High-Repetition-Rate Femtosecond Laser System with Time-Domain Shaping and Cooperative Chirped Pulse Amplification

Ytterbium-doped femtosecond fiber lasers are widely used in scientific research, industrial processing, and other fields due to their high quantum efficiency, wide gain bandwidth, and compact structure. This article addresses the problems of low processing efficiency and difficulty in increasing the average power of femtosecond lasers. A high repetition rate fiber chirped pulse amplification system is built, which uses a high repetition rate Figure-9 fiber laser as the seed source and an acousto-optic modulator (AOM) to shape the dense pulse train in the time domain. The main amplification stage uses a large mode field ytterbium-doped fiber to achieve full fiberization of the amplification system, and a volume grating (VBG) is selected as the pulse compressor to make the laser system highly integrated. When the repetition rate is 67.5 MHz, the compressed output laser has an average power of 20.5 W, a pulse width of 447 fs, a pulse train energy of 750 μJ, a spot ellipticity of 0.96, and a beam quality M2 better than 1.4 (Mx2=1.33, My2=1.16).