This PDF file contains the front matter associated with SPIE Proceedings Volume 11822, including the Title Page, Copyright information and Table of Contents

The ASTRI Mini-Array (MA) is an INAF project to build and operate an experiment to study astronomical sources emitting gamma-rays at very high-energies. The ASTRI MA consists of a group of nine innovative Imaging Atmospheric Cherenkov telescopes. The array will be installed at the Teide Astronomical Observatory of the Instituto de Astrofisica de Canarias (IAC) in Tenerife (Canary Islands, Spain), on the basis of a host agreement with INAF. Thanks to its expected overall performance, better than current Cherenkov telescopes' arrays for energies above ~5 TeV and up to 100 TeV and beyond, the ASTRI MA will represent an important instrument to perform deep observations of the Galactic and extra-Galactic sky at these extreme photon energies. The design of the telescopes forming the MA is an evolution of the two-mirror end-to-end ASTRI-Horn telescope successfully implemented and tested in the past years at the Serra La Nave Astronomical Station on Mount Etna operated by INAF-Catania. In particular, with the detection of the Crab at energies larger than 3.5 TeV by ASTRI-Horn, it has been proved the validity of the dual-mirror design for Cherenkov telescopes that was never been adopted before. The new MA telescope aplanatic design will implement a larger field of view (more than 10^o in diameter) and will be equipped with the updated version of the compact ASTRICAM camera, based on Hamamatsu silicon photomultipliers (SiPM) and on the CITIROC ASIC, specifically developed by the French firm Weeroc in collaboration with INAF for the read-out electronics. In order to simplify the site infrastructure design, reduce operation, maintenance and personnel costs, the ASTRI MA has been designed to be operated in fully automatic mode with remote supervision. In this contribution we describe the functional and physical architecture of the array and the evolution of the design of telescopes and cameras. Finally, the status of the site implementation and of the production of the main ASTRI MA subsystems is reviewed..

Current generation Imaging Atmospheric Cherenkov Telescopes (IACTs) like HESS, MAGIC and VERITAS, operated in array-mode, have opened a new astronomical window in high energy gamma-ray band from a few tens GeV to a hundred TeV, allowing to observe the most energetic phenomena on going in our Universe. New generation arrays like ASTRI, with its 9 small-class telescopes operated at Tenerife, Canary Islands, and the very ambitious Cherenkov Telescope Array Observatory (CTAO - with its two sites at the northern and southern hemispheres and about 70 telescopes of different classes) will need to fabricate a few thousand square meters of reflective segments of about 1 m² area and different shapes for making the primary mirrors. Different low-cost technologies have been used so far, like the direct figuring and polishing of glass slabs, the diamond turning of pre-formed aluminum sandwiched panels and the replica of thin glass foils for making composite sandwiched mirrors. In this paper we will present a further alternative solution, based on the replica of aluminum foils - precoated with a high reflectivity and durability multilayer film - for making sandwiched mirrors. This approach will simplify a lot the production chain, allowing us to make low-cost panels entirely made of aluminum. The method of production of the aluminum replicated panels is discussed and the preliminary performance results obtained with a prototype mirror presented.

The ATHENA (Advanced Telescope for High ENergy Astrophysics) mission is steadily progressing both in terms of system studies and technology developments. The mission is currently in Phase B1 and is maturing towards a successful mission adoption. This paper describes the mission status including the main accomplishments achieved during this phase in terms of convergence of system and technological aspects. An overview of the different system studies is given including the latest programmatic assumptions, emphasizing on the Mirror Assembly demonstration and the critical interfaces between the mirror and the different facilities that are being developed in tandem to the mission. The reference telescope design is also described based on the Silicon Pore Optics (SPO) technology. The main design choices are explained as well as the modelling performed to ensure that all technological and system level constraints are met from plate level all the way to the mirror assembly level. The resulting effective area performance and budgeting is briefly described and future improvements are identified.

The ATHENA (Advanced Telescope for High ENergy Astrophysics) mission studies and technology preparation are continuing to progress. The optics for this future space observatory is based on the Silicon Pore Optics (SPO), and is being evolved in a joint effort by industry, research institutions and ESA. The SPO technology uses the superb properties of monocrystalline Silicon, and spins in technologies developed for the semiconductor industry, benefiting from excellent materials, processes and equipment. In a holistic approach the technical and programmatic challenges of the ATHENA optics are being addressed simultaneously. A comprehensive Technology Development Plan (TDP) was defined and is being implemented to develop this novel X-ray optics technology. The performance, environmental compatibility and serial automated production and testing are being addressed in parallel, aiming at the demonstration of the required technology readiness for the Athena Mission Adopt ion Review (MAR) expected in 2022.

