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

Abstract

LINC-NIRVANA (LN) is a MCAO module currently mounted on the Rear Bent Gregorian focus of the Large Binocular Telescope (LBT). It mounts a camera originally design to realize the interferometric imaging focal station of the LBT. LN follows the LBT strategy having two twin channels: a double Layer Oriented multi-conjugate adaptive optics system assists the two arms, supplying 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. The soft real-time computer load the matrix corresponding to the needed at one degree step. Calibrations were performed in daytime only and using optical fibers.