Pulsed X-Ray Radiation Response of Ultralow Loss Pure-Silica-Core Optical Fibers

The transient radiation response from the visible to the infrared (IR) domains (400-2200 nm) of an ultralow loss pure-silica-core and fluorine-doped single-mode optical fiber (ULL-SMF) exposed to a short (tens of ns) 1 MeV X-ray pulse is investigated. Online (hundredths of millisecond time resolution) radiation-induced attenuation (RIA) spectra measurements are performed at both room and liquid nitrogen temperatures (RT and LNT). The main goals are to assess the vulnerability of this class of fibers as well as to characterize the metastable defects recovering just after the shot and responsible for the RIA decay kinetics. Their identification relies on a Gaussian spectral decomposition exploiting the optical absorption bands characteristics of point defects already known in literature. By comparing the ULL-SMF behaviors at the two temperatures, the RIA unstable contributions are highlighted from the visible to IR domains, in particular the ones that are bleached in a timescale faster than the time resolution of a few milliseconds at RT. The origin of the induced losses is discussed revealing the fundamental role of the self-trapped holes as intrinsic metastable defects in the response of this class of pure-silica-core OF.