Athena, the largest space-based x-ray telescope to be flown by the European Space Agency, uses a new modular technology to assemble its 2.5 m diameter lens. The lens will consist of several hundreds of smaller x-ray lenslets, called mirror modules, which each consist of up to 76 stacked mirror pairs. Those mirror modules are arranged in circles in a large optics structure and will focus x-ray photons with an energy of 0.5 to 10 keV at a distance of 12 m onto the detectors of Athena. The point-spread function (PSF) of the optic shall achieve a half-energy width (HEW) of 5” at an energy of 1 keV, with an effective area of about 1.4 m2, corresponding to several hundred m2 of super-polished mirrors with a roughness of about 0.3 nm and a thickness of down to 110 µm. This paper will present the status of the technology and of the mass production capabilities, show latest performance results and discuss the next steps in the development.

The Silicon Pore Optics (SPO) technology has been established as a new type of X-ray optics and will enable future X-ray observatories such as Athena and Arcus. SPO is being developed at cosine Research B.V. together with the European Space Agency (ESA) and academic as well as industrial partners. For Athena, about 150,000 mirror plates are required. With the technology spin-in from the semiconductor industry, mass production processes can be employed to manufacture rectangular SPO mirror plates in high quality, large quantity and at low cost. Over the last years, several aspects of the SPO mirror plates have been reviewed and undergone further developments in terms of effective area, intrinsic behavior of the mirror plates and mass production capability. The paper will provide an overview of most recent SPO plate designs, mirror plate production status and plan forward including reflective coating process as well as mass production developments.

The mirror modules composing Athena’s X-ray optics are made with the Silicon Pore Optics (SPO) technology. SPO is produced as stacks of 38 mirror plates, which are paired to form X-ray Optics Units (XOUs) following a modified Wolter I geometry. In the current design, a mirror module is composed of two confocal XOUs glued in between a pair of brackets that freeze the configuration and provide interfaces to the mirror structure. Mirror modules are assembled at the XPBF2 beamline of PTB at the synchrotron radiation facility BESSY II, using dedicated jigs. In this paper we present the latest developments regarding the assembly of confocal mirror modules for Athena with an emphasis on alignment tolerances and gluing accuracy.

The European Space Agency (ESA) is developing the Athena (Advanced Telescope for High ENergy Astrophysics) X-ray telescope, an L-class mission in their current Cosmic Vision cycle for long-term planning of space science missions. Silicon Pore Optics (SPO) are a new type of X-ray optics enabling future X-ray observatories such as Athena and are being developed at cosine with ESA as well as academic and industrial partners. These high-performance, modular, lightweight yet stiff, high-resolution X-ray optics shall allow missions to reach unprecedented combination of large effective area, good angular resolution and low mass. As the development of the Athena mission progresses, it is necessary to validate the SPO technology under launch conditions. To this end, ruggedisation and environmental testing studies are being conducted to ensure mechanical stability and optical performance of the optics before, during and after launch. In this paper, we report on the results of our completed environmental testing campaigns on mirror modules of middle radius (about 700 mm) of curvature. In these campaigns, each mirror module is first integrated then submitted to sine and random vibration tests, as well as shock tests, all in accordance with the upcoming Ariane launch vehicle and the mission requirements. Additionally, the mirror modules are characterized with X-ray before and after each test to verify the optical performance remains unchanged.

The thin film coating technology for the European Space Agency mission, Advanced Telescope for High-Energy Astrophysics (Athena) has been established. The X-ray optics of the Athena telescope is based on Silicon Pore Optics (SPO) technology which is enhanced by the thin film coatings deposited on the reflective surface of the SPO plates. In this work, we present a literature study of the coating process parameter space and provide an overview of the thin film properties with a focus on micro roughness, chemical composition and wear resistance when deposited under various process conditions. We determined, that the thin film density depends strongly on the mobility of the adatoms on the substrate surface. Some coating process parameters, which have a significant impact on the adatom mobility are the discharge voltage, the working gas pressure and the substrate temperature.

The development of high-quality thin film coatings for the Athena X-ray optics is progressing, following the commissioning of an industrial scale coating facility. The assembly of silicon pore optics into mirror modules for the Athena telescope requires wet-chemical exposure of coated mirror plates to prepare bonding areas for stacking, as well as an annealing step to improve bond strength. It is therefore critical to evaluate how these post-coating processes could affect the mirror coating performance and stability. We present X-ray reflectometry characterization of iridium thin films deposited on photoresist patterned Silicon Pore Optics plates to investigate the compatibility with the stacking process steps for the manufacturing of the Athena optics.

