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SPIE Optical Engineering + Applications, San Diego, United States, 11 Aug 2019 - 15 Aug 2019; Journal of astronomical telescopes, instruments, and systems 8, 014005 (2022). doi:10.1117/1.JATIS.8.1.014005, The Cherenkov Telescope Array (CTA) is the next ground-based γ-ray observatory in the TeV γ-ray spectral region operating with the Imaging Atmospheric Cherenkov Technique. It is based on almost 70 telescopes of different class diameters - LST, MST and SST of 23, 12, and 4 m, respectively - to be installed in two sites in the two hemispheres (at La Palma, Canary Islands, and near Paranal, Chile). Several thousands of reflecting mirror tiles larger than 1 m$^2$ will be produced for realizing the segmented primary mirrors of a so large number of telescopes. Almost in parallel, the ASTRI Mini-Array (MA) is being implemented in Tenerife (Canary Islands), composed of nine 4 m diameter dual-mirror Cherenkov telescopes (very similar to the SSTs). We completed the mirror production for all nine telescopes of the ASTRI MA and two MST telescopes (400 segments in total) using the cold glass slumping replication technology. The results related to the quality achieved with a so large-scale production are presented, also discussing the adopted testing methods and approaches. They will be very useful for the adoption and optimization of the quality assurance process for the huge production (almost 3000 m$^2$ of reflecting surface) of the MST and SST CTA telescopes., Published by SPIE, [Bellingham, Wash.]

The VERT-X X-ray calibration facility, currently in prototypal realization phase supported by ESA, will be a vertical X-ray beamline able to test and calibrate the entire optical assembly of the ATHENA X-ray telescope. Owing to its long focal length (12 m), a full-illumination test of the entire focusing system would require a parallel and uniform X-ray beam as large as the optical assembly itself (2.5 m). Moreover, the module should better be laid parallel to the ground in order to minimize the effects of gravity deformations. Therefore, the ideal calibration facility would consist of a vertical beam, with the source placed at very large distance (>> 500 m) under high vacuum (10-6 mbar). Since such calibration systems do not exist, and also appear to be very hard to manufacture, VERT-X will be based on a different concept, i.e., the raster scan of a tightly (≈ 1 arcsec) collimated X-ray beam, generated by a microfocus source and made parallel via a precisely shaped Wolter-I mirror. In this design, the mirror will be made of two segments (paraboloid + hyperboloid) that, for the X-ray beam collimation to be preserved, will have to be accurately finished and maintain their mutual alignment to high accuracy during the scan. In this paper, we show simulations of the reflected wavefront based on physical optics and the expected final imaging quality, for different polishing levels and misalignments for the two segments of the VERT-X collimator.

The optics of ATHENA (Advanced Telescope for High-ENergy Astrophysics) consists of several hundreds of Silicon Pore Optics mirror modules integrated and co-aligned onto a Mirror Assembly Module (MAM). The selected integration process exploits an optical bench to capture the focal plane image of each mirror module when illuminated by an UV plane wave at 218 nm. Each mirror module focuses the collimated beam onto a CCD camera placed at the 12 m focal position of the ATHENA telescope and the acquired point spread function is processed in real time to calculate the centroid position and intensity parameters. This information is used to guide the robot-assisted alignment sequence of the mirror modules. The ATHENA Assembly Integration and Testing (AIT) facility has been designed and is now under construction. It consists of a vertical tower, in which clean room conditions are maintained. Inside the tower, the MAM is supported at ground level on a gravity release system and a robot device above the MAM is used for alignment of the SPO Mirror modules. A paraboloid mirror that collects the light from an ultraviolet point source and generates a single reference plane wave large enough to illuminate the 2.6 m aperture of the X-ray telescope is placed 6 m below the MAM, whereas a CCD camera for the detection of the focused beam is placed at the top of the tower, 12 m above the MAM.

ATHENA (Advanced Telescope for High-ENergy Astrophysics) is the next high-energy astrophysical mission of the European Space Agency currently planned to be launched in the early 2030s, as part of its Cosmic Vision program, on the scientific topic of “Hot and Energetic Universe”. The optics technology is based on the Silicon Pore Optics (SPO). About 678 SPO mirror modules will have to be integrated and co-aligned onto the optical bench of the Mirror Assembly Module (MAM) of ATHENA. This activity will have to be completed in about two years. Media Lario leads an industrial and scientific team that has developed the process to align and integrate the SPO Mirror module with an accuracy better than 1 arcsec. The process is based on position of the centroid of the point spread function produced by each mirror module when illuminated by a collimated planewave at 218 nm taken at 12 m focal length. Experimental tests, using two SPO mirror modules, and correlation with X-ray measurement at the PANTER test facility in Munich have demonstrated that this process meets the accuracy requirement. It was also demonstrated, that a mirror module can be removed again from the MAM, and re-installed, without compromising the adjacent mirror modules. This technique allows arbitrary integration sequence and integration of two Mirror Modules per day. Moreover, it enables monitoring the telescope point spread function during the whole integration phase.

