High-power, high-beam-quality spectral beam combination of six narrow-linewidth fiber amplifiers with two transmission diffraction gratings.

We demonstrate 10 kW spectral beam combination of six narrow-linewidth fiber amplifiers by two transmission gratings with a combining efficiency about 90%. The wavelengths of incident beams range from 1056 to 1088 nm. Each fiber amplifier delivers 2 kW output power laser with 0.25 nm root-mean-square (RMS) linewidth. A dual-grating beam-combining system is constructed to combine the six beams into a 10 kW level high-power beam and control the beam quality factor ${{\rm M}^2} \lt {2}$M<2 by dispersion compensation. To the best of our knowledge, this is the highest output power combined by transmission gratings, which verifies the feasibility of transmission grating under high-power density laser radiation and provides an alternative approach for high-power beam combining.