Single-frequency 332 W, linearly polarized Yb-doped all-fiber amplifier with near diffraction-limited beam quality

A 332 W all-fiber amplifier chain with single frequency and single polarization (average extinction ratio >21 dB) is presented based on master oscillator power amplification configuration. A highly Yb-doped concentration fiber of 2.8 m with a core diameter of 30 μm is utilized as the gain fiber in the final fiber amplifier. The slope efficiency of the main amplifier is measured to be 83.7% and the beam quality (M² factor) is measured to be 1.4. By measuring the polarization extinction ratio (PER) of the amplifier in a different power, we conclude that the PER degrades little as the output power enhances. The output power of backward light reveals that stimulated Brillouin scattering effect is not induced in the configuration. To the best of our knowledge, this is the highest power of all-fiber single frequency and single polarization amplifier with near-diffraction-limited beam quality.