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The favorite solution foreseen for the realization of future very large x-ray mirror modules (diameters above 1 m) is the partition of the optics in azimuthal and radial modules. Even if this approach solves the initial problem of the procurement and the handling of very large substrates, it moves the difficulties in the second phase, when thousands of segments have to be aligned and assembled without degrading their optical performances. The usage of large monolithic shells would provide indubitable advantages with respect to the segmented approach, but poses challenging procurement problems. For example, in the case of Lynx, where superb imaging capabilities are combined with a very large effective area, a mirror module with 3mdiameter is foreseen. One of the three technologies considered by the Study Team for the realization of the mirrors is based on monolithic glass (fused silica) shells, figured with direct polishing technique. The simplicity of the full shell concept is quite attractive: the complete optics module could be composed of few hundreds of parts instead of several thousands of pieces. As a drawback, to be compliant with the mass budget, the shell thickness should be maintained very small even for larger mirror shells. Given that the glass is a brittle material, the procurement of such large raw shells, and of their spares, is considered the major critical issue of the process. In order to overcome the difficulties and the cost related to the assembly of thousands of segments, a straightforward way to realize very large monolithic raw mirrors shells is needed. In this paper we present the first results related to an alternative approach, based on light-weighted metal sheets, which could have an astonishing impact on the full shell concept, providing very large shells at negligible costs. In particular, we focus on spin forming technology, commonly used for the realization of axial-symmetric parts. This process makes use of a rotating machine to deform metal over a pre-shaped mold. As a replica approach, it allows the realization of several back up optics without major impacts on the costs, as it would be the case if the mirror shell realization starts from blanks machining. Aluminium is commonly used in plate turning. Given its low density and good mechanical properties, it may represent an effective and cheap alternative to more exotic low-density materials or to the glass itself. Metal optics, made of Aluminium 6061, are already widely used to fulfil the demands of a-thermal instrument design. Starting from aluminum substrates, diamond turning can be used for figuring the optic. An additional thin layer of electro-less nickel will allow final figuring and polishing. These further figuring processes are nowadays well proven on thick substrates, allowing the realization of optics with cutting-edge performances. Their successful employ on thin shell substrates would open new window on x-ray optics realization.

The Lynx X-ray Observatory, with superb imaging capabilities and with large throughput, is one of the four large strategic missions considered in the Astro2020 decadal survey. The realization of the mirror assembly within the desired tolerances is quite challenging and different mirror module concepts are proposed. The simplest mirror module design corresponds to less than a few hundred monolithic shells made of fused silica. The complete optomechanical design, compliant with the mass budget, foresees that the shell thickness ranges between 2 and 4 mm (for mirror shells between 0.4 and 3 m diameter). A technology development roadmap for this approach is funded in Italy by ASI and pursued out by INAF-OAB. In this paper, we present the advancements obtained in the procurement of new raw glass shells, in the development of the different phases of the process, and in the realization of a new single-reflection shell, representative of the final optical configuration suitable to validate the

Spectroscopic observations in the vacuum (VUV, 115-200 nm) and extreme ultraviolet (EUV, 40-115 nm) is of fundamental importance in solar physics, in the physics of interstellar medium, in the study of planetary exospheres. The PLUS project is focused on the development of a high performance spectrograph for the observations of planetary exospheres in the 55-200 nm range. The instrument layout is based on a two channels (VUV/EUV) design. It will be characterized by improved detection limit, shorter observations integration time and unprecedented performance in terms of dynamic range. Such characteristics will be obtained thanks to the development and combination of two key technologies: high efficiency optical components optimized for each channel and high resolution/dynamic range solar blind photon counting detector. The photon counting detector will be based on a Micro-Channel Plate coupled with ROIC ASIC read out system.

