210 W, 8.4 mJ Yb:YAG picosecond bulk amplifier

We present a high-power, high-energy Yb:YAG picosecond laser system delivering 210.9 W average power at 25 kHz repetition rate. A cascaded chirped fiber Bragg grating stretcher provides 3.6 ns stretched pulses, while a fiber pre-amplifier enhances the seed energy to mitigate period-doubling bifurcation in the regenerative amplifier (RA), ensuring stable operation of the RA with M² < 1.1. A three-stage thin-rod traveling-wave amplifier (TA) incorporating water-immersed heat sinks, undoped end caps, and off-focus beam arrangement achieves polarized output power of 227.5 W with a depolarization ratio below 3.6%. Following compression by transmission gratings with 92.7% efficiency, the system produces 8.4 mJ pulse energy and 1.64 ps pulse duration, with power stability of 0.12% root-mean-square (RMS) and beam quality of M² < 1.35.