Enhancement of TMI Threshold in Yb-Doped Fiber Laser by Optimizing Pump Wavelength

Transverse mode instability (TMI) is one of the main limitations for the power scaling of high-power fiber lasers. In order to suppress TMI and increase the output power of the fiber laser, we demonstrated a novel strategy by shifting the center wavelength of the pump source, i.e., laser diodes (LDs), from conventional 976 nm to the optimized 981 nm. A fiber oscillator is built to investigate the TMI effect in different pump wavelengths. Compared with 976 nm LDs, the TMI threshold increases from 208 W to 448 W when the laser is pumped by 981 nm LDs, indicating a 2.2 times enhancement of the TMI threshold. We also simulated and analyzed that the main heat source leading to TMI effect is the thermal effect caused by pump absorption, followed by quantum defect. We believe the optimized pump source has potential applications for suppressing TMI and in the power scaling of both broadband and narrow linewidth fiber lasers.