In this paper we work out the optical design of, basically, a limited Field of View off-axis camera. This element is the
ingredient of a much more complex very wide field of view spectrograph and it is intended to avoid technological
difficulties related with huge optics by replicating such element (or family of such elements). The optical design has to
deal with the large off-axis aberration at a point in the Field of View as far from the optical axis as about 0.75 degree.
This requires special tools for treating the convergence of the optical design as, for instance, vignetting on the edges can
be severe because of the strong aberrations at the field lens entrance. Constraints into the optical design are particularly
interesting as well: in fact the overall cross section of the design have to lie within the footprint of the entrance Field of
View in order to allow for an array of such a design to be assembled together and guarantee the space for the allocation
of micro-mechanisms required for movable slits and grisms in each module.
PLATO is the acronym of PLAnetary Transits and Oscillations of stars, and it is a mission proposed for the ESA Cosmic
Vision program in the Medium size program, with the target to detect and characterize exoplanets by the means of their
transit on a bright star. The instrumental overall layout proposed by the Plato Payload Consortium consists in a multitelescope
concept instrument, composed by several tens of telescope units, for which we are developing an all refractive
optical solution. These devices are characterized by a very large Field of View (more than 20 degrees on one side) with
an optical quality that fits most of the energy into a single CCD pixel. Such a goal can be achieved in a variety of
solutions, some including aspheric elements as well. A complete prototype of one telescope unit is foreseen to be built
initially (during phase B1) to show the alignment feasibility and, only in a second moment (Phase B2), to perform full
environmental and functional test. The aim of this article is to describe the alignment, integration and verification
strategy of the opto-mechanics of the prototype. Both the approaches of testing the telescope at the target working
temperature or to test it at ambient temperature around a displaced zero point, taking into account the effects of thermal
deformations, are considered and briefly sketched in this work.
The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the three medium class (M class) missions
selected in 2010 for definition study in the framework of the ESA Cosmic Vision 2015-2025 program. The main
scientific goals of PLATO are the i) discovery and study of extra-solar planetary systems, (including those hosting Earth-like
planets in their habitable zone) by means of planetary transits detection from space and radial velocity follow-up
from ground, and ii) the characterization of the hosting stars through seismic analysis, in order to determine with high
accuracy planetary masses and ages. According to the study made by the PLATO Payload Consortium (PPLC) during
the PLATO assessment phase, the scientific payload consists of 34 all refractive telescopes having small aperture (120
mm) and wide field of view (greater than 1000 degree2) observing over 0.5-1 micron wavelength band. The telescopes
are mounted on a common optical bench and are divided in four families with an overlapping line-of-sight in order to
maximize the science return. In this paper, we will describe the detailed design of the Telescope Optical Units (TOUs)
focusing on the selected optical configuration and the expected performances.
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.
We describe the opto-mechanical implementation of a group of wavefront sensors able to drive an MCAO system in
order to cover a Field of View of the order of 1-2 arc-minutes, but getting advantages from the starlight coming from a
Field of View as large as 10 arc-minutes in diameter. This involves a number of arms with a miniaturized, very small
Field of View, single reference Adaptive Optics systems. A pyramid wavefront sensor working in close loop is fed
through a small Deformable Mirror that is continuously monitored by an extremely high dynamic range wavefront
sensor, whose signal has similar modality than the Pyramid one, namely YAW.
In this way, a very compact wavefront sensor with a dynamic range limited by the stroke of the Deformable Mirror is
achieved. Such a sensor is characterized by a limiting magnitude performances typical of a closed loop coherent
wavefront sensor. This concept, in addition with an architecture of a Wavefront Computer that allows the
implementation of a number of virtual Deformable Mirrors, allows for the development of a NGS based concept
described elsewhere. Emphasis is given in this talk to the practical implementation and to the opto-mechanical details,
including an overview of the required components, especially the detectors and the deformable mirrors and we show that
the goal is attainable with today existing components.
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.
