title: Mitigating transverse mode instability in all-fiber laser oscillator and scaling power up to 2.5 kW employing bidirectional-pump scheme.
abstract: Transverse mode instability (TMI) is one of the main limiting factors in kW-level fiber lasers. Unlike fiber amplifiers, TMI in fiber laser oscillators attracts less attention from researchers. In this work, we construct an all-fiber ytterbium-doped laser oscillator and investigate the performance in co-pumping and bidirectional-pumping configurations, respectively. In the co-pumping scheme, TMI occurs at ~1.6kW and restricts further output power scaling. Different from the characteristic of dynamic TMI in fiber amplifiers, quasi-static TMI is observed in the laser oscillator. Details of the temporal characteristic around the TMI threshold are provided. In the bidirectional-pumping scheme, experimental results validate that the TMI is mitigated notably by employing bidirectional-pumping instead of co-pumping. The output laser power is further scaled to 2.5kW with a slope efficiency of 74.5% and good beam quality (M2~1.3). At the maximum power, the FWHM bandwidth of optical spectra is 5.2nm, and the Raman stokes light is ~20dB below the signal.
authors.forename: Baolai
authors.initials: B
authors.lastname: Yang
authors.forename: Hanwei
authors.initials: H
authors.lastname: Zhang
authors.forename: Chen
authors.initials: C
authors.lastname: Shi
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Wang
authors.forename: Pu
authors.initials: P
authors.lastname: Zhou
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Xu
authors.forename: Jinbao
authors.initials: J
authors.lastname: Chen
authors.forename: Zejin
authors.initials: Z
authors.lastname: Liu
authors.forename: Qisheng
authors.initials: Q
authors.lastname: Lu