MHz repetition rate femtosecond Yb:CaGdAlO4 regenerative amplifier generating 20-W 168-fs pulses

In this letter, a Yb:CaGdAlO 4 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 μJ and peak power of 105 MW are obtained. Benefiting from the good thermal management and the great optical-optical efficiency, the beam quality (M 2 ) on both axes is less than 1.2.