MHz Repetition Rate Femtosecond Yb:CaGdAlO4 Regenerative Amplifier Generating 20-W 168-fs Pulses

In this letter, a Yb:CaGdAlO4 crystal-based femtosecond regenerative amplifier with a repetition rate of 1 MHz is demonstrated. The amplifier delivers an average output power of 21.8 W with an absorbed pump power of 47.8 W before compression. The slope efficiency and the optical-to-optical efficiency, measured with respect to the absorbed pump power, are 54.9% and 45.6%, respectively. Upon using a grating-pair for compression, 168-fs pulses with pulse energy of $20 ~\mu \text{J}$ and peak power of 105 MW are obtained. Benefiting from the good thermal management and the great optical-optical efficiency, the beam quality (M2) on both axes is less than 1.2.