrared Domains of Multimode Phosphosilicate Optical Fibers for Dosimetry Applications

Abstract

We systematically explore the suitability of two radiation-sensitive multimode optical fibers with either P or GeP-doped cores, to serve as the sensing elements in point or distributed dosimeters. To this end, we measured the dependences of their spectral Radiation-Induced Attenuation (RIA) in the visible and near-infrared (near-IR) domain (400 - 2100 nm) up to total ionizing dose (TID) of 5 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), while varying the irradiation temperature from -80 °C to +80 °C and the dose rate between 1 mGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s and 10 Gy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s. To assess the fiber radiation sensitivity calibration coefficients, we studied the linearity of the RIA vs TID response across our whole spectral range. Once confirmed, their “radiation sensitivity calibration” curves are obtained in the tested ranges of environmental parameters, including the dispersion related to dose rate and temperature. Both fibers present very similar curves despite their different chemical compositions. We then studied the recovery kinetics at the different temperatures of the two fibers to investigate the stability of the RIA response. Our results show that the Ge-codoping only slightly increases the IR sensitivity related to P1 defects while keeping unchanged the visible – near-IR RIA, where the contribution of phosphorus-oxygen-hole centers (POHC) is dominant. On the contrary, after the irradiation the responses of the two fibers differ, as the recovery kinetics of the GeP fiber are strongly affected by temperature, limiting its dosimetry capabilities with respect to the P fiber.