High-power long-picosecond pulse fiber laser at 2 μm with a narrow spectral width

•The nearly transform-limited pulse with a narrow spectral width at 2 μm is presented.•Stable pulses with a duration of ∼105.6 ps and a linewidth of ∼86 pm were obtained.•The pulse laser system can deliver ∼19.42 W output power with a narrow linewidth.•The maximum output power of ∼100.7 W was obtained.