Large Binocular Telescope Interferometer Adaptive Optics: On-sky performance and lessons learned

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 10(3) - 10(4) contrast at 10 mu m, while the 4 mu m imaging science drivers require even greater contrasts, but at scales >0.2". In imaging mode, LBTI's Adaptive Optics system is already delivering 4 mu m contrast of 10(4) - 10(5) 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 mu m, 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.