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We have developed a new method for the determination of photoabsorption at extreme ultraviolet wavelengths longer than 20 nm, where reliable refractive index values are sparse or non-existent. Our method overcomes the obstacle of multiple reflections that occur inside thin films in this spectral range, which up until now has prevented the accurate determination of photoabsorption from transmittance measurements. We have derived a mathematical expression that is independent of internal reflection amplitudes, while taking advantage of the transmittance oscillations stemming from such reflections. The method is validated on measurements of aluminum thin films. This advance will enable accurate refractive index values for many important materials for optical instrumentation, thus facilitating high-priority research on topics including coherent light sources, planetary and solar physics, and semiconductor manufacturing.

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.

International audience; This paper demonstrates that highly reflective Cr/B 4 C multilayer interference coatings with nano-metric layer thicknesses, designed to operate in the soft X-ray photon energy range, have stable reflective performance for a period of 3 years after deposition. The microstructure and chemical composition of layers and interfaces within Cr/B 4 C multilayers is also examined, with emphasis on the B 4 Con -Cr interface where a significant diffusion layer is formed and on the oxide in the top B 4 C layer. Multiple characterization techniques (X-ray reflectivity at different photon energies, X-ray pho-toelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction) are employed and the results reveal a consistent picture of the Cr/B 4 C layer structure.

This manuscript presents the structural characterization of Al/Sc-based periodic multilayer coatings for the extreme ultraviolet (EUV) spectral range. Based on transmission electron microscopy and electron diffraction as well as grazing-incidence and large-angle x-ray diffraction, a model for the layer structure and the interfacial effects of Al/Sc coatings is built. The onset of crystallization in nanoscale Al and Sc layers as a function of thickness is also revealed in these characterizations. The Al/Sc layer model is validated and further refined by fitting in-band and out-of-band EUV reflectance measurements across 5 orders of magnitude in an extended wavelength range from 17 to 80 nm. The same type of EUV reflectance measurements is used to test the Al/Sc aging properties and to demonstrate the spectral response of optimized two- and tri-material multilayers including Al/Sc, Al/Sc/SiC and Mo/Al/Sc.

We present an experimental, self-consistent determination of the optical constants (refractive index) of Pt using a combination of photoabsorption and reflectance data in the photon energy range 25–778 eV, which includes the N- and O-shell electronic absorption edges of Pt. We compare our new experimental values with Pt optical constant data sets from the literature. Our Pt optical constant values reveal highly resolved absorption-edge fine structure around the O2,3 and N6,7 edges in both the absorptive and dispersive portions of the refractive index, which were missing in the earlier literature.We present an experimental, self-consistent determination of the optical constants (refractive index) of Pt using a combination of photoabsorption and reflectance data in the photon energy range 25–778 eV, which includes the N- and O-shell electronic absorption edges of Pt. We compare our new experimental values with Pt optical constant data sets from the literature. Our Pt optical constant values reveal highly resolved absorption-edge fine structure around the O2,3 and N6,7 edges in both the absorptive and dispersive portions of the refractive index, which were missing in the earlier literature.

Efficient multilayer optics for radiation in the water window range are difficult to manufacture due to extremely small layer thicknesses and severe intermixing of elements between the layers. Therefore, adequate analytics and short feedback loops are of utmost importance for manufacturers to improve performance and efficiency. We show the possibility for non-destructive elemental depth profiling with commercial laboratory equipment using four real-life CrSc multilayer samples. Comparative measurements at the laboratory of PTB at the synchrotron radiation facility BESSY II confirm the results and prove the potential of laboratory equipment for the reliable analysis of stratified materials with sub-nanometer layer thicknesses.

International audience; The Kossel effect is the diffraction by a periodically structured medium, of the characteristic X-ray radiation emitted by the atoms of the medium. We show that multilayers designed for X-ray optics applications are convenient periodic systems to use in order to produce the Kossel effect, modulating the intensity emitted by the sample in a narrow angular range defined by the Bragg angle. We also show that excitation can be done by using photons (X-rays), electrons or protons (or charged particles), under near normal or grazing incident geometries, which makes the method relatively easy to implement. The main constraint comes from the angular resolution necessary for the detection of the emitted radiation. This leads to small solid angles of detection and long acquisition times to collect data with sufficient statistical significance. Provided this difficulty is overcome, the comparison or fit of the experimental Kossel curves, i.e., the angular distributions of the intensity of an emitted radiation of one of the element of the periodic stack, with the simulated curves enables getting information on the depth distribution of the elements throughout the multilayer. Thus the same kind of information obtained from the more widespread method of X-ray standing wave induced fluorescence used to characterize stacks of nanometer period, can be obtained using the Kossel effect.

