Context.The Extreme Ultraviolet Imager (EUI) is part of the remote sensing instrument package of the ESA/NASA Solar Orbiter mission that will explore the inner heliosphere and observe the Sun from vantage points close to the Sun and out of the ecliptic. Solar Orbiter will advance the “connection science” between solar activity and the heliosphere.Aims.With EUI we aim to improve our understanding of the structure and dynamics of the solar atmosphere, globally as well as at high resolution, and from high solar latitude perspectives.Methods.The EUI consists of three telescopes, the Full Sun Imager and two High Resolution Imagers, which are optimised to image in Lyman-αand EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere up to corona. The EUI is designed to cope with the strong constraints imposed by the Solar Orbiter mission characteristics. Limited telemetry availability is compensated by state-of-the-art image compression, onboard image processing, and event selection. The imposed power limitations and potentially harsh radiation environment necessitate the use of novel CMOS sensors. As the unobstructed field of view of the telescopes needs to protrude through the spacecraft’s heat shield, the apertures have been kept as small as possible, without compromising optical performance. This led to a systematic effort to optimise the throughput of every optical element and the reduction of noise levels in the sensor.Results.In this paper we review the design of the two elements of the EUI instrument: the Optical Bench System and the Common Electronic Box. Particular attention is also given to the onboard software, the intended operations, the ground software, and the foreseen data products.Conclusions.The EUI will bring unique science opportunities thanks to its specific design, its viewpoint, and to the planned synergies with the other Solar Orbiter instruments. In particular, we highlight science opportunities brought by the out-of-ecliptic vantage point of the solar poles, the high-resolution imaging of the high chromosphere and corona, and the connection to the outer corona as observed by coronagraphs.

We report on the fabrication of an all-glass vapor cell with a thickness varying linearly between (exactly) 0 and ∼1  μm. The cell is made in Borofloat glass that allows state-of-the-art super polish roughness, a full optical bonding assembling and easy filling with alkali vapors. We detail the challenging manufacture steps and present experimental spectra resulting from fluorescence and transmission spectroscopy of the cesium D1 line. The very small surface roughness of 1 Å rms is promising to investigate the atom-surface interaction or to minimize parasite stray light.

In this paper, we report on the design, synthesis and characterization of extreme ultraviolet interferential mirrors for solar imaging applications in the spectral range 17nm–34nm. This research is carried out in the context of the preparation of the European Space Agency Solar Orbiter mission. The purpose of this study consists in optimizing the deposition of Al-based multilayers by ion beam sputtering according to several parameters such as the ion beam current and the sputtering angle. After optimization of Al thin films, several kinds of Al-based multilayer mirrors have been compared. We have deposited and characterized bi-material and also tri-material periodic multilayers: aluminum/molybdenum [Al/Mo], aluminum/molybdenum/boron carbide [Al/Mo/B4C] and aluminum/molybdenum/silicon carbide [Al/Mo/SiC]. Best experimental results have been obtained on Al/Mo/SiC samples: we have measured reflectivity up to 48% at 17.3nm and 27.5% at 28.2nm on a synchrotron radiation source.

Since more than 20 years, Laboratoire Charles Fabry and Institut d’Astrophysique Spatiale are involved in development of the EUV multilayer coating for solar imaging. Previous instruments, such as the SOHO EIT and STEREO EUVI telescopes, employed the Mo/Si multilayer coatings, which offered at that time the best efficiency and stability. We present here recent results of the development of highly efficient EUV multilayers coatings at 17.4 nm and 30.4 nm for the Solar Orbiter mission. New multilayer structures, based on a combination of three materials including aluminum, have been optimized both theoretically and experimentally. We have succeeded to reduce interfacial roughness of Albased multilayers down to 0.5 nm via optimization of the multilayer design and the deposition process. The EUV peak reflectance of Al/Mo/SiC and Al/Mo/B4C multilayer coatings reaches 56% at 17.4 nm, the highest value reported up to now for this wavelength. We have also optimized specific bi-periodic structures that possess two reflection bands in the EUV range with high spectral selectivity. The EUV reflectivity of these Al-based dual-band coatings are compared with the Si/Mo/B4C baseline coating for Solar Orbiter. Since the stability of reflecting multilayer coating is an important issue for space missions, we have also studied the temporal stability as well as the resistivity of the coatings to thermal cycling and to proton irradiation. Experimental results confirm that Al/Mo/SiC and Al/Mo/B4C multilayer coatings are good candidates for the Solar Orbiter EUV imaging telescopes.

