41 W, 206 fs regenerative amplifier based on CPA-free amplification of femtosecond pulses

We present a low-cost method to mitigate the gain narrowing effects during regenerative amplification based on a high-repetition-rate, high-power continuously pumped Yb:YAG thin disk regenerative amplifier (RA). By inserting a 1-mm-thick SiO 2 plate on a certain position in the RA, the narrowed bandwidth of the amplified spectrum of 3 nm was significantly broadened to a root-mean-square (RMS) bandwidth of 6.9 nm, which reveals the effectiveness of the method. At a repetition rate of 200 kHz, an output power of 41 W was obtained with a compressed pulse duration of 206 fs. The amplifier displayed stability with a root-mean-square power noise as low as 0.46%. The optical resonator remained nearly diffraction-limited beam quality (M 2 < 1.35) until the maximum output power.