Photoinduced processes in Sn-doped silica fiber preforms

Effects induced by KrF ultraviolet excimer laser on Sn-doped silica fiber p erforms were analyzed by means of optical and electron paramagnetic resonan ce (EPR) techniques. Bond breaking in substitutional Sn sites was evidenced by the Sn-E-' EPR signal due to sp(3) unpaired electrons in threefold coor dinated Sn sites. Red photoluminescence excited at 633 nm, due to nonbridgi ng-oxygen sites, was also observed after laser exposure. The intensity of t his emission did not follow the Sn concentration profile, being observed at the core-cladding interface and in the core center. Birefringence data sho wed that these effects are accompanied by stress relief in the Sn-doped reg ion. Different structural features of core and cladding were evidenced by m icro-Raman measurements and related to the observed photosensitivity. (C) 2 000 American Institute of Physics. [S0003-6951(00)00150-9].