GRAVITY+ adaptive optics

Abstract

GRAVITY+ is an upgrade of the VLTI infrastructure, providing unprecedented spatial resolution and sensitivity. One of the project's objectives was to replace the low-order NGS SCAO systems with four high-order AO modules incorporated in the Coudé train of each VLT UT: GRAVITY+ Adaptive Optics (GPAO). This paper presents GPAO, focusing on the AO design and highlighting technical peculiarities and novel approaches, possibly of interest for future ELT AO systems. First, the NGS AO modes in visible and infrared wavelengths are described in terms of implementation, on-sky performance, and scientific impact. Then, we introduce the recently commissioned LGS AO modes, starting with the performance of the LGS systems, a copy of the ELT ones. The delivered wavefront correction is shown as a function of NGS magnitude. Finally, we highlight some key technical aspects relevant for future AO systems, notably Rayleigh background scattering management and other works in progress.