Laser Guide Stars are, in spite of their name, all but “stars”. They do not stand at infinite distance, neither on a plane. If fired from the side of a large telescope their characteristics as seen from various points on the apertures changes dramatically. As they extend in a 3D world, there is need of a WFS that deploy in a similar 3D manner, in the conjugated volume, resembling the approach that MCAO required long time ago to overcome the usual limitations of conventional AO. We describe a class of a novel kind of WFS that employ a combination of refraction and reflection, such that they can convey the light from an LGS into a limited number of pupils, making the device compact, doable with a single piece of glass, and able to feed a minimum sized format detector where the information is collected maximizing the information depending from which part of the LGS the light is coming from, and on which portion of the telescope aperture the light is landing. They represent, in our opinion, the best-known adaptation of the pyramid WFS for NGS to the LGS world. As in the natural reference case the practical advantages come along with some fundamental advantages. Being a pupil plane WFS with the perturbator placed on the (3D) loci of focus of the various portions of the source of light they have the potentiality to extend WFS to a number of issues, including the ability to sense the islands effect, where non-contiguous portions of the main apertures are optically displaced. Further to their description and the main recipes we speculate onto possible variations on cases where the LGS is fired from the back of the secondary mirror and we exploit some potential features when implementing onto an extremely large aperture.
As the deep field surveys strategy represents a well popular way to study the cosmology and the formation and evolution of galaxies, we investigated how the new generation of extremely large telescopes (ELTs) will perform in this field of research. Our simulations, which combine a number of technical, tomographic and astrophysical information, take advantages of the Global-MCAO approach, a well demonstrated method that can be applied in absence of laser guide stars because it exploits only natural references. A statistics of the expected performance in a sub-sample of 22 well-known surveys are presented here.
We present a new testing facility hosted at the Coude focus of the INAF-Padova Copernico Telescope, a project carried on within the ADaptive Optics National Italian laboratories - ADONI. A permanent laboratory for on-sky experimentation accessible to the AO community, with the aim of hosting visiting multi-purpose instrumentation that may be directly tested on sky. We will give an overview of the activities carried on, describing the refurbishment activities at the hosting structure that allowed the opening of the facility: the implementation of the opto-mechanical train down to the Coude focus, and the creation of the laboratory. This facility provides a powerful scientific and technical test bench for new instrumental concepts, which may eventually be incorporated later in the next generation ELTs telescopes.
Exo-Planets search and characterization has been the science case driving the SHARK-NIR design, which is one of the two coronagraphic instruments proposed for the Large Binocular Telescope. In fact, together with SHARK-VIS (working in the visible domain), it will offer the possibility to do binocular observations combining direct imaging, coronagraphic imaging and coronagraphic low resolution spectroscopy in a wide wavelength domain, going from 0.5μm to 1.7μm. Additionally, the contemporary usage of LMIRCam, the coronagraphic LBTI NIR camera, working from K to L band, will extend even more the covered wavelength range. The instrument has been designed with two intermediate pupil planes and three focal planes, in order to give the possibility to implement a certain number of coronagraphic techniques, with the purpose to select a few of them matching as much as possible the requirements of the different science cases in terms of contrast at various distances from the star and in term of required field of view. SHARK-NIR has been approved by the LBT board in June 2017, and the procurement phase started just after. We report here about the project status, which is currently at the beginning of the AIV phase at INAF-Padova, and should last about one year. Even if exo-planets is the main science case, the SOUL upgrade of the LBT AO will increase the instrument performance in the faint end regime, allowing to do galactic (jets and disks) and extra-galactic (AGN and QSO) science on a relatively wide sample of targets, normally not reachable in other similar facilities.
SHARK-NIR is a coronagraphic camera that will be implemented at the Large Binocular Telescope. SHARK-NIR will offer extreme AO direct imaging capability on a field of view of about 18" x 18", and a simple coronagraphic spectroscopic mode offering spectral resolution ranging from 100 to 700. In order to meet the SHARK-NIR main scientific driver, i.e., searching for giant planets on wide orbits, a high contrast is necessary. A set of corona-graphic masks were tested, we selected the best performing configurations for the instrument: the Gaussian-Lyot coronagraph, a Shaped Pupil (SP) with 360° of discovery space and two SP masks with asymmetric detection area but with a small inner working angle and the Four Quadrant phase mask. Many simulations were performed to obtain the performance in different atmospheric conditions, including seeing variations, by using magnitude guide star from R = 8 to R = 14 and testing also the jitter value. These changes in simulation parameters reflected a variation in the corona-graphic performance. We analysed the simulation images by searching the best post processing to obtain the best performance for the coronagraph, moreover, we have taken account the fact that using, in the ADI technique, small subsets to generate the reference PSF can help attenuating the speckle noise, but it also results in a growing risk of planet removal if not enough field rotation occurs in the subset itself. We analysed the results after this effect is included, so the performances were shown as function of the Strehl Ratio condition to obtain mass and age limits for the detection of the planets.
