Target-in-the-loop coherent combining of 7 fiber lasers: first results

We developed a laser testbed coherently combining seven 1.5-µm fiber lasers through active phase control, using frequency-tagging to assess the phase fluctuations to be compensated for. In this paper, we present the testbed and its components as well as the results obtained in direct coherent combining, operated at the output of the lasers, without target-in-the-loop feedback. We then introduce the basic principle and show the first indoor results of target-in-the-loop coherent beam combining experiments at a shorter distance of 15 meters. We then describe the outdoor facility that was chosen for longer range experiments and show qualitative results and qualitative comparisons of the target-in-the-loop coherent beam combining challenge when the target is moved farther away, increasing the range from 15 meters to up to 1 km.