As part of the manufacturing process of mirror modules for the Athena X-ray telescope, Silicon Pore Optics plates are assembled into mirror module stacks. The plates that form each stack are held together by direct bonding, relying on van der Waals forces and covalent bonds for adhesion. One way to increase the strength of the covalent bonds is through annealing of the mirror stacks. It is of critical importance to the mission to ensure compatibility between the reflective coating and any post-coating processing of the plates. We present our findings of the impact of annealing on the X-ray re ectance of coated mirrors relevant for the Athena mission. These are Ir single layers, as well as Ir/B₄C, Ir/SiC, and Ir/C bilayers. We investigate the effect on the performance of the coatings after annealing at atmospheric pressure and at a low vacuum using X-ray reflectometry. B₄C is found to suffer degradation from annealing under atmospheric conditions but not when annealed in vacuum. All other materials investigated are robust to atmospheric annealing.

Silicon Pore Optics (SPO) have been chosen as the X-ray optics technology for the European Space Agency's Athena mission. Although in principle SPO can be used to realize classical Wolter-I or Wolter-Schwarzschild systems, technological and manufacturing considerations introduce constraints that lead to a system where some of the parameters of the optics are altered with respect to the classical description. In this paper we describe some of the constraints and how they affect the way one goes about designing optics based on SPO. Further we present ray-tracing results that show how these constraints do not impact the performance goals of a large mission like Athena.

Silicon Pore Optics are a novel technology for focusing high-energy photons, where pairs of mirror plates stacked into mirror modules. This paper presents a study of the angular resolution of SPO mirror assemblies, using a selection of sagittal mirror curvatures. Results were achieved by ray-tracing the different configurations of the mirror with the ray tracing software SPORT, or Silicon Pore Optics Ray Tracer, using an observation of the Crab Nebula originally obtained by Chandra. It is found that a true Wolter geometry most closely reproduces the original image, while geometries with a conic approximation on either their primary or secondary mirrors create the most diffuse image. A geometry with conic approximations on both primary and secondary mirrors falls in between the two extremes.

The European Space Agency ATHENA mission is an x-ray observatory that will study the formation of galaxy clusters and the growth of black holes within the energy range of 0.5 to 10 keV. Due for launch in early 2030s, ATHENA will use silicon pore optic (SPO) mirror modules to create the x-ray mirror. The first confocal SPO mirror module (MM) was entered into a preliminary environmental test program for the ATHENA mission. The objective of this program was to determine whether particulate contamination causes loss of effective area for silicon pore optics. The confocal MM under test was manufactured by cosine measurement systems and first tested at MPE’s PANTER x-ray test facility in July 2019. After this campaign, it was contaminated with a total of 2000 ppm in two 1000-ppm-level contamination periods. After each 1000-ppm contamination step, x-ray measurements were made to determine the effective area. The pre- and post-contamination effective area measurements, and the contamination of the optic, were carried out at the PANTER facility. The paper provides an overview of the contamination testing carried out at PANTER, and the corresponding results for each contamination level. We find no measurable degradation in effective area on a 5% level. We also look into the possibilities and limitations for the determination of the effective area within our facility. In future campaigns we plan to reach a 2% accuracy for the determination of the effective area for similar type optics.

The ATHENA (Advanced Telescope for High Energy Astrophysics) X-ray observatory is the European Space Agency - selected L2 class mission, with launch scheduled in early 2030s. The observatory hosts a large X-ray telescope designed to have 5 arcseconds resolution with an effective area larger than 1.4 m² at 1 keV. To meet these performance requirements ESA developed the Silicon Pore Optics technology: ribbed Si plates are shaped on a proper mould to copy the defined optical design and then stacked into modules. This technological solution, taking advantage of both replica process and modular implementation, is effective to populate ATHENA’s large aperture (diameter of ~2.5 m). As a result the optical pupil of an SPO will be very different than the classical nested shell one since it would be composed by a high number of small channels (about 10⁶ channels of ~ 1 mm² in ATHENA current design) and hence requires specific tool to be studied. To this end ESA financed the SIMPOSIuM project aimed to develop an open source, user-friendly SPOs simulation tool. The project is now at a good level of maturity and it offers 2 Graphical User Interfaces implementing a variety of simulation features. The SPORT GUI manages a full ray-tracing code and an analytical effective area calculator. The SWORDS GUI runs a SPOs diffraction effects simulator. In this paper we present the SImPOSIuM package and its collocation in ATHENA optics development framework.

