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One of the causes of power loss in a free-space optical communication link is beam motion or received spot wander. The power spectrum of the spot motion indicates that most of the frequency content is less than ~500 Hz. A fast steering mirror (FSM) controlled by a position-sensing detector (PSD) has the potential to correct for a significant portion of the focal spot position fluctuations and thus the power loss. A FSM controlled with a Germanium PSD was installed on the receiver at the NRL Chesapeake Bay free-space lasercomm test facility. Results are presented from the initial tests performed using this system to measure and correct for wander of an optical beam propagated across the bay (20 mile round-trip).

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