3.5??kW narrow-linewidth monolithic fiber amplifier at 1064??nm by employing a confined doping fiber

A high-power monolithic continuous-wave fiber amplifier at 1064 nm has been demonstrated based on a piece of confined ytterbium-doped fiber, which generated 3.5 kW narrow-linewidth laser with near-diffraction-limited beam quality. By tailoring the diameter of gain dopant across the fiber core, and optimizing the profile of refractive index and doping concentration, the confined doping fiber works making the fundamental mode more dominant in transverse mode competition, while suppressing the high-order mode. In a kilowatt-level narrow-linewidth fiber master oscillator power amplifier (MOPA) system, the threshold of mode instability (MI) is about 2.2 times as much as that of the conventional fiber amplifier. Then, by increasing seed power and utilizing a MOPA configuration with four amplifier stages, up to 3.57 kW signal output, a slope efficiency of 61% without any sign of MI or stimulated Raman scattering for a spectral dynamic range of higher than −50dB is obtained. A further increase of the output power was only limited by the available laser-diode pump power. To the best of our knowledge, this is the highest narrow-linewidth laser power generated from the confined doping monolithic fiber amplifier.