Dual-Grating Spectral Beam Combination of High-Power Fiber Lasers

We describe a dual-grating spectral beam combination (SBC) system to combine multiple high-power fiber laser outputs while maintaining near-diffraction-limited beam quality. The two gratings are parallel in a grating rhomb configuration, with input and output beams that are parallel but shifted with wavelength, rather than the typical angular dispersion of a single grating. The resulting advantage of the dual-grating SBC over other beam combination systems is the relaxation of the linewidth requirement. We combined two fiber lasers with output powers of 115 W each and linewidths of about 0.15 nm (similar to 40 GHz) to produce a combined beam of 1.90 W power with near-diffraction-limited beam quality (M(2) similar to 1.18).