We present highly efficient three-channel dual-grating spectral beam combining with a combined signal output power of 5.5 kW at an excellent beam quality of M<sup>2</sup> = 1.5. Three 2-kW all-fiber narrow-linewidth continuous-wave Ytterbium-doped fiber amplifiers at 1050 nm, 1070 nm and 1090 nm were combined using in-house fabricated polarizationindependent dielectric reflection gratings. The total combining efficiency was 94% at full power level, which is close to the expected value referred to the incorporated grating’s efficiency in a dual-grating setup.
We present and compare the performance of bidirectionally pumped Yb-doped monolithic amplifier and oscillator setups in 20/400 μm geometry tested up to signal powers of 3.5 kW and 5 kW without the occurrence of transverse mode instabilities and maintaining a single mode beam quality of M<sup>2</sup> ~ 1.3. The scaling was primarily limited by the nonlinear effect of Stimulated Raman Scattering. This contribution contains detailed analysis of the temporal and spectral behavior of both configurations. The results show the excellent feasibility of monolithic oscillators and FBG for high power operation, even outperforming the amplifier pendant in terms of output power.
We demonstrate a quasi-continuous wave laser amplifier with a peak output power of 6.8 kW pumped by an industrial thin-disk laser. A high slope efficiency of 84 % has been obtained within a duty cycle of 10 % at a signal wavelength of 1071 nm. For cw-pumping we measured a maximum output power of 985W. The amplifier fiber had a step index profile with a core diameter of 45μm and a pump core diameter of 120μm. A signal to ASE peak ratio of 48 dB could be determined.