High power and efficiency tandem-pumping of a widely tunable Tm-doped all-fiber MOPA

In this study, we demonstrate a high-power and widely-tunable Tm-doped all-fiber master oscillator power amplifier (MOPA) in a core- and tandem-pumping configuration. The ground-state bleaching effect of Tm-doped fiber tandem-pumped at 1943nm was investigated. The master oscillator is a Tm-doped fiber ring laser incorporating a tunable bandpass filter to realize a narrow linewidth and wavelength-tunable operation. The MOPA delivered 103 W of output power at 1980nm, with >83 W maintained over a 60 nm tuning range from 1960 to 2020nm, achieving a high slope efficiency of ∼ 80%. The laser exhibited a spectral linewidth of ∼0.15 nm and a high optical signal-to-noise ratio (OSNR) of >42 dB, attributed to the effective suppression of amplified spontaneous emission (ASE) by tandem pumping. The power stability (RMS) at a scale of ∼10 min was measured to be approximately 0.75%. A diffraction-limited beam quality factor M² of ∼1.18 (horizontal) and 1.16 (vertical) was measured at the maximum laser output. The laser power is pump-limited without the onset of parasitic oscillation or thermal-induced transverse mode instability (TMI) effect, even at the maximum power level. This represents the first demonstration, to the best of our knowledge, of an all-fiber-integrated, wavelength-tunable Tm-doped fiber laser reaching the 100-watt level under efficient tandem pumping.