Prototype of a laser guide star wavefront sensor for the Extremely Large Telescope

TL;DR

This paper presents a laboratory prototype of a laser guide star wavefront sensor for the ELT, addressing complex issues like finite LGS distance and focus anisoplanatism through experimental testing and simulation validation.

Contribution

The study develops and tests a prototype LGS wavefront sensor for the ELT, providing insights into mitigation strategies for wavefront sensing challenges in large telescopes.

Findings

Noise affects centroiding precision

LGS image truncation impacts wavefront accuracy

Sodium density profile influences LGS image evolution

Abstract

The new class of large telescopes, as the future ELT, are designed to work with Laser Guide Star (LGS) tuned to a resonance of atmosphere sodium atoms. This wavefront sensing technique presents complex issues for an application to big telescopes due to many reasons mainly linked to the finite distance of the LGS, the launching angle, Tip-tilt indetermination and focus anisoplanatism. The implementation of a laboratory Prototype for LGS wavefront sensor (WFS) at the beginning of the phase study of MAORY, the Multi-conjugate Adaptive Optics RelaY for the ELT first light, has been indispensable to investigate specific mitigation strategies to the LGS WFS issues. This paper shows the test results of LGS WFS Prototype under different working conditions. The accuracy within which the LGS images are generated on the Shack-Hartmann (SH) WFS has been cross-checked with the MAORY simulation code. The experiments show the effect of noise on the centroiding precision, the impact of LGS image truncation on the wavefront sensing accuracy as well as the temporal evolution of sodium density profile and LGS image under-sampling.