Several hundreds of Silicon Pore Optics (SPO) mirror modules will be integrated and co-aligned onto the ATHENA (Advanced Telescope for High-ENergy Astrophysics) Mirror Assembly Module (MAM). The selected integration process, developed by Media Lario, exploits a full size optical bench to capture the focal plane image of each mirror module when illuminated by an UV plane wavefront at 218 nm. Each mirror module, handled by a manipulator, focuses the collimated beam onto a CCD camera placed at the 12 m focal position of the ATHENA telescope. The image is processed in real time to calculate the centroid position and overlap it to the centroid of the already integrated Mirror modules. Media Lario has designed the ATHENA Assembly Integration and Testing facility to realize the integration process for the flight telescope and has started its construction. The facility consists of a vertical optical bench installed inside a tower with controlled cleanroom conditions. The MAM axis is aligned along gravity and supported on actuators to compensate for gravity deformations. A robot device above the MAM is used for aligning the SPO Mirror modules. The 2.6 m paraboloid mirror that collects the light emitted by a UV source is in final polishing. The alignment system, the cell support and the metrology system for the UV collimator have been qualified and accepted for installation. Details about the optical bench and the status of the facility construction will be presented.

The ATHENA X-ray telescope will be the largest X-ray optics ever built. The ground calibration of this mirror assembly raises significant difficulties due to its unprecedented size, mass and focal length. The VERT-X project aims at developing an innovative calibration system which will be able to accomplish to this extremely challenging task.The design is based on an X-ray parallel beam produced by an X-ray source positioned in the focus of a highly performing X-ray collimator; the beam will be accurately moved by a raster-scan mechanism covering all the ATHENA optics at different off-axis angles. The main driving factor in the VERT-X design is the ATHENA calibration requirement on the accuracy in the HEW measure which is 0.1”, all over the field of view. The VERT-X project, started in January 2019, is financed by ESA and conducted by a consortium that includes INAF together with EIE, Media Lario, BCV Progetti and GPAP.

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.

BEaTriX (Beam Expander Testing X-ray) is the X-ray facility under construction at the INAF-Osservatorio Astronomico Brera (Merate, Italy) to prove that it is possible to perform the X-ray acceptance tests (PSF and Aeff) of the ATHENA mirror modules at the required rate and with the required accuracy. The unique optical setup makes use of a micro-focus X-ray source with anode in Titanium, a paraboloidal mirror with small radius of curvature, and a set of crystals to monochromate and expand the beam to fully illuminate the entrance pupil of the ATHENA MMs. The quality of the optical components, and their precise alignment, guarantees the production of a parallel beam at 4.51 keV, to be extended in a second phase to 1.49 keV in order to complete the acceptance requirements for the ATHENA MMs. The completion of the facility is expected to occur in July this year, while the commissioning will start in September. In this paper, we present the current status.

The BEaTriX (Beam Expander Testing X-ray) facility under construction at INAF-Brera Astronomical Observatory aims at performing the acceptance tests of the Silicon Pore Optics mirror modules of the ATHENA (Advanced Telescope for High-ENergy Astrophysics) X-ray observatory. The facility implements a grazing-incidence collimating mirror that, together with a monochromator and a beam expander stages based on crystals, enables the full X-ray illumination of the mirror modules under test. We present the development and test of the collimating mirror, a paraboloid sector having an optical surface of 400 mm ´ 60 mm and sagittal radii of about 155 mm. The ground and lapped optics made of HOQ 310 fused quartz was corrected by bonnet polishing. In this paper, we report on the smoothing of mid-to-high spatial frequency error by pitch-tool polishing process, and on the correction of residual surface shape errors by ion-beam figuring process, both performed at INAF-Brera Astronomical Observatory. We present the X-ray test campaigns carried out on the mirror at PANTER facility, before and after coating it with a Pt layer via magnetron sputtering at DTU Space. The results provide an overview of the mirror performance in terms of angular resolution pre- and post-coating deposition.

We describe an implementation of a broad-band soft X-ray polarimeter, substantially based on previous designs. The Globe-Orbiting Soft X-ray Polarimeter (GOSoX) is a SmallSat. As in a related mission concept the PiSoX Polarimeter, the grating arrangement is designed optimally for the purpose of polarimetry matching the dispersion of a spectrometer to a laterally graded multilayer (LGML). For GOSoX, the optics are lightweight Si mirrors in a one-bounce parabolic configuration. The instrument covers the wavelength range from 31 A to 75 A (165 - 400 eV). Upon satellite rotation, the intensities of the dispersed spectra, after reflection and polarizing by the LGMLs, give the three Stokes parameters needed to determine a source's linear polarization fraction and orientation. The design can be extended to higher energies as LGMLs are developed further. We describe the potential scientific return and the proposed mission concept following the results of a JPL Team X concept study.

