Effects induced by 4.7 eV UV laser irradiation on pure silica core multimode optical fibers investigated by in situ optical absorption measurements

摘要

We investigated by in situ optical absorption measurements the effects induced by 4.7 eV UV laser irradiationudon pure silica core optical fibers. Laser irradiation with 100 MWcm−2 laser intensity generates in the fiber E′udcenters which partially decay after irradiation due to their reaction with diffusing H2. An absorption bandudpeaked at 5.3 eV is observed to grow in the post-irradiation stage with a kinetics anti-correlated to the decayudof the 5.8 eV band of the E′ centers. The defect absorbing at 5.3 eV is proposed to be formed by trapping onudpre-existing precursors of hydrogen atoms made available by breaking of H2 on E′.We also show by repeatedudirradiation experiments that the 5.3 eV-absorbing center is photochemically destroyed by 4.7 eV laser light,udand we estimate the cross section of this process. Possible structural models for this defect are discussed.