Investigation of gain-filtering Yb-doped fibers with different gain-dopant doping ratios for high power amplifier.

• We theoretically and experimentally presented an investigation on the difference of TMI effect based on a series of gain-filtering Yb-doped fibers with different doping ratios, which is of interest to the community of high-power fiber lasers. • Four gain-dopant diameter ratio fibers, entailing 100% doping, ∼73% doping, Gaussian doping, and ∼57% doping, were fabricated by MCVD combined with solution doping technique. The TMI thresholds of four fibers were measured to be ∼1753 W, ∼3089 W, ∼3048 W, and over 3301 W, respectively, of which below the TMI threshold, the beam quality M2 factors were tested to be ∼1.52, ∼1.40, ∼1.45, and ∼1.32, respectively. • It meant that the TMI thresholds of ∼73%-doped, Gaussian-doped, and ∼57%-doped fibers were 1.76 times, 1.74 times, and over 1.88 times as much as that of 100%-doped fiber, respectively. Meanwhile, the simulated results also agreed well with the experimental results. The experimental and simulated results indicated that as the gain-dopant doping diameter reducing, the better gain-filtering effects of higher TMI threshold and more superior beam quality was manifested. We presented an investigation on gain-filtering Yb-doped fiber for the mitigation of transverse mode instability (TMI). The gain-filtering Yb-doped fibers were fabricated by modified chemical vapor deposition (MCVD) combined with solution doping technique. Four gain-dopant diameter ratio fibers, entailing 100% doping, ∼73% doping, Gaussian doping, and ∼57% doping, presented similar parameters with the core/inner cladding diameter of ∼30/400 μm and core numerical aperture (NA) of ∼0.061. The laser performances of four fibers were demonstrated by a bidirectional pumping all-fiber amplifier. The TMI thresholds of 100%-doped, ∼73%-doped, Gaussian-doped, and ∼57%-doped fibers, were measured to be ∼1753 W, ∼3089 W, ∼3048 W, and over 3301 W, corresponding to the M2 factors of ∼1.52, ∼1.40, ∼1.45, and ∼1.32, respectively. The experimental results indicated that by reasonably tailoring the gain-dopant doping diameter, better gain-filtering effect was manifested, exactly as higher TMI threshold and more superior beam quality. This contribution could provide an effective approach for obtaining high-brightness Yb-doped fiber amplifiers based on gain-filtering effect. [ABSTRACT FROM AUTHOR]