Abstract
Abstract Mode distortion induced by stimulated Raman scattering (SRS) has become a new obstacle for the further development of high-power fiber lasers with high beam quality. Here, an approach for effective suppression of the SRS-induced mode distortion in high-power fiber amplifiers has been demonstrated experimentally by adjusting the seed power (output power of seed source) and forward feedback coefficient of the rear port in the seed source. It is shown that the threshold power of the SRS-induced mode distortion can be increased significantly by reducing the seed power or the forward feedback coefficient. Moreover, it has also been found that the threshold power is extremely sensitive to the forward feedback power value from the rear port. The influence of the seed power on the threshold power can be attributed to the fact that the seed power plays an important role in the effective length of the gain fiber in the amplifier. The influence of the forward feedback coefficient on the threshold power can be attributed to the enhanced SRS configuration because the end surface of the rear port together with the fiber in the amplifier constitutes a half-opening cavity. This suppression approach will be very helpful to further develop the high-power fiber amplifiers with high beam quality.
Highlights
High-power fiber lasers have found a wide variety of applications in industry, science, and defense owing to high conversion efficiency, robustness, easy thermal management, and especially excellent beam quality[1,2,3]
We propose and demonstrate an approach to suppress stimulated Raman scattering (SRS)-induced mode distortion in high-power fiber amplifiers by adjusting the seed power and forward feedback coefficient of the rear port in the seed source
It can been found that the SRS-induced mode distortion could originate directly from the nonlinear effects in MM fibers, rather than the thermallyinduced transverse mode instability (TMI) due to the quantum defect indirectly caused by the SRS process
Summary
High-power fiber lasers have found a wide variety of applications in industry, science, and defense owing to high conversion efficiency, robustness, easy thermal management, and especially excellent beam quality[1,2,3]. The evolution is suffering from a sudden halt owing to mode degradation phenomena[5,6]. Tao et al studied systematically the influence of a series of parameters of fiber lasers on the thermally-induced TMI[11,12,13], and established a comprehensive theoretical model[14]. Gao et al explained the sudden-change mechanism of the thermally-induced TMI from the perspective of non-equilibrium phase transition[15]
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