In this Letter, we have developed new and highly efficient periodic multilayer mirrors Al/Sc, Al/Sc/SiC, and Mo/Al/Sc with optimized reflectance at wavelengths between 40 and 65 nm. We have reached record values in measured peak reflectance: 57.5% at 44.7 nm and 46.5% at 51 nm, with Al/Sc/SiC at near-normal incidence. Furthermore, to the best of our knowledge, we have achieved the largest reported bandwidth with Mo/Al/Sc at 57 nm and the narrowest bandwidth with Al/Sc at a 60 nm wavelength. These new and promising results demonstrate that Al/Sc-based multilayer coatings are excellent candidates for future generations of extreme ultraviolet (EUV) instruments for solar physics, EUV lasers, and attosecond science, in a wavelength range that has not been fully explored.

This paper demonstrates that highly reflective Cr/B₄C multilayer interference coatings with nanometric layer thicknesses, designed to operate in the soft X-ray photon energy range, have stable reflective performance for a period of 3 years after deposition. The microstructure and chemical composition of layers and interfaces within Cr/B₄C multilayers is also examined, with emphasis on the B₄C-on-Cr interface where a significant diffusion layer is formed and on the oxide in the top B₄C layer. Multiple characterization techniques (X-ray reflectivity at different photon energies, X-ray photoelectron spectroscopy, transmission electron microscopy, electron diffraction and X-ray diffraction) are employed and the results reveal a consistent picture of the Cr/B₄C layer structure.

The Extreme Ultraviolet Imager (EUI) instrument for the Solar Orbiter mission will image the solar corona in the extreme ultraviolet (17.1 nm and 30.4 nm) and in the vacuum ultraviolet (121.6 nm) spectral ranges. The development of the EUI instrument has been successfully completed with the optical alignment of its three channels’ telescope, the thermal and mechanical environmental verification, the electrical and software validations, and an end-toend on-ground calibration of the two-units’ flight instrument at the operating wavelengths. The instrument has been delivered and installed on the Solar Orbiter spacecraft, which is now undergoing all preparatory activities before launch.

The thin film optical constants are key parameters to carry out optical simulation or optimization of multilayer mirrors with high efficiency. However, for most materials, different sets of optical constants can be found in the literature especially in the EUV range, as these parameters are not as well-known in the EUV as in the visible or wavelength range. In this work, we have used several reflectance and transmittance measurements in the wavelength range from 10 nm to 60 nm. Different optical constant files have been tested and compared with the IMD simulation software. We will present some experimental spectra and theoretical simulations to highlight the existing problem on the reliability of optical constants sets and to discuss potential solutions. We focus our research on a few materials of particular interest in the EUV range such as aluminum, aluminum oxide, molybdenum, zirconium, magnesium, silicon carbide, and boron carbide. These analyses lead us to select the most reliable and accurate optical constants set, or to create the best one from the concatenation of existing data for each material of interest.

