The calibration procedure of the LINC-NIRVANA ground and high layer WFS

TL;DR

This paper details the calibration procedure for LINC-NIRVANA's ground and high layer wavefront sensors, addressing the challenges posed by pupil image rotation due to derotation mechanisms in an adaptive optics system.

Contribution

It presents a specific calibration method for the pupil image rotation caused by derotation in the LINC-NIRVANA MCAO system, enhancing wavefront sensor accuracy.

Findings

Calibration procedure effectively compensates pupil image rotation.

Improved wavefront correction accuracy demonstrated.

Method applicable to similar MCAO systems.

Abstract

LINC--NIRVANA (LN) is an MCAO module currently mounted on the Rear Bent Gregorian focus of the Large Binocular Telescope (LBT). It mounts a camera originally designed to realize the interferometric imaging focal station of the telescopes. LN follows the LBT binocular strategy having two twin channels: a double Layer Oriented Multi-Conjugate Adaptive Optics system assisting the two arms, supplies high order wave-front correction. In order to counterbalance the field rotation, a mechanical derotation is applied for the two ground wave-front sensors, and an optical (K-mirror) one for the two high layers sensors, fixing the positions of the focal planes with respect to the pyramids aboard the wavefront sensors. The derotation introduces a pupil images rotation on the wavefront sensors, changing the projection of the deformable mirrors on the sensor consequently.