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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.

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; The investigation of some solar radiations of interest for astrophysicists requires optics in the 80–130 nm vacuum ultra-violet spectral range (VUV). In this domain, where both transmittance and reflectance of most materials are very low, the measurement of optical constants is specifically difficult, and optical data are consequently often either inexistent or uncertain. Reliable modelling of optical components for VUV, like polarizing multi-layered mirrors, necessitates prior measurement of complex indices of the thin films involved in the coating. Fluorides like MgF2 or AlF3 are among the rare materials capable to contribute to multi-layer mirrors in the VUV. We have determined optical constants of thin films of these two materials by using a two media reflectance method at normal incidence and a graphical determination particularly suited to this VUV region, which we presented in a previous paper. Optical constants are determined in the range 60–124 nm with 2 nm step, and are compared to existing data. On the basis of these measured indices, polarizing mirrors for k1 = 121.6 nm or k2 = 103.2 nm have been modelled and fabricated. Their reflectance measured versus incidence angle by using monochromatized synchrotron radiation at the above wavelengths is found in agreement with the calculated predictions.

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.

The 80–120 nm spectral range is a key domain for solar physics. Below 105 nm solids do not transmit light and the reflectance of available mirrors is particularly low which makes optical measurements specifically difficult. Optical constants of the materials may consequently be unavailable or unreliable. We present here a two media reflectance method at normal incidence suited to this VUV range, in which the variable is not the incidence angle but the thickness of the top layer made of the material to be analyzed. The real ( n ) and imaginary ( k ) parts of the complex index are directly and graphically determined in the ( n , k ) plane as the common intersection point of isoreflectance curves corresponding to samples different only in the thickness of the top layer. The method is tested and illustrated with ZnSe films evaporated on Al covered float glass substrates. In the literature, the reflectance magnitudes measured on ZnSe crystals differ strongly from an author to the other, leading to discrepant data for ZnSe in the VUV domain. We obtain precise and reliable values of ( n , k ), which fit the experimental values determined on freshly cleaved ZnSe crystals by J.L. Freeouf and the theoretical values calculated from the electronic band structure of ZnSe by John P. Walter and Marvin L. Cohen, but strongly differ from the optical constants selected by E.D. Palik in his tables.

We present the characterization of Mg-Co-Zr tri-layer stacks by using x-ray fluorescence induced by x-ray standing waves, both in the grazing incidence (GI) and grazing exit (GE) modes. The introduction of a slit in the direction of the detector improves the angular resolution by a factor 2 and significantly the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kalpha and Co Lalpha characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, we show that the interfaces of the Si/[Mg/Co/Zr] x30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co] x30 multilayer a strong intermixing occurs at the Co-on-Zr interfaces. The explanation of this opposite behaviour of the Co-on-Zr and Zr-on-Co interfacesis given by the calculation of the mixing enthalpies of the Co-Mg, Co-Zr and Mg-Zr systems, which shows that the Co-Zr system presents anegative value and the two others positive values. Together with the difference of the surface free energies of Zr and Co, this leads us to consider the Mg/Zr/Co system as aMg/Co x Zr y bi-layer stack, with x/y estimated around 3.5., Published in Journal of Synchrotron Radiation 22, 1419 (2015)http://scripts.iucr.org/cgi-bin/paper?S1600577515016239

L'elaboration de nouveaux revetements interferentiels multicouches est motivee par la demande de l'astrophysique solaire et par le developpement de nouvelles sources de rayonnement EUV (source a generation d'harmoniques d'ordre eleve, laser X, rayonnement synchrotron). Nous avons etudie et developpe differents systemes multicouches possedant a la fois des proprietes optiques optimisees (reflectivite et/ou bande passante) et une bonne stabilite temporelle et thermique pour la gamme de longueurs d'onde comprise entre λ. = 30nm et λ = 50nm. Une augmentation significative de la reflectivite des multicouches dans la gamme spectrale de 30 a 40nm a ete obtenue par l'addition d'un troisieme materiau dans l'empilement. Une etude comparative des courbes de reflectivites theorique et experimentale en fonction de la longueur d'onde a ete menee. Les differences observees ont pu etre expliquees notamment a l'aide de l'analyse des proprietes physiques des differents materiaux en couche mince. Nous montrons egalement que l'utilisation de ces multicouches a trois materiaux par periode permet le developpement d'empilements repondant a des demandes specifiques (miroirs a large bande passante, miroirs a double bande). Pour les longueurs d'ondes comprises entre 35 nm et 50nm nous avons developpe des multicouches a base de scandium. Cette etude a permis d'obtenir des multicouches avec de forts pouvoirs reflecteurs et une bonne stabilite temporelle. La stabilite de ces empilements a pu etre amelioree a l'aide de l'insertion aux interfaces de couches barrieres.