International audience

International audience; Soft X-ray and Extreme Ultraviolet (EUV) radiation (defined as light with wavelength in the 1 to 100 nm range) has been playing a growing role in major scientific and industrial applications over the last 20 years: astrophysics and solar physics, materials sciences, biology, semiconductor industry, plasma diagnostics. Especially the emergence of novel EUV/X-ray sources with unprecedented brightness and coherence (4th generation synchrotrons, free-electron lasers, tabletop lasers, high-harmonic generation and attosecond sources) has ushered a new era in the fields of materials science, chemistry, plasma physics, biology and life sciences. Several scientific and technological breakthroughs have been achieved recently. X-ray radiation from the SPRING-8 synchrotron light source in Japan has been focused on a spot with diameter smaller than 10 nm; this constitutes the smallest spot of light ever produced and could enable studies with the most exquisite spatial resolution. The generation of ultrashort EUV pulses with a duration less than 0.1 femtosecond (= 100 attosec-onds) made it possible for the first time to observe electron orbitals in molecules. Photolithography scanners based on EUV light have entered the world of semiconductor manufacturing in order to produce the next generation of computer chips. In 2007, the EUV telescopes aboard NASA's Solar Terrestrial Relations Observatory (STEREO) mission provided the first 3D images of the solar corona with its protuberances. Furthermore, since 2010, the Solar Dynamics Observatory (SDO), NASA's most advanced solar mission , has been continuously transmitting full-disk images of the solar corona every 10 seconds, simultaneously at 7 EUV wavelengths with 1 arcsec resolution. Observing the Sun with such unprecedented temporal and spatial resolution has led to groundbreaking discoveries related to the Sun's extremely complex magnetic field and has led to better understanding of extreme events such as solar flares and coronal mass ejections, which can seriously affect earth and space environments. These breakthroughs have been enabled by the development of new optical components dedicated to the EUV/ X-ray spectral range. The main challenges in fabricating EUV/X-ray optics come from the properties of materials in this spectral range. With the refractive index of any material being very close to 1, the refractive phenomena at any interface are weak and the reflectivity of any single material at non-grazing incidence angles is near zero. Moreover, all materials strongly absorb X-rays, so the transmission of any component is almost zero. Multi-layer interference mirrors are enabling optical components in most EUV/X-ray optical systems. Demonstrated experimentally for the first time in the 1970s by E. Spiller, these mirrors consist of periodic or aperiodic structures of alternating thin film layers of 2 or more materials with nanometer-scale thickness, deposited on an optical sub-strate. The constructive interference between the layers results in efficient reflectance at EUV/X-ray wavelengths even at near-normal incidence angles thus enabling the operation of a wide range of optical components including imaging and illumination systems, reflective filters, grating spectrometers and polarizers. However, the fabrication of high-performance multi-layer coatings poses serious technical challenges. Multi-layer coatings need to obey several stringent (and often conflicting) requirements, including: (i) contain materials with good optical contrast in the wavelength region of operation (ii) contain tens or hundreds of layers with nanometer-scale thickness, where each layer is deposited with picometer-scale precision (iii) form stable layer interfaces with minimal interdiffusion and with smoothness on the order of the atomic dimension, (iv) have low thin film stress, (v) have stable reflective performance for periods up to 10 years, or even longer. This special section aims to provide a survey of current topics and major development lines in the very active research area of X-ray and EUV multilayer coating development. It gathers studies of the properties of these nanoscale structures (microstructure, mechanical stress, lifetime stability) with a focus on new promising material combinations and on short-period multilay-ers, with individual layer thicknesses around (or less than) 1 nm. Technological developments, new characterization 516

International audience; The Kossel interferences generated by characteristic x-ray lines produced inside a periodic multilayer have been observed upon proton irradiation, by submitting a Cr/B4C/Sc multilayer stack to 2 MeV protons and observing the intensity of the Sc and Cr Kα characteristic emissions as a function of the detection angle. When this angle is close to the Bragg angle corresponding to the emission wavelength and period of the multilayer, an oscillation of the measured intensity is detected. The results are in good agreement with a model based on the reciprocity theorem. The combination of the Kossel measurements and their simulation, will be a useful tool to obtain a good description of the multilayer stack and thus to study nanometer-thick layers and their interfaces.

International audience; Sirius is a beamline designed for studying soft interfaces and semiconductor or magnetic nanostructures. It has recently got a new multilayer grating monochromator covering the 1 – 4 keV band which complements its already existing two crystal monochromator covering the 3 - 11 keV energy range. Besides the grating, this kind of monochromator requires a mirror with a matched multilayer coating to reflect the beam back in it initial direction at any wavelength. The grating and the matched mirrors of Sirius monochromator have been fabricated at the CeMOX facility of Laboratoire Charles Fabry (LCFIO) and characterized both there and on SOLEIL Metrologie beamline. The monochromator is under commissioning and its first results look very promising. A first experimental EXAFS spectrum will be presented.Cr and B4C have been selected as a suitable couple of material for the targeted range. The characterization of the achieved ML grating with 35 periods of Cr (2.5 nm) /B4C (4.1 nm), showed a 1st order of diffraction efficiency of 55% at 4.4 keV. A very special care has been given to the optimal match between the grating and the deflecting mirror. A very high sensitivity to period mismatch has been simulated and measurements have been done in order to reduce the impact of period inhomogeneity along the 250 mm length of the mirror. Design simulations, reflectivity measurements of actual grating and mirrors will be shown and compared to fits with different multilayer and grating models.

