Limpert, J.J.LimpertSchmidt, O.O.SchmidtRothhardt, J.J.RothhardtRöser, F.F.RöserSchreiber, T.T.SchreiberTünnermann, A.A.TünnermannErmeneux, S.S.ErmeneuxYvernault, P.P.YvernaultSalin, F.F.Salin2022-03-032022-03-032006https://publica.fraunhofer.de/handle/publica/21052110.1364/OE.14.002715We report on an ytterbium-doped photonic crystal fiber with a core diameter of 60 µm and mode-field-area of about 2000 µm2 of the emitted fundamental mode. Together with the short absorption length of 0.5 m this fiber possesses a record low nonlinearity which makes this fiber predestinated for the amplification of short laser pulses to very high peak powers. In a first continuous-wave experiment a power of 320 W has been extracted corresponding to 550 W per meter. To our knowledge this represents the highest power per unit length ever reported for fiber lasers. Furthermore, the robust single-transverse-mode propagation in a passive 100 µm core fiber with a similar design reveals the potential of extended large-mode-area photonic crystal fibers.en620621journal article