Numerical investigation of dynamic coherent beam combining in turbulent atmosphere with taking into account the double-pass delay

Abstract

The paper is devoted to numerical investigation of coherent beam combining of 7-channel laser radiation and its focusing on the remote receiver in dynamic turbulent medium using the two-step stochastic parallel gradient (SPG) algorithm with the double-pass delay included in the step time or in the temporal shift between steps. Dynamic turbulent medium has been modelled using one phase screen approximation based on the Taylor hypothesis. The spatial spectrum of turbulent distortions has corresponded to the von Kármán spectrum and has been characterized by the atmospheric coherence radius (the Fried parameter) r0. Combining efficiency has been estimated for various ratios of the aperture size d to r0 and ratios of the phasing frequency νph (reciprocal value of time interval required to achieve the Strehl ratio equaled 0.8 in the nonturbulent medium) to the Greenwood frequency νG. The requirements for d/r0 and νph / νG values have been determined, under which the SPG coherent beam combining with taking into account the double-pass delay provides the Strehl ratio level of ~0.7 or higher.