The Marshall 100-Meter X-ray Beamline is a world class facility utilized for testing X-ray and EUV optics and instrumentation. Also known as the Stray Light Test Facility, the beamline has been consequential in the calibration of flight missions such as ART-XC and IXPE. Additionally, the beamline is effectively used for APRA-funded projects and in MSFC own internal optic development campaigns. The Marshall 100-Meter X-ray Beamline a flexible and affordable facility that easily accommodates many of the astrophysical community’s needs. With its recent and upcoming improvements, the Marshall 100-Meter X-ray Beamline will continue to be a user-friendly calibration resource for decades to come.

AstroX is an add-on toolbox to the open source X-ray simulation software package McXtrace, which introduces Astronomical telescope optics and features to the package. Thus, enabling users to draw from the experience and developments of two communities. It may also shed further light into calibration results when measuring optics in ground based test-setups, at synchrotrons and specialized facilities. AstroX now includes a range of optical elements for Wolter class optics, extended source models, lobster eye optics, and gratings etc. Furthermore the open modular nature of McXtrace makes it fairly simple to connect to other software packages. We present a range of simulations of various aspects of telescopes: • A simulation work ow capable of quantifying stray light from Compton scattering at mirror substrates. • A study on the effect of dust contamination inside small-pore silicon pore optics. • A mechanism to include gratings for spectrometry in a telescope simulation..

The PANTER X-ray test facility of the Max Planck Institute for Extraterrestrial Physics (MPE) has been testing and calibrating optics from various space missions world-wide for more than 40 years. Recently, PANTER measured the performance of the latest x-ray optic technologies of SVOM, Einstein Probe and Athena. Towards accelerating calibrations, we aim to predict the behavior of optics when introduced into vacuum. The optics are modeled with computer aided design (CAD) and ray-traced with Zemax' non-sequential mode. This allows tracing the point spread function (PSF) on the detector plane from complex X-ray optics, including Wolter-type optics, Parabolic mirror, Hybrid KirkPatrick Baez and Lobster Eye optics. We compare PANTER experiments to equivalent simulation setups, including a focal scan. We find good agreement between simulations and experiments in terms of PSF, and location of the focal plane. Zemax ray tracing appears to be a powerful and flexible tool to understand and predict calibration experiments at PANTER.

It has been known for quite some time that thin, low atomic number (Z) overcoats on x-ray mirrors with high-Z coatings, for example, carbon on iridium, can provides acceptable reflectivity response at high x-ray energies while boosting reflectivity in the low energy range. Recent published work has complemented this idea by adding an intermediate-Z coating interposed between the low and high Z coatings—a so-called graded-Z coating—which also offers improved reflectivity response at mid-range x-ray energies. In this paper I discuss a simple methodology for designing and optimizing graded-Z coatings in the 0.1-10 keV energy band.

The fabrication of a large number of high-resolution, grazing-incidence, thin-shell mirror segments for space X-ray telescopes is still challenging. We have developed an X-ray mirror correction method, using a femtosecond laser to remove selective regions of a stressed film on the mirror back surface to modify the stress states. Our recent experiments have created both isotropic and anisotropic stress states on thin flat silicon mirrors with thermal oxide films using a green light femtosecond laser. An Abaqus finite element model has achieved good comparison between simulations and experiments in the bending of thin-shell mirrors under different stressed film patterns.

Publisher’s Note: This conference presentation, originally published on 5 August 2021 was withdrawn on 13 August 2021 per author request.

Currently, high-resolution X-ray telescope mirrors, such as for the Lynx X-Ray Observatory concept, are measured using a Fizeau interferometer with a cylindrical null corrector. Uncertainties in the null wavefront directly couple into the surface measurement uncertainty, including the axial figure and cone angle variation. We extend the absolute surface metrology method of lateral shift mapping for measuring X-ray telescope mirror segments. Lateral shift mapping involves laterally shifting the surface under test relative to the null to multiple positions. The null wavefront can be extracted from the difference between these shifted measurements, leaving only the surface under test. Accurately extracting quadratic terms of the surface under test requires measuring its tilt during shifting. We will show surface metrology results of optical flats measured by Fizeau-based lateral shift mapping with the required angle measured using an autocollimator and compare these results against a three-flat test. We will show how we plan to extend this method to conical X-ray telescope mirror metrology. The lateral shift mapping method reduces the uncertainty introduced by the cylindrical null, a critical step toward making high-resolution X-ray telescope mirrors.

