The Large Binocular Telescope Interferometer is a high contrast imager and interferometer that sits at the combined bent Gregorian focus of the LBT’s dual 8.4 m apertures. The interferometric science drivers dictate 0.1” resolution with 10³ − 10⁴ contrast at 10 μm, while the 4 μm imaging science drivers require even greater contrasts, but at scales <0.2”. In imaging mode, LBTI’s Adaptive Optics system is already delivering 4 μm contrast of 10⁴ − 10⁵ at 0.3" − 0.75" in good conditions. Even in poor seeing, it can deliver up to 90% Strehl Ratio at this wavelength. However, the performance could be further improved by mitigating Non-Common Path Aberrations. Any NCPA remedy must be feasible using only the current hardware: the science camera, the wavefront sensor, and the adaptive secondary mirror. In preliminary testing, we have implemented an “eye doctor” grid search approach for astigmatism and trefoil, achieving 5% improvement in Strehl Ratio at 4 μm, with future plans to test at shorter wavelengths and with more modes. We find evidence of NCPA variability on short timescales and discuss possible upgrades to ameliorate time-variable effects.

Date Published: 21 July 2014
PDF: 11 pages
Proc. SPIE 9148, Adaptive Optics Systems IV, 914803 (21 July 2014); doi: 10.1117/12.2057138

Published in SPIE Proceedings Vol. 9148:
Adaptive Optics Systems IV
Enrico Marchetti; Laird M. Close; Jean-Pierre Véran, Editor(s)