Sensitivity to differential piston and to adaptive optics errors with the Large Binocular Telescope Interferometer

Abstract

On-sky adaptive optics wavefront screens have been used and random optical path fluctuations - differential pistons - have been included in numerical simulations for the Large Binocular Telescope Interferometer. We characterize the Point Spread Function (PSF) and the Optical Transfer Function (OTF) by computing respectively the interferometric Strehl and the visibility criteria. We study the contribution of the wavefront disturbance induced by each adaptive optics system and by the optical path difference between the arms of the LBTI. To provide an image of quality (Strehl above 70%) suitable with standard science cases , the requirements for a LBTI mode in the visible wavelengths (750nm) must be at least an adaptive optics wavefront RMS fluctuations below λ/18≈40nm (Strehl above 90%) provided by each adaptive optics system, and a differential piston RMS fluctuations below λ/8≈100nm in the overall LBTI system. The adaptive optics wavefront errors - mainly the differential tip-tilt - appear to be more critical than the differential piston.