Mode dynamics in high-power Yb-Raman fiber amplifier

Area of Science:

• Fiber laser technology
• Nonlinear optics
• Laser engineering

Background:

• Ytterbium-Raman fiber amplifiers (YRFAs) offer compact solutions for high-power, narrow linewidth, and special wavelength lasers.
• Understanding mode interaction dynamics is crucial for optimizing YRFA performance.

Purpose of the Study:

• To realize a high-power Ytterbium-Raman fiber amplifier (YRFA) at 1150 nm.
• To investigate the beam cleanup effect and mode instability (MI) in YRFAs.
• To develop a model explaining Raman mode interaction and its impact on MI.

Main Methods:

• Tandem-pumping a Ytterbium-Raman fiber amplifier with a 1018 nm fiber laser.
• Utilizing seed wavelengths of 1090 nm and 1150 nm.
• Observing and modeling mode interaction dynamics, beam cleanup, and mode instability.

Main Results:

• Achieved a 1338 W, 1150 nm laser output, a reported record power for this wavelength.
• Observed a beam cleanup effect in large mode area, step-index fiber for pump powers from 800 W to 1700 W.
• Identified mode instability (MI) onset at approximately 2 kW, attributed to stimulated Raman scattering, with a lower threshold than conventional Ytterbium-doped fiber amplifiers.

Conclusions:

• The developed Ytterbium-Raman fiber amplifier (YRFA) successfully generated record high power at 1150 nm.
• A novel beam cleanup effect was observed and explained by a proposed model considering Raman mode interaction.
• Mode instability (MI) in YRFAs is influenced by stimulated Raman scattering and occurs at a lower threshold than in conventional amplifiers.