title: Efficient Yb laser fibers with low photodarkening by optimization of the core composition.
abstract: We report on photodarkening (PD) investigations at Yb doped fibers with specific variation of the concentrations of the codopants aluminum and phosphorus, measured during cladding pumping at 915 nm. A core composition with equal content of Al and P is most promising to achieve Yb fibers with low PD, high laser efficiency and low numerical aperture of the laser core despite of high codoping. A laser output power of more than 100 W was demonstrated on such a fiber with a slope efficiency of 72%. The correlation of the PD loss with the NIR-excited cooperative luminescence encourages the supposition that cooperative energy transfer from excited Yb(3+) ions to the atomic defect precursors in the core glass enables the formation of color centers in the pump-induced PD process.
authors.affiliation: Institute of Photonic Technology, Albert-Einstein-Str. 9, 07745 Jena, Germany. sylvia.jetschke@ipht-jena.de
authors.forename: Sylvia
authors.initials: S
authors.lastname: Jetschke
authors.forename: Sonja
authors.initials: S
authors.lastname: Unger
authors.forename: Anka
authors.initials: A
authors.lastname: Schwuchow
authors.forename: Martin
authors.initials: M
authors.lastname: Leich
authors.forename: Johannes
authors.initials: J
authors.lastname: Kirchhof
mesh_terms: D000535:Aluminum / Q000737:chemistry; D004867:Equipment Design; D005453:Fluorescence; D007259:Infrared Rays; D007477:Ions; D007700:Kinetics; D007834:Lasers; D008027:Light; D055095:Optics and Photonics; D010758:Phosphorus / Q000737:chemistry; D015018:Ytterbium / Q000737:chemistry*
chemical_list: D007477:Ions; D010758:Phosphorus; D000535:Aluminum; D015018:Ytterbium