2 kW narrow spectral width monolithic continuous wave in a near-diffraction-limited fiber laser

We demonstrate a monolithic continuous wave (CW) fiber laser source at 1070 nm, producing 2 kW laser power with a very narrow spectral width (∼75  GHz) and near-diffraction-limited beam quality (M2<1.4). The laser consists of a CW fiber laser oscillator and two double cladding fiber amplifiers in the master oscillator-power amplifier configuration. The master oscillator is a distributed Bragg reflected fiber laser, producing ∼6  W laser power with ∼25  GHz spectral width. The two double cladding fiber amplifiers were developed to enhance the laser power up to ∼200 and ∼2050  W, respectively. The slope efficiency of the main amplifier reaches 84.8%. Under the full power output, the 3 dB spectral width and 20 dB spectral width of the laser emission spectrum was ∼75  GHz and 1.2 nm, respectively.