title: Photodarkening-induced increase of fiber temperature.
abstract: We examine the effect of photodarkening-induced pump light absorption on Yb-doped fiber thermal loading. In these experiments, the fiber is cladding pumped at 915nm, air cooled by natural convection, and monitored with a midinfrared thermal camera. The fiber temperature is found to correlate with progressive photodarkening. The maximum observed fiber temperature was 120 degrees C, recorded at a pump power of 10.5W. The observed increase in fiber temperature can be explained by a model that takes into account the combined effects of the Yb-silica quantum defect, the temperature dependence of the Yb-absorption cross section, and photodarkening-induced loss at 915nm. We hypothesize that the latter effect results in the progressive activation of temperature-dependent photochemical processes (e.g., bleaching) and is an important consideration with regard to the accurate modeling of Yb-doped fiber photodarkening kinetics.
authors.affiliation: Aalto University School of Sciences and Technology, Tietotie 3, 02150 Espoo, Finland. joan.montiel@tkk.fi
authors.forename: Joan J
authors.initials: JJ
authors.lastname: Montiel I Ponsoda
authors.forename: Mikko J
authors.initials: MJ
authors.lastname: Söderlund
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Koplow
authors.forename: Joona J
authors.initials: JJ
authors.lastname: Koponen
authors.forename: Seppo
authors.initials: S
authors.lastname: Honkanen