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24 February 2012 Turbulence-corrected adaptive laser beam focusing on a remote image-resolved target
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Proper operation of an adaptive optics (AO) system requires the laser beacon to be on or near the image-resolved target along the line of site. Characterization of the wave returned from the beacon spot (the references wave) allows for the derivation of wavefront perturbations along the beacon-to-receiver range - data that can then be used to solve two problems: (i) restoration of the turbulence-corrupted image; and (ii) pre-distortion of the outgoing laser beam for turbulence effect compensation and beam focusing on the target. Implementation of this technique is based on the assumption that propagation of the beacon wave and the outgoing beam are reciprocal. This paper presents results of studies done on the effects associated with beacon formation on an image-resolved target, laser-illuminated from the detector site. In this method, the target-returned wave measured at the detector site is formed as a result of laser light scattering on a rough-surface target and is a superposition of multiple target-sourced spherical waves. Consequently, the returned reference wave's structure substantially differs from the structure of the illuminating wave on the target surface; therefore, for these two contra-propagated waves, the reciprocity conditions are not satisfied. This makes conventional AO approaches not directly applicable to such propagation geometry and instead requires essential modifications to the AO implementation for correct operation.
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Anatoliy I. Khizhnyak and Vladimir B. Markov "Turbulence-corrected adaptive laser beam focusing on a remote image-resolved target", Proc. SPIE 8238, High Energy/Average Power Lasers and Intense Beam Applications VI; Atmospheric and Oceanic Propagation of Electromagnetic Waves VI, 82380K (24 February 2012);

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