Lynx is an X-ray mission concept with superb imaging capabilities (< 1arcsec Half Energy Width, HEW) and large throughput (2 m2 effective area @1keV). Several approaches are being considered to meet the challenging technological task of the mirror fabrication. Thin and light substrates are necessary to meet mass constraints. Monolithic fused silica shells are a possible solution if their thickness can be maintained to below 4 mm for mirror shells up to 3 m diameter. In this paper we present the opto-mechanical design of the mirror assembly, the technological processes, and the results achieved so far on a prototypal shells under development. In particular, emphasis is placed on the figuring process that is based on direct polishing and on ion beam figuring and on a temporary stiffening structure designed to support the shell during the figuring and polishing operations and to manage the handling of the shell through all phases up to integration into the telescope supporting structure.

ASTRI SST-2M is the end-to-end prototype telescope under development by the Italian National Institute of Astrophysics, INAF, proposed for the investigation of the highest-energy gamma-ray band in the framework of the Cherenkov Telescope Array, CTA. The ASTRI SST-2M prototype will be installed in Italy at the INAF station located at Serra La Nave on Mount Etna during Fall 2014. The calibration and scientific validation phase will start soon after. The calibration of a Cherenkov telescope includes several items and tools. The ASTRI SST- 2M camera is equipped with an internal fiber illumination system that allows to perform the relative calibration through monitoring of gain and efficiency variations of each pixel. The absolute calibration of the overall system, including optics, will take advantage from auxiliary instrumentation, namely UVscope and UVSiPM, two small-aperture multi-pixels photon detectors NIST calibrated in lab. During commissioning phase, to measure the main features of ASTRI SST-2M, as its overall spectral response, the main telescope and the auxiliary UVscope-UVSiPM will be illuminated simultaneously by a spatially uniform flux generated by a ground-based light source, named Illuminator, placed at a distance of few hundreds meters. Periodically, during clear nights, the flux profiles of a reference star tracked simultaneously by ASTRI SST-2M and UVscope-UVSiPM will allow to evaluate the total atmospheric attenuation and the absolute calibration constant of the ASTRI SST-2M prototype. In this contribution we describe the auxiliary UVscope-UVSiPM and Illuminator sub-system together with an overview of the end-to-end calibration procedure foreseen for the ASTRI SST-2M telescope prototype.

ASTRI SST-2M is a prototype dual mirror Small Size class of Telescope for the Cherenkov Telescope Array (CTA). Its innovative design based on a Schwarzschild-Couder configuration will permit use Silicon Photo-multipliers as focalplane detectors. The dual mirror configuration is a challenge for the realization of both the primary and secondary. Accurate tests and characterization are mandatory to understand the behavior of the optical configuration, its limits and the possibility of improvements of the full CTA array. Moreover, optical alignment requires solutions and procedures that have not been used so far on Cherenkov telescopes. The aim of paper is to provide an analysis of these topics in the context of the ASTRI SST-2M telescope.

During 2013, a new visible camera has been finally installed and tested at the 60cm, robotic REM telescope in the la Silla Observatory. REM is an Italian, fast-reacting telescope initially designed and built for the immediate response to GRB automatic alerts, but since the first light in 2003 its usage has been covering a wider range of astronomical interests. While the IR camera REMIR was reaching the expected limiting magnitudes, the original ROSS visible camera suffered, since the beginning, of a rather poor performance. We set therefore to implement a newer optical camera, leading to the design, tests and integration of ROS2, a dichroic-based four channels imaging camera. The four Sloan-like pass bands are imaged, at the same time, in four quadrants of the CCD, an Andor multilevel Peltier detector. The tests during the science commissioning show an impressive improvement in the limiting magnitudes, reaching two magnitudes fainter than ROSS. Here we show the concept, the tests and the user level product we are now offering at REM.

