Beam Pointing Estimation in Target-in-the-loop Coherent Beam Combination through 300m Atmospheric Turbulence

A laser testbed based on active coherent combination (CBC) of seven 1.5 µm fiber amplifiers has been developed for applications requiring high power such as power density deposition on target or free space laser communication. The seven 3W fiber amplifiers are combined using the frequency-tagging LOCSET technique in a Target-in-the-loop (TIL) configuration [1] as shown in fig. 1 . In situ Piston and Tilt (PISTIL) interferometer provides the relative phase of each emitter in the emitter plane [2] . Successful combination has been achieved after a 300m horizontal propagation, 1.5m above the ground, with low wind velocity and an average estimated turbulence strength $C_n^2 = {10^{ - 13}}{m^{ - 2/3}}$ .