Recent progress in high-power ultrafast thulium-doped fiber lasers and mid-infrared supercontinuum sources

The research on high-power ultrafast thulium-doped fiber lasers at 2 μm wavelength and mid-infrared (mid-IR) supercontinuum sources at 2~5 μm wavelength is one of these hot spots because of their potential applications in eye-safe radar, material processing, and electro-optical countermeasure system, which has an irreplaceable role compared to other wavelength fiber lasers. Here, we review the recent work of our group at 2 μm high-power ultrafast thulium-doped fiber lasers and 2~5 μm high-power mid-IR supercontinuum sources. Firstly, we demonstrate a high-power picosecond-pulsed thulium-doped all-fiber master-oscillator power-amplifier (MOPA), which yielded 120 W of average output power at central wavelength of 1963 nm with pulse duration of 16 ps. And then, we demonstrate a 203 W average power all-polarization-maintaining (all-PM) thulium-doped fiber MOPA system delivering picosecond pulses without using conventional chirped pulse amplication (CPA) technique. The pulse duration of 15 ps at 611.5 MHz repetition-rate results in a peak-power of 22 kW in the final PM thulium-doped fiber power amplifier. The polarization extinction ratio (PER) at the highest average output power was measured to be >15 dB, further power scaling is limited by available pump power. Finally, we demonstrate a high-power mid-IR supercontinuum generation with up to 21.8 W average power and spectrum spanning from 1.9 to beyond 3.8 μm in a single-mode ZBLAN fiber pumped by a 2 μm amplified picosecond pulses from a single-mode thulium-doped all-fiber MOPA.