We have developed a commercial 4-kW fiber laser consisting of seven, 600-W modules whose outputs are combined
with a fused-fiber combiner. The system architecture has several practical advantages, including pumping with reliable
single-emitter diodes, monolithic fused-fiber construction (no free-space beams), and end pumping using a 91:1 pump
combiner (eliminating the need for complex pump/signal combiners). Typical results at 4-kW output power are a beamparameter
product of 2.6 mm-mrad, 8-hr power stability of < 0.5% rms, central wavelength of 1080 nm, and linewidth of
1.2 nm FWHM. These lasers have been incorporated into Amada machines used for cutting metal sheet and plate and
have been used to cut aluminum, mild steel, stainless steel, brass, titanium, and copper with a thickness up to 19 mm. A
world-record cutting speed of 62 m/min has been demonstrated for 1-mm aluminum sheet metal.