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High power fiber lasers are widely used in industrial processing such as cutting and welding. A high-power single-mode fiber laser emits laser beams in a single transverse mode (fundamental mode), exhibiting near-diffraction-limited laser transmission characteristics. It can converge into smaller light spots and achieve higher power density. Therefore, it serves as a preferred laser source for precision machining tasks involving high-speed and high-precision cutting, such as cutting of high-reflective materials, welding of dissimilar metal materials, and other industrial precision processing scenarios. It can also serve as a basic module for achieving higher laser power output with good beam quality through beam combining. The power scaling of a single fundamental mode fiber laser is limited by factors, such as transverse mode instability and nonlinear effects. This article introduces multi-stage amplified structures that employs wavelength-stabilized 976nm pump diodes, homemade fiber gratings, cladding light strippers and pump combiners. With the high-performance homemade Raman scatter suppressor and a well-designed fiber coiling approach, the high-order modes and Raman light in fiber laser are suppressed effectively. A single fundamental mode continuous laser has been achieved stably at maximum output power of 3 kW, optical slope efficiency of 79.97 %, M2 factor of 1.05, and Raman suppressed ratio of ≥ 35dB. Further improvements can be made by increasing the pump source power and enhancing the filtering efficiency of the Raman scatter suppressor, which is expected to enable higher single fundamental mode power output.
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