High-efficient kW-level single-mode ytterbium fiber lasers in all-fiber format with diffraction-limited beam at wavelengths in 1000-1030 nm spectral range

The kW-level single-mode Yb fiber lasers at wavelengths in 1000 -1030nm spectral range with diffraction-limited beam and with direct diode pumping are remarkable high brightness and low quantum defect sources for tandem pumping of multi-kilowatt fiber and crystal laser systems. In this paper we present SM Yb fiber lasers in all-fiber format with powers 0.75kW, 0.90kW, 1.33kW and 1.40kW at 1007nm, 1010nm, 1018nm and 1030nm respectively with M² values of output beams < 1.1. These are the highest powers of single mode CW Yb fiber lasers at wavelengths near 1 micron to the best of our knowledge. The fiber oscillators with direct diode pumping are highly efficient and have optical slope efficiencies from 64% at 1007nm to 78% at 1018nm relative to total laser diode pump power. The fiber lasers have 3-5m output delivery cable terminated with a LC-8 connector in dependence on power level and MFD of output fiber. The pump and non-linear process (SRS and MI) limitations are discussed.