The next generation of imaging atmospheric Cherenkov telescopes will require the production of thousands of mirror segments; an unprecedented amount of optical surface. To accomplish this, the Italian Istituto Nazionale di AstroFisica (INAF) has recently developed a successful technique. This method, called glass cold-shaping, is mainly intended for the manufacturing of mirrors for optical systems with an angular resolution of a few arcminutes, intended to operate in extreme environments. Its principal mechanical features are very low weight and high rigidity of the resulting segments, and its cost and production time turn out to be very competitive as well. The process is based on the shaping of thin glass foils by means of forced bending at room temperature; a sandwich structure is then assembled for retaining the imposed shape. These mirrors are composted of commercial, off-the-shelf materials. In this contribution we give an overview of the latest results achieved in the manufacturing of the pre-production series of mirrors for the Medium Size and Small Size Telescopes of the Cherenkov Telescope Array observatory.

In the context of the Cherenkov Telescope Array observatory project, the ASTRI SST-2M end-to-end prototype telescope, entirely supported by the Italian National Institute of Astrophysics, is designed to detect cosmic primary gamma ray energies from few TeV up to hundreds of TeV. The ASTRI SST-2M prototype camera is part of the challenging synergy of novel optical design, camera sensors, front-end electronics and telescope structure design. The camera is devoted to imaging and recording the Cherenkov images of air showers induced by primary particles into the Earth’s atmosphere. In order to match the energy range mentioned above, the camera must be able to trigger events within a few tens of nanoseconds with high detection efficiency. This is obtained by combining silicon photo-multiplier sensors and suitable front-end electronics. Due to the characteristic imprint of the Cherenkov image that is a function of the shower core distance, the signal dynamic range of the pixels and consequently of the front-end electronics must span three orders of magnitude (1:1000 photo-electrons). These and many other features of the ASTRI SST-2M prototype camera will be reported in this contribution together with a complete overview of the mechanical and thermodynamic camera system.

The Cherenkov Telescope Array (CTA) observatory will represent the next generation of Imaging Atmospheric Cherenkov Telescopes. Using a combination of large-, medium-, and small-scale telescopes (LST, MST, SST, respectively), it will explore the Very High Energy domain from a few tens of GeV up to few hundreds of TeV with unprecedented sensitivity, angular resolution and imaging quality. In this framework, the Italian ASTRI program, led by the Italian National Institute of Astrophysics (INAF), is currently developing a scientific and technological SST prototype named ASTRI SST-2M; a 4-meter class telescope, it will adopt an aplanatic, wide-field, double-reflection optical layout in a Schwarzschild-Couder configuration. In this contribution we give an overview of the technological solutions adopted for the ASTRI SST-2M prototype. In particular we focus on the manufacturing of the telescope structure and mirrors. We will also describe early results from tests.

The Cherenkov Telescope Array (CTA) observatory will represent the next generation of Imaging Atmospheric Cherenkov Telescope. Using a combination of large-, medium-, and small-scale telescopes (LST, MST, SST, respectively), it will explore the Very High Energy domain from a few tens of GeVup to about few hundreds of TeV with unprecedented sensitivity, angular resolution and imaging quality. In this framework, the Italian ASTRI program, led by the Italian National Institute of Astrophysics (INAF) developed a 4-meter class telescope, which will adopt an aplanatic, wide-field, double-reflection optical layout in a Schwarzschild- Couder configuration. Within this program INAF assigned to the consortium between Galbiati Group and EIE Group the construction, assembly and tests activities of the prototype named ASTRI SST-2M. On the basis of the lesson learnt from the prototype, other telescopes will be produced, starting from a re-design phase, in order to optimize performances and the overall costs and production schedule for the CTA-SST telescope. This paper will firstly give an overview of the concept for the SST prototype mount structure. In this contest, the technologies adopted for the design, manufacturing and tests of the entire system will be presented. Moreover, a specific focus on the challenges of the prototype and the strategies associated with it will be provided, in order to outline the near future performance goals for this type of Cherenkov telescopes employed for Gamma ray science.

