Implementation of a projection-on-constraints algorithm for beam intensity redistribution

Abstract

Multi-Conjugate Adaptive-Optical (MCAO) systems have been proposed as a means of compensating both intensity and phase aberrations in a beam propagating through strong-scintillation environments. Progress made on implementing a MCAO system at the Starfire Optical Range (SOR), Air Force Research Laboratory, Kirtland AFB, is discussed. In previous work, it was shown that the First-stage Intensity Redistribution Experiment (FIRE) controlled and compensated wavefront intensity for static cases. As a secondary step toward controlling a two deformable mirror (DM) system, the FIRE experimental layout is used to examine another aspect of an MCAO system faster control of wavefront intensity. The FIRE experimental layout employs two wavefront sensors (WFS) and a single DM. One WFS is placed conjugate to the DM while the second WFS is located at a distance which produces a desired Fresnel number for the propagation between theWFSs. A modified Gerchberg- Saxton (GS) algorithm that propagates between image planes is employed for determining DM commands. The forward and back propagation portion of each GS iteration are computed in software. Using the GS solution, a control loop is closed on a WFS reconstructor in order to maintain beam shape in moving optical turbulence. The forward propagation phase pattern produced by the GS algorithm is tailored, via constraints, so that beam propagation along the path between the two WFSs produces a desired intensity profile and minimizes phase aberrations at the second WFS. In the next phase of MCAO development, a second DM will be added conjugate to the second WFS in order to correct the remaining phase aberrations.