In this work, we employed gain-managed nonlinear amplification (GMNA) technology to achieve a pulse characterized by a smooth spectral profile and an exceptionally wide spectral bandwidth. Then this pulse was injected into a chirped pulse amplification (CPA) system for amplification, and a high energy, narrow pulse duration fiber laser system was successfully built. The initial seed source for system was a self-made mode-locked fiber oscillator that utilized a nonlinear amplifying loop mirror (NALM). This oscillator produced ultrashort pulses with a pulse duration of 10.96 ps at a repetition rate of 11.52 MHz. The spectral width of the mode-locked oscillator was significantly broadened from 5.83 nm to 63.97 nm using GMNA technology. Furthermore, the spectral profile, which initially exhibited severe oscillation structures, was reshaped into a smooth profile through the application of GMNA. Subsequently, the pulse energy was increased through CPA amplification. Finally, in the case of a central wavelength of 1064 nm and a repetition rate of 500 kHz, a pulse with an average power of 20.02 W, a single pulse energy of 40 μJ, a pulse duration of 179 fs, and a peak power of 224 MW was obtained. This fiber laser system has great prospect of application in clinical medicine and precision manufacturing due to its high energy and ultra-short pulse duration.
In this work, we demonstrate a gain-managed nonlinear amplifier with a large mode area fiber numerically and experimentally. The seed source was a home-made mode-locked fiber oscillator using a Nonlinear Amplifying Loop Mirror (NALM) that delivered ultrashort pulses with a pulse width of 8.77 ps at a repetition rate of 1 MHz. The corresponding optical spectrum centered at 1029 nm with a 3dB bandwidth of 13 nm. The pulse energy was increased to 5 nJ by a core-pumped fiber pre-amplifier. After then, a narrow-band spectral filter was inserted to reduce the pulse width and injected into a 3 m long double-clad Yb-doped fiber with a core diameter of 20 μm, which was forward pumped with a 976 nm laser diode. Finally, we obtained 1.33 μJ pulses energy delivering after amplification, and 50 fs pulses output was obtained by post compression through 600 line/mm reflective grating pairs. The numerical work has been carried out as well, which has good agreement with the experimental result. This highly compact femtosecond fiber laser system with an ultrashort pulse width has potential applications in scientific research and precision manufacturing.
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