The next generation of Imaging Atmospheric Cherenkov Telescope will explore the uppermost end of the Very High Energy domain up to about few hundreds of TeV with unprecedented sensitivity, angular resolution and imaging quality. To this end, the Italian National Institute of Astrophysics (INAF) is currently developing a scientific and technological telescope prototype for the implementation of the Cherenkov Telescope Array (CTA) observatory. The Italian ASTRI program foresees the full design, development, installation and calibration of a Small Size 4-meter class Telescope, adopting an aplanatic, wide-field, double-reflection optical layout in a Schwarzschild-Couder configuration. In this paper we discuss about the technological solutions adopted for the telescope and for the mirrors. In particular we focus on the structural and electro-mechanical design of the telescope, now under fabrication. The results on the optical performance derived from mirror prototypes are here described, too.

ESPRESSO is the next European exoplanets hunter. It will combine the efficiency of modern echelle spectrograph with extreme radial-velocity precision. It will be installed at Paranal's VLT in order to achieve two magnitudes gain with respect to its predecessor HARPS, and the instrumental radial-velocity precision will be improved to reach 10 cm/s level. We have constituted a Consortium of astronomical research institutes to fund, design and build ESPRESSO on behalf of and in collaboration with ESO, the European Southern Observatory. The project has passed the final design review in May 2013. The spectrograph will be installed at the Combined Coude Laboratory of the VLT, it will be linked to the four 8.2 meters Unit Telescopes through four optical "Coude trains" and will be operated either with a single telescope or with up to four UTs, enabling an additional 1.5 magnitude gain. Thanks to its characteristics and ability of combining incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in many fields of astronomy. Our main scientific objectives are, however, the search and characterization of rocky exoplanets in the habitable zone of quiet, near-by G to M-dwarfs, and the analysis of the variability of fundamental physical constants. In this paper, we will present the scientific objectives, the capabilities of ESPRESSO, the technical solutions for the system and its subsystems, enlightening the main differences between ESPRESSO and its predecessors. The project aspects of this facility are also described, from the consortium and partnership structure to the planning phases and milestones.

We present a method developed by INAF (Italian National Institute for Astrophysics) for the manufacturing of mirrors by using commercial of-the-shelf materials. It is based on the shaping of thin glass foils by means of forced bending; then a sandwich structure is assembled for retaining the imposed shape. These mirrors are intended for optical systems with few arcmin in angular resolution working in extreme environments, being their principal mechanical features the very low weight and high rigidity. The cost and production time also turns to be very competitive. In this paper we report the main achievements of the R&D performed. We recall the investigation of the theoretical limits with finite element analyses and the process implementation. Finally, the case of the mirrors for IACT (Imaging Atmospheric Cherenkov Telescope) is presented with respect to the ASTRI project (Astrofisica con Specchi a Tecnologia Replicante Italiana).

We present an optical method for free-form mirrors qualification developed by the Italian National Institute for Astrophysics (INAF) in the context of the ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana) Project which includes, among its items, the design, development and installation of a dual-mirror telescope prototype for the Cherenkov Telescope Array (CTA) observatory. The primary mirror panels of the telescope prototype are free-form concave mirrors with few microns accuracy required on the shape error. The developed technique is based on the synergy between a Ronchi-like optical test performed on the reflecting surface and the image, obtained by means of the TraceIT ray-tracing proprietary code, a perfect optics should generate in the same configuration. This deflectometry test allows the reconstruction of the slope error map that the TraceIT code can process to evaluate the measured mirror optical performance at the telescope focus. The advantages of the proposed method is that it substitutes the use of 3D coordinates measuring machine reducing production time and costs and offering the possibility to evaluate on-site the mirror image quality at the focus. In this paper we report the measuring concept and compare the obtained results to the similar ones obtained processing the shape error acquired by means of a 3D coordinates measuring machine.

