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LINC-NIRVANA (LN) is an instrument built to be a Fizeau interferometric imager for the Large Binocular Telescope that will achieve ELT-like spatial resolution. Of course achieving this outstanding resolution requires a very complex instrument, assuring the delivery of plane wavefronts, parallel input beams, homoteticity and zero Optical Path Difference. LN will be one of the most complex ground-based instruments ever built, consisting of a Multi-Conjugate Adaptive Optics (MCAO) system, a fringe tracker, a beam combiner and a Near-InfraRed science camera, for a total of more than 250 indivudual lenses and mirrors.The MCAO sub-unit itself is the state of the art in the sector of wide field adaptive optics. It consists of 4 Wavefront Sensors (WFSs), two for each arm of the telescope, to sense the turbulence at the ground layer and at 7.1 km above the telescope. They operate in a layer oriented, Multiple Field of View mode, using up to 12 Natural Guide Stars (NGSs) for the ground layer correction and up to 8 NGSs for the mid layer correction.The ambitious nature of LN, which compels us to meet very tight requirements, together with the high number of subsystems lead to a challenging alignment procedure of the instrument. Despite of the complexity, the Alignment, Integration and Verification phase of the instrument has been recently completed with success in Heidelberg and LN is currently on its way to the LBT, where it will be re-aligned and finally mounted at one of the bend focal stations of the telescope. In this paper the integration and alignment procedure of the MCAO subsystem to the rest of LN is described and results are presented.

The full LINC-NIRVANA instrument will be one of the most complex ground-based astronomical systems ever built. It will consist of multiple subsystems, including two multi-conjugate ground layer AO systems (MCAO) that drive the LBT adaptive secondaries, two mid-high layer AO systems with their own Xynetics 349 actuator DM's , a fringe tracker, a beam combiner, and the NIR science camera. In order to mitigate risk, we take a modular approach to instrument testing and commissioning by decoupling these subsystems individually. The first subsystem tested on-sky will be one of the ground-layer AO systems, part of a test-bed known as the Pathfinder. The Pathfinder consists of a 12-star pyramid wavefront sensor (PWFS) that drives one of the LBT's adaptive secondaries, a support structure known as "The Foot," and the infrared test camera (IRTC), which is used for acquisition and alignment. The 12 natural guide stars are acquired by moveable arms called "star enlargers," each of which contains its own optical path. The Pathfinder was shipped from MPIA in Heidelberg, Germany to the LBT mountain lab on Mt. Graham, Arizona in February 2013. The system was unpacked, assembled in the LBT clean room, and internally optically aligned. We present the results of our system tests, including star enlarger alignment and system alignment. We also present our immediate plans for on-sky closed loop tests on the LBT scheduled for late Fall. Because plans for all ELTs call for ground layer correction, the Pathfinder provides valuable preliminary information not only for the full LINC-NIRVANA system, but also for future advanced MCAO systems., 2013 AO4ELT Proceedings

LINC-NIRVANA is an imaging Fizeau interferometer, for use in near infrared wavelengths, being built for the Large Binocular Telescope. Multi-conjugate adaptive optics (MCAO) increases the sky coverage and the field of view over which diffraction limited images can be obtained. For its MCAO implementation, Linc-Nirvana utilizes four total wavefront sensors; each of the two beams is corrected by both a ground-layer wavefront sensor (GWS) and a high-layer wavefront sensor (HWS). The GWS controls the adaptive secondary deformable mirror (DM), which is based on an DSP slope computing unit. Whereas the HWS controls an internal DM via computations provided by an off-the-shelf multi-core Linux system. Using wavefront sensor data collected from a prior lab experiment, we have shown via simulation that the Linux based system is sufficient to operate at 1 kHz, with jitter well below the needs of the final system. Based on that setup we implemented an adaptive optics loop control application which includes the back-end number crunching loop pipeline from camera readout to the DM. All intermediate steps of the loop are controlled by modular engineering GUI front- ends for diagnostic and configuration. Those engineering front-ends can either be used together with the slope computing unit (Basic Computation Unit BCU) which is used by the GWS and the initial Pathfinder setup or with the Linux based system (for MCAO operation of the HWS). The implementation of the Linux based system is done similar to the internal process of the BCU. In this way both systems provide the same functionalities and can be maintained more easily.

The near infrared interferometer LINC-NIRVANA combines the beams coming from the two primary mirrors of the Large Binocular Telescope to increase the resolution of the science camera image. LINC-NIRVANA is using layer-oriented multi-conjugate adaptive optics (MCAO) to reduce the influence of the atmospheric turbulence. The deformable mirrors of the MCAO systems are conjugated to the ground layer and a second layer in the upper atmosphere, respectively. Ground layer wavefront sensors and high layer wavefront sensors measure the wavefront in these two layers. Due to geometrical constraints unique to this type of instrument, it is not possible to provide a single derotator at the entrance of each incoming beam. Due to that fact, field derotation has to be applied for each wavefront sensor and for the science detector separately. The fields of the high layer wavefront sensors are derotated by the use of K-Mirrors, whereas the ground layer wavefront sensors and the science detector rotate themselves to compensate field rotation. All derotators are driven by common software that provides functionality to generate, execute, and maniulate a trajectory. The trajectory handling for these field derotators will be discussed in this paper. We introduce an algorithm that translates a requested trajectory into motor controller commands in due consideration of the required accuracy. Finally, we present the achieved positioning accuracy of the translated trajectory and compare that result with the traced position path of the derotator.

This paper describes the positioning routine for the pickup optics of LINC-NIRVANA’s wavefront sensors which is executed during the acquisition of multiple natural guide stars. The near-infrared interferometric imaging camera for the LBT, LINC-NIRVANA, incorporates layer oriented multi-conjugate adaptive optics sys- tems. They can use up to 20 natural guide stars within a 6 arcminute field of view for wavefront sensing. Each guide star is used to sense the turbulence in one of two discrete atmospheric layers. To be able to combine the wavefront information from each natural guide star, opto-mechanical pickup units have to be positioned in the physically large focal planes of the wavefront sensors. These pickup units contain the pyramids of the wavefront sensors. They will be moved in parallel and have to be accurately positioned on the targets. Collisions have to be prevented. The exploitation of large fields of view for multi-object Adaptive Optics is a challenge that will become more and more prevalent with increasing aperture sizes, especially for the upcoming generation of extremely large telescopes.