International audience; Grazing X-ray reflectometry is used in order to characterize thin layer stacks, in particular periodic multilayers. The specular reflectivity depends on the thickness, the complex refractive index of each layer and on the roughness of the interfaces. By a trial and error method, the experimental reflectivity curve can be fitted with a theoretical one, and so, the parameters of the stack can be obtained. This numerical method needs usually initial guess of the kind of results. Fourier transform method allows to obtain directly the values of distances between interfaces, with a good approximation depending on the maximum angular scan of the measure. It can also reveal some particularity of the multilayer, i.e. periodic multilayered structures with more than two layers per period. As an illustration of this characterization method, some examples in XUV optical domain will be shown. This method can also be used for the characterization of many kinds of multilayer stacks, in particular semi-conductor heterostructures ones, under the condition that adjacent layers have sufficient contrast index at the wavelength of the X-ray source.

We present the physico-chemical and optical study of Mo/Si multilayer interferential mirrors (MIM) with a Si thickness of 2 nm and a Mo thickness varying from 1 to 4 nm. In two other samples, barrier layers of B4C have been added either at the Mo/Si interface or at the Si/Mo interface to enhance the optical index contrast in the soft X rays and to minimize the growth of molybdenum silicides. The physico-chemical analysis is carried out by X-ray emission spectroscopy (XES) induced by electrons. The Si 3p density of valence states of the silicon atoms that are present in the multilayers are obtained via the analysis of the band Si Kβ (3p→1s transition) emission band. The emission band of the multilayer is fitted by a weighted sum of the compounds likely to be present at the interfaces: amorphous silicon, MoSi2 and Mo5Si3. From the contribution of the silicides, the thickness of the transition layer is determined. The optical analysis is performed by X-ray reflectivity (XR) at two wavelengths (0.154 and 0.712 nm). The simulation of the results reveals the importance of considering a four-layer model to describe one period in the stack. Moreover, we evidence the good performance of the multilayer with a Mo thickness of 3 nm. Copyright © 2006 John Wiley & Sons, Ltd.

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.

Nous avons etudie par spectroscopie d'emission X induite par electrons (EXES) et par reflectometrie X (RX), un empilement periodique constitue de bicouches Mo/Si, destine a servir de miroir interferentiel dans le domaine des rayons X mous. Les resultats de RX rasante (λ = 0,154 nm) peuvent etre interpretes par une succession de couches ou les atomes de Si se melangent aux couches Mo et reciproquement, avec de plus une rugosite interfaciale. D'apres l'analyse EXES, les atomes de silicium sont presents dans deux environnements physico-chimiques differents. Au centre des couches Si, se trouve du silicium amorphe et au niveau des interfaces se trouve une interphase sur une epaisseur d'environ 2 nm ou les atomes de Si sont sous forme de siliciures (Mo 5 Si 3 et MoSi 2 ). La composition de cette interphase a ete determinee et a permis de reproduire d'une maniere satisfaisante les mesures de reflectivite absolue effectuees en RX mou (λ = 1,33 nm).

Nous presentons dans une premiere partie une etude de miroirs interferentiels multicouches composes de divers materiaux pour des longueurs d'onde de l'ordre de 30 nm. Les quatre systemes etudies, Mo/Si recouvert de Si ou de B 4 C, B 4 C/Si et Mo/B 4 C/Si/B 4 C, presentent des pouvoirs reflecteurs de l'ordre de 24% autour de 30 nm. Les multicouches B 4 C/Si et Mo/B 4 C/Si/B 4 C presentent une meilleure selectivite que les multicouches Mo/Si. Sur ces dernieres, la couche de protection en B 4 C ne permet pas d'ameliorer la stabilite en temperature, par contre l'ajout de B 4 C aux interfaces ameliore considerablement cette stabilite. Dans une seconde partie, nous presentons la realisation et la calibration de lames separatrices a 13,9 nm pour un interferometre de Michelson. Les lames separatrices que nous avons developpees presentent des proprietes symetriques : les reflectivites de chaque face ne different que de 6%. Le produit reflectivite - transmission de ces lames peut etre optimise au-dessus de 2% pour une longueur d'onde fixee dans la gamme 12,6-15,5 nm.

