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.
The Large Binocular Telescope is one of the most unusual 8 m class telescope and surely it has been inspirational to a number of novel concepts and innovations. We present here a couple of recently traced opto-mechanical designs to fit some niches in the parameters space of astrophysical usage. A coronagraph, as simple as possible, to take advantage of the LBT XAO ability dedicated to the ExoPlanets detection and a multiple very wide field spectrograph in which a large number of tiny cameras is foreseen, all with equal optical elements but for the pupil aberration corrector.
One possible key reference element in optical alignment is represented by the rotational stage, a mechanical bearing, or
any similar suitable device having enough accuracy and precision so that optical tolerances are reasonably relaxed wrt
imperfections in the rotational movement. This allows a safe, reliable, easy to reproduce, determination of both rays
parallel to the axis or to their centering within almost any plane. An image derotator, that in its simplest form is made up
by three flat mirrors arranged in a so called K-mirror layout, moving together on a precision rotating stage, seems to be
the most safe, strong, and self built-in alignment tool. Moreover you can use the mechanical part as well as the optical
one. Care has to be given when internally and externally aligning has to be accomplished within a certain degree of
precision. To further make the situation more complex, the technical overall requirements can be tight enough that the
distribution of the error budget among the various components (imperfect mechanical rotation, imperfect internal
alignment, flexures during rotations) is not due to a single item. In this case, in fact, a number of tips and tricks can be
useful to find out which is the best approach to follow. The specific case of the two K-mirrors on board LINCNIRVANA
is here illustrated in a few lessons.
Because of its nicely chromatic behavior, Calcium Fluoride (CaF2) is a nice choice for an optical designer as it can easily
solve a number of issues, giving the right extra degree of freedom in the optical design tuning. However, switching from
tablet screens to real life, the scarcity of information -and sometimes the bad reputation in term of fragility- about this
material makes an overall test much more than a "display determination" experiment. We describe the extensive tests
performed in ambient temperature and in thermo-vacuum of a prototype, consistent with flight CTEs, of a 200mm class
camera envisaged for the PLATO (PLAnetary Transit and Oscillations of Stars) mission. We show how the CaF2 lens
uneventfully succeeded to all the tests and handling procedures, and discuss the main results of the very intensive test
campaign of the PLATO Telescope Optical Unit prototype.
In ELTs the larger size of the aperture will translates into different categories of problems and different kind of solutions.
The concept of Global Multi Conjugated Adaptive Optics is here introduced. In this, the wavefront sensing is extended to
a much larger Field of View, practically limited by the telescope optics or optomechanics and by the limit given by the
coverage of the metapupil at the highest altitude of interest. The correction of these layers is employed in a numerical
fashion and the information is retrieved in order to compensate for a much limited Field of View. All this, being done in
a layer oriented fashion, does allow for a simplified treatment of the Signal to Noise Ratio and to an estimate of the
performances in the plot h vs. spatial scales where layers and the related Kolmogorov distributed turbulence are plotted.
Once this information is retrieved it is fed back into the existing Deformable Mirror with a back-projection that allow for
the most efficient way in terms of coverage of the spatial frequencies. The nature of the closed- vs open-loop of such an
approach is also briefly discussed. The aim of a sky coverage and of performances getting closer or exceeding the ones
provided by Laser Guide Stars can be at hands.
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
deformable Mirror.
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.
In MCAO the correction of the wavefront for an extended Field of View is obtained at the expense of a stretching of the
actual instantaneous meta-pupils over the high altitude layers, just to compensate their average curvature. While this
effect does average out in long term exposures and is of secondary interest in compensated imaging, it gives the input for
the idea of using MCAO-like information, collectable over a certain Field of View, to assess in a time resolved mode
(not necessarily in real time) the actual geometrical light throughput in a given direction. In principle this would allow,
with proper time tagging, to achieve high precision photometry, as part of the scintillation could be measured on line
during the observation. Simple averaging of neighbor stars to flat field starlight, for example, represents the equivalent of
this concept for the ground-layer correction only. It can be seen that, once a direction is defined, it is relevant only the
derivative of the wavefront around or in the proximity of that edges, but the range at which this happen is a crucial
parameter. However, the strong interest in high precision measurements of exoplanetary transits or asteroseismology
could make this approach not as lunatic as it could sound. view
In the framework of the European ELT design, partially open-loop MCAO systems, coupled with virtual DMs, have
been proposed to achieve AO correction using solely NGSs, to be selected in a FoV as wide as allowed by the Telescope optical design. The conceptual design of a very compact wavefront sensor, exploiting the just mentioned concept and characterized by a dynamic range limited by the stroke of the Deformable Mirror and by a limiting magnitude performance typical of a closed loop coherent wavefront sensor, have been presented in the past. This concept was based on the usage of a very linear wavefront sensor, like a YAW sensor, but a DM having the actual shape known “a-priori” could simplify a lot the design of such a compact WFS.
