The LBTI - Pioneering the ELT Era

The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument which combines the two 8.4m apertures of the LBT for sensitive, high-angular-resolution imaging and interferometric observations in the thermal infrared. Through its observing modes utilizing adaptive optics, Fizeau imaging, and nulling interferometry, the LBTI is in many respects the first ELT; it serves as a pioneer for upcoming ELTs in terms of both science and instrumentation. LBTI has completed a large survey for habitable-zone dust around main sequence stars, exploiting its angular resolution to obtain 100x better sensitivity than space-based photometric observations. Recently we have emphasized Fizeau imaging, supporting high-contrast and precision-astrometric observations. We obtained the first extragalactic and N band observations in this mode, demonstrating high-fidelity, high-sensitivity imaging on a 23 m baseline. We are now pushing to image the first rocky planet in the habitable zone around a nearby Sun-like star. In this paper we present an overview of the LBTI's design and capabilities as a 23 m telescope. In particular, we focus on open loop Fizeau imaging, presenting the state of the art. We measure the stability of the Fizeau PSF, test frame selection criteria, and demonstrate PSF deconvolution. Finally, we outline future developments and synergies with current and upcoming facilities.