Nous presentons les modulations d'intensite de la raie Si Kα emise par une structure multicouche en fonction de l'angle de sortie des photons. L'observation est realisee autour de la direction correspondant a la direction de Bragg de la raie Si Ka par la multicouche. L'echantillon est irradiee par un faisceau d'electrons dont l'energie est comprise entre 2 et 6 keV. Une importante variation d'intensite est observee dans le domaine angulaire correspondant a la figure de diffraction de la structure emissive. Une augmentation voisine de 15% de l'intensite de la raie est mesuree dans la direction de Bragg de la multicouche quelle que soit l'energie des electrons incidents. La modulation est interpretee sur la base du theoreme de reciprocite. A la suite de la proposition de Yariv and Yeh [J. Opt. Soc. Am 67 (1977) 438], nous envisageons une application des structures multicouches comme resonateur pour parvenir a un laser X a retroaction distribuee.

The double Kirkpatrick–Baez (DBA) microscope is derived from the grazing x-ray Kirkpatrick–Baez (KB) microscope. The KB is compound of two concave spherical mirrors working at grazing incidence and in an energy range about 100 eV–10 keV. The combination of two similar mirrors in the DKB increases the useful field. This device only requires spherical mirrors, more easy to manufacture (precision and roughness) than aspherical ones. In order to image a laser plasma source in a large field of view and within a bandpass of 0.6 keV around 3.4 keV, a KB optic covered with multilayers is developed. In fact, a compromise has to be found between the resolution of the optic (better with a less grazing angle), and the reflectivity (better with more grazing angle). We have chosen to keep the average grazing incidence on the four mirrors around 2°–3° just as for a first uncoated DKB made in our laboratory. This allows us to keep the same radius of curvature for the mirrors. At this energy multilayers are needed, due to...

The principle of a multilayer monochromator with a narrow bandwidth and a low specular background is recalled. The elaboration of such a monochromator obtained from a Mo/Si multilau-yer mirror is briefly described. The performance of the device measured at 1500 and 98 eV is presented. Le principe d'un monochromateur multicouche a bande passante etroite et presentant un faible fond continu est rappele. Nous decrivons brievement la fabrication d'un tel monochromateur obtenu a partir d'un miroir multicouche Mo/Si. Les performances de ce dispositif mesurees a 1500 et 98 eV sont presentees.

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.

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.

A new soft-x-ray multilayer monochromator with an improved resolution and a low specular background is presented. The principles of the device, based on the use of a lamellar multilayer amplitude grating (LMAG), are summarized. The techniques of fabrication of the monochromator (multilayer deposition, UV lithography and reactive ion etching) are given. The performance of this new monochromator at photon energies around 1500 eV is demonstrated. Copyright © 2001 John Wiley & Sons, Ltd.

A new kind of xuv multilayer monochromator with a narrow spectral bandwidth is introduced. This monochromator is based on a Mo/Si multilayer mirror etched according to the profile of a lamellar grating. The fabrication of such a device involving multilayer deposition, UV lithography and reactive ion etching is presented. The monochromator has been characterized by means of the synchrotron radiation around the Si–L edge (100 eV). A reduction of the bandwidth has been observed with respect to the unpatterned mirror by a factor close to 3.

Le contraste d'indices des deux elements (B,Si) est en general petit dans le domaine spectral des X-UV, ce qui fait que des ecarts d'indices, meme faibles, de chacun des elements constitutifs de la bicouche vont modifier les proprietes optiques du miroir. Il est donc necessaire d'etudier le mieux possible les caracteristiques de l'empilement afin de prevoir les conditions optimales de realisation et d'utilisation (de 100 eV a 1 keV).

On etudie la reflexion rasante des rayons X par un cermet en couche mince realise par co-evaporation de platine et d'alumine. On discute de quelques modeles d'interpretation possibles comme la diffusion par les nano agregats spheriques, la variation de l'indice avec l'angle et le comportement similaire a celui d'un milieu homogene. On montre que cette derniere approximation est valable pour des angles de rasance assez faibles.

En utilisant les principaux elements d'un diffractometre a rayons X classique, nous avons mesure les variations angulaires de l'intensite du rayonnement de fluorescence Kα du fer emis par une multicouche periodique Fe/C et montre qu'elles dependaient notablement de l'angle d'incidence du faisceau monochromatique excitateur lorsqu'il est proche de l'angle de Bragg du premier ordre de la multicouche. Une modelisation de l'intensite de fluorescence emise par une multicouche supposee parfaite et realisee en utilisant les methodes de calcul des proprietes optiques des multicouches montre que cette variation d'intensite est provoquee par le deplacement des extrema de l'onde excitatrice quasi-stationnaire par rapport aux interfaces dans l'empilement lorsque l'angle d'incidence varie a proximite de l'angle de Bragg. Les defauts de la multicouche tels que l'elargissement des interfaces par la rugosite ou l'interdiffusion et les ecarts de densite par rapport aux materiaux massifs ont ensuite ete pris en compte pour obtenir une simulation quantitative des courbes experimentales. La comparaison des resultats avec ceux des mesures de reflectivite en X mous suggere la presence d'oxygene en concentration de l'ordre de 16% (en nombre d'atomes) dans les couches elementaires de fer.

