Numerical analysis of the effects of aberrations on coherently combined fiber laser beams

Numerical analysis of the effects of aberrations on coherently combined fiber laser beams is presented. We prove that traditional beam quality criteria, such as the M2 factor and the Strehl ratio, do not consider necessary information to evaluate the quality of a coherently combined laser beam. The beam propagation factor (BPF) is introduced and studied as a proper beam quality factor for the coherently combined beam. Two main categories of aberrations, geometry and nongeometry factors, are numerically studied to investigate their effect on beam quality by using the BPF criterion. For a ring-distributed fiber laser array with certain vacancy factor and a RMS value of tilt error, we obtain a semianalytical equation to evaluate their effect on beam quality. We present a brief discussion of those aberrations at the end of this paper. Our generalized methodology offers a good reference for investigating coherent combining of fiber laser beams in a comprehensive way.