title: Experimental evidence for the formation of divalent ytterbium in the photodarkening process of Yb-doped fiber lasers.
abstract: In this work we present experimental evidence that the valence instability of the ytterbium ion play a key role for the observed photodarkening mechanism in Yb-doped fiber lasers. Luminescence and excitation spectroscopy performed on UV irradiated Yb/Al doped silica glass preforms and near-infrared diode pumped photodarkened fibers show a concentration increase of Yb(2+) ions. A concentration decrease in Yb(3+) could also be observed for the UV irradiated preform. The findings contribute to an increased understanding of the kinetic processes related to photodarkening in Yb-doped high power fiber lasers.
authors.affiliation: Mid Sweden University, S-851 70 Sundsvall, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Rydberg
authors.forename: M
authors.initials: M
authors.lastname: Engholm
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005336:Fiber Optic Technology / Q000295:instrumentation*; D007834:Lasers; D015018:Ytterbium / Q000737:chemistry*
chemical_list: D015018:Ytterbium