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.

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.

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; In 1948, P. Kirkpatrick and A. V. Baez developed an x-ray microscope (energy range about 100 eV-10 keV) composed of two concave spherical mirrors working at grazing incidence. That device, named KB microscope, presents a 3-5 μm resolution within a field having a radius about 100 μm; outside that field, its resolution lowers rapidly when the object point recedes from the center. The adjunction of two similar mirrors can notably increase the useful field (typically, the resolution can be better than 10 μm within a 2-mm-diam field of view), which is necessary for studying laser plasmas. Its main advantage with respect to more simple optics, as the pinhole, is that it can be located far enough from the plasma to avoid any destruction during the shot. We describe such a microscope that we call KBA microscope and present some images of fine metallic grids. Those grids were backlighted by x-raysources, either a cw one or a series of laser plasmas from the Octal-Héliotrope facility. Examining the films in detail shows that the experimental results are very close to the theoretical characteristics; hence the interest of this device for the x-raydiagnostics on the future powerful laser facilities.

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)

On a mesuré la variation angulaire de l'intensité du rayonnement de fluorescence Kα du fer émis sous émergence rasante par une multicouche périodique Fe/C. On observe une forte modulation de l'intensité émise au voisinage de l'angle d'émergence correspondant à la direction de diffraction de Bragg du rayonnement caractéristique du fer par le milieu stratifié périodique. Cette modulation est semblable aux lignes de Kossel observables sur les diagrammes de fluorescence de monocristaux ; sa position et sa forme sont bien reproduites par un calcul basé sur l'utilisation du théorème de réciprocité et du formalisme de calcul des propriétés optiques des couches minces. La multicouche a ensuite été irradiée avec un rayonnement quasi-monochromatique (raies Kα du cuivre) sous incidence rasante au voisinage d'un angle de Bragg afin de moduler l'intensité du champ électrique excitateur en fonction de la profondeur. On met en évidence les variations de l'intensité du rayonnement de fluorescence du fer en fonction de l'angle d'incidence du rayonnement excitateur.

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.

International audience; We present a comparative study of B4C/Mo and B4C/Mo2C periodic multilayer structures deposited by magnetron sputtering. The characterization was performed by grazing incidence X-ray reflectometry at two different energies and high resolution transmission electron microscopy. The experimental results indicate the existence of an interdiffusion layer at the B4C-on-Mo interface in the B4C/Mo system. Thus, the B4C/Mo multilayers were modeled by an asymmetric structure with three layers in each period. The thickness of B4C-on-Mo interfacial layer was estimated about 1.1 nm. The B4C/Mo2C multilayers present less interdiffusion and are well modeled by a symmetric structure without interfacial layers. This study shows that B4C/Mo2C structure is an interesting alternative to B4C/Mo multilayer for X-ray optic applications.

We will present recent advances in the design and deposition of EUV multilayer mirrors. Efficient control of the spectral shape has been achieved by using three material structures. Applications to dual-band and broadband mirrors will be discussed.

Dans la gamme de longueur d'onde des X-UV (3 - 40 nm ou 400 - 30 eV), il est possible de realiser des optiques a partir de miroirs revetus de multicouches constituees de materiaux alternes, dont l'un est plus specifiquement reflechissant (habituellement de numero atomique eleve), et l'autre plus specifiquement espaceur (de numero atomique faible), de maniere a ce que dans la periode elementaire constituee par la bicouche, les interferences soient en phase pour la longueur d'onde et l'angle d'incidence considere. Ces deux materiaux sont habituellement designes par lourd et leger. On montre quelques exemples ou, selon la longueur d'onde d'utilisation, le materiau dit lourd peut etre remplace avantageusement par un element de faible numero atomique.

poster; International audience

International audience

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 physi cs, high-order harmonic generation or synchrotron r adiation. It was found that an introduction of refractory metal in A l-based periodic stack helps to reduce significantl y an interfacial roughness and provides for a higher theoretical ref lectance in the spectral range from 17 to 40 nm. Th e normal incidence reflectivity as high as 55 % at 17 nm, 50 % at 21 n m and 42 % at 30 nm was achieved with the new Al/Mo/SiC and Al/Mo/B 4C multilayer mirrors, which have been optimized, fa bricated and characterized with x-rays and synchrot ron radiation. A good temporal and thermal stability of the tri-component Al-based multilayers has been ob served 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.

