Abstract:
Background Gigahertz-repetition-rate femtosecond fiber lasers have attracted increasing attention for applications requiring high temporal resolution and high average power, while most existing GHz fiber amplification systems are limited to fixed repetition rates.
Purpose This work aims to realize tunable repetition-rate amplification of gigahertz femtosecond pulses within a single fiber-based platform by employing a passively harmonic mode-locked fiber laser as the seed source.
Methods The seed laser provides stable pulse operation with repetition rates tunable from 1 to 3 GHz. A two-stage fiber amplification scheme combined with dispersion management is implemented to maintain stable amplification over the entire tuning range. In the pre-amplification stage, a controllable chirp is introduced to achieve near-linear temporal broadening, which effectively suppresses excessive nonlinear effects during power scaling. Pulse compression is subsequently implemented at the output using a single-mode fiber.
Results Experimental results show that stable pulse trains with regular temporal distribution are preserved throughout the tuning range. The maximum average output power reaches 2.1 W at a repetition rate of 3.1 GHz, while the shortest pulse duration of 195 fs is obtained at 2.0 GHz. After amplification, the side-mode suppression ratio remains higher than 33 dB.
Conclusions These results indicate the feasibility of gigahertz tunable repetition-rate amplification of femtosecond fiber lasers on a single all-fiber platform.
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