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Laboratory Demonstrations of 10-m Multi-Object Adaptive Optics in V-band and Implications for ELTs

Abstract 183

Submitted by Stephen MARK AMMONS


S. M. Ammons (1), L. Johnson (1), E. A. Laag (2), R. Kupke (1), D. T. Gavel (1), B. J. Bauman (3), C. E. Max (1)


(1) CfAO; (2) UC Riverside; (3) LLNL.


A key emphasis over the next two decades will be to push astronomical AO to visible wavelengths on 8-10 m telescopes and ELTs. In pursuit of this goal, we have conducted the first laboratory simulations of wide-field, laser guide star adaptive optics at visible wavelengths on a 10-meter-class telescope. These experiments, utilizing the UCO/Lick Observatory’s Multi-Object / Laser Tomography Adaptive Optics (MOAO/LTAO) testbed, demonstrate new techniques in wavefront sensing and control that are crucial to future on-sky MOAO systems. We (1) test and confirm the feasibility of highly accurate atmospheric tomography with laser guide stars, (2) demonstrate key innovations allowing open-loop operation of Shack-Hartmann wavefront sensors (with errors of 30 nm) as will be needed for MOAO, and (3) build a complete error budget model describing system performance. With 5 Na laser guide stars and 80x80 wavefront sensor subapertures, the AO system maintains a performance of 20% Strehl at a science wavelength of 550 nm (V-band) over a 25" field of regard. Our error budget is composed of terms verified through independent, empirical experiments. Significantly, the total of all error terms arising from calibration inaccuracies and optical drift are comparable in magnitude to traditional terms like fitting error and tomographic error. We discuss implications of these experiments for visible-light LGS AO on ELTs, stressing that layer-dependent tomographic wind predictor/corrector schemes must be combined with LGS power amplification techniques (like uplink correction) and extensive optical calibration. We show through simulation that these approaches may reduce tomographic and LGS shot noise errors and thus the total LGS wattage required to achieve good, narrow-field correction at visible wavelengths with ELTs.

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