Final performance and lesson-learned of SAXO, the VLT-SPHERE extreme AO: from early design to on-sky results

Abstract

The extreme AO system, SAXO (SPHERE AO for eXoplanet Observation), is the heart of the SPHERE system, feeding the scientific instruments with flat wave front corrected from all the atmospheric turbulence and internal defects. We will present the final performance of SAXO obtained during the instrument AIT in Europe as well as the very first on-sky results. The main requirements and system characteristics will be recalled and the full AO loop performance will be quantified and compared to original specifications. It will be demonstrated that SAXO meets or even exceeds (especially its limit magnitude and its jitter residuals) its challenging requirements (more than 90% of SR in H band and a 3 mas residual jitter). Finally, after 10 years of AO developments, from early design to final on-sky implementations, some critical system aspects as well as some important lesson-learned will be presented in the perspective of the future generation of complex AO systems for VLTs and ELTs.

Pushing point-spread function reconstruction to the next level: application to SPHERE/ZIMPOL

“…We have measured the PSF Full Width at Half Maximum (FWHM) of the five stars as reported in Tab. 3, that indicates that the AO system did not reach the diffraction at 554 nm, which was expected (Fusco et al 2014). However, separation between the AO correction area and PSF wings is not very clear in Fig.…”

Adaptive Optics for Extremely Large Telescopes

“…It goes without saying that the current, often already the second generation of AO systems on 8-10 m class telescopes, has generated a wealth of experience. These experiences and lessons learned (see for example Lloyd-Hart et al (2003); Wizinowich (2012); Fusco et al (2014); Lozi et al (2017)) are of course incorporated into the design and simulations of the AO facilities to be built. Since it would go beyond the scope of this review, here are just two current examples.…”

Optical turbulence forecast in the Adaptive Optics realm

“…Adaptive Optics applied to ground-based astronomy is indeed able to provide, at present, images with angular resolution that is up to three time that achievable with Hubble on space. A Strehl Ratio as high as 80-90 % in H band has been obtained on sky by extreme adaptive optics (XAO) systems mounted on 8-meters class telescopes (FLAO on Large Binocular Telescope [1], SPHERE on the Very Large Telescope [2], GPI on Gemini South [3]). Equivalent or even better performance are foreseen for the Extremely Large Telescope (diameter of the order of 40 m) and this will open to scenarios of observations never done before with potential exciting discoveries in different fields of the astronomy.…”