Modal instability-suppressing, single-frequency photonic crystal fiber amplifier with 811 W output power

An acoustic- and gain-tailored Yb-doped polarization-maintaining photonic crystal fiber is used to demonstrate 811 W single-frequency output power with near diffraction-limited beam quality. The fiber core is composed of 7 individually doped segments arranged to create three distinct transverse acoustic regions; including one region that is Yb-free. The utility of the Yb-free region is to reduce coupling between the LP01 and LP11 modes to mitigate the modal instability. The application of thermal gradients is utilized in conjunction with the transverse acoustic tailoring to suppress stimulated Brillouin scattering. To the best of our knowledge, the 811 W output represents the highest power ever reported from a near diffraction-limited single-frequency fiber laser.