Transient optical absorption in pulsed-X-ray-irradiated pure-silica-core optical fibers: Influence of self-trapped holes

We investigated pulsed-X-ray-induced attenuation in two pure-silica-core (PSC) optical fibers with low-chloride (Cl) and different hydroxyl (OH) contents. We measured at room temperature the temporal (100 ms–1000 s) and spectral (0.73–3.1 eV) variation of the induced optical absorption after a 1 MeV X-ray pulse in both low- and high-OH PSC multi-mode fiber samples. A component of the transient loss in the low-OH sample was found to comprise absorption bands at 1.63 and 1.88 eV (760 and 660 nm) arising from self-trapped holes (STHs). Already known to be unstable at room temperature, STHs appear to play a key role in the transient responses of low-OH/low-Cl pure-silica-core fibers in the visible/near-infrared part of the spectrum.