Nanosecond-pulsed thulium-Raman hybrid fiber amplifier at 2.1 µm

We demonstrate a hybrid thulium-Raman pulsed fiber amplifier operating at 2109 nm by combining Tm laser amplification with Raman frequency shifting to access wavelengths beyond the effective thulium gain window. The system delivers 157 µJ, 20 ns square pulses (8 kW peak power) at 100 kHz, with linear polarization (25 dB polarization extinction ratio), a 239 pm (10 dB) linewidth, and near diffraction-limited beam quality (M²=1.03). The results highlight hybrid Tm-Raman gain as a practical route to nanosecond pulse generation in fiber-based sources in the >2.1 µm regime.