Nous avons démontré la faisabilité de mesures de corrélations vectorielles dans la photoionisation dissociative de H2 auprès d'une source XUV femtoseconde d'harmonique d'ordre élevé cadencée à 1 kHz [1]. Dans ce contexte, nous présentons les miroirs multicouches conçus, réalisés et caractérisés par la Centrale d'Elaboration et de Métrologie d'Optiques X pour sélectionner cette harmonique 21 à ∼32 eV (∼40 nm). Nous avons mesuré une série d'observables, de la distribution en coïncidence des énergies cinétiques de l'ion fragment et de l'électron aux distributions angulaires du photoélectron émis dans le référentiel moléculaire (MFPADs), ainsi que leur évolution avec l'énergie cinétique de l'ion fragment. Ces résultats ouvrent la voie à des études résolues en temps, basées sur la mesure des MFPADs, de la dynamique femtoseconde des états doublements excités Q1 et Q2 de H2.

We report on further development of reflective multilayer coatings containing aluminum as low absorbing material for the extreme ultra-violet (EUV) applications, in particular for solar physics. Optimizations of the multilayer design and deposition process have allowed us to produce Al-based multilayers having relatively low interface roughness and record EUV reflectances in the range from 17 to 40 nm. The peak reflectance values of 56 % at 17.5 nm, 50 % at around 21 nm, and 42 % at 32 nm were achieved with new three-material multilayers Al/Mo/SiC and Al/Mo/B4C at near-normal incidence. We observe a good temporal stability of optical parameters of the multilayers over the period of 4 years. Moreover, the multilayer structure remains stable upon annealing at 100 C in air during several weeks.We will discuss the optical properties of more complex Al-based systems with regard to the design of multilayer coatings that reflect more than one wavelength and reject some others within the spectral range from 17 to 40 nm. Such multi-channel systems with enhanced reflectance and selectivity would provide a further advance in optical performance and compactness of EUV solar imaging instruments. We will discuss general aspects of design, optimization and fabrication of single- and multi-channel multilayer mirrors made with the use of aluminum. We will present recent results on the EUV reflectivity of multilayer coatings based on the Al/Mo/SiC and Al/Mo/B4C material combinations. Al-based multilayer systems are proposed as optical coatings in EUV telescopes of future space missions and in other EUV applications.

We report the first results of molecular frame photoelectron emission for dissociative photoionization (DPI) of H2 and D2 molecules induced by a spectrally filtered single high harmonic of a few femtosecond duration, using coincident electron–ion velocity vector correlation techniques. For the studied photon energies around 32 eV, where the resonant excitation of the Q1 and Q2 doubly excited states occurs, autoionization and nuclear dynamics are coupled on a few femtosecond timescale, giving rise to quantum interferences. Molecular frame photoelectron angular distributions (MFPADs), traced as a function of the kinetic energy release of the atomic fragments, provide the most sensitive observables for such complex dynamics. These results compare well with recent spectrally resolved experiments using synchrotron radiation which are also reported. As a novel XUV light source running at multi-kHz repetition rate and synchronized with laser pulses, high-order harmonic generation (HHG) opens new possibilities for extending these investigations to time-resolved studies at the femtosecond scale.

Single-photon dissociative photoionization of H2/D2 in the Q1, Q2 doubly excited states resonance regions, where ultrafast electronic and nuclear dynamics are coupled, is studied using the vector-correlation method with single selected femtosecond high-order harmonic and synchrotron radiation in the VUV. Results are compared at the level of electron-ion kinetic energy correlation diagrams, asymmetry parameters, and the molecular frame photoelectron angular distributions.

We report on further development of three-material multilayer coatings made with a use of aluminum for the extreme ultra-violet (EUV) applications such as solar physics, high-order harmonic generation or synchrotron radiation. It was found that an introduction of refractory metal in Al-based periodic stack helps to reduce significantly an interfacial roughness and provides for a higher theoretical reflectance in the spectral range from 17 to 40 nm. The normal incidence reflectivity as high as 55 % at 17 nm, 50 % at 21 nm and 42 % at 30 nm was achieved with the new Al/Mo/SiC and Al/Mo/B4C multilayer mirrors, which have been optimized, fabricated and characterized with x-rays and synchrotron radiation. A good temporal and thermal stability of the tri-component Al-based multilayers has been observed over 3 years.

