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

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.

Operation of a layer-oriented multiconjugate adaptive optics system in the partial illumination regime

“…For our system, θ°¼ 1 deg of sky rotation. 43,44 This arrangement has the advantage that the position of the stars does not change in the focal plane of the WFS. Therefore, the illumination region also remains unchanged.…”

“…We apply the push-pull history of the modes defined by the M2C to the high-altitude DM and measure the corresponding slopes. 44 Analyzing the slopes, we extract the IM. The calibration procedure is laid out as a flowchart in Fig.…”