FLORIS (FLuorescence Imaging Spectrometer) is the single High-Resolution Spectrometer instrument of the FLEX (FLuorescence EXplorer) mission, currently under development by the European Space Agency as the eighth Earth Explorer Mission. The goal of the mission is the monitoring of the chlorophyll fluorescence of plants giving information about their photosynthetic activity. Leonardo Avionics & Space System Division is the prime contractor for the FLORIS Instrument for which Media Lario is manufacturing the QM unit of the spherical mirror included in the High-Resolution Spectrometer (HRSPE), hereafter called HRM mirror. The High-Resolution Mirror is a 250-mm diameter spherical mirror with a radius of curvature of approximately 440 mm. For the mirror substrate, Leonardo has selected the Aluminium alloy AlSi40, a special alloy with 40% Silicon content, coated with a hard polishing layer of Nickel Phosphorus (NiP), deposited by electroless chemical process. The Silicon content allows this special Aluminium alloy to have the same coefficient of thermal expansion (CTE) of the NiP layer, therefore preventing thermal deformations deriving from the bimetallic effect. The mirror structure is light-weighted to approximately 2.8 kg. The required wave-front error of the mirror is better than 0.5 fringes PV, while the surface microroughness has been specified at 0.5 nm RMS due to stringent straylight requirements of the FLORIS instrument. Media Lario has been selected for the mirror development phase because of their experience in the design and manufacturing of AlSi/NiP mirrors demonstrated in the development of the Earth Observation optical payload for small satellites (called STREEGO), based on an AlSi40 TMA telescope. The manufacturing process includes precision diamond turning, optical figuring and super-polishing. The optical coating will be done by Leonardo at their thin-films facility of Carsoli, Italy. Since the recipe prescribes to pre-heat the mirror surface at 100° C, Media Lario will qualify the mirror substrate with -25/+110°C thermal cycles to ensure adequate thermal stability for the coating process.

The ATHENA X-ray observatory is a large-class ESA approved mission, with launch scheduled in 2028. The technology of Silicon Pore Optics (SPO) was selected since 2004 as the baseline for making the X-ray Mirror Assembly. Up to 700 mirror modules to obtain a nested Wolter like optics. The maximum diameter of the shells will be 2.5 m while the focal length is 12 m. The requirements for on-axis angular resolution and effective area at 1 keV are 5 arcsec HEW and 1.4 m2, while the field of view will be 40 arcmin in diameter (50 % vignetting). While in this moment there an on-going effort aiming at demonstrating the feasibility of a so large optics with so stringent scientific requirements, an important aspect to be considered regards the scientific calibrations of the X-ray optics. In this respect, the Point Spread Function and effective area have to be correctly measured and calibrated on-ground at different energies across the entire field of view, with a low vignetting. The approach considered so far foresees the use of a long (several hundreds of meters) facility to allow a full illumination with low divergence of the entire optics module (or at least of large sections of it). The implementation of similar configurations in a completely new facility to be realized in Europe (friendly called "super Panter") or the retrofitting existing facilities like the XRCF at NASA/MSFC are being considered. In both cases the costs and the programmatic risks related to the implementation of these huge facilities, with their special jigs for the alignment of the ATHENA optics, represent important aspects to be considered. Moreover, the horizontal position of the optics to be used in full illumination facilities would determine gravitational deformations, not easy to be removed with actuators or by modeling. In this talk we will discuss a completely different concept, based on the mount of the optics in vertical position and the use of a raster scan of the ATHENA optics with a small (a few cm2 wide) highly collimated (1 arcsec or so) white beam X-ray. This system will allow us to operate a much compact system. The use of a vertical configuration will imply smaller gravitational deformations, that can be controlled with actuators able to compensate them. A proper camera system with a sufficient energy resolution will be able to grant a correct measurement of both PSF and effective area of the Mirror Assembly within the calibration requirements and in a reasonable integration time. Moreover, it may allow us also to perform end-to-end tests using the two flight focal plane instruments of ATHENA. The cost and risks for the implementation would be much lower than for the full illumination systems. The conceptual configuration and preliminary expected performance of the facility will be discussed.

ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) has been selected by ESA as the next mediumclass science mission (M4) to be launched in 2028. The aim of the ARIEL mission is to study the atmospheres of a selected sample of exoplanets. The payload is based on a 1-m class telescope ahead of a suite of instruments: two spectrometric channels covering the band 1.95 to 7.80 μm and four photometric channels working in the range 0.5 to 1.9 μm. The production of the primary mirror (M1) is one of the main technical challenges of the mission. A trade-off on the material to be used for manufacturing the 1-m diameter M1 was carried out, and aluminium alloys have been selected as the baseline materials both for the telescope mirrors and structure. Aluminium alloys have demonstrated excellent performances both for IR small size mirrors and structural components, but the manufacturing and thermo-mechanical stability of large metallic optics still have to be demonstrated especially at cryogenic temperatures. The ARIEL telescope will be realized on-ground (1 g and room temperature), but it shall operate in space at about 50 K. For this reason a detailed tolerance analysis was performed to assess the telescope expected performance. M1 is an off-axis section of a paraboloidal mirror and will be machined from a single blank as a stand-alone part. To prove the feasibility of such a large aluminium mirror, a pathfinder mirror program has been started. The prototype has been realized and tested, so far at room temperature, by Media Lario S.r.l.. Cryogenic testing of the prototype will be performed during Phase B1.

