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.
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.
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.
The LINC-NIRVANA Pathfinder<sup>1</sup> (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,<sup>2, 3</sup> 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.
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.<sup>19</sup> 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 approach<sup>3</sup> 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.
The LINC-NIRVANA Pathfinder experiment is a test-bed to verify a very complex sub-system: the Ground-layer Wavefront Sensor, or GWS. Pathfinder will test the GWS in its final working environment and demonstrate on-sky the performance achievable with a multiple natural guide star, ground-layer adaptive optics system with a very wide FoV. The GWS uses up to 12 natural guide stars within a 2.8'-6' annular field of view and drives the LBT adaptive secondary mirror to correct the lower layers of atmospheric turbulence. This paper will trace the path of the instrument on its way to First Light on-sky in November 2013, from its installation on the telescope to the calibrations to its final operation, focusing in particular on opto-mechanical and software aspects and how they lead to the main achieved results.
The LBT (Large Binocular Telescope) located in Mount Graham near Tucson/Arizona at an altitude of about
3200m, is an innovative project being undertaken by institutions from Europe and USA. The structure of the
telescope incorporates two 8.4-meter telescopes on a 14.4 center-to-center common mount. This configuration
provides the equivalent collecting area of a 12m single-dish telescope.
LINC-NIRVANA is an instrument to combine the light from both LBT primary mirrors in an imaging Fizeau
interferometer. Many requirements must be fulfilled in order to get a good interferometric combination of the
beams, being among the most important plane wavefronts, parallel input beams, homotheticity and zero optical path
difference (OPD) required for interferometry. The philosophy is to have an internally aligned instrument first, and
then align the telescope to match the instrument.
The sum of different subsystems leads to a quite ambitious system, which requires a well-defined strategy for
alignment and testing. In this paper I introduce and describe the followed strategy, as well as the different solutions,
procedures and tools used during integration. Results are presented at every step.
LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the large binocular telescope (LBT) on Mt. Graham, Arizona (elevation of 3267 m). The instrument is currently being built by a consortium of German and Italian institutes under the leadership of the Max Planck Institute for Astronomy in Heidelberg, Germany. It will combine the radiation from both 8.4 m primary mirrors of LBT in such a way that the sensitivity of a 11.9 m telescope and the spatial resolution of a 22.8 m telescope will be obtained within a 10.5×10.5 arcsec 2 scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1 and 1.5 arcmin. In addition, both incoming beams are individually corrected by LN’s multiconjugate adaptive optics system to reduce atmospheric image distortion over a circular field of up to 6 arcmin in diameter. A comprehensive technical overview of the instrument is presented, comprising the detailed design of LN’s four major systems for interferometric imaging and fringe tracking, both in the near infrared range of 1 to 2.4 μm, as well as atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 to 0.9 μm. The resulting performance capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the related assembly, integration, and verification process are discussed. To avoid late interface-related risks, strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship LN to the LBT in 2014.
LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the Large Binocular Telescope
(LBT) on Mt. Graham, Arizona, USA (3267m of elevation). The instrument is currently being built by a consortium of
German and Italian institutes under the leadership of the Max Planck Institute for Astronomy (MPIA) in Heidelberg,
Germany. It will combine the radiation from both 8.4m primary mirrors of LBT in such a way that the sensitivity of a
11.9m telescope and the spatial resolution of a 22.8m telescope will be obtained within a 10.5arcsec x 10.5arcsec
scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1
and 1.5arcmin. In addition, both incoming beams are individually corrected by LN’s multi-conjugate adaptive optics
(MCAO) system to reduce atmospheric image distortion over a circular field of up to 6arcmin in diameter.
This paper gives a comprehensive technical overview of the instrument comprising the detailed design of LN’s four
major systems for interferometric imaging and fringe tracking, both in the NIR range of 1 - 2.4μm, as well as
atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 - 0.9μm. The resulting performance
capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the
related assembly, integration and verification (AIV) process will be discussed. To avoid late interface-related risks,
strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship
LN to the LBT in 2014.
LINC-NIRVANA is the near-infrared interferometric imaging camera for the Large Binocular Telescope. Once
operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view.
