Scalable hybrid beam combining of kilowatt fiber amplifiers into a 5-kW beam

We report on the hybrid beam combination of five unpolarized fiber lasers with the output power of 5.02 kW. Each fiber laser provides the output with average power of 1.1 kW and full width half maximum (FWHM) linewidth of 0.3 nm. The five beams with different wavelength are first split into two orthogonal linear polarizations, spectrally combined by dual multilayer dielectric (MLD) diffraction gratings in turn, finally combined into a single beam using a polarization beam combiner. This hybrid system features a combining efficiency of 91.2%, the beam quality of M2=2.96×1.52, and excellent prospects for significant power scaling.