International audience; A further progress in scientific and industrial applications of multilayer optics in the extreme ultra-violet range (EUV) requires a high efficiency, specific spectral shape and good stability of multilayer coating as well as some new optical functions such as a control of phase and polarization of reflected EUV radiation.Laboratoire Charles Fabry (LCF) has been involved in development of multilayer optics since more than 35 years (both theoretical and experimental studies). For instance, in the field of space applications, the EUV multilayer coatings for imaging telescopes of several solar missions were designed, fabricated and characterized. There were the telescopes of SOHO, STEREO and Solar Orbiter (to be launched in 2018 [1]). The latter is realized with Al/Mo/SiC multilayer coatings.In the last PXRMS conference in 2010 we presented the first results of studies of multilayers made with the use of aluminum as a low absorbing material beyond 17 nm. A significant increase of the measured reflectance of periodic multilayers was obtained by applying a three- material design for the multilayer structure [2]. Here we will report on the progress achieved since then in the development and fabrication of Al-based multilayer coatings for EUV applications in the spectral range between 17 and 40 nm. We will discuss the design of various multilayer structures which is performed by using the IMD simulation software [3] and/or a home-made Matlab code with optimization algorithms. We will describe how complex multilayer systems can be designed and optimized for specific applications in the EUV range.We will present and discuss the structural parameters and optical performance of periodic and aperiodic Al-based multilayer systems that have been designed and produced in our laboratory. Most of the multilayer mirrors were deposited by magnetron sputtering and characterized by grazing incidence x-ray (GIXR) and EUV reflectivity. The EUV reflectivity measurements were performed at the BEAR beamline of ELETTRA Sincrotrone Trieste and at the metrology beamline of Soleil synchrotron.

International audience

International audience; We present an experimental study of the effect of layer interfaces on the x-ray reflectance in Cr/B4C multilayer interference coatings with layer thicknesses ranging from 0.7 nm to 5.4 nm. The multilayers were deposited by magnetron sputtering and by ion beam sputtering. Grazing incidence x-ray reflectometry, soft x-ray reflectometry, and transmission electron microscopy reveal asymmetric multilayer structures with a larger B4C-on-Cr interface, which we modeled with a 1–1.5 nm thick interfacial layer. Reflectance measurements in the vicinity of the Cr L2,3 absorption edge demonstrate fine structure that is not predicted by simulations using the currently tabulated refractive index (optical constants) values for Cr.

Commissioned in May 2004 on the SLS machine, the LUCIA beamline was moved to the synchrotron SOLEIL during the summer of 2008. To take advantage of this new setting several changes to its design were introduced. Here, a review of the various improvements of the mechanics and, mostly, of the optics is given. Described in detail are the results of a new multilayer grating monochromator implemented on the Kohzu vessel already holding the two-crystal set-up. It consists of a grating grooved onto a multilayer (replacing the first crystal) associated to a multilayer (as a second crystal). It allows a shift of the low-energy limit of the beamline to around 500 eV with an energy resolution and a photon flux comparable with those of the previous couples of crystals (KTP and beryl).

In this study, we determine with improved accuracy the complex index of refraction n = 1 − δ + iβ of sputtered chromium thin films for photon energies ranging from 25 eV to 813 eV. These data include the first absolute measurements of the absorption fine structure near the Cr-L edge. First, we verified by combining Rutherford Backscattering Spectrometry and grazing-incidence x-ray reflectometry that the sputtered thin films were pure Cr with a density consistent with tabulated values. Then, we demonstrated that the Cr surface oxide layer remains stable when the samples are exposed to air for up to 4 years. The Cr absorption coefficient β was determined from the transmittance of freestanding Cr thin films with various thicknesses, measured at the ALS synchrotron radiation source. A model is proposed to correct the transmittance data from the spectral contamination of the source. Finally, we used the new β values, combined with theoretical and tabulated data from the literature, in order to calculate the δ values by the Kramers-Kronig relation. The improvement in the accuracy of β values is demonstrated by the f-sum rule. An additional validation of the new Cr optical constants (δ, β) is performed by comparing the simulated and experimental reflectance of a Cr/B4C multilayer mirror near the Cr-L2,3 edge.

