Investigation on the effect of transverse phase error in tiled-array based coherent beam combining

Abstract

Coherent combining of an array of laser beams through a tiled aperture configuration is an effective method for scaling the far-field intensity. However, several parameters including the array fill factor, longitudinal as well as transverse phase errors, and mismatch in beam quality limit the maximum achievable beam combination efficiency in the far field. Optimizing such parameters and mitigating the effect of phase errors requires in-depth investigation of the tiled array beam combining system. We numerically analyze the performance of such a system in the presence of all the above errors using the band-limited angular spectrum method of field propagation, while employing the Stochastic Parallel Gradient Descent (SPGD) technique to synchronize the phase of the constituent elements. Based on simulations, we find that the fill factor of the array and the pointing error of the constituent beams are the major factors that degrade the beam combining efficiency and we quantify the degradation due to such factors. The simulation results are validated using a 7-channel tiled aperture beam combining experimental setup with a provision of tip-tilt adjustment for the individual beams.