Its layer-oriented MCAO systems (one for each arm of the interferometer) are conjugated to the ground layer
and an additional layer in the upper atmosphere. The wavefront sensors can use up to 12 natural guide stars
for wavefront sensing. Up to 12 opto-mechanical units have to be accurately positioned to coincide with the
positions of the natural guide stars in the focal plane. A positioning software will coordinate the motion of
these units. It has to fulfill a number of requirements: Collisions between the opto-mechanical units have to be
prevented at any time. The units shall be positionable as close as possible to each other without touching their
neighbors. To reduce the acquisition overhead, the units shall move in parallel. Different positioning modes
have to be supported: Guide star acquisition, but also positioning model corrections and common offsets will be
In this presentation we will outline the requirements and use cases of the positioning software. The logic
that will be used to prevent collisions will be discussed as well as the algorithm that can be used to assign the
opto-mechanical units to the guide stars.
LINC-NIRVANA will employ four wave front sensors to realize multi-conjugate correction on both arms of a Fizeau interferometer for LBT. Of these, one of the two ground-layer wave front sensors, together with its infrared test camera, comprise a stand-alone test platform for LINC-NIRVANA. Pathfinder is a testbed for full LINC-NIRVANA intended to identify potential interface problems early in the game, thus reducing both technical, and schedule, risk. Pathfinder will combine light from multiple guide stars, with a pyramid sensor dedicated to each star, to achieve ground-layer AO correction via an adaptive secondary: the 672-actuator thin shell at the LBT. The ability to achieve sky coverage by optically coadding light from multiple stars has been previously demonstrated; and the ability to achieve correction with an adaptive secondary has also been previously demonstrated. Pathfinder will be the first system at LBT to combine both of these capabilities.
Since reporting our progress at A04ELT2, we have advanced the project in three key areas: definition of specific goals for Pathfinder tests at LBT, more detail in the software design and planning, and calibration. We report on our progress and future plans in these three areas, and on the project overall.
LINC-NIRVANA is the Fizeau beam combiner for the LBT, with the aim to retrieve the sensitivity of a 12m telescope
and the spatial resolution of a 22.8m one. Despite being only one of the four wavefront sensors of a layer-oriented
MCAO system, the GWS, which is retrieving the deformation introduced by the lower atmosphere, known to be the main
aberration source, reveals a noticeable internal opto-mechanical complexity.
The presence of 12 small devices used to select up to the same number of NGSs, with 3 optical components each,
moving in a wide annular 2'-6' arcmin Field of View and sending the light to a common pupil re-imager, and the need to
obtain and keep a very good super-imposition of the pupil images on the CCD camera, led to an overall alignment
procedure in which more than a hundred of degrees of freedom have to be contemporary adjusted.
The rotation of the entire WFS to compensate for the sky movement, moreover, introduces a further difficulty both in the
alignment and in ensuring the required pupil superposition stability.
A detailed description of the alignment procedure is presented here, together with the lessons learned managing the
complexity of such a WFS, which led to considerations regarding future instruments, like a possible review of numerical
versus optical co-add approach, above all if close to zero read-out noise detectors will be soon available.
Nevertheless, the GWS AIV has been carried out and the system will be soon mounted at LBT to perform what is called
the Pathfinder experiment, which consists in ground-layer correction, taking advantage of the Adaptive Secondary
LINC-NIRVANA is a near infrared interferometric imager with a pair of layer-oriented multi-conjugate adaptive
optics systems (ground layer and high layer) for the Large Binocular Telescope. To prepare for the commissioning
of LINC-NIRVANA, we have integrated the high layer wavefront sensor and its associated deformable mirror (a
Xinetics-349) in a laboratory, located at Max Planck Institute for Astronomy, in Heidelberg, Germany. Together
with a telescope simulator, which includes a rotating field and phase screens that introduce the effects of the
atmosphere, we tested the acquisition of multiple guide stars, calibrating the system with the push-pull method,
and characterizing the wavefront sensor together with the deformable mirror. We have closed the AO loop with
up to 200 Zernike modes and with multiple guide stars. The AO correction demonstrated that uniform correction
can be achieved in a large field of view. We report the current status and results of the experiment.
LINC-NIRVANA is the near-infrared homothetic imaging camera for the Large Binocular Telescope. Once
operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view. Its
layer-oriented MCAO systems (one for each arm of the interferometer) are conjugated to the ground layer and
an additional layer in the upper atmosphere. In this contribution MCAO wavefront control is discussed in the
context of the overall control scheme for LINC-NIRVANA. Special attention is paid to a set of auxiliary control
tasks which are mandatory for MCAO operation: The Fields of View of each wavefront sensor in the instrument
have to be derotated independent from each other and independently from the science field. Any wavefront
information obtained by the sensors has to be matched to the time invariant modes of the deformable mirrors
in the system. The tip/tilt control scheme is outlined, in which atmospheric, but also instrumental tip/tilt
corrections are sensed with the high layer wavefront sensor and corrected by the adaptive secondary mirror of
the LBT. Slow image motion effects on the science detector have to be considered, which are caused by flexure
in the non-common path between AO and the science camera, atmospheric differential refraction, and alignment
tolerances of the derotators. Last but not least: The sensor optics (pyramids) have to be accurately positioned
at the images of natural reference stars.