Expected to launch in Fall 2021, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Astrophysics Small Explorer Mission with significant contributions from the Italian space agency (ASI). Three identical x-ray telescopes combine to form the IXPE observatory. Each is comprised of a 4-m-focal length mirror module assembly (MMA, provided by NASA MSFC) that focuses x-rays onto a polarization-sensitive, imaging detector (contributed by ASI-funded institutions). This paper describes the now-completed assembly process for the 3 flight mirror modules and spare, and compares as-tested calibrated performance with as-built metrology data. Unexpected challenges and lessons-learned are also discussed.

Exquisite angular resolution (< 0.5 arcsec) and high effective area (≥ 2 m^2 @ 1 keV) are requirements for a next-generation X-ray observatory capable of tackling outstanding problems in high energy astrophysics, including understanding how black holes grow over cosmic time and how hot baryonic material is distributed on the largest scales. However, realizing a telescope with this performance is challenging, as the thin optics required are susceptible to fabrication errors, thin film stress, and mounting deformations. One potential method of addressing these errors to fabricate adjustable X-ray optics – mirrors with actuators capable of correcting the optic’s figure following mounting. In this work, we present interferometric measurements of an adjustable X-ray optics prototype with lead titanate zirconate (PZT) actuators. We detail the realized actuator performance and correctability of the mirror prototype, and discuss the implications for the next-generation of adjustable mirrors.

The realization of active full-shell x-ray optics will provide groundbreaking capability for future missions. Future X-ray missions, such as Lynx, require high angular resolution, large effective area, and as wide a field of view (FOV) as possible. It is currently not possible to perform high-resolution imaging of both wide and narrow FOVs with a single X-ray telescope. In this paper, we discuss the use of actuators to switch the optical surface of full shell x-ray optics between prescriptions optimized for narrow-field and wide-field viewing, as well as correct for low-spatial-frequency errors in the optics. Previously, a pathfinder was developed using finite-element modeling (FEM). Using a combination of the model’s influence functions, the capacity of active full-shell optics was shown to switch between prescriptions with high accuracy. The analytical pathfinder also demonstrates the capability to correct low-spatial frequency errors, which comprise a large percentage of the MSFC full-shell x-ray optics root-mean-square (RMS) slope error. In order to verify the pathfinder, a surface-parallel actuator was bonded to a nickel-replicated coupon. After the actuator was bonded to the coupon, the slope of the surface was measured while the actuator was activated. The proof-of-concept demonstrator development, the influence function data, and the resulting implications on the analytical pathfinder are reported and discussed.

Adjustable X-ray mirror facets have been identified as a technology that could enable >2m² effective area X-ray optics with sub-arcsecond angular resolution. Electroactive polymers can produce high strains at low voltages, being able to correct the deformations that submillimeter-thick mirror shells experience during mounting and assembly of the optical system. In this paper, we describe the fabrication of μm-scale poly-vinylidene fluoride- co-trifluoroethylene (PVDF-TrFE) electroactive polymer films on at Si substrates with individually-addressable electrodes. The fabrication protocol is low-cost, scalable, and can easily be translated to production by industrial partners. With fabrication temperatures below 150° C, PVDF-TrFE actuator arrays can be deposited on mirror substrates inducing minimal thermal and coating stress.

The development of thin, segmented, grazing-incidence X-ray optics is the basis of future large-area X-ray missions such as Lynx. Adjustable mirror segments have been proposed to achieve sub-arcsecond angular resolution for mm-thickness segments that will deform during mounting and assembly of the optical system. In this paper, we present the development of a novel class of low-voltage thin-film actuators based on electroactive poly-vinylidene fluoride-co-trifluoroethylene (PVDF-TrFE) polymer. Fabrication of PVDF-TrFE thin films is a low-cost, scalable technology that can be easily be translated to production by industrial partners. With processing temperatures below 140 C, electroactive polymer films can be deposited on mirror substrates inducing minimal thermal and coating stress. A full characterization of electrical properties, fabrication yields, and influence functions of PVDF-TrFE actuator arrays deployed on flat Si substrates will be presented.

