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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.

The exoplanet revolution is well underway. The last decade has seen order-of-magnitude increases in the number of known planets beyond the Solar system. Detailed characterization of exoplanetary atmospheres provide the best means for distinguishing the makeup of their outer layers, and the only hope for understanding the interplay between initial composition chemistry, temperature-pressure atmospheric profiles, dynamics and circulation. While pioneering work on the observational side has produced the first important detections of atmospheric molecules for the class of transiting exoplanets, important limitations are still present due to the lack of systematic, repeated measurements with optimized instrumentation at both visible (VIS) and near-infrared (NIR) wavelengths. It is thus of fundamental importance to explore quantitatively possible avenues for improvements. In this paper we report initial results of a feasibility study for the prototype of a versatile multi-band imaging system for very high-precision differential photometry that exploits the choice of specifically selected narrow-band filters and novel ideas for the execution of simultaneous VIS and NIR measurements. Starting from the fundamental system requirements driven by the science case at hand, we describe a set of three opto-mechanical solutions for the instrument prototype: 1) a radial distribution of the optical flux using dichroic filters for the wavelength separation and narrow-band filters or liquid crystal filters for the observations; 2) a tree distribution of the optical flux (implying 2 separate foci), with the same technique used for the beam separation and filtering; 3) an 'exotic' solution consisting of the study of a complete optical system (i.e. a brand new telescope) that exploits the chromatic errors of a reflecting surface for directing the different wavelengths at different foci. In this paper we present the first results of the study phase for the three solutions, as well as the results of two laboratory prototypes (related to the first two options), that simulate the most critical aspects of the future instrument.

ASTRI is the end-to-end prototype for the CTA small-size class of telescopes in a dual-mirror configuration (SST-2M) proposed by the Italian National Institute of Astrophysics (INAF) in the framework of the Cherenkov Telescope Array. ASTRI SST-2M has been installed at the Serra La Nave Astrophysical Observatory on Mount Etna (Sicily) and its Performance Verification Phase will start in autumn 2016. For the relative pixel calibration and gain monitoring, the ASTRI SST-2M camera is equipped with an internal illumination device, while an external, portable, illumination system, placed at a few km distance from the telescope, will be used for the absolute end-to-end calibration of the telescope spectral response. Moreover analysis of signals induced in the camera pixels by the night sky background (diffuse emission and reference stars) will be used to monitor the long term evolution of the telescope calibration. We present an overview of the ASTRI SST-2M absolute calibration strategy and the external illuminating device that will be used for its spectral calibration

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.

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.

This Letter describes an efficient three-step synthesis route of symmetric and asymmetric phenyl-substituted photochromic 1,2-dithienylethenes bearing unprotected functional groups (i.e., alcohols, carboxylic acids or amines). These products can be easily obtained by typical Suzuki cross-coupling between photochromic dichlorides and commercial available boronic acids or pinacol esters.

The peculiar property of reversible change of the refractive index (Δn) of photochromic systems, is suitably exploited to realize volume phase holographic gratings (VPHGs), which are finding applications in optics and in spectroscopic instrumentations. A large modulation of the refractive index between the two photochromic states and a relatively thick layer of good optical quality are the fundamental requirements for the materials to achieve a good diffraction efficiency. A backbone diarylethene polymer which combines good processing properties with a proper photochromic sensitivity is synthesised and studied. The large Δn between the two isomer states (i.e. Δn=0.03 measured at 1500 nm and the value is even higher at shorter wavelengths, approaching 0.1 near the visible) and the high transparency in the near infrared range make it a promising substrate for the realization of efficient VPHGs. First prototype of VPHGs based on photochromic diarylethene polymer films has been written by transferring the pattern of lines from a master and its functionality is shown.

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

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 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.

Volume phase holographic gratings (VPHGs) are becoming widespread dispersing elements in the modern spectrograph. Different materials can be used to make such gratings. We developed photochromic polymers based on a diarylethene unit that make VPHG suitable for observations in the near infrared region (1 - 2 μm) where the materials are highly transparent and show large modulation of the refractive index. This modulation was measured on films of different polymers by using spectral reflectance obtaining values of the order of 10 -2 , These values are large enough to make efficient VPHGs if the thickness of the films are about 25 μm. The sensitivity of the photochromic polyesters was measured at 514 and 633 nm. Prototype of photochromic VPHGs were made by transferring a 600 l/mm pattern of a Ronchi ruling glass slide on a photochromic polyester film (4 μm thick) by using a green laser (543 nm, 30 mW). The grating was successfully transferred as shown by optical microscopy and by the diffraction pattern induced by a white light.

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.

ESPRESSO is the next generation ground based European exoplanets hunter. It will combine the efficiency of modern echelle spectrograph with extreme radial-velocity and spectroscopic 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 spectrograph will be installed at the Combined Coude Laboratory (CCL) 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. The project is, for most of its workpackages, in the procurement or development phases, and the CCL infrastructure is presently under adaptation work. In this paper, we present the scientific objectives, the capabilities of ESPRESSO, the technical solutions for the system and its subsystems. The project aspects of this facility are also described, from the consortium and partnership structure to the planning phases and milestones.