The 1.5 m telescope at the Starfire Optical Range, USAF Phillips Laboratory, Albuquerque, NM, USA is equipped with laser beacon adaptive optics and a high speed full aperture tilt correction system. The laser beacon is formed by a copper vapor laser propagated out the full 1.5 m aperture and focused at 14 km range. The laser operates at 5,000 pulses per second, 50 ns per pulse, with approximately 60-70 watts average power into the atmosphere. Light backscattered from the laser beacon between the ranges of 12 and 16 km is sensed by an unintensified, Pockels-cell-gated, silicon-based CCD Shack-Hartmann wave front sensor. The optics are configured such that it is also possible to use natural stars as beacons for the higher-order adaptive optics. Wave front corrections are applied to a 241 actuator continuous facesheet deformable mirror operated at approximately 100 Hz closed loop bandwidth.
Intensity mapping aberrations for high average power laser beams are examined from the point of view of diffraction theory. For the Fresnel ripple aberrations, it was determined that indeed they behave like a circular diffraction grating where energy is diffracted into the far wings of the far-field intensity distribution without significantly affecting the width of the central diffraction lobe, only its energy. It was further established that the effect of such aberrations on the far field may well be characterized by techniques where the aberration is randomized, and on-axis intensities are obtained through approximate methods.
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