Generation of 125-GHz millijoule-level ultrashort pulse-train from a Yb:YAG regenerative amplifier and PMF-polarization-mode-based pulse division

This paper presents an ultrafast laser pulse train that delivers millijoule-class energy in 125 GHz train repetition rate, achieved mainly through a Yb:YAG regenerative amplifier (RA) combined with a polarization-maintaining fiber (PMF)-based pulse division scheme. The RA operates at a 5 kHz repetition rate in a mode-symmetrically distributed standing-wave resonant cavity incorporating a Yb:YAG crystal. The PMF-based pulse divider exploits the birefringence properties of PMF to realize pulse division at train repetition rates reaching the hundred-gigahertz or even terahertz regime, providing in a simple, stable, and cost-effective solution. Based on the integration of the RA and the pulse divider, the generation and evolution of satellite pulses induced by the Kerr nonlinear optical effect during the amplification of 125 GHz pulse trains are systematically investigated. Both numerical calculations and the experimental results confirm the temporal smoothing effect produced by a large sub-pulse number of pulse trains and its suppression effect on satellite pulse formation, and ultimately yielding a pulse train output with <i>N</i> = 32, an average power of 5.12 W, pulse energy of 1.024 mJ, and pulse duration of 2 ps.