Yb-free Er-doped 980 nm pumped single-frequency fiber amplifier with output power of 54W and near-diffraction limited beam quality

The recent significant increase in output power of high brightness pump diodes has led to interest in high power cladding pumped Yb-free Er-doped fiber laser systems. Here, resonant pumping between 1480 and 1530 nm is attractive due to the low quantum defect, but has the drawback of limited pump power from especially commercially available high brightness pump diodes. Therefore, we decided to investigate the power scaling of Yb-free Er-doped single frequency amplifiers to output power levels of multiple 10 W with non-resonant pumping around 980 nm. To the best of our knowledge, the achieved power levels are several times higher than reached with previous Yb-free Er-doped amplifier systems with comparable near-diffraction limited beam quality.