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12 September 2007 Enabling laboratory demonstrations of multi-object adaptive optics with linearity calibrations
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We present a method of calibrating nonlinear Shack-Hartmann wavefront sensors to enable open-loop wavefront sensing of atmospheric turbulence. Involving a two-dimensional raster scan of a point source behind a telescope's primary, this method is robust to aliasing, non-common path errors, linearity error, and truncation error. We have implemented this technique on the UCO/Lick Laboratory for Adaptive Optics Multi-Conjugate AO (MCAO) and Multi-Object AO (MOAO) testbed. This testbed has 5 laser guide stars with star-oriented Shack-Hartmann wavefront sensors that have 4x4 pixel subapertures. We show that the disagreement between these multiple wavefront sensors on a simulated 10 meter telescope is decreased from 0.80 radians to 0.30 radians RMS for a full atmosphere (0.6" seeing) with our linearity calibration. This linearity calibration enables simulation of open-loop MOAO with good Strehl (36% with a simulated science wavelength of 950 nm on-axis) on a 10 meter aperture. We present a complete error budget for this case, with all budget terms empirically verified through interferometric methods. We verify that the tomographic error (due to blind modes) as empirically measured on the testbed is consistent with that predicted by tomographic reconstructions of simulated atmospheres.
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S. Mark Ammons, Edward A. Laag, Renate Kupke, Donald T. Gavel, and Claire E. Max "Enabling laboratory demonstrations of multi-object adaptive optics with linearity calibrations", Proc. SPIE 6691, Astronomical Adaptive Optics Systems and Applications III, 669108 (12 September 2007);

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