Kilowatt Average Powers from a Nanosecond, Polarization Maintaining, Large Mode Area Yb Fiber Amplifier

Large mode area (LMA) fibers with enhanced higher-order mode (HOM) loss enable average output power up to 5 kW in continuous wave (CW) operation while avoiding transverse mode instabilities in a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$22 \mu \mathrm{m}$</tex> core [1]. A <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$30 \mu \mathrm{m}$</tex> core fiber utilizing this strategy achieved nanosecond pulse energy of 1 mJ at kW average powers with diffraction limited output [2]. It is desirable to extend this performance to polarization maintaining (PM) fiber for enhanced environmental stability to support applications including micro-machining, light detection and ranging, quantum computing, and sources for scientific research.