The power of the Large Binocular Telescope (LBT) with its two 8.4m primary mirrors sharing a common mount
will unfold its full potential with the LINC-NIRVANA (LN) instrument. LINC-NIRVANA is a German-Italian
beam combiner for the LBT and will interfere the light from the two 8.4m mirrors of the LBT in Fizeau mode.
More than 140 motors have to be handled by custom developed Motor Controllers (MoCons). One important
feature of the MoCon is the support of externally computed trajectories. Motion profiles provide information on
the movement of the motor along a defined path over a certain period of time. Such profiles can be uploaded
to the MoCon over Ethernet and can be started at a specific time. For field derotation it is critical that the
derotation trajectories are executed with a very precise relative and absolute timing. This raises the problem
of the synchronization of the MoCon internal clock with the system time of the servers that are hosting LINCNIRVANA's
Instrument Control Software. The MoCon time should be known by the servers with an uncertainty
of few milliseconds in order to match the start time of the motion profile and the field rotation trajectory. In
this paper we will discuss how to synchronize the MoCon internal time and the PC system time.
We present a new and flexible developer framework for high performance service oriented architecture (SOA)
based systems, using the middleware called ICE by ZeroC Inc. for interprocess communication. The framework
was developed at the Max Planck Institute for Astronomy within the scope of the LBT interferometer LINC-NIRVANA
control software, but may also be used, in respect of its flexibility, for other astronomical instruments.
The systems architecture was designed to decrease the development effort of large SOA (Service Oriented Architecture)
based systems like astronomical instrument control software. The advantages of this new framework
are a combination of the online instrument data management, the validation and the ability to integrate user
defined data manipulation.
LINC-NIRVANA is an infrared camera working in Fizeau interferometric mode. The beams coming from the two
primary mirrors of the LBT are corrected for the effects of the atmospheric turbulence by two Multi-Conjugate Adaptive
Optics (MCAO) systems, working in a scientific field of view of 2 arcminutes. One single arm MCAO system includes
two wave-front sensors, driving two deformable mirrors, one for the ground layer correction (LBT secondary mirror)
and one for the correction of a mid-high layer (up to a maximum distance of 15 km). The first of the two Mid-High
Wavefront Sensors (MHWS) was integrated and tested as a stand-alone unit in the laboratory at INAF-Osservatorio
Astronomico di Bologna, where the telescope was simulated by means of a simple afocal system illuminated by a set of
optical fibers. Then the module was delivered to the MPIA laboratories in Heidelberg, where is going to be integrated
and aligned to the post-focal optical relay of one LINC-NIRVANA arm, including the deformable mirror. A number of
tests are in progress at the moment of this writing, in order to characterize and optimize the system functionalities and
performance. A report is presented about the status of this work.
For various astronomical instruments developed at the Max-Planck-Institute-Heidelberg there was a
need for a highly flexible display and control tool. Many display tools (ximtool, DS9, skycat,...) are
available for astronomy, but all this applications are monolitic and can't be easily enriched by plugins
for interaction with the graphical display, and other functionalities for remote access and control
of the instrument and data pipepline. It was developed on top of Trolltechs Cross-Platform Rich
Client Development Framework Qt,<sup>1</sup> the modern middleware Internet Communications Engine <sup>2</sup>
from ZeroC and the template based SOA developer framework for astronomical instrumentation -
NICE.<sup>3 </sup>The display tool is used on the Calar Alto Observatory (Spain) as a guider, for a wide field
imager and guider at the Wise Observatory (Israel) and for the LBT interferometer 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.
The MPIA is leading an international consortium of institutes in building an instrument called LINC-NIRVANA, the LBT INterferometric Camera and Near-IR / Visible Adaptive INterferometer for Astronomy. LINC-NIRVANA is a Fizeau interferometer for the Large Binocular Telescope doing imaging in the near infrared (J, H, K - band). Multi-conjugated adaptive objects is used to increase sky coverage and to get diffraction limited images over a 2 arcminute field of view. The LN Common Software provides a software infrastructure common to all partners and consists of a documented collection of common patterns in control systems and of services, which implement those patterns. The heart of LCSW is an object model of controlled devices, implemented as ICE network objects. A code generator creates application from templates for these network objects.