Nanometer-thick Al/SiC periodic multilayers, designed for the Extreme Ultra Violet (EUV) range, have been characterized by different techniques dedicated to such thin multilayers (each between 4 and 10 nm thick). In order to decrease the roughness and to improve the optical performances of the stacks, an ultrathin (2 nm) refractory metal layer has also been introduced, thus making Al/W/SiC and Al/Mo/SiC multilayer systems with three layers in period. The samples are deposited by magnetron sputtering. The stacks have a period ranging between 16 and 18 nm. Time-of-Flight SIMS (ToF-SIMS) is used here to determine the depth profiles of the different elements present within the multilayers. It is observed that the interfaces of the Al/W/SiC and Al/Mo/SiC multilayers are sharper than those of the Al/SiC system. X-ray emission spectroscopy (XES) is used to identify the chemical state of the Al and Si atoms within the multilayers and to check if there is any interfacial compound. The results show that there is no interaction between the Al and SiC layers leading to the formation of an interfacial compound. The results are confirmed by X-ray reflectivity (XRR) measurements. They show that the Al/SiC multilayers present large interfacial roughnesses, but the Al/W/SiC and Al/Mo/SiC multilayers have the lower roughness values. Copyright © 2010 John Wiley & Sons, Ltd.

International audience; 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.

16 pages; International audience; The interplay between optical performance and the thermally activated interface chemistry of periodic Mg/SiC multilayers designed for application at 30.4 nm are investigated by optical (hard x-ray, soft x-ray and ultraviolet ranges, i.e. from 0.154 to 30.4 nm) reflectivity and x-ray emission spectroscopy. The multilayers are prepared by magnetron sputtering and then annealed up to a temperature of 500°C. Two clear changes take place in the multilayer upon annealing. At first, between 200 and 300°C a strong decrease of the reflectivity is observed, due to the development of interfacial roughness following the crystallization of the Mg layers. No interfacial compound is detected. Then, between 350 and 400°C there is formation of the Mg2Si magnesium silicide at the interfaces following the reaction between the Mg and SiC layers. This also leads to the almost total loss of reflectivity of the multilayer. Thus, this kind of multilayer is thermally stable only for application requiring no heating above 200°C.

The authors present an experimental study of Cr∕Sc multilayer mirrors optimized for the detection of the nitrogen Kα-emission line (λ=3.16nm) at a grazing incidence around 23°, for electron probe microanalysis applications. The multilayers were deposited onto silicon substrates using a dc magnetron sputtering system. They were characterized with grazing incidence copper Kα x-ray reflectometry and atomic force microscopy, as well as with at-wavelength reflectometry using synchrotron radiation. These various characterization methods pointed out that the interfacial roughness of these multilayers increases drastically with the number of bilayers. Growth parameters were then optimized, and it is shown that the structure and reflectivity of such multilayers can be considerably improved by optimizing the sputter gas pressure during the deposition process. Reflectivity higher than 37% were measured at 22.3° grazing angle for the nitrogen Kα-emission line.

OPT2X gathers researchers of the newly formed Paris-Saclay University with the goal of building an instrumental platform dedicated to the control, characterization and transport of ultra-short coherent XUV light pulses, in view of cross disciplinary applications in ultrafast science

Laboratoire Charles Fabry develops multilayer mirrors for University of Paris-Saclay state-of-the-art coherent XUV sources. We report on the recent advances in multilayer optics including mirrors for as/fs delay line and for a 10-100 eV polarizer.

We present recent advances in Al-based multilayer mirrors for EUV applications including high efficiency narrowband, dual-band and broadband mirrors. Applications to solar physics and to ultrafast dynamics with coherent EUV sources will be discussed.

International audience

International audience; We will report and discuss on some aspects of the design, deposition and characterization of reflecting multilayer coatings with specific spectral characteristics and enhanced temporal, thermal and radiation stability for extreme ultra-violet (EUV) applications, such as synchrotron radiation (SR), free-electron lasers (FEL) and solar plasma diagnostics.We will present our recent results on multilayer-coated beamline optics with high uniformity of the period (in the order of ± 0.5 %) along the entire length of 250 mm. We will also show some examples of highly reflective Al-based tri-component multilayers, which were fabricated in our laboratory and characterized by grazing x-ray reflectometry and with EUV radiation. These coatings were realized for various applications in the EUV range from 17 to 35 nm including a delay line project of FEL facility in Trieste and, very recently, the FSI (full Sun imager) and HRI (high-resolution imager) EUV telescopes of future Solar Orbiter space mission.

