Impact of seed source types on the stimulated Raman scattering threshold in high-power tandem pumped Yb-doped fiber amplifiers

This study presents a comprehensive analysis of stimulated Raman scattering (SRS) threshold behaviors in high-power tandem-pumped fiber amplifiers using three distinct seed sources: fiber oscillator lasers (FOLs), random fiber lasers (RFLs), and superfluorescent fiber sources (SFSs). Through precise regulation of operational parameters (including output power, beam quality, spectral wavelength, and Raman noise levels), the investigation identified temporal stability is the dominant factor in the effect of seed source type on the SRS performance of tandem pumped amplifiers. This findings aligns with prior research outcomes derived from laser diode-pumped amplifiers, confirming that temporal stability retains its critical influence even in systems employing ultra-long gain fibers. Experimental result revealed that SFS-seeded amplifiers achieved superior SRS thresholds, surpassing both FOL and RFL configurations. Conversely, RFL-seeded amplifiers exhibited the lowest thresholds owing to significant temporal instability. The SFS-seeded amplifier based on 25/250 µ m double-clad Yb-doped fiber achieved an SRS threshold exceeding 6000 W, surpassing the RFL-seeded counterpart by over 15% and the FOL by 7%. The results offer practical guidelines for optimizing SRS suppression in high-power tandem-pumped ytterbium-doped fiber laser systems.