Pathfinder first light: alignment, calibration, and commissioning of the LINC-NIRVANA ground-layer adaptive optics subsystem

We present descriptions of the alignment and calibration tests of the Pathfinder, which achieved first light during our 2013 commissioning campaign at the LBT. The full LINC-NIRVANA instrument is a Fizeau interferometric imager with fringe tracking and 2-layer natural guide star multi-conjugate adaptive optics (MCAO) systems on each eye of the LBT. The MCAO correction for each side is achieved using a ground layer wavefront sensor that drives the LBT adaptive secondary mirror and a mid-high layer wavefront sensor that drives a Xinetics 349 actuator DM conjugated to an altitude of 7.1 km. When the LINC-NIRVANA MCAO system is commissioned, it will be one of only two such systems on an 8-meter telescope and the only such system in the northern hemisphere. In order to mitigate risk, we take a modular approach to commissioning by decoupling and testing the LINC-NIRVANA subsystems individually. The Pathfinder is the ground-layer wavefront sensor for the DX eye of the LBT. It uses 12 pyramid wavefront sensors to optically co-add light from natural guide stars in order to make four pupil images that sense ground layer turbulence. Pathfinder is now the first LINC-NIRVANA subsystem to be fully integrated with the telescope and commissioned on sky. Our 2013 commissioning campaign consisted of 7 runs at the LBT with the tasks of assembly, integration and communication with the LBT telescope control system, alignment to the telescope optical axis, off-sky closed loop AO calibration, and finally closed loop on-sky AO. We present the programmatics of this campaign, along with the novel designs of our alignment scheme and our off-sky calibration test, which lead to the Pathfinder's first on-sky closed loop images

Final integration and alignment of LINC-NIRVANA

The LBT (Large Binocular Telescope), located at about 3200m on Mount Graham (Tucson, Arizona) is an innovative project undertaken by institutions from Europe and USA. LINC-NIRVANA is an instrument which provides MCAO (Multi-Conjugate Adaptive Optics) and interferometry, combining the light from the two 8.4m telescopes coherently. This configuration offers 23m-baseline optical resolution and the sensitivity of a 12m mirror, with a 2 arc-minute diffraction limited field of view. The integration, alignment and testing of such a big instrument requires a well-organized choreography and AIV planning which has been developed in a hierarchical way. The instrument is divided in largely independent systems, and all of them consist of various subsystems. Every subsystem integration ends with a verification test and an acceptance procedure. When a certain number of systems are finished and accepted, the instrument AIV phase starts. This hierarchical approach allows testing at early stages with simple setups. The philosophy is to have internally aligned subsystems to be integrated in the instrument optical path, and extrapolate to finally align the instrument to the Gregorian bent foci of the telescope. The alignment plan was successfully executed in Heidelberg at MPIA facilities, and now the instrument is being re-integrated at the LBT over a series of 11 campaigns along the year 2016. After its commissioning, the instrument will offer MCAO sensing with the LBT telescope. The interferometric mode will be implemented in a future update of the instrument. This paper focuses on the alignment done in the clean room at the LBT facilities for the collimator, camera, and High-layer Wavefront Sensor (HWS) during March and April 2016. It also summarizes the previous work done in preparation for shipping and arrival of the instrument to the telescope. Results are presented for every step, and a final section outlines the future work to be done in next runs until its final commissioning...

Design and implementation of a service-oriented driver architecture for LINC-NIRVANA

LINC-NIRVANA (LN) is a German-Italian Fizeau (imaging) interferometer for the Large Binocular Telescope (LBT). The Instrument Control Software (ICS) of this instrument is a hierarchical, distributed software package, which runs on several computers. In this paper we present the bottom layer of the hierarchy - the Basic Device Application (BASDA) layer. This layer simplifies the development of the ICS through a general driver architecture, which supports different types of hardware. This generic device architecture provides a high level interface to encapsulate the hardware dependent driver. The benefit of such a device architecture is to keep the basic device-driver layer flexible and independent from the hardware, and to keep the hardware transparent to the ICS. Additionally, the basic device-driver layer supports interfaces to IDL based applications for calibration and laboratory testing of astronomical instruments, and interfaces to engineering GUIs that allow to maintain the software components easily

Ground layer correction: the heart of LINC-NIRVANA

The delivered image quality of ground-based telescopes depends greatly on atmospheric turbulence. At every observatory, the majority of the turbulence (up to 60-80% of the total) occurs in the ground layer of the atmosphere, that is, the first few hundred meters above the telescope pupil. Correction of these perturbations can, therefore, greatly increase the quality of the image. We use Ground-layer Wavefront Sensors (GWSs) to sense the ground layer turbulence for the LINC-NIRVANA (LN) instrument, which is in its final integration phase before shipment to the Large Binocular Telescope (LBT) on Mt. Graham in Arizona.19 LN is an infrared Fizeau interferometer, equipped with an advanced Multi-Conjugate Adaptive Optics (MCAO) module, capable of delivering images with a spatial resolution equivalent to that of a ~23m diameter telescope. It exploits the Layer-Oriented, Multiple Field of View, MCAO approach3 and uses only natural guide stars for the correction. The GWS has more than 100 degrees of freedom. There are opto-mechanical complexities at the level of sub- systems, the GWS as a whole, and at the interface with the telescope. Also, there is a very stringent requirement on the superposition of the pupils on the detector. All these conditions make the alignment of the GWS very demanding and crucial. In this paper, we discuss the alignment and integration of the left-eye GWS of LN and detail the various tests done in the lab at INAF-Padova to verify proper system operation and performance

Aligning the LINC-NIRVANA Natural Guide Stars MCAO system

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

Acquiring multiple stars with the LINC-NIRVANA Pathfinder

The LINC-NIRVANA Pathfinder1 (LN-PF), a ground-layer adaptive optics (AO) system recently commissioned at the Large Binocular Telescope (LBT), is one of 4 sensors that provide AO corrected images to the full LINC-NIRVANA instrument. With first light having taken place on November 17, 2013,2, 3 the core goals for the LN-PF have been accomplished. In this report, we look forward to one of the LN-PF extended goals. In particular, we review the acquisition mechanism required to place each of several star probes on its corresponding star in the target asterism. For emerging AO systems in general, co-addition of light from multiple stars stands as one of several methods being pursued to boost sky coverage. With 12 probes patrolling a large field of view (an annulus 6-arcminutes in diameter), the LN-PF will provide a valuable testbed to verify this method

Aligning the LINC-NIRVANA Natural Guide Stars MCAO system

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

First laboratory results with the LINC-NIRVANA high layer wavefront sensor

In the field of adaptive optics, multi-conjugate adaptive optics (MCAO) can greatly increase the size of the corrected field of view (FoV) and also extend sky coverage. By applying layer oriented MCAO (LO-MCAO) [4], together with multiple guide stars (up to 20) and pyramid wavefront sensors [7], LINC-NIRVANA (L-N for short) [1] will provide tw