Continuous Tracking and Pointing of Coherent Beam Combining System via Target-in-the-Loop Concept

We demonstrate a technique to realize fine target tracking and pointing using target-in-the-loop (TIL) concept via a coherent beam combining (CBC) system. A tracking and pointing system is composed of a densely packed array of 7 phase-control elements with simultaneous piston and tilt controls of the outgoing beams wavefront phases. A photo-detector (PD) with a pinhole is used as target detection and installed on a translation stage. Energy detected by the mobile PD is used for evaluating the beam combining and scanning performance, and to provide the feedback signal for controls of piston and tilt phases of the transmitted beams by using the stochastic parallel gradient descent (SPGD) algorithm for merit function maximization.