Modal instability induced by stimulated Raman scattering in high-power Yb-doped fiber amplifiers

Modal instability (MI) and stimulated Raman scattering (SRS) are the main obstacles in the power scaling of fiber lasers and amplifiers. In the power scaling of a high-power ytterbium (Yb)-doped master oscillator power amplifier system, a new type of MI has occurred. Experimentally, it is shown that just at the onset of the SRS effect, MI takes place, and the degradation of the beam quality is observed. By the spectra and beam quality measurements, it is revealed that this type of MI can be mitigated firmly by suppressing the SRS effect in high-power Yb-doped fiber amplifiers.