Authors

Serge Meimon, Cédric Plantet, Thierry Fusco, Jean-Marc Conan

Affiliations

ONERA

Abstract

Laser-assisted adaptive optics (AO) systems should increase dramatically the system sky coverage. Unfortunately, the laser guide star (LGS) wavefront sensing (WFS) principle is insensitive to tip/tilt, and focus measurement is corrupted by the evolution of the sodium concentration in altitude. Additionally, volumic structures of the LGS may induce quasi-static WFS errors.

Hence, low-order modes have to be measured separately using faint natural guide stars (NGSs), and a so-called "truth sensor" has to be used to calibrate higher order LGS induced WFS errors. In that framework, we have proposed a new focal-plane WFS concept called the linearized focal-plane technique (LIFT), which allows us to efficiently deal with low-order mode measurement under low flux conditions. It can also be used on long exposure as a truth sensor without any hardware modification.

We show here an experimental validation of LIFT in both low-order and truth sensor configurations. We compare the experimental linearity and noise propagation of LIFT to classical sensors, such as the quad-cell wavefront sensor (WFS), pyramid WFS, and Shack–Hartmann WFS.