Wide field spectrograph at the largest optical telescopes will be decisive to address the main open questions in modern
astrophysics. The key feature of this instrument is the modular concept: the spectrograph is the combination of about one
thousand identical small cameras, each carrying a few slits and operating at low to moderate spectral resolution, to be
illuminated at the Cassegrain focus of an existing 8m class telescope. The dispersing element to be used in these small
cameras has to satisfy some requirements in term of efficiency, resolution, size, small series production. Moreover the
cameras have to work both in imaging and spectroscopy modes, therefore a GRISM configuration of the dispersing
element is suitable. Based on these considerations, we have focused our attention to Volume Phase Holographic Gratings
(VPHGs) since they show large peak efficiency in the target spectral range (400-800 nm), they can be arranged in a
GRISM configuration reaching relative large resolution. The main constrains concern the available room for the
dispersing element, indeed the camera design is very compact. As a consequence, slanted VPHGs are studied and
optimized in combination with normal and Fresnel prisms.
The concept of segmenting the focal plane of an existing 8m class telescope in order to fill it with an array of several fast
cameras has been developed further and in this work the status of an engineering program aimed to produce a design
qualified for the construction, and to assess its cost estimates is presented. The original concept of just having simple
cameras with all identical optical components other than a pupil plane corrector to remove the fixed aberrations at the
off-axis field of a telescope has been extended to introduce a spectroscopic capability and to assess a trade-off between a
very large number (of the order of thousand) of cameras with a small single Field of View with a smaller number of
cameras able to compensate the aberration on a much larger Field of View with a combination of different optical
elements and different ways to mount and align them.
The scientific target of a few thousands multi-slit spectra over a Field of View of a few square degrees, combined with
the ambition to mount this on an existing 8m class telescope makes the scientific rationale of such an instrument a very
interesting one. In the paper we describe the different options for a possible optical design, the trade off between
variations on the theme of the large segmentation and we describe briefly the way this kind of instrument can handle a
multi-slit configuration. Finally, the feasibility of the components and a brief description of how the cost analysis is
being performed are given. Perspectives on the construction of this spectrograph are given as well.
A lot of scientific interest around both seeing limited wide field imaging and wide field spectroscopy has been shown in
the recent past. Technological difficulties have indeed been identified when proposing classical prime focus corrector for
8 meters class telescopes with Field of View bigger than one degree, because of the huge opto-mechanics and of the very
large arrays of detectors required. A new concept, the Smart Fast Camera, has been recently proposed: the idea behind
relays on splitting the huge Field of View in smaller portions, each of them re-imaging onto a reasonable size detector a
part of the scientific Field of View. In this way, one could think to build a modular instrument, with most of the
components identical for each module, with the exception of the field corrector, which is of course radial dependent. In
this paper, a further development of this concept, allowing for spectroscopy, is presented, applied to an existing 8 meter
class telescope, the Large Binocular Telescope. A preliminary study is traced out, with the aim to find a feasible optical
design for such an instrument.
The Multiconjugate Adaptive optics Demonstrator (MAD) had successfully demonstrated on sky both Star
Oriented (SO) and Layer Oriented (LO) multiconjugate adaptive optics techniques. While SO has been realized
using 3 Shack-Hartmann wavefront sensors (WFS), we designed a multi-pyramid WFS for the LO. The MAD
bench accommodates both WFSs and a selecting mirror allows choosing which sensor to use. In the LO approach
up to 8 pyramids can be placed on as many reference stars and their light is co-added optically on two different
CCDs conjugated at ground and to an high layer. In this paper we discuss LO commissioning phase and on sky
operations.
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.
Since the very beginning of 2008, the Large Binocular Telescope (LBT) is officially equipped with it's first binocular
instrument ready for science observations: the Large Binocular Camera (LBC). This is a double CCD imager, installed at
the prime focus stations of the two 8.4m telescopes of LBT, able to obtain deep and wide field images in the whole
optical spectrum from UV to NIR wavelengths.
We present here the overall architecture of the instrument, a brief hardware review of the two imagers and notes how
observations are carried on. At the end we report preliminary results on the performances of the instrument along with
some images obtained during the first months of observations in binocular mode.
In this article activities on the Optomechanics of the Prime Focus Red Channel alignment are described from the moment
in which the instrument left Italy to be shipped to LBT site to the moment in which it has been successfully placed on the
second LBT arm. An overview is given, starting from the realization of a "clean laboratory" at LBT, going through the
alignment check and finally with the mounting operations of the instrument at the telescope and its alignment with the
"second eye" primary mirror, with tolerances good enough to perform the fine alignment on the sky with the telescope
Active Optics.
