Diffractive coherent combining of a 25 kW fiber laser array into a 19 kW Gaussian beam

Five 500 W fiber amplifiers were coherently combined using a diffractive optical element combiner, generating a 1.93 kW beam whose M2=1.1 beam quality exceeded that of the inputs. Combining efficiency near 90% at low powers degraded to 79% at full power owing to thermal expansion of the fiber tip array.