Narrow-line, 1178nm CW bismuth-doped fiber laser with 6.4W output for direct frequency doubling

We achieved a 0.2nm linewidth output at 1178nm with powers up to 6.4W in a linear 80m Bismuth-doped fiber cavity pumped by a 55W Yb fibre laser. The potential of frequency doubling of the non-polarized output at 1178nm in MgO doped periodically poled lithium niobate was demonstrated and resulted in 125mW average power at 589nm. The approach can be extended to a linearly-polarized large mode area format with under 0.1nm linewidth capable of scaling to Watts level in the 560-620nm range.