ESPRESSO, the VLT rocky exoplanets hunter, will combine the efficiency of modern echelle spectrograph with extreme radial-velocity precision. It will be installed at Paranal on ESO's VLT in order to achieve a gain of two magnitudes with respect to its predecessor HARPS, and the instrumental radial-velocity precision will be improved to reach 10 cm/s level. We have constituted a Consortium of astronomical research institutes to fund, design and build ESPRESSO on behalf of and in collaboration with ESO, the European Southern Observatory. The project has passed the preliminary design review in November 2011. The spectrograph will be installed at the so-called "Combined Coude Laboratory" of the VLT, it will be linked to the four 8.2 meters Unit Telescopes (UT) through four optical "Coude trains" and will be operated either with a single telescope or with up to four UTs. In exchange of the major financial and human effort the building Consortium will be awarded with guaranteed observing time (GTO), which will be invested in a common scientific program. Thanks to its characteristics and the ability of combining incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in many fields of astronomy. Our main scientific objectives are, however, the search and characterization of rocky exoplanets in the habitable zone of quiet, near-by G to M-dwarfs, and the analysis of the variability of fundamental physical constants. In this paper, we present the ambitious scientific objectives, the capabilities of ESPRESSO, the technical solutions for the system and its subsystems, enlightening the main differences between ESPRESSO and its predecessors. The project aspects of this facility are also described, from the consortium and partnership structure to the planning phases and milestones.

The challenge of building extremely large telescope pushes forward the parallel ability to measure and test optical components of large sizes. Here we present the optical bench setup for the Demonstration Prototype (DP) of the voice coil controlled adaptive mirror M4AU of the E-ELT. A set of three devices has been chosen and used for the tests, whose results are also shown. The performance demonstrated that this is a viable and trusted technology and the DP tests were highly representative of the whole procedure that could be applied to the real, full size unit.

A prototype for a compact and relatively simple system capable to measure the refraction index of glasses, between 0.4 to 1.7 micron, at room and cryogenic temperatures (T=100-300 K), with an absolute precision of few parts of 100'000 has been developed at INAF facilities in Merate. It is based onto the measurement of the deviation angle of monochromatic light passing through a prism sample placed in the cryogenic chamber. The precision of the measurements depends on many factors, in particular the angle measurement and the thermal stability. Different subsystems have been studied to keep all these parameters under accurate control. One of the main issues has been the trade-off between the simplicity of the set-up and the precision of the refractive index measurement.

Organic photochromic materials have been studied as active materials in optical devices since they show a reversible change of color in the visible region and appreciable reversible changes of the refractive index (' n) in the NIR. The latter peculiar property can be suitably exploited for the realization of holographic optical elements (HOEs) and in particular volume phase holographic gratings (VPHGs). Photochromic polyester based on diarylethene alcohol was synthesized and characterized both in solution and in thin film. The optical properties of the films were good enough for making optical devices and the modulation of the refractive index (measured by spectral ellipsometry) was large at 1.5 micron and it became even larger at shorter wavelength where the material is still transparent. Such photochromic material is a good candidate for making rewritable efficient HOEs. Keywords: photochromism, refraction index, diarylethenes, VPHG, ellipsometry 1. INTRODUCTION Materials showing a change in refractive index have attracted attention in different technological fields to develop holographic optical elements

Volume phase holographic gratings (VPHGs) are becoming an interesting alternative to the ruled gratings in modern astronomical instrumentation. Photochromic materials with thermal stability are good candidates for the development of holographic optical elements and in par ticular for VPHGs. VPHGs ba sed on photochromic materials can be written and erased many times without the degradation of the material; moreover the material does not need any developing process after the exposure, making the writing process very simple. We have already studied photochromic materials for this aim in the framework of the JRA6 (Opticon Project, FP6) and we found that large modulations of the refractive index can be achieved using diarylethene polymers. Going from the materials characterization to technology, substrates with larger thickness and good optical properties are required. Herein we present the development of new technique to tailor the thickness of the photochromic films in two ranges: 5 – 30 micron and 700 – 1000 micron. The former are suitable for the development of broadband VPHGs, whereas the latter are suitable for narrow band t unable filters application. Details on the optical properties of the films are reported. Finally, a holographic set-up based on an Ar+ laser has been optimized in order to write the gratings. Keywords: VPHG, refraction index, photochromic materials, holographic materials

We present the development of a demonstration prototype for a compact and relatively cheap system capable to measure the refraction index of glasses, between 0.4 to 1.7 micron, at room and cryogenic temperatures (T=100-300 K), with an absolute precision of few parts of 10 -5 . The basic concept is the measurement of the deviation angle of monochromatic light passing through a prism sample placed in the cryogenic chamber. The precision of the measurements depends on many factors, in particular the angle measurement and the thermal stability, therefore the system can control its alignment. The main issue is the trade-off between the simplicity of the set-up and the precision of the refractive index measurement.

