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.
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.
In the last years we have operated two very similar ultrafast photon counting photometers (Iqueye and Aqueye+) on different telescopes. The absolute time accuracy in time tagging the detected photon with these instruments is of the order of 500 ps for hours of observation, allowing us to obtain, for example, the most accurate ever light curve in visible light of the optical pulsars. Recently we adapted the two photometers for working together on two telescopes at Asiago (Italy), for realizing an Hanbury-Brown and Twiss Intensity Interferometry like experiment with two 3.9 km distant telescopes. In this paper we report about the status of the activity and on the very preliminary results of our first attempt to measure the photon intensity correlation.
Since a number of years our group is engaged in the design, construction and operation of instruments with very high time resolution in the optical band for applications to Quantum Astronomy and more conventional Astrophysics. Two instruments were built to perform photon counting with sub-nanosecond temporal accuracy. The first of the two, Aqueye+, is regularly mounted at the 1.8 m Copernicus telescope in Asiago, while the second one, Iqueye, was mounted at the ESO New Technology Telescope in Chile, and at the William Herschel Telescope and Telescopio Nazionale Galileo on the Roque (La Palma, Canary Islands). Both instruments deliver extraordinarily accurate results in optical pulsar timing. Recently, Iqueye was moved to Asiago to be mounted at the 1.2 m Galileo telescope to attempt, for the first time ever, experiments of optical intensity interferometry (à la Hanbury Brown and Twiss) on a baseline of a few kilometers, together with the Copernicus telescope. This application was one of the original goals for the development of our instrumentation. To carry out these measurements, we are experimenting a new way of coupling the instruments to the telescopes, by means of moderate-aperture, low-optical-attenuation multi-mode optical fibers with a double-clad design. Fibers are housed in dedicated optical interfaces attached to the focus of another instrument of the 1.8 m telescope (Aqueye+) or to the Nasmyth focus of the 1.2 m telescope (Iqueye). This soft-mount solution has the advantage to facilitate the mounting of the photon counters, to keep them under controlled temperature and humidity conditions (reducing potential systematics related to varying ambient conditions), and to mitigate scheduling requirements. Here we will describe the first successful implementation of the Asiago intensity interferometer and future plans for improving it.
Spreading the PSF over a quite large amount of pixels is an increasingly used observing technique in order to reach
extremely precise photometry, such as in the case of exoplanets searching and characterization via transits observations.
A PSF top-hat profile helps to minimize the errors contribution due to the uncertainty on the knowledge of the detector
flat field. This work has been carried out during the recent design study in the framework of the ESA small mission
CHEOPS. Because of lack of perfect flat-fielding information, in the CHEOPS optics it is required to spread the light of
a source into a well defined angular area, in a manner as uniform as possible. Furthermore this should be accomplished
still retaining the features of a true focal plane onto the detector. In this way, for instance, the angular displacement on
the focal plane is fully retained and in case of several stars in a field these look as separated as their distance is larger
than the spreading size. An obvious way is to apply a defocus, while the presence of an intermediate pupil plane in the
Back End Optics makes attractive to introduce here an optical device that is able to spread the light in a well defined
manner, still retaining the direction of the chief ray hitting it. This can be accomplished through an holographic diffuser
or through a lenslet array. Both techniques implement the concept of segmenting the pupil into several sub-zones where
light is spread to a well defined angle. We present experimental results on how to deliver such PSF profile by mean of
holographic diffuser and lenslet array. Both the devices are located in an intermediate pupil plane of a properly scaled
laboratory setup mimicking the CHEOPS optical design configuration.
The VLT Survey Telescope (VST) is the latest telescope installed at ESO’s Paranal Observatory in northern Chile. The
exceptional quality of this site imposes tight requirements on the telescope performance in terms of pointing modeling
and tracking. This paper describes the control strategy and the results obtained during the commissioning of the
The VLT Survey Telescope (VST) has started the scientific operations on the ESO Paranal observatory after a successful
commissioning period. It is currently the largest telescope in the world specially designed for surveying the sky in visible
light. The VST is dedicated to survey programmes, supporting the VLT with wide-angle imaging by detecting and pre-characterising
sources, which the VLT Unit Telescopes can then observe further.
In a wide-field telescope like the VST, the requirements for alignment are tighter than for traditional instruments. The
same amount of misalignment can be negligible in traditional telescopes with fields of some arc minutes, but
unacceptable when the field is one order of magnitude larger. We describe the alignment procedure implemented during
the telescope commissioning on the Paranal ESO's observatory, as well as the final results.
The active optics system of the VLT Survey Telescope (VST) adopts a positioning system for the secondary mirror, a
system to support and modify the shape of the 2.6-m primary mirror, and a Shack-Hartmann wavefront sensor. This
paper describes the concepts of the VST active optics and the commissioning of the whole system on the ESO's Paranal
The VLT Survey Telescope is a f/5.5 modified Ritchey-Chretien imaging telescope, which is being installed at
the ESO-Paranal Observatory. It will provide a one square degree corrected field of view to perform surveyprojects
in the wavelength range from UV to I band. In this paper we describe the opto-mechanical alignment
procedure of the 2.61m primary mirror, the secondary and correctors lenses onto the mechanical structure of the
telescope. The alignment procedure does not rely on the mechanical precision of the mirrors. It will be achieved
using ad-hoc alignment tools, described in the paper, which allows the spatial determination of optical axes (and
focuses where necessary) of the optical components with respect to the axis defined by the rotation of a laser
beam mounted on the instrument bearing.
The VST telescope is going to be commissioned in Paranal, together with its main sub-systems, such as the Image
Analysis and Auto-Guiding system. A preliminary work of fine tuning of each sub-system has been performed in Italy
before their shipping to Paranal, where they are waiting for the telescope AIV to be completed in a way to start the final
commissioning of the overall system. Each unit has been extensively characterized and tested, with particular care to the
Active Optics Shack-Hartmann sensor and to the Auto-Guiding arm. We describe here the phases concerning the
integration and test of all the VST Auxiliary Units performed in Italy before their shipping to Paranal.
The VST telescope is equipped with an Atmospheric Dispersion Corrector to counterbalance the spectral dispersion
introduced by the atmosphere. The well known effect of atmospheric refraction is the bending of incoming light due to
variable atmospheric density along the light path. This effect depends on the tangent of the zenith angle and also varies
with altitude, humidity and wavelength. Since the magnitude of refraction depends on the wavelength, the resulting
effect is not only a deviation of the light beam from its original direction but also a spectral dispersion of the beam. This
effect can be corrected by introducing a dispersing element in the instrument. In the VST case the device that
compensates for this effect is based on a set of four prisms in two cemented doublet pairs. The system provides an
adjustable counter dispersion by counter-rotating the two pairs of prisms. The counter-rotating angle depends on the
atmospheric dispersion, which is computed with an atmospheric model using both environmental data (temperature,
pressure, humidity) and the telescope position. Two different approaches have been compared for the computations to
cross-check the results. The electromechanical system has been assembled, tested and debugged prior to the shipping to
Chile. This paper describes the atmospheric models used in the VST case and the most recent phases of work.