In this paper, we present the development of Al-based multilayer mirrors for the spectral range [17 nm - 34 nm]. The purpose of presented study is to optimize the deposition of Al-based multilayers by the ion beam sputtering (IBS) technique according to several parameters such as the ion beam current and the angle of inclination of targets, which allowed us to vary the energy of ad-atoms deposited onto a substrate. We expected to achieve good reflectivity values for both two- and three-material stacks: aluminum/molybdenum Al/Mo, aluminum/molybdenum/boron carbide Al/Mo/B4C and aluminum/molybdenum/silicon carbide Al/Mo/SiC. We have undertaken a series of structural and chemical analyses of these systems. We present their optical characteristics in the EUV range.

Ce travail porte sur la conception, la realisation et la caracterisation de nouveaux miroirs interferentiels extreme ultra-violet (EUV) pour des applications en imagerie spatiale. Ce sujet se situe dans la continuite des etudes menees au laboratoire Charles Fabry de L’institut d’Optique depuis de nombreuses annees. Les resultats vises seront particulierement importants pour la preparation de la mission Solar Orbiter.

We report on the development of multilayer optics for the extreme ultra-violet (EUV) range. The optical performance of Al-based multilayer mirrors is discussed with regard to promising reflectivity and selectivity characteristics and the problems of the interfacial roughness for this type of multilayers. We demonstrate a possibility to reduce the average roughness by introducing additional metal layer (W or Mo) rather than depositing a buffer layer at each interface. We have prepared and tested Al/SiC, Al/W/SiC and Al/Mo/SiC multilayers of various periods for the spectral range from 15 to 40 nm, which is the range of increasing interest for high-order harmonic generation, synchrotron radiation and astrophysics. The structure of the three-component systems has been optimized in order to obtain the best reflectivity for each wavelength within the spectral range. We have shown that introduction of refractory metal in Al-based periodic stack can improve the optical performance of multilayer reflecting coatings designed for the EUV applications.

Scandium/silicon multilayers have been deposited by magnetron sputtering and characterized by several techniques. Experimental peak reflectances of 0.22 and 0.37 have been measured respectively at wavelengths of 40 nm and 46 nm, for 10° incidence angle. The corresponding theoretical values for a perfect Sc/Si structure are respectively 0.38 and 0.57. In order to explain these differences between calculated and measured reflectivity, thin film and multilayer characterizations have been done. Effects of multilayer imperfections on the reflectivity have been estimated independently by means of simulation. Based on these results, a new design of Sc/Si multilayer is proposed with top layer thickness optimization. With this design, the experimental peak reflectance reaches 0.46 at a wavelength of 46 nm.

An alternate multilayer (AML) grating is a 2 dimensional diffraction structure formed on an optical surface, having a 0.5 duty cycle in the in‐plane and in the in‐depth direction. It can be made by covering a shallow depth laminar grating with a multilayer stack. We show here that their 2D structure confer AML gratings a high angular and energetic selectivity and therefore enhanced diffraction properties, when used in grazing incidence. In the tender X‐ray range (500eV – 5000 eV) they behave much like blazed gratings. Over 15% efficiency has been measured on a 1200 lines/mm Mo/Si AML grating in the 1.2 – 1.5 keV energy range. Computer simulations show that selected multilayer materials such as Cr/C should allow diffraction efficiency over 50% at photon energies over 3 keV.