Optics for EUV, X-Ray, and Gamma-Ray Astronomy IX : [Proceedings] - SPIE, 2019. - ISBN 97815106293189781510629325 - doi:10.1117/12.2531157 Optics for EUV, X-Ray, and Gamma-Ray Astronomy IX, San Diego, United States, 11 Aug 2019 - 15 Aug 2019; SPIE 9 pp. (2019). doi:10.1117/12.2531157, The Cherenkov Telescope Array (CTA) will be the next generation ground-based observatory for gamma-ray astronomyat very-high energies. It will consist of over a hundred telescopes of different sizes (small, medium, and large) located inthe northern and southern hemispheres. The Italian National Institute of Astrophysics (INAF) contributes to CTAthrough the ASTRI project (Astrofisica con Specchi a Tecnologia Replicante Italiana), whose main aim is to provide aseries of dual-mirror small-sized telescopes (SST-2M ASTRI) and the mirrors for the single-mirror design of themedium-sized telescopes (MST). Both the primary mirror of the SST-2M ASTRI and the mirror of the MST aresegmented, and such segments are realized with cold-slumping technology already used for the mirror facets of MAGIC,a system of two Cherenkov telescopes operating on the Canary Island of La Palma. On the other hand, the secondarymirror of the SST-2M ASTRI is monolithic and is realized with hot-slumping technology. Currently, we have completedthe mirror production for nine SST-2M ASTRI telescopes, which will form the so-called ASTRI Mini-Array. Moreover,we have almost completed also the production of mirrors for two MSTs. In this paper, we present the mirror designs anddescribe the qualification activities that were performed to assess and consolidate the production process. Moreover, wereport on the quality assurance approach we adopted to monitor and verify the production reliability. Finally, we presentthe performance of the produced mirrors and discuss their compliance with the CTA requirements., Published by SPIE

ATHENA (Advanced Telescope for High-ENergy Astrophysics) is the next high-energy astrophysical mission of the European Space Agency. Media Lario leads an industrial and scientific team that has developed a process to align and integrate more than 700 silicon pore optics mirror modules into the ATHENA X-ray telescope. The process is based on the ultra-violet imaging at 218 nm of each mirror module on the focal plane of a 12 m focal length optical bench. Specifically, the position of the centroid of the point spread function produced by each mirror module when illuminated by a collimated plane is used to align each mirror module. Experimental integration tests and correlation with X-ray measurement at the PANTER test facility in Munich have demonstrated that this process meets the accuracy requirement. This technique allows arbitrary integration sequence and mirror module exchangeability. Moreover, it enables monitoring the telescope point spread function during the integration phase.

ATHENA (Advanced Telescope for High-ENergy Astrophysics) is the next high-energy astrophysical mission selected by the European Space Agency for launch in 2028. The X-ray telescope consists of 1062 silicon pore optics mirror modules with a target angular resolution of 5 arcsec. Each module must be integrated on a 3 m structure with an accuracy of 1.5 arcsec for alignment and assembly. This industrial and scientific team is developing the alignment and integration process of the SPO mirror modules based on ultra-violet imaging at the 12 m focal plane. This technique promises to meet the accuracy requirement while, at the same time, allowing arbitrary integration sequence and mirror module exchangeability. Moreover, it enables monitoring the telescope point spread function during the planned 3-year integration phase.

The effect of charge recombination on the noise associated with the signal current at the anode of a semiconductor drift detector is studied for both time and amplitude measurements. The analysis is performed by fully taking into account the diffusion of electrons in the semiconductor, the electrostatic induction process that gives rise to the signal, and the correct boundary condition at the anode for the electron density. Both the time variance and the amplitude noise-to-signal ratio are calculated as a function of the filter width for different values of the time constant of the recombination process. A comparison with previous results based on more simplified treatments is also given.

A design of a two-reflection mirror for nested grazing-incidence optics is proposed in which maximum overall reflectivity is achieved by making the two grazing-incidence angles equal for each ray. The design is proposed mainly for application to nonimaging collector optics for extreme-ultraviolet microlithography where the radiation emitted from a hot plasma source needs to be collected and focused on the illuminator optics. For completeness, the design of a double- reflection mirror with equal reflection angles is also briefly outlined for the case of an object at infinity for possible use in x-ray applications.