Abstract

Tandem pumping is a promising technique for gaining higher power from ytterbium-doped fiber (YDF) lasers. However, the characteristics of tandem pumped laser light, especially their variation with the lasing wavelengths, were not thoroughly investigated. We investigated the characteristics with the first 1018-nm tandem-pumped high-power tunable YDF laser. The 1018-nm tandem pumping was not applicable in tunable fiber lasers before because its much-lower absorption requires compensation of long YDFs, which enhances destructive nonlinear effects as a barrel effect for tuning wavelengths. Here, the setup used a fiber ring-cavity as seed, which was much more cost-effective than conventional setups, and only three stages of amplification, of which the last stage was unidirectional tandem-pumped. By deliberate system design, it gained over 1-kW output powers at wavelengths tuning from 1060–1090 nm with ∼100-pm 3 dB linewidths and 79.4%∼85.6% slope efficiencies. Amplified spontaneous emissions (ASE) and stimulated Brillouin scattering (SBS) caused no limits for further scaling powers. Variations of spectra and beam qualities of the outputs with the tuning wavelengths were revealed in detail in the experiment. Drastically varying linewidths at ∼1062 and ∼1080 nm suggested complex evolution of the nonlinear effects with the pump light. This study offers not only an economic seed setup to high-power narrow-linewidth tunable fiber lasers, but detailed characteristics of laser amplified with 1018-nm pump in YDFs. The knowledge of the characteristics can usefully guide future design of high-performance tandem-pumped fiber lasers.

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