Thin adjustable X-ray mirrors can correct deformations generated from fabrication, gravity release, mounting stresses, drifting stresses in the reflecting layer(s) and thermal variations while maintaining high angular resolution (< 0.5 arcsecond) and large effective area (< 2 m2) required for future X-ray missions. This work presents fabrication process developments for adjustable mirror segments with actuators for the Lynx X-ray observatory mission concept. Piezoelectric actuator arrays were fabricated on the convex side of precision slumped glass or curved silicon mirror segments using a 1.5 μm thick lead zirconate titanate (PZT) film. A two-layer metal routing scheme with a polymeric insulator was used to independently address 288 actuators on the mirror. The two-layer metal allows narrow kerfs between actuators and increased actuator density. Anisotropic conductive film was used to bond thin flexible copper cables to flat edges of the mirror to interface with external control electronics. This prototype mirror has eight cables with a total of 290 connections to access the array. To reduce the cabling complexity for future mirrors, thin film transistors have been fabricated on the curved mirror to function as access switches. To facilitate this, a mask aligner that allows precision alignment on curved mirror segments was developed and arrays of thin film transistors (TFT) on curved substrates have been tested. TFT and actuator integration on future mirrors will reduce external connections to just two cables with a total of 30 connections. Keywords: Lynx, adjustable optics, X-ray optics, thin film piezoelectric, curved substrate aligner

Adjustable X-ray optics represent a potential mirror technology for the NASA Lynx X-ray observatory mission concept. Adjustable optics employ an integrated micron-thick piezoelectric film deposited on the convex side of silicon Wolter-type mirror segments. Discrete, independently addressable electrodes on the convex surface form individual actuators; the applied voltages are used to correct the shape of the mirror segments for figure errors resulting from a change in thermal environment, epoxy creep, or failure of an epoxy bond. On-orbit correction requires a metrology system to provide real-time feedback of mirror figure. We are examining the use of deposited semiconductor strain gauges to monitor mirror mechanical strains and surface temperatures. To establish requirements for monitoring we modeled a variety of thermal and mechanical disturbances to a mirror segment such as might occur on-orbit or from launch. Models are described and resulting requirements and performance discussed.

The soft x-ray band covers the characteristic lines of the highly ionized low-atomic-number elements, providing diagnostics of the warm and hot plasmas in star atmospheres, interstellar dust, galaxy halos and clusters, and the cosmic web. High-resolution spectroscopy in this band is best performed with grating spectrometers. Soft x-ray grating spectroscopy with R = λ / Δ λ = > 10⁴ has been demonstrated with critical-angle transmission (CAT) gratings. CAT gratings combine the relaxed alignment and temperature tolerances and the low mass of transmission gratings with high diffraction efficiency blazed in high orders. They are an enabling technology for the proposed Arcus grating explorer and were selected for the Lynx Design Reference Mission grating spectrometer instrument. Both Arcus and Lynx require the manufacture of hundreds to perhaps ~2000 large-area CAT gratings. We are moving toward CAT grating volume manufacturing using 200 mm silicon-on-insulator wafers, 4X optical projection lithography tools, deep reactive-ion etching, and KOH polishing. We have, for the first time, produced high-throughput 200 nm-period CAT gratings ~50% deeper than previously fabricated. X-ray diffraction efficiency is significantly improved in the ~1:25 - 1.75 nm wavelength range, peaking above 40% (sum of blazed orders). A new grating-to-grating alignment technique utilizing cross-support diffraction of visible light is presented, as well as the results of CAT grating emissivity measurements.λ

The proposed Lynx X-Ray Observatory aims to achieve an on-axis point spread function (PSF) of about 0.5 arc-second half-power diameter (HPD) and a 2 m^2 effective area. Thousands of extremely thin silicon mirrors with reflective x-ray coatings are needed to reach these goals and reduce mass per area. The coatings create film stress that can deform the mirrors. Stress relaxation in the film can cause the mirrors to disfigure over time and broaden the PSF. Typically, coating stability is measured by coating a mirror and measuring over a period of years in an x-ray beam line, or by measuring bending of flat mirror coupons. We discuss a novel device to measure the stress stability of reflective coatings that does not require flight mirrors or x-rays, and has a higher sensitivity compared to substrate bending. The device measures the resonant frequency of coated silicon membranes which can be related to film stress.

Sol-gel bonding, an alternate bonding technique, is proposed and demonstrated through experimentation for potentially reducing x-ray mirror distortion and cure times. The current state-of-the-art adhesives for bonding posts and mirrors are known to cause shrinkage when cured. This shrinkage causes stress at the epoxy contact point and distorts the entire mirror. This problem needs to be addressed to meet future telescope requirements. Specifically, advancements in thin segmented-optical mirrors to achieve high angular-resolution and large collecting-area in X-ray telescopes (such as the Lynx mission concept) will benefit from low stress bonding.

