This paper reports an ytterbium-doped linear-cavity fiber laser with the optical length of 1.6 km passively modelocked by a high modulation depth semiconductor saturable absorber mirror (SESAM). An ultra-low repetition rate of 191 kHz was achieved. The laser delivered the highly-chirped output pulses with the energy up to 75.2 nJ.Intensity, a.u. Pulse spectrum of 400-m mode-locked ytterbium-doped fiber laser where the central wavelength was 1033 nm and FWHM is 3.5 nm

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