International audience; We propose a new model enabling the extraction of the phase of a multilayer mirror from photocurrent measure- ments in the soft x rays. In this range, the effects of the mean free path of the electrons inside the stack can no longer be neglected, which prevents the phase reconstruction by conventional photocurrent measurements. The new model takes into account this phenomenon and thus extends up to the x rays the applicability range of the technique. This ap- proach has been validated through a numerical and exper- imental study of chromium/scandium multilayers used near 360 eV. To our knowledge, this work constitutes the first measurement of the phase of a multilayer mirror in the soft x-ray range.

Le Laboratoire Charles Fabry concoit de nombreuses optiques dont certaines pour les applications dans le spectre EUV. Pour les besoins de caracterisation, il est necessaire de posseder une metrologie a la longueur d'onde d'utilisation proche des moyens de fabrication. Ceci permet d'etudier les composants des leur conception et de caracteriser les optiques. Nous presentons ici les performances d'un reflectometre automatise EUV large spectre. Il a ete developpe dans le cadre de la centrale CEMOX 1 , initiee par le pole PRaXO 2 .

This work was partly carried out at BESSY II in the framework of the project BESSY Number HPP33/150902 and supported by the European Commission under the ‘Human Potential Programme, Transnational Access to Major Research Infrastructures’, Contract No HPRI-1999-00028.; International audience; A La/B4C multilayer interferential mirror with small period d (4.8 nm) was produced by diode sputtering for the detection of the boron K emission by wavelength-dispersive x-ray spectrometry at a large Bragg angle (close to 45°). The structure of the mirror has been characterized by grazing incidence x-ray reflectometry, and its performance at the energy of the boron K emission (183 eV) was evaluated by means of polarized synchrotron radiation. A spectrometric measurement shows that the La/B4C mirror has improved the detection limit of boron using by a factor of 2 with respect to similar Mo/B4C mirrors, and by a factor of 4 with respect to a lead stearate crystal.

After a brief description of the theoretical principles of multilayer mirrors, we present the state of the art of experimental results obtained in the XUV range. We then focus on the specificities of multilayer mirrors for pico- and femtosecond sources, in terms of reflectivity, selectivity and stability. Finally, we report the recent advances in the development of multilayer mirrors for attosecond sources, from the design of the mirror to the characterization of such a component.

International audience; We study Cr/Sc-based multilayer mirrors designed to work in the water window range using hard and soft x-ray reflectivity as well as x-ray fluorescence enhanced by standing waves. Samples differ by the elemental composition of the stack, the thickness of each layer, and the order of deposition. This paper mainly consists of two parts. In the first part, the optical performances of different Cr/Sc-based multilayers are reported, and in the second part, we extend further the characterization of the structural parameters of the multilayers, which can be extracted by comparing the experimental data with simulations. The methodology is detailed in the case of Cr/B4C/Sc sample for which a three-layer model is used. Structural parameters determined by fitting reflectivity curve are then introduced as fixed parameters to plot the x-ray standing wave curve, to compare with the experiment, and confirm the determined structure of the stack.

International audience; Phase controlled multilayer mirrors provide an efficient solution to transport, focus and/or compress attosecond pulses in the extreme ultraviolet (EUV) domain (30 – 100 eV). In this spectral range, one can access the spectral phase of the multilayer stack by measuring the photocurrent generated at the mirror surface as a function of the incoming photon energy. It has been already demonstrated that one can extract the spectral phase from such measurements under specific hypotheses. In this paper, we present the experimental protocol for such measurements and discuss the validity of this technique in the EUV and in the soft x-ray domains. In the EUV spectral range, our experimental results are in good agreement with simulations. However, the previous hypotheses are no longer valid at shorter wavelengths, in the soft xrays domain. This is mainly due to the fact that the electron mean free path becomes comparable to the individual layer thickness in the multilayer mirror. Here we propose a new method that enables one to extend the validity of phase characterization using photocurrent measurements in the soft x-ray domain (100 – 1000 eV). We present the first experimental results concerning the phase characterization of Cr/Sc multilayer mirrors in the water window and compare these results with simulation.

