MAORY/MORFEO and LIFT: can the low order wavefront sensors become phasing sensors?

TL;DR

This paper investigates whether low order wavefront sensors, typically used for tip-tilt and focus correction, can be repurposed as phasing sensors for segmented telescopes like ELT, potentially simplifying system design.

Contribution

It explores the feasibility of using existing low order wavefront sensors with the linearized focal-plane technique (LIFT) for telescope segment phasing, addressing a current sensor gap in MORFEO.

Findings

Low order wavefront sensors can be adapted for phasing using LIFT.

Potential for simplified system architecture in ELT adaptive optics.

Improved segmentation error correction methods.

Abstract

The Multiconjugate adaptive Optic Relay For ELT Observations (MORFEO, formerly known as MAORY) is the adaptive optics (AO) module for the Extremely Large Telescope (ELT) aimed at providing a 1 arcmin corrected field to the Multi-AO Imaging CamerA for Deep Observations (MICADO) and to a future client instrument. It should provide resolution close to the diffraction limit on a large portion of the sky and in a wide range of atmospheric conditions. Its ability to provide a flat wavefront must face the known aspect of the atmospheric turbulence and telescope environment, but also the final characteristic of a telescope still to be fully developed and built. In this work we focused on issues related to the segmentation of the telescope pupil (like low wind effect, residual phasing error at handover and control related issues), that could limit the system performance. MORFEO currently does not foresee a dedicated sensor to measure the phase step between adjacent mirror segments: in this work we study the possibility to use the low order wavefront sensors designed to sense and correct tip-tilt and focus as phasing sensors thanks to the linearized focal-plane technique (LIFT).