20 kW fiber laser with high beam quality enabled by tapered ytterbium-doped fiber

The tapered fiber with varied core diameter along the longitudinal direction has a unique advantage in balancing Stimulated Raman Scattering (SRS) suppression and beam quality, making it a promising approach for purchasing high power laser with high beam quality. Recently, a monolithic high power fiber laser counter pumped by 1018 nm fiber lasers has been experimentally established employing tapered ytterbium-doped fiber made in house. A maximum power of 20.2 kW is achieved with the beam quality factor β<2 and Raman-suppression ratio of 33 dB. The results have demonstrated the great potential of tapered fiber in power scaling to tens of kW fiber laser while achieving good beam quality.