High SBS-threshold, narrowband, erbium codoped with ytterbium fiber amplifier pulses frequency-doubled to 770 nm.

We present results of pulsed, narrowband amplification at 1540.6nm using a polarization maintaining, large mode area gain fiber codoped with erbium and ytterbium. At a repetition rate of 55 kHz, 2.9 W of average 1540.6nm power were generated with a pulse duration of 136 ns, corresponding to an SBS free peak power of 360 W. The amplified signal was frequency doubled in peridically poled potassium titanyl phosphate and conversion efficiencies of up to 56% were generated. When varying the repetition rate between 55-150 kHz the conversion efficiency changed from 56% to 35% due to the limited pump power.