High average power large-pitch fiber amplifier with robust single-mode operation

Ytterbium-doped large-pitch fibers with very large mode areas are investigated in a high-power fiber amplifier configuration. An average output power of $294\mathrm{W}$ is demonstrated, while maintaining robust single-mode operation with a mode field diameter of $62\mathrm{\mu m}$. Compared to previous active large-mode area designs, the threshold of mode instabilities is increased by a factor of about 3.