Nanosecond-pulsed fiber lasers are widely used in laser processing, remote sensing, and communications. Their performances are often limited by nonlinear effects such as four-wave mixing (FWM) which causes unstable sub-peaks and restricts further power scaling. 

In a study published in Optics and Lasers in Engineering, a research team led by Prof. ZHAO Wei from the Xi'an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences greatly enhanced the performance of high-energy, narrow-linewidth, nanosecond-pulsed fiber lasers by using stimulated Brillouin scattering (SBS) for pulse shaping.

Researchers introduced a segment of polarization-maintaining large-mode-area germanium-doped fiber into the pre-amplifier stage. The SBS was successfully induced to reshape the temporal profile of the injected pulse, which effectively suppressed the unwanted sub-peaks and increased the nonlinear threshold of the main amplifier.

Experiments demonstrated that the SBS-induced pulse shaping method increased the output power of the main amplifier from 3.4 W to 5.8 W with pulse energy rising from 0.34 mJ to 0.58 mJ, while maintaining a narrow linewidth of 0.082 nm, a pulse width of 4 ns, a repetition rate of 10 kHz, and near-diffraction-limited beam quality.

Unlike electro-optic or acousto-optic pulse shaping techniques limited to hundreds of nanoseconds and low power levels, the SBS-based method operates during the amplification process and is capable of shaping pulses at the 10 ns scale. It improves the pulse profile and enhances the overall energy extraction efficiency by broadening the spectral sidebands and reducing peak power density, thereby mitigating FWM and other nonlinear effects.

This study provides a new method for overcoming power limitations in narrow-linewidth pulsed fiber amplifiers, and highlights the positive role of SBS in laser amplification systems. The findings are expected to benefit applications requiring high-energy, high-quality nanosecond pulses such as precision manufacturing and nonlinear frequency conversion.