A 42 meters telescope does require adaptive optics to provide few milli arcseconds resolution images. In the current design of the E-ELT, M4 provides adaptive correction while M5 is the field stabilization mirror. Both mirrors have an essential role in the E-ELT telescope strategy since they do not only correct for atmospheric turbulence but have also to cancel part of telescope wind shaking and static aberrations. Both mirrors specifications have been defined to avoid requesting over constrained requirements in term of stroke, speed and guide stars magnitude. Technical specifications and technological issues are discussed in this article. Critical aspects and roadmap to assess the feasibility of such mirrors are outlined.

The ability to manufacture larger adaptive optics mirror rely also on the availability of metrology tools suitable for the purpose to validate the mirrors. In the framework of the ELT M4 adaptive, 2.5 m diameter, plane mirror we devised a series of tools able to certify that the plane wavefront is achieved and kept in place. A stitching series of small beams is conjugated with a whole image of the mirror thanks to a big, grazing incidence interferometric cavity. The set is completed by a novel piston sensing device which collate different segments of the (possibly) multiple mirror. We describe here the foreseen procedure and the status of the prototype realization.

The thinking about possible instruments for the future ELTs has just started and the current phase allows to pursue non-traditional solutions. Following the guidelines of the Science Case for an ELT 1,2 our team searched for possible intersections with innovative technologies we currently deal with in our research. We found that Volume Phase Holographic Gratings and advanced dichroics could be suited to design a non-traditional narrow band imager. We propose in this paper a comparative analysis of a VPHG based and a dichroic based configurations for the imager. Keywords: Narrow band imager, non conventional diffraction, dichroic mirror, infrared spectroscopy. 1. INTRODUCTION The giant new collecting area of future big telescopes leads to new concepts for the astronomical instrumentation in a natural way. These areas, hundred times bigger than the actual ones of the 10m class telescopes, will be characterized by meter-sized focal planes and pupils. The extension of these planes is overfilled of instrumentation, and therefore the “field of view” or the “pupil” should be split up. In the first case, it should be possible to make the same measure on different objects, while splitting up the pupil the same object can be investigated with different measurements. Considering the focal plane fragmentation, the project we’re going to introduce (called “AGAR-AGAR project”) is conceived for the limit case of a 100m F/6 telescope. Shortly we are situated between the first one and the second micron of the IR infrared band and, the measure that AGAR proposes, can be interpreted as borderline case of a 3D low resolution spectroscopy (about RS50) or of multi Imaging and narrow band, around 20nm. Agar is founded on a repeated use of dichroics multilayer mirror which return a series of channels every characterized by own spectral band of work. Every channel, provided of own camera, reform the image of the field in the short band filtered by dichroics. The total result are 64 images to cover in full the interval 1-2.2 microns, on a field of view equal to 10 arcseconds. The results that we go to expose want to relate the simplicity of the idea of the tool, through its conceptual scheme, its optical characterization, showing the beyond expectation reached efficiency.

The use of high diffraction efficiency Volume Phase Holographic grating as central element in a spectrograph allows to consistently increase the instrumental throughput. Moreover the geometry they use allow them to be located in simplified optical designs and their manufacturing characteristics make them ideal also for the high resolution (R > 20,000) domain. VPHG are the perfect solution for high resolution spectrograph coupled with moderate collecting areas such as those of robotic telescopes nowadays distributed worldwide. We present in this paper the spectrograph, currently under construction, that will equip the REM telescope at la Silla Observatory, Chile.