Generation of 431 fs, 321 μJ femtosecond pulses from chirped-pulse Yb-fiber and Yb:YAG hybrid amplifiers by using FBG spectral shaping technique

A hybrid chirped pulse amplification (CPA) system is demonstrated based on a fiber seed source and a three-stage Yb:YAG crystal amplifier. We investigate the mechanism of gain narrowing in a CPA system through theoretical and experimental research. The gain narrowing can be suppressed by pre-shaping the pulse spectrum via a fiber Bragg grating (FBG) with a specifically designed spectral characteristic before amplification. The compact compressor is based on a transmission diffraction grating with a line density of 1739 lines/mm. The high-order dispersion within the CPA system is compensated by a tunable dispersion stretcher. At a repetition rate of 200 kHz, the compressed average power of 64.15 W and pulse duration of 431 fs, corresponding to a pulse energy of 321 μJ and a peak power of 744 MW, is obtained. The polarization extinction ratio of the pulses is about 23 dB, and the M² factor is less than 1.16. In addition, the long-term power stability is tested, and the root mean square of the average power is below 0.17% over 39.5 hours. Such good performance is beneficial to ultrafast material processing in scientific research and industrial fields.