PLATO (Planetary Transits and Oscillations of stars) is a new space telescope selected by ESA to detect terrestrial exoplanets in nearby solar-type stars. The telescope is composed by 26 small telescopes to achieve a large instantaneous field of view. INAF-OAPD is directly involved in the optical design and in the definition and testing of the alignment strategy. A prototype of the Telescope Optical Unis (TOU) was assembled and integrated in warm condition (room temperature) and then the performance is tested in warm and cold temperature (-80C). The mechanical structure of the TOU is representative in terms of thermal expansion coefficient and Young's modulus with respect to the actual one. A dedicated GSE (Ground Support Equipment) is used to manipulate the lenses. By co-align an interferometer and a laser with respect to the center of the third CaF2 lens, a several observables references are used to define the position and tilt of the chief ray. The total procedure tolerances for every lens is 30'' in tilt, between 15-40 μm for focus and 22 μm for decentering and the total error budget of the optical setup bench is below this requirement. In this paper, we describe the AIV procedure and test performed on the prototype of the TOU in the INAF laboratory.
PLATO (PLAnetary Transits and Oscillation of stars) is the ESA Medium size dedicated to exo-planets discovery, adopted in the framework of the Cosmic Vision program. The PLATO launch is planned in 2026 and the mission will last at least 4 years in the Lagrangian point L2. The primary scientific goal of PLATO is to discover and characterize a large amount of exo-planets hosted by bright nearby stars, constraining with unprecedented precision their radii by mean of transits technique and the age of the stars through by asteroseismology. By coupling the radius information with the mass knowledge, provided by a dedicated ground-based spectroscopy radial velocity measurements campaign, it would be possible to determine the planet density. Ultimately, PLATO will deliver the largest samples ever of well characterized exo-planets, discriminating among their ‘zoology’. The large amount of required bright stars can be achieved by a relatively small aperture telescope (about 1 meter class) with a wide Field of View (about 1000 square degrees). The PLATO strategy is to split the collecting area into 24 identical 120 mm aperture diameter fully refractive cameras with partially overlapped Field of View delivering an overall instantaneous sky covered area of about 2232 square degrees. The opto-mechanical sub-system of each camera, namely Telescope Optical Unit, is basically composed by a 6 lenses fully refractive optical system, presenting one aspheric surface on the front lens, and by a mechanical structure made in AlBeMet.
The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the selected medium class (M class)
missions in the framework of the ESA Cosmic Vision 2015-2025 program. The mean scientific goal of PLATO is the
discovery and study of extrasolar planetary systems by means of planetary transits detection. The opto mechanical
subsystem of the payload is made of 32 normal telescope optical units (N-TOUs) and 2 fast telescope optical units (FTOUs).
The optical configuration of each TOU is an all refractive design based on six properly optimized lenses. In the
current baseline, in front of each TOU a Suprasil window is foreseen. The main purposes of the entrance window are to
shield the following lenses from possible damaging high energy radiation and to mitigate the thermal gradient that the
first optical element will experience during the launch from ground to space environment. In contrast, the presence of the
window increases the overall mass by a non-negligible quantity. We describe here the radiation and thermal analysis and
their impact on the quality and risks assessment, summarizing the trade-off process with pro and cons on having or
dropping the entrance window in the optical train.
Thermal effects in PLATO are analyzed in terms of uniform temperature variations, longitudinal and lateral temperature gradients. We characterize these effects by evaluating the PSF centroid shifts and the Enclosed Energy variations across the whole FoV. These patterns can then be used to gauge the thermal behavior of each individual telescope in order to improve the local photometric calibration across the PLATO field of view.
The project PLAnetary Transits and Oscillations of stars (PLATO) is one of the selected medium class (M class)
missions in the framework of the ESA Cosmic Vision 2015-2025 program. The main scientific goal of PLATO is the
discovery and study of extrasolar planetary systems by means of planetary transits detection.