With regards to the future Laser Megajoules french facility (LMJ), our laboratory is developing advanced time-resolved High Resolution X-ray Imaging (HRXI) systems to diagnose laser produced plasma. Shrapnel and X-ray loading on this laser imposes to place any HRXI as far away from the source as possible. Grazing incidence X-ray microscopes are the best solution to overpass this limitation. These imagers combine therefore grazing X-ray microscope and camera. We designed imaging diagnostics, mainly with a long working distance (> 50 cm) and high spatial resolution. All of them are composed of single or multi-toroidal(s) mirror(s). To increase the bandwidth of reflectivity of all these mirrors, multilayer coatings have been deposited. We present mainly microscopes using non-periodic W/SiC multilayer coatings (Supermirrors), developed in collaboration with Institut d'Optique. Supermirrors were designed for a first set of diagnostics to work at 0.7° grazing incidence. Secondly, we have implemented this supermirror on a Wolter-type microscope used at a smaller grazing incidence (0.6° angle) in order to increase the bandwidth of reflectivity up to 12 keV. Metrology for x-ray reflectance in the whole range on the synchrotron radiation facility BESSY II is also presented.

International audience

Efficient polarizing as well as non-polarizing mirrors for a wavelength of λ=121.6 nm (hydrogen Lyman-α radiation) are necessary to achieve an experimental determination of the magnetic field in the solar corona through the Hanle effect. We have designed, realized and characterized such mirrors. These consist of glass coated with a thin-film stack. The coatings use the most reflective (Al) and most transparent (fluorides) materials at this wavelength. Different coatings were explored which involve an increasing number of films in the coating stack. At the incident angle of maximum polarization where the p-polarized reflectivity R p is minimized, an s-polarized reflectivity R s as high as 69% is experimentally obtained with a coating made of a Fabry–Perot resonator. To our knowledge, this value is the highest ever reported for a polarizing mirror at this wavelength. Additionally, efficient non-polarizing mirrors have been designed and realized by using a two-layer coating (MgF2/Al/glass). By optimizing the fluoride layer thickness, a mirror with non-polarizing properties in the whole range of incident angles was realized.

poster; International audience

International audience

Resume. Ce papier presente une etude de miroirs interferentiels multicouches B4C/Mo en vue d’utilisation dans la fabrication des reseaux MultiCouches Alternes (MCA). L’objectif consiste donc a etudier particulierement la formation des couches d’interface entre deux materiaux consecutifs. Les multicouches sont deposees sur des substrats polis de silicium. Elles sont caracterisees par reflectometrie en incidence rasante. Les ajustements numeriques a l’aide d’un modele a trois couches montrent la formation a l’echelle nanometrique d’une couche d’inter-diffusion a l’interface B4C/Mo.

Ellipsometric measurements performed on TiO 2 films, 7−170 nm thick, evaporated on glass substrates using an electron gun have been successfully interpreted in terms of inhomogeneities in the depth of the films. In a first attempt, the complex index of refraction was calculated by assuming a one-layer model (ambient/homogeneous film/substrate). For thin films ( d nm ), the dispersion of the real part of the index n is smooth, as expected, and the mean value of the imaginary part k is zero, except for wavelengths lower than 0.4 μm, when TiO 2 becomes absorbing. For thicker films ( d > 60 nm ), non-physical oscillations in n and even more in k appear, indicating that the one-layer model is no longer valid. A two-layer model was then used, which assumes the existence of a superficial layer in TiO 2 films. The oscillations in k are suppressed for all films when this superficial layer is about 3−5 nm thick and is less dense than the main part of the film (Δ n ≈0.4). The existence of such a surface layer has been confirmed by X-ray reflectometry at grazing incidence.

In this paper, we present a brief history of EUV multilayer mirrors and recent results achieved at Institut d'Optique in the fields of space science and ultra-fast pulses. Concerning space science, we present two solutions to improve reflectivity of EUV multilayer for solar imaging: three material multilayers and Al-based multilayers. Concerning attosecond pulses, we demonstrate the possibility to realize multilayer mirrors for an efficient transport of high harmonics on a broad energy band with high efficiency.

National audience