The development of new high power EUV sources and EUV space imaging requires optics having specific properties which depend on applications and operating conditions. These both applications are very different in the working multilayers environment. For the high power sources, multilayers are submitted to short pulses with high energy peak whereas, for the space imaging, multilayers are submitted to continuous flux with low level. Moreover photon energy and environment for both applications may be different. The environment may affect structure and top layer contamination when optics are stored, handled, mounted on the final device and finally operating. Main environmental parameters investigated are temperature and humidity variation.One objective is the optimisation of multilayer coatings to offer the highest resistance under photonic, ionic fluxes and temperature cycle. This means that interfacial diffusion between thin layers and degradation of the capping layers have to be avoided or reduced. The present study relies with designing, depositing and testing different structures of multilayer coatings in order to minimise the influence of the environment. Multilayer coatings based on molybdenum, silicon and silicon carbide materials have been deposited by magnetron sputtering on silicon and zerodur substrates. Samples were submitted to radiations emitted by an EUV source at wavelength closed to 13.5 nm. Furthermore they were also submitted to thermal cycles and annealing under warm humidity in the aim to simulate extremes storage or handling conditions as space mission's conditions.The damages and the performance of the multilayers were evaluated by using grazing incidence reflectometry at 0.154 nm and EUV reflectometry at the operating wavelength. After a presentation of the multilayer design, deposition and metrology tools, we will describe the different environmental effects on the coatings to take in care during EUV source exposure, handling and storage conditions. First results on multilayers performances to EUV source exposure and space specification tests are presented. Main damages studies were on annealing, thermal cycling and warm humidity.

We present the analysis of a B4C/Mo/Si multilayer interferential mirror (MIM) by secondary ion mass spectrometry (SIMS). The sample is prepared by magnetron cathodic sputtering and consists of a succession of 20 B4C (4.0 nm)/Mo (2.2 nm)/Si (12.0 nm) tri‐layers deposited on a silicon substrate. Two types of ions have been used for bombardment: Cs+ at an impact energy of 2 keV and O2+ at 0.5 keV. An artefact is clearly observed on the BCs+ profile which presents two maxima and a pronounced minimum at the maximum of the C profile, while the B profile obtained upon oxygen sputtering has its maximum in coincidence with that of the C profile. It is clearly seen under Cs and O sputtering that the B4‐on‐Mo and Si‐on‐B4C interfaces are more abrupt than the Mo‐on‐Si interfaces, evidencing the role of the boron carbide layer as a diffusion barrier. It is also observed that the B4C layers are inhomogeneous, some boron being present in excess with respect to C at the B4C‐on‐Mo and Si‐on‐B4C interfaces. These results evidence the importance of the interaction between the primary ions and some elements (boron in our case) present in the samples. Copyright © 2006 John Wiley & Sons, Ltd.

Le Laboratoire Charles Fabry conçoit de nombreuses optiques dont certaines pour les applications dans le spectre EUV.Pour les besoins de caractérisation, il est nécessaire de posséder une métrologie à la longueur d'onde d'utilisation proche des moyens de fabrication.Ceci permet d'étudier les composants dès leur conception et de caractériser les optiques.Nous présentons ici les performances d'un réflectomètre automatisé EUV large spectre.Il a été développé dans le cadre de la centrale CEMOX 1 , initiée par le pôle PRaXO 2 .

We have tested and validated a non-destructive analysis method of multilayer structure, which combine X-ray emission spectroscopy and X-ray reflectometry at 0.154 and 1.33 nm. In this purpose, a series of Mo/Si and Mo/B4C/Si/B4C multilayers, deposited by magnetron sputtering, have been designed. The thickness of the Mo layer is 2 nm and that of the Si layers varies between I and 4 nm. The B4C layer thickness introduced at the Mo/Si and Si/Mo interfaces is 0.3 or 1 nm. It is shown that the reflectivity of the multilayers lowers with the decreasing silicon thickness. This is correlated to the diffuse character on the nanometer scale of the Mo/Si and Si/Mo interfaces as shown by secondary ion mass spectrometry, and the formation of silicides (MoSi2 and Mo5Si3) at these interfaces as evidenced by X-ray emission spectroscopy. As expected, the introduction of B4C diffusion barriers considerably improves the reflectivity coefficient in the soft X-ray range, due to thinner and more abrupt interfaces. (c) 2006 Elsevier B.V. All rights reserved.

In the race towards attosecond (as) pulses for which high order harmonics generated in rare gases are the best candidates, both the Harmonic spectral range and spectral phase have to be controlled. We present in this proceeding four mirrors numerically optimized and designed to compensate for the intrinsic Harmonic chirp recently discovered and which is responsible for a temporal broadening of the pulses. They are capable of compressing the duration down to 100 as. We present the fabrication of those aperiodic multilayers and show the measurement of reflectivity, which prooves that those multilayers are in agreement with the specifications and so let us think that they will be able to compress attosecond high harmonics trains.