High-power mid-infrared picosecond pulse bunch generation through difference frequency generation

We report a high average power mid-infrared picosecond (ps) pulse bunch output by means of direct difference frequency generation (DFG) in periodically poled magnesium-doped lithium niobate between a linearly polarized ps pulse bunch Yb fiber laser and a synchronized Er fiber laser. The ps pulse bunch Yb fiber laser was composed of an all polarization maintained "figure of eight" structured mode-locked Yb fiber laser as the seed, a pulse multiplier, and two stages of Yb fiber amplifiers. The mode-locked Yb fiber laser has an output ps laser pulse at 1030 nm with a repetition rate of 16.32 MHz. The pulses were then transformed to the pulse bunches through the pulse multiplier. Within each bunch, there were 16 equally spaced pulses with pulse widths of 8.5 ps and time intervals around 300 ps. The Er fiber laser had a gain switched seed laser diode working at 1550 nm with a pulse width around 5.1 ns, which was synchronized to the mode-locked Yb fiber laser pulse bunch, and two stages of Er fiber amplifiers. Under the average power of 27.8 W of Yb fiber laser, we obtained an average output power of 3.1 W at 3.07 µm. This is, to the best of our knowledge, the highest average power mid-infrared ps pulse bunch obtained via DFG directly.