Power Scaling of Single-Frequency Ytterbium-Doped Fiber Master-Oscillator Power-Amplifier Sources up to 500 W

TLDR

The paper investigates continuous‑wave single‑frequency Ytterbium‑doped fiber MOPA sources, focusing on recent advances and presenting experimental results. The authors built 402‑W plane‑polarized and 511‑W random‑polarized MOPA systems, achieving 70–80 % efficiency, >20 dB gain, and near diffraction‑limited output. The MOPAs delivered 70–80 % efficiency and >20 dB gain, with a 7‑dB increase in SBS threshold for the PM YDF, no SBS up to the maximum power, and only weak SBS near 500 W in the non‑PM YDF due to thermal Brillouin gain broadening.

Abstract

We discuss continuous-wave single-frequency master- oscillator power-amplifier (MOPA) sources based on ytterbium- doped fibers (YDFs) with particular attention to their recent advances and our experimental results. This includes a 402-W plane-polarized MOPA source and a 511-W random-polarized MOPA source. In these MOPAs, the final-stage high-power amplifier operates with high efficiency of 70%-80%, and a high gain of over 20 dB in a near diffraction-limited beam. We report at least 7-dB enhancement of the stimulated Brillouin scattering (SBS) threshold for the 402-W polarization-maintaining (PM) YDF. In fact, we did not see any sign of SBS even at the highest output power. We eventually observed SBS appearance at around 500 W for the non-PM YDF. The observed SBS strengths were far weaker than expected in theory, unless we allowed for the Brillouin gain reduction from thermal Brillouin gain broadening induced by the quantum-defect heating.