In the framework of the Extremely Large Telescope design study, the Work Package (WP) 12000 is studying the Site
Characterization for an European Extremely Large Telescope. In particular, INAF is in the WP 12300 group for the
Large scale atmospheric properties study. Previous studies done in many astronomical sites have been optimized on
spatial scales comparable with 3-4meter to 10meter class telescopes. The strong interest of the Astronomical Community
in giant telescopes imposes a different site characterization opportune for 30-40meter class telescopes.
One of the central point in the Adaptive Optics for Extremely Large Telescopes is given from the achievable sky
coverage. Generally speaking, sky coverage is dominated by the high altitude layers correction. In other words ground
layer adaptive optics has a sky coverage much larger than other kind of corrections. That means that ways to meliorate
the sky coverage in the sensing of high altitude layers can be very effective in terms of overall performances. Moreover,
there are good reasons to translate high coherence time of flowing layers, in a generalized Taylor assumption, into larger
sky coverages.
This poster presents the optical design of TOE, The Onduline Experiment, a WaveFront Sensor for sensing a Very Large
Field of View on-board the VLT and possibly other telescopes as Gran TeCan in Canary islands. Such a WFS is to be
intended as a tool to probe the atmospheric parameters in the free atmosphere (i.e. far from the ground layer) on a linear
scale of the same order of magnitude of the diameter of the ELTs under consideration in this period.
LINC-NIRVANA is an infrared camera that will work in Fizeau interferometric way at the Large Binocular Telescope (LBT). The two beams that will be combined in the camera are corrected by an MCAO system, aiming to cancel the turbulence in a scientific field of view of 2 arcminutes. The MCAO wavefront sensors will be two for each arm, with the task to sense the atmosphere at two different altitudes (the ground one and a second height variable between a few kilometers and a maximum of 15 kilometers). The first wavefront sensor, namely the Ground layer Wavefront sensor (GWS), will drive the secondary adaptive mirror of LBT, while the second wavefront sensor, namely the Mid High layer Wavefront Sensor (MHWS) will drive a commercial deformable mirror which will also have the possibility to be conjugated to the same altitude of the correspondent wavefront sensor. The entire system is of course duplicated for the two telescopes, and is based on the Multiple Field of View (MFoV) Layer Oriented (LO) technique, having thus different FoV to select the suitable references for the two wavefront sensor: the GWS will use the light of an annular field of view from 2 to 6 arcminutes, while the MHWS will use the central 2 arcminutes part of the FoV. After LINC-NIRVANA has accomplished the final design review, we describe the MFoV wavefront sensing system together with its current status.
It is generally believed that very fast cameras imaging large Fields of View translate into huge optomechanics
and mosaics of very large contiguous CCDs. It has already been suggested that seeing limited imaging cameras
for telescopes whose diameters are larger than 20m are considered virtually impossible for a reasonable cost.
It has also been suggested that using existing technology and at a moderate price, one can build a Smart Fast
Camera, a device that placed on aberrated Field of View, including those of slow focal ratios, is able to provide
imaging at an equivalent focal ratio as low as F/1, with a size that is identical to the large focal ratio focal plane
size. The design allows for easy correction of aberrations over the Field of View. It has low weight and size
with respect to any focal reducer or prime focus station of the same performance. It can be applied to existing
8m-class telescopes to provide a wide field fast focal plane or to achieve seeing-limited imaging on Extremely
Large Telescopes. As it offers inherently fast read-out in a massive parallel mode, the SFC can be used as a
pupil or focal plane camera for pupil-plane or Shack-Hartmann wavefront sensing for 30-100m class telescopes.
Basing upon Smart Fast Camera concept, we present a study turned to explain the pliability of this instrument
for different existing telescopes.
The Large Binocular Telescope is currently equipped with a couple of wide field Prime Focus. The two cameras are optimized for, respectively, the blue and the red portion of the visible spectrum. The history of this project is here sketched up and the current status is shown. The Blue channel is currently working onboard the telescope and provided what has been named the first-light of the telescope in single eye configuration.
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