According to the current baseline, the scientific payload consists of 34 all refractive telescopes having small aperture
(120mm) and wide field of view (diameter greater than 37 degrees) observing over 0.5-1 micron wavelength band. The
telescopes are mounted on a common optical bench and are divided in four families of eight telescopes with an
overlapping line-of-sight in order to maximize the science return. Remaining two telescopes will be dedicated to support
on-board star-tracking system and will be specialized on two different photometric bands for science purposes.
The performance requirement, adopted as merit function during the analysis, is specified as 90% enclosed energy
contained in a square having size 2 pixels over the whole field of view with a depth of focus of +/-20 micron. Given the
complexity of the system, we have followed a Montecarlo analysis approach for manufacturing and alignment
tolerances. We will describe here the tolerance method and the preliminary results, speculating on the assumed risks and
PLATO stands for PLAnetary Transits and Oscillation of stars and is a Medium sized mission selected as M3 by the
European Space Agency as part of the Cosmic Vision program. The strategy behind is to scrutinize a large fraction of the
sky collecting lightcurves of a large number of stars and detecting transits of exo-planets whose apparent orbit allow for
the transit to be visible from the Earth. Furthermore, as the transit is basically able to provide the ratio of the size of the
transiting planet to the host star, the latter is being characterized by asteroseismology, allowing to provide accurate
masses, radii and hence density of a large sample of extra solar bodies. In order to be able to then follow up from the
ground via spectroscopy radial velocity measurements these candidates the search must be confined to rather bright stars.
To comply with the statistical rate of the occurrence of such transits around these kind of stars one needs a telescope with
a moderate aperture of the order of one meter but with a Field of View that is of the order of 50 degrees in diameter. This
is achieved by splitting the optical aperture into a few dozens identical telescopes with partially overlapping Field of
View to build up a mixed ensemble of differently covered area of the sky to comply with various classes of magnitude
stars. The single telescopes are refractive optical systems with an internally located pupil defined by a CaF2 lens, and
comprising an aspheric front lens and a strong field flattener optical element close to the detectors mosaic. In order to
continuously monitor for a few years with the aim to detect planetary transits similar to an hypothetical twin of the Earth,
with the same revolution period, the spacecraft is going to be operated while orbiting around the L2 Lagrangian point of
the Earth-Sun system so that the Earth disk is no longer a constraints potentially interfering with such a wide field
continuous uninterrupted survey.
In the context of ADONI, the newly constituted laboratory for INAF Adaptive Optics activities, it is foreseen to set-up a facility accessible to the Italian and international AO community, with the purpose of facilitating the testing of critical sub-systems or components (which may be part of instruments under construction), or prototypes of innovative concepts which may require on-sky demonstrations. The 182cm Copernico Telescope located in Asiago (Italy) has been selected to be a suitable place to set-up this public facility, where a common optical bench will be made available at the Coudé focus to host visiting instrumentation. In this paper we describe the opto-mechanical train to the Coudé focal station to be implemented for the laboratory set-up, and we sketch out the foreseen telescope refurbishing activities to implement this multi-purpose testing facility dedicated to AO related projects.
In this paper is described a "push-pull" deformable mirror which has the advantage that the mirror membrane can either be attracted from the back or from the front giving several advantages such as: doubled dynamic, better accuracy in mode reproduction, and bidirectional deformation. The key idea when developing this push-pull deformable mirror was to have good compromise between performances and practical applicability for series production. An analysis of the constraints/practical limitations is described using simulations and laboratory tests. Following the results, we forsee the benefits of inserting the push-pull DM (Saturn, Adaptica Srl) in practical applications such as ophthalmology and microscopy.
Typical radio telescopes have the primary reflector surface which is composed of several single panels that have
dimensions of a meter a side. The manufacturing of these radio panels yield a micrometric precision over the volume on
the single panel, hence the surface roughness of the panels can be measured with very high accuracy by means of the low
coherence interferometry (LCI) technique which reaches micrometric spatial and depth resolution and has the advantage
of being contact-less.
We have developed a multi-channel partially coherent light interferometer to realize non contact 3D surface topography.
The technique is based on the LCI principle, for which a bi-dimensional sensor - a CMOS - has been developed to
directly acquire images. Tri-dimensional measures are recovered with a single scanning along the depth direction in a
millimetric range, and every single pixel of the bi-dimensional sensor measures a point on the object, this allows a fast
analysis in real time on square centimeter areas.
In this paper we show the results obtained by applying the LCI technique method to analyze the surface roughness of the
panels of a large radio antenna of 64 m of width and used for astronomical observations at 100 GHz; by measuring their
3D structure at micrometric resolution it is possible to verify their fabrication errors.