1090 nm all-fiberized and Polarization-maintained fiber laser with narrow linewidth and near-single-mode beam quality is demonstrated. We obtain a 668 W narrow linewidth linearly laser output with a linewidth of about 22GHz, the polarization extinction ratio is about 14dB, and the M2 is less than 1.1 at the maximum output power.
We proposed a simple O-shaped cylinder all-fiber-integrated laser without inter-cladding-power-strippers (CPS) based on a quasi-bidirectional pumping scheme. The fiber grooves were inscribed on the outside of an O-shaped aluminium cylinder with both straight and curved tracks. The curved track with a diameter of 10 cm could suppress the high order modes and keep a stable beam quality with the increases of output power, while the straight parts improve the robustness for fusion points and unpackaged optical components. The simplified configuration of no CPS between the oscillator and the amplifier could also improve the total efficiency. The output power, the optical-to-optical efficiency, the beam quality, and the Raman suppression are systematically investigated. It is verified that this design introduces a practical way to simultaneously improve the transverse mode instability (TMI) and SRS thresholds in a high-power fiber laser system with a simple configuration and high efficiency.
In this paper, we report the experimental study on stimulated Raman scattering (SRS) induced mode instabilities (MI) in large mode area step-index fiber in a counter-pumped all-fiberlized amplifier. When the output power is scaled to 1560W, the ratio of SRS is 2% and the beam quality factor M2 is about 1.4. With the further scaling of output power, the SRS power begins to increase nonlinearly, and then the beam quality degrades obviously when the ratio of SRS exceeds 3%, and the M2 is about 2.1 at 1910W, that is the SRS induced MI. The phenomenon is accompanied by the temperature increasing of output passive fiber, which is caused by heat deposition of quantum defect between signal light and Raman light. The temporal dynamics of SRS induced MI is studied in detail for the first time, which are characterized by using both camera measurement and photodiode traces. The experiment results express that both the output power and output beam profile remain stable before the MI occurs, and fluctuate obviously after the onset of SRS induced MI. The temporal frequency investigation indicates that the SRS induced MI is a dynamic process with slow speed fluctuation at second level, and the Fourier spectrum of time trace is within 10Hz, and the SRS induced mode degradation is different from the Yb-gain induced MI effect.
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