MAORY/MORFEO and rolling shutter induced aberrations in laser guide star wavefront sensing

TL;DR

This paper investigates how rolling shutter CMOS detectors used in laser guide star wavefront sensing for ELTs introduce aberrations, particularly from LGS tilt jitter, affecting adaptive optics correction.

Contribution

It provides an analysis of rolling shutter-induced aberrations in LGS wavefront sensing for ELTs and discusses mitigation strategies.

Findings

Rolling shutter can cause up to 100nm rms aberrations.

Aberrations are significant for fast varying LGS tilt jitter.

Mitigation strategies are proposed to reduce these aberrations.

Abstract

Laser Guide Star (LGS) Shack-Hartmann (SH) wavefront sensors for next generation Extremely Large Telescopes (ELTs) require low-noise, large format (about 1Mpx), fast detectors to match the need for a large number of subapertures and a good sampling of the very elongated spots. One path envisaged to fulfill this need has been the adoption of CMOS detectors with a rolling shutter read-out scheme, that allows low read-out noise and fast readout time at the cost of image distortion due to the detector rows exposed in different moments. In this work we analyze the impact of the rolling shutter read-out scheme when used for LGS SH wavefront sensing of the Multiconjugate adaptive Optic Relay For ELT Observations (MORFEO, formerly known as MAORY) for ESO ELT; in particular, we focus on the impact on the adaptive optics correction of the distortion-induced aberrations created by the rolling exposure in the case of fast varying aberrations, like the ones coming from the LGS tilt jitter due to the up-link propagation of laser beams. We show that the LGS jitter-induced aberration for MORFEO can be as large as 100nm rms and we discuss possible mitigation strategies.