RISTRETTO: a VLT XAO design to reach Proxima Cen b in the visible

Abstract

RISTRETTO is the evolution of the original idea of coupling the VLT instruments SPHERE and ESPRESSO \cite{lovis_2016a}, aiming at High Dispersion Coronagraphy. RISTRETTO is a visitor instrument that should enable the characterization of the atmospheres of nearby exoplanets in reflected light, by using the technique of high-contrast, high-resolution spectroscopy. Its goal is to observe Prox Cen b and other planets placed at about 35mas from their star, i.e. $2\lambda /D$ at $\lambda$=750nm. The instrument is composed of an extreme adaptive optics, a coronagraphic Integral Field Unit, and a diffraction-limited spectrograph (R=140.000, $\lambda =$620-840 nm). We present the RISTRETTO XAO architecture that reach the specification, providing contrasts down to $5\times 10^{-5}$ at 2$\lambda /D$ from the star in the visible, in the presence of atmosphere and low wind effect. This performance is allowed by a new two-sensors-one-dm architecture, some variations to the already known concepts of unmodulated pyWFS and zWFS, and exploiting to the maximum of their capabilities the state-of-the-art high speed, low noise cameras \& fast DM. We present the result of end-to-end simulations, that demonstrate stable closed loop operation of an unmodulated pyramid and a zernike WFS (together), and in presence of low wind effect.

13 pages, 12 figure, SPIE Astronomical Telescopes + Instrumentation, 2024, Yokohama, Japan

References in corpus (6)

• Atmospheric characterization of Proxima b by coupling the Sphere high-contrast imager to the Espresso spectrograph
• Simultaneous phase and amplitude aberration sensing with a liquid-crystal vector-Zernike phase mask
• The focal-plane assisted pyramid wavefront sensor: enabling frame-by-frame optical gains tracking
• AO3000 at Subaru: Combining for the first time a NIR WFS using First Light's C-RED ONE and ALPAO's 64x64 DM
• Adapting the pyramid wavefront sensor for pupil fragmentation of the ELT class telescopes
• Upgrading SPHERE with the second stage AO system SAXO+: frequency-based data-driven controller for adaptive optics