International audience; Development of multilayer coated optics with specific spectral characteristics and enhanced temporal, thermal and radiation stability requires an innovative approach to the design of reflecting multilayers and optimization of the coating process. Here we report on the progress in design, calculations and fabrication of reflecting multilayer coatings for solar imaging in the extreme ultra-violet (EUV) range. We will present recent results of characterization of new tri-component periodic multilayer structures containing aluminum as a low absorbing material within the spectral range from 17 to 40 nm. The EUV peak reflectance of these coatings (for instance, the Al/Mo/SiC multilayers) reaches 56% at 17.4 nm and 42% at 30 nm, highest reported up to now for these wavelengths. We have studied the temporal and thermal stability of structural and optical parameters of Al-based multilayer coatings as well as the resistivity of the coatings to high-energgy anf high-dose proton irradiation. A special attantion will be drawn to specific bi-periodic systems with enhanced selectivity, which possess two efficient reflection bands and attenuate some unwanted emission lines in the EUV range. Experimental results show that such multilayer coatings are good candidates for the EUV imaging telescopes of Solar Orbiter and future solar missions.

National audience

An alternate multilayer (AML) grating has been prepared by coating an ion etched lamellar grating with a B4C/Mo2C multilayer (ML) having a layer thickness close to the groove depth. Such a structure behaves as a 2D synthetic crystal and can reach very high efficiencies when the Bragg condition is satisfied. This AML coated grating has been characterized at the SOLEIL Metrology and Tests Beamline between 0.7 and 1.7 keV and at the four-crystal monochromator beamline of Physikalisch-Technische Bundesanstalt (PTB) at BESSY II between 1.75 and 3.4 keV. A peak diffraction efficiency of nearly 27% was measured at 2.2 keV. The measured efficiencies are well reproduced by numerical simulations made with the electromagnetic propagation code CARPEM. Such AML gratings, paired with a matched ML mirror, constitute efficient monochromators for intermediate energy photons. They will extend the accessible energy for many applications as x-ray absorption spectroscopy or x-ray magnetic circular dichroism experiments.

An alternate multilayer (AML) grating has been prepared by coating an ion etched lamellar grating with a B4C/Mo2C multilayer (ML) having a layer thickness close to the groove depth. Such a structure behaves as a 2D synthetic crystal and can reach very high efficiencies when the Bragg condition is satisfied. This AML coated grating has been characterized at the SOLEIL Metrology and Tests Beamline between 0.7 and 1.7 keV and at the four-crystal monochromator beamline of Physikalisch-Technische Bundesanstalt (PTB) at BESSY II between 1.75 and 3.4 keV. A peak diffraction efficiency of nearly 27% was measured at 2.2 keV. The measured efficiencies are well reproduced by numerical simulations made with the electromagnetic propagation code CARPEM. Such AML gratings, paired with a matched ML mirror, constitute efficient monochromators for intermediate energy photons. They will extend the accessible energy for many applications as x-ray absorption spectroscopy or x-ray magnetic circular dichroism experiments.

In this paper, we report on the design, synthesis and characterization of extreme ultraviolet interferential mirrors for solar imaging applications in the spectral range 17 nm–34 nm. 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/B 4 C] 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 17.3 nm and 27.5% at 28.2 nm on a synchrotron radiation source.

We have developed and used a soft x-ray Michelson interferometer to probe large laser-produced plasmas. The aim investigated is to obtain electron density profiles and thus important informations on the plasma dynamic. This paper describes our design and presents some preliminary results using a nickel-like x-ray laser operating at 13.9 nm. Wewill present numericals results which show the interest of using x-ray laser to probe laser-produced plasma by interferometry.

International audience; CEA implemented an absolutely calibrated broadband soft X-ray spectrometer called DMX on the Omega laser facility at the Laboratory for Laser Energetics (LLE) in 1999 to measure radiant power and spectral distribution of the radiation of the Au plasma. The DMX spectrometer is composed of 20 channels covering the spectral range from 50 eV to 20 keV. The channels for energies below 1.5 keV combine a mirror and a filter with a coaxial photo-emissive detector. For the channels above 5 keV the photoemissive detector is replaced by a conductive detector. The intermediate energy channels (1.5 keV < photon energy < 5 keV) use only a filter and a coaxial detector. A further improvement of DMX consists in flat-response X-ray channels for a precise absolute measurement of the photon flux in the photon energy range from 0.1 keV to 6 keV. Such channels are equipped with a filter, a Multilayer Mirror (MLM), and a coaxial detector. We present as an example the development of channel for the gold M emission lines in the photon energy range from 2 keV to 4 keV which has been successfully used on the OMEGA laser facility. The results of the radiant power measurements with the new MLM channel and with the usual channel composed of a thin titanium filter and a coaxial detector (without mirror) are compared. All elements of the channel have been calibrated in the laboratory of the Physikalisch-Technische Bundesanstalt, Germany's National Metrology Institute, at the synchrotron radiation facility BESSY II in Berlin using dedicated well established and validated methods.

