Femtosecond pulse amplification system with GHz adjustable repetition rate based on harmonic mode locking
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摘要: 报道了一种基于被动谐波锁模种子源的 GHz 重复频率飞秒光纤激光放大系统,实现了1~3 GHz范围内的稳定运行。系统采用两级放大器并结合色散管理技术,在全调谐范围内均保持稳定输出。在脉冲重复频率为3.1 GHz和2.0 GHz的条件下,分别实现了2.1 W的平均输出功率和195 fs的最窄脉冲宽度,且相应放大后的边模抑制比均保持在33 dB以上。结果表明,该方案能够在宽频率范围内实现稳定的高功率放大与脉冲压缩,为高重复频率超快光纤激光的应用奠定了实验基础。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 repetition-rate-tunable 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, 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 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 repetition-rate-tunable amplification of femtosecond fiber lasers on a single all-fiber platform. -
表 1 不同谐波锁模状态下主放大后脉冲输出特性
Table 1. Amplified pulse characteristics at different repetition rates
repetition
rate/GHzpre-amp pump power
(forward)/mWpre-amp pump power
(backward)/mWmain amp pump
powe/Waverage output
power/Wcompressed pulse
width/fsSMSR/dB SNR/dB 1.1 326 292 9.5 1.41 305 34.1 63.3 1.6 498 556 9.5 1.68 195 38.1 63.8 2.0 672 735 9.5 1.85 195 35.4 58.1 2.8 672 735 9.5 2.03 269 34.0 51.0 3.1 672 735 9.5 2.10 370 35.3 53.2 -
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