We investigate here the realm of possible opto-mechanical realization of a probe, capable to co-exist with the currently foreseen E-ELT LGS probes and giving the possibility to exploit the open loop wavefront sensing operation with the aim of reaching a preliminary design of such a system.
Furthermore, we devise a conceptual opto-mechanical design of a precursor of such a system, which could exploit at the VLT Global MCAO correction on the lower part of the atmosphere.
The Atacama Large Millimeter Array (ALMA) consists of a large number of 12m diameter antennas that will operate up
to 950GHz. The antenna must meet all primary operational performances also during solar observation. When the
antenna is pointing directly the sun or when the sun is close to the boresight axis, the solar power concentrated by the
mirrors cannot damage any part of the antenna. When the antenna is pointing toward the sun, the power absorbed by a
black body positioned in the secondary focal area shall not exceed 0.3 W/cm2.
To achieve these requirements, the primary surface of the antenna has a suitable surface scattering treatment. The same
thing was done for the surface of the subreflector. Specific tests were performed on the panels surface and secondary
mirror during the prototype and production phase in order to optimize the best behaviour. A particular care must be
applied in the control of the secondary area, where the entire solar power spectrum, from the UV to the infrared,
reflected by the primary mirror, can contribute to overheat reflecting areas support structures.
In this report we provide a series of analysis and results obtained during the solar observation.
Adaptive Optics (AO) concepts involve sometimes very complex behaviors of rays, waves and optical elements. Just
think, to be convinced, the way multiple probes aim to correct for a large field of view Multi Conjugated AO, and to how
these deploy onto a dynamic turbulent atmosphere. In order to explain the behavior of novel concepts we developed
visualization techniques that involve the display of three dimensional images and the creation of movies to explain how
the concept deals with an evolving situation, or, in other words, adding the fourth dimension of time. We produce solid
models of the optical concepts we are developing, including the evolving temporal behavior of the turbulence, and these
can be manipulated in a virtual manner in order to allow for the production of different means of visualization. These
ranges from so called "static movies" where a three dimensional concept is just explored in three dimension by handling
it around the observer, to the creation of three dimensional anaglyphs or anaglyphs movies. While the paper is mainly
focused onto the ways these techniques are exploited in order to produce satisfactory results, the poster allow the visitor
to experience some of these images and movies. The aim of this work is not only of a sort of high level didactical
purpose, but we think it would be useful into scientific discussion and during meeting to develop engineering concepts of
several AO concepts.
The LINC-NIRVANA wavefront sensors are in their AIT phase. The first Ground-layerWavefront Sensor (GWS)
is shaping in the Adaptive Optics laboratory of the Astronomical Observatory of Padova, while both the Mid-
High Wavefront Sensors (MHWSs) have been aligned and tested as stand-alone units in the Observatory of
Bologna (MHWS#1 aligned to LINC-NIRVANA post focal relay optics).
LINC-NIRVANA is a Fizeau infrared interferometer equipped with advanced, MultiConjugated Adaptive
Optics (MCAO) for the Large Binocular Telescope. The aim of the instrument is to allow true interferometric
imagery over a 10" square Field of View (FoV), getting the sensitivity of a 12m telescope and the spatial resolution
of a 22.8m one. Thanks to the MCAO concept, LINC-NIRVANA will use up to 20 Natural Guide Stars (NGS)
which are divided, according to Layer-Oriented Multiple Field of View technique, between the GWSs and the
MHWSs. To find such a large number of references, the AO systems will use a wide FoV of 6' in diameter and
the light coming from the references used by each WFS will optically sum on its CCD camera.
The MHWSs will detect the deformations due to the high layers and will select up to 8 NGSs in the inner 2'
FoV.
The GWSs, instead, will reconstruct the deformations introduced by the lower atmosphere, which was found
out to be the main source of seeing. Their peculiarity is the highest number of references (up to 12) ever used
in a single instrument, selected in an annular 2'-6' FoV.
LINC-NIRVANA is an infrared camera that will work in Fizeau interferometric way at the Large Binocular Telescope
(LBT). It will take advantage of a field corrected from two MCAO systems, one for each arm, based on the Layer
Oriented Technique and using solely Natural Guide Stars. For each arm, there will be two wavefront sensors, one
conjugated to the Ground and one conjugated to a selectable altitude, ranging from 4 to 15 Km. They will explore
different fields of view for the wavefront sensing operations, accordingly to the Multiple Field of View concept, and
particularly the inner 2 arcminutes FoV will be used to select the references for the high layer wavefront sensor while the
ground one will explore a wider anular field, going from 2 to 6 arcminutes in diameter. The wavefront sensors are under
INAF responsibility, and their construction is ongoing in different italian observatories. Here we report on progress, and
particularly on the test ongoing in Padova observatory on the Ground Layer Wavefront Sensor.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.