International audience; We present procedures to develop and characterise chirped multilayer mirrors for attosecond pulses. The design procedure involves a simulated annealing optimisation algorithm to obtain a multilayer structure with the desired performances. The characterisation step requires the use of well-calibrated attosecond and synchrotron beam lines, allowing one to measure the amplitude and phase response of the mirror. We illustrate these approaches with a set of mirrors designed to have zero or negative dispersion. The remarkable agreement between theoretical and experimental performances validates this overall process, and demonstrates the capability of such mirrors to control the temporal profile of attosecond pulses. These tools and techniques for developing attosecond chirped mirrors will facilitate the generalisation of such components on attosecond experiments.

The present article reports a study of current–voltage (J–E) and capacitance–voltage (C–V) measurements on metal–insulator–semiconductor diodes, using SiNx:H as an insulator layer and Si or InP as semiconductors. We have deposited SiNx:H films by distributed electron cyclotron resonance plasma enhanced chemical vapor deposition at floating temperature, with physical properties similar to films prepared at 800 °C by low pressure chemical vapor deposition. Silane and nitrogen were used as the reactive gases. The experimental results show that the resistivity (ρ) and the critical field (EC) are a strong function of the dielectric composition. For films deposited under optimum conditions, ρ was equal to 1016 Ω cm and EC reached 3.65 or 4.5 MV/cm for Al/SiNx:H/Si and Al/SiNx:H/InP diodes, respectively. The dominant mode of electronic conduction appears to be the Poole–Frenkel emission. The postmetallization annealing (PMA) has no significant effect on these bulk properties (ρ, EC and electronic conduction). On...

International audience

International audience; 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.

International audience; One of the pioneers in coatings for optics in the extreme ultraviolet (EUV) spectral range (typically 10 to 60 nm), the "XUV Optics" team of Laboratoire Charles Fabry (LCF) study and optimize interferential mirrors based on multilayers for several applications since more than 25 years. Today, the main applications are related to the observation of the solar corona in astrophysics, optics for new x-ray sources (X-ray lasers, High Harmonics Generation Sources, Free Electron Lasers), optics for ultrashort pulses (attosecond science) or diagnostics of hot plasmas. After a brief introduction on the history of EUV multilayer mirrors and solar corona imaging, we will present recent results achieved at LCF. Periodic Mo/Si multilayers have been extensively studied and used since more than 20 years. Some years ago, we have been able to increase the reflectivity in the wavelength range 20 nm to 40 nm by adding a third material in the periodic structure [1]. Such B4C/Mo/Si multilayers have been designed for imaging the HeII emission line of the Sun (at 30.4nm) and have been deposited on EUV imager of HECOR mission [2]. By using a superposition of two periodic multilayers with three materials per period, we have designed dual channel mirrors [3, 4] that will be deposited on the EUV telescopes of Solar Orbiter (ESA mission). Moreover, we have recently shown that the use of Al instead of Si in periodic multilayer structure allows increasing mirror performances [5] (see figure). We will compare the results obtain with multilayer mirrors deposited by ion beam sputtering or magnetron sputtering. Reflectivity higher than 50% at 17 nm have been measured on synchrotron radiation source with SiC/Mo/Al structures. These results have required a systematic optimisation of deposition parameters in order to obtain aluminium thin films with low interfacial roughness. [1] J. Gautier et al., Applied Optics 44, 384 (2005) [2] Frédéric Auchère et al., Proc. SPIE 6689, 66890A (2007) [3] J. Gautier et al., Optics Communications 281, 3032 (2008) [4] C. Hecquet et al., Appl Phys A 95, 401 (2009) [5] E. Meltchakov et al., Appl Phys A 98, 111 (2010)

International audience; This paper presents a study of B4C/Mo2C multilayers mirrors with the aim of using it in the achievement of Alternate MultiLayer (AML) grating. Such component allows a high efficiency in the 500-2500 eV energy range for the DEIMOS beamline. Multilayers were deposited on silicon substrate. They are characterized by reflectometry under grazing incidence. Numerical adjustments were performed with a model of two layers in the period without any interfacial. A prototype of AML grating was fabricated and characterized. The efficiency of the first order of diffraction was worth 15% at 1700 eV.