We report the effective suppression of stimulated Raman scattering (SRS) in a high-power fiber laser oscillator with 15 m long delivery fibers by the insertion of a single chirped and tilted fiber Bragg grating (CTFBG). Inscribed in 20/400 μm fiber, the single CTFBG has been carefully designed and fabricated with a filter bandwidth of 22.8 nm to match the Raman gain spectrum. A maximum suppression ratio over 30 dB is achieved when the oscillator operates at 2.7 kW, with beam quality factor M2 of ~1.4. Moreover, the signal insertion loss is measured to be around 0.2 dB and the maximum temperature is about 41.6 °C at a room temperature of 25 °C. By improving the performance of CTFBG, a further power scaling and longer delivery distance of high-power fiber lasers could be achieved.
With a homemade (1+1) side-pumped fiber and 1018 nm tandem-pumping strategy, we report an experimental demonstration of 17.4 kW power output, which is apparently a remarkable achievement. The (1+1) side-pumped fiber consists of an active core, highly doped with Ytterbium up to 2000 ppm, and a pump core to transport intensive pumping power through a homemade 5×1 combiner. Stimulated Raman scattering suppression ratio at maximum power is improved to 37.8 dB due to an array of connected tilted fiber Bragg gratings performance. So, the experimental result clarifies the feasibility of combining side- and tandem- pumping in ultra high power scale of tens of kilowatts.
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