Wolter-I Optics for SmallSat Astronomy Mission (WOSAM) are a highly adaptable option for SmallSat missions for a number of astronomical uses. These compact Wolter-I optics with focal lengths on the order of 0.5 - 1 m are able to fit within strict mass and volume constraints and can be designed to fit the scientific requirements of exoplanet, solar, and lunar missions. In order to maximize Effective Area the telescope’s collecting area, graze angle, and vignetting need to be balanced. These factors are primarily affected by the optics’ focal length, outer diameter, shell length, and shell spacing. We show the modeling results of three SmallSat missions, the SmallSat Exosphere Explorer of hot Jupiters (SEEJ), the SmallSat Solar Axion and Activity X-ray Imager (SSAXI), and the Lunar X-ray Imaging Spectrometer (LuXIS). These missions have a range of Effective Area, Energy band, and Field of View requirements that can all be met with WOSAM telescopes.

The Lobster Eye X-ray Telescope (LEXT) is one of the payloads on-board the Gamow Explorer, which will be proposed to the 2021 NASA Explorer MIDEX opportunity. If approved, it will be launched in 2028, and is optimised to identify high-z Gamma Ray Bursts (GRBs) and enable rapid follow-up. The LEXT is a two module, CCD focal plane, large field of view telescope utilising Micro Pore Optics (MPOs) over a bandpass of 0.2 - 5 keV. The geometry of the MPOs comprises a square packed array of microscopic pores with a square cross-section, arranged over a spherical surface with a radius of curvature of 600 mm, twice the focal length of the optic, 300 mm. Working in the photon energy range 0.2 - 5 keV, the optimum L/d ratio (length of pore L and pore width d) is 60, and is constant across the whole optic aperture. This paper details the baseline design for the LEXT optic in order to full the science goals of the Gamow mission. Extensive ray-trace analysis has been undertaken and we present the development of the optic design along with the optimisation of the field of view, effective area and focal length using this analysis. Investigations as to the ideal MPO characteristics, e.g. coatings, pore size, etc., and details of avenues for further study are also given.

Multilayer (ML) coatings are a crucial technology for the development of EUV and SXR solar instrumentation, as they represent the only viable option for the development of high-efficiency normal incidence mirrors in such spectral range. However, the current standard MLs are characterized by a very narrow spectral band which is incompatible with the science requirements expected in the next generation of solar instruments. Nevertheless, recent advancement in ML technology has made the development of non-periodic stacks repeatable and reliable, enabling the manufacturing of mirrors with either multi-band or broad-band high efficiency. In this work, after briefly reviewing the state-of-the-art ML coatings for the EUV/SXR range, we investigate the possibility of using non-periodic stacks for the development of multiband and broad-band normal-incidence mirrors to be used in the next-generation missions.

Low energy (< 200 keV) protons entering the field of view of the XMM-Newton telescope and scattering with the mirror surface are observed in the form of a sudden increase in the background level. Such flaring events, a effecting about 30-40% of XMM-Newton observing time, can hardly be disentangled from true X-ray events and cannot be rejected on board. A response matrix for protons would allow a better understanding of the proton radiation environment, with the aim of modeling the in-flight non X-ray background of current (e.g. XMM-Newton, eROSITA) and future (e.g. ATHENA) X-ray focusing telescopes. Thanks to the latest validation studies on the physics models describing the reflection process of protons at grazing angles, we propose to build a prototype XMM-Newton EPIC proton response matrix describing the effective area and energy redistribution of protons entering the mirror aperture. The simulation pipeline comprises two independent simulation frameworks for the X-ray optics reflectivity, based on ray-tracing and Geant4, and a Geant4 simulation for the proton transmission efficiency caused by the combination of optical filters, on-chip electrodes and the detection depletion regions, requiring a detailed mass model of the MOS focal plane assembly. We present here the pipeline design, the characterization and verification of the proton transmission efficiency, and the algorithms for the effective area and energy redistribution computation. After the verification and validation activity, an opportune data formatting of the tool and its interface with widely-used analysis software (e.g. XSPEC) will allow the distribution of the proton response matrix to the scientific community.

Text mining is the process of transforming unstructured text into structured data for easy analysis. It uses natural language processing tools to interpret the human language and process text documents automatically. The extracted insights provide a valuable evaluation tool, which can provide systematic feedbacks and can drive machine-learning algorithms. We have applied these techniques to the SPIE proceeding papers, dedicated to the x-ray optics with special regards to the Optics for EUV, X-Ray, and Gamma-Ray Astronomy conference text data corpus, accessible through the ADS website. In particular, we worked on the collection of text formed by titles, abstracts, authors and affiliations to extract patterns, correlations and knowledge.

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

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.