title: Narrow linewidth, single mode 3 kW average power from a directly diode pumped ytterbium-doped low NA fiber amplifier.
abstract: We report on a newly designed and fabricated ytterbium-doped large mode area fiber with an extremely low NA (~0.04) and related systematic investigations on fiber parameters that crucially influence the mode instability threshold. The fiber is used to demonstrate a narrow linewidth, continuous wave, single mode fiber laser amplifier emitting a maximum output power of 3 kW at a wavelength of 1070 nm without reaching the mode-instability threshold. A high slope efficiency of 90 %, excellent beam quality, high temporal stability, and an ASE suppression of 70 dB could be reached with a signal linewidth of only 170 pm.
authors.forename: F
authors.initials: F
authors.lastname: Beier
authors.forename: C
authors.initials: C
authors.lastname: Hupel
authors.forename: J
authors.initials: J
authors.lastname: Nold
authors.forename: S
authors.initials: S
authors.lastname: Kuhn
authors.forename: S
authors.initials: S
authors.lastname: Hein
authors.forename: J
authors.initials: J
authors.lastname: Ihring
authors.forename: B
authors.initials: B
authors.lastname: Sattler
authors.forename: N
authors.initials: N
authors.lastname: Haarlammert
authors.forename: T
authors.initials: T
authors.lastname: Schreiber
authors.forename: R
authors.initials: R
authors.lastname: Eberhardt
authors.forename: A
authors.initials: A
authors.lastname: Tünnermann