Kilowatt-level high-repetition-frequency picosecond lasers are widely used in fields such as free-electron lasers, attosecond science, and high-precision material processing. Currently, the average output power of commercial ultrafast lasers is on the order of hundreds of watts, and the pulse energy is on the order of tens of millijoules. However, some scientific and industrial applications require a higher average output power with high pulse energy. Thin-disk lasers have centimeter-level laser spots on the gain medium and low-thermal-distortion characteristics, thus rendering them ideal for achieving average power levels on the order of kilowatts and pulse energies on the order of millijoules.

Based on the 72-pass self-developed thin-disk pump module, a thin-disk regenerative amplifier with a large stable range was designed, thus allowing the regenerative amplification cavity to achieve favorable mode matching within the operation range. To avoid damage to key optical components, the thin-disk regenerative amplifier was designed based on chirped pulse-amplification technology. The experimental setup is shown in Fig. 1. After injecting the seed laser, the high-voltage loading time of the Pockels cell or the number of round trips in the regeneration cavity was controlled, and a high-power picosecond laser output was obtained.

As shown in Fig. 2(a), under a maximum continuous pump power of 650 W, a regenerative-amplifier laser output with an average power of 312 W and a repetition frequency of 50 kHz is obtained, which corresponds to an optical efficiency of 48.1% and a slope efficiency of 53.8%. The output pulse sequences at repetition rates of 50/100/200 kHz are shown in Fig. 2(d); the RMS of the single-pulse energy is 0.5% at 50 kHz. The beam quality factor M² at a maximum output power of 312 W is 1.05/1.09 and the near-field output laser spot roundness is 91%. Owing to the gain-narrowing effect, the spectral width of the amplified laser is 1.80 nm, which theoretically supports the compression of the pulse width to 867 fs.

Based on the self-packaged thin-disk and 72-pass thin-disk pump module, an amplified laser output with an average power of 312 W, a pulse width of 720 ps, and an optical efficiency of 48.1% is achieved at a repetition frequency of 50 kHz. To the best of our knowledge, this is the highest output power and optical?optical efficiency reported for thin-disk regenerative amplifiers in China. In the future, our group shall further optimize the thin-disk packaging technology, increase the pump power to increase the output power to the kilowatt level, and compress the output pulse width to less than 1 ps.