Controllable quasi-CW lasers for SRS suppression in optical fibers

Suppression of stimulated Raman scattering (SRS) is essential in high-power fiber lasers. Regarding temporal intensity stability, phase-modulated single-frequency lasers (PM-SFLs) are considered the optimal seed lasers for SRS suppression in high-power fiber amplifiers. This study proposes and demonstrates a category of quasi-continuous-wave (quasi-CW) lasers with controllable temporal intensity stability, achieved by combining two PM-SFLs. The theoretical analysis reveals the potential and mechanism of the controllable quasi-CW lasers for higher Raman thresholds than PM-SFLs. Notably, the dispersion makes them close to CW pumps for Raman Stokes light, and their broadband spectrum contributes to a higher Raman threshold. The experimental results verify that an appropriate wavelength interval enables the controllable quasi-CW lasers to have slightly better SRS suppression than a single PM-SFL. This study could provide new insights for designing lasers with tunable spectral and temporal properties, especially for SRS suppression in optical fibers.