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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.

Among X-ray and extreme ultraviolet light sources able to produce shorter and shorter, coherent and intense pulses, High order harmonics generated in rare gases are currently the unique way to generate attosecond pulses. However, the manipulation and transport of attosecond pulses require the development of dedicated optics for reaching specific characteristics in terms of amplitude but also in terms of spectral phase control. We present here a multilayer design for chirp compensation of attosecond pulses. We also present an application of these multilayers mirrors for attosecond train pulse holography experiment with high harmonics. This experience took benefit of both temporal and spatial phase properties of high harmonics. A resolution of 750 nm has been achieved by using a 350 as train pulse for the reference wave constituted of four consecutive harmonics (λ=28 nm to λ=41 nm). This new method will allow making ultra fast movies with attosecond resolution of transient phenomena with quasi-3D resolution.

Since the first seeding of an OFI soft x-ray laser in 2004, we progressed towards the full characterization of the output beam. The final is to be able to deliver to users well-known beam. Temporal as well as spatial parameters have been measured for different conditions of amplification. We observed a strong enhancement of the spatial coherence due to the amplification process with a far-field pattern exhibiting an airy-like shape. The gain zone having strong discontinuity behaves like a hard pinhole. Spatial filtering has been also observed on the wave front (δ/5 root-mean-square, rms, before seeding and δ/20 rms after amplification). Temporal coherence has been studied thanks to the use of a Fourier- Transform spectrometer. Spectral widths, δδ/δ, around 10-5 have been measured for different plasma lengths or gas pressures. Departure from Gaussian shape has been clearly observed on the spectral line for some cases.

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.

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.

We present an experimental study of aging and thermal stability of Sc/Si multilayers deposited by magnetron sputtering. These multilayers have been characterized by using hard X-ray grazing incidence reflectometry at 0.154 nm and synchrotron radiation reflectometry at near normal incidence. The reflectivity was found to be stable after one year. A maximum reflectivity of 46% has been measured at 46 nm. However a 20% relative decrease of the reflectivity have been observed after one hour thermal annealing at 200°C. In order to improve thermal stability, we studied two different barriers layers (B4C and ScN ). We compare the decrease of peak reflectivity and its wavelength shift after one hour annealing at 200°C under argon atmosphere. The best result was observed with the design using 0.3 nm B4C barrier layers. A relative decrease of 2% of the reflectivity peak has been observed with this design as compared to a 20% decrease without barrier layers.

Theoretically, periodic three component multilayers as B 4 C/Mo/Si allow an improvement of the reflectivity in the 25 nm-40 nm range as compared to two component multilayers as B 4 C/Si. Optimized B 4 C/Mo/Si and B 4 C/Si multilayers have been deposited by magnetron sputtering and ion beam sputtering. The multilayers have been characterized by x-ray grazing reflectometry (λ = 0.154 nm) and synchrotron radiation measurements at near normal incidence. The maximum experimental reflectivity for B 4 C/Si is 25% at 32 nm and 23% at 38 nm. For B 4 C/Mo/Si multilayers, we obtained an experimental reflectivity of 34% at 32 nm and 29% at 39.5 nm. Moreover the width of the Bragg peak is larger for B 4 C/Mo/Si than for B 4 C/Si. We have used these multilayers in a non periodical structure in order to produce broadband mirrors. It consists of the superposition of two periodic B 4 C/Mo/Si multilayers with different period thickness. Theoretical optimization of such structure by simulation is presented. Preliminary experimental results demonstrate the interest of such structure : two broadband mirrors have been deposited and measured over a wide wavelength range (12 nm to 45 nm). The first mirror presents a broadband spectrum centered at 32 nm with peak reflectivity of 22% and bandwidth larger than 9 nm. The second mirror has been optimized to produce theoretically an average reflectivity of 19% from 25 nm to 35 nm.

The observation of hot plasmas in the interstellar medium requests efficient mirrors in the 80-120 nm wavelength range. Contrary to that of most metals, the high reflectivity of pure aluminum is maintained close to 80% in this range. Unfortunately, it is drastically reduced to values lower than 10% by the strongly absorbing thin alumina layer which spontaneously forms itself upon air contact. Usually the deposition of thin fluorides films on aluminum (MgF2 or LiF) is used to prevent the alumina formation and consequently extend the high reflectivity range from visible towards shorter wavelengths. But this approach works only from the alumina to the fluoride bandgap (λ ≈ 100 nm). Other materials were studied by Larruquert who reported a measured reflectivity as high as 34% at l = 90 nm by using a Al/MgF2/SiC thin films stack. The aim of the investigation reported here is to define and test different and original aluminum based thin films stacks which optimize the mirror reflectivity in the 80-120 nm range. We present the results of our simulations from a large number of materials and the first experimental tests of the predicted best solutions.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Imaging of the solar corona by selecting Fe IX (λ=17.1nm,), Fe XII (λ=19.5nm), Fe XV (λ=28.4nm) and He II (λ=30.4nm) emission lines with a Ritchey-Chretien telescope requires to coat the optics with multilayers having a high accuracy in their layer thicknesses, a high reflectivity and an optimal bandpass. Multilayers were simulated in order to determine the most adequate formula for each wavelength channel. Mo/Si coatings were deposited by using the ion beam sputtering technique in a high vacuum chamber equipped with a micro balance and an in-situ reflectometer. The multilayers were studied by grazing angle reflectometry at 0.1541nm, and their reflectances around the operating wavelengths were measured on the SA62 IAS/LURE beam line of the SuperACO synchrotron facility located at Orsay. In addition, aging versus time and behavior of the multilayers under a rapid thermal annealing were investigated. Performances of the ion-beam deposited multilayers have been improved compared to the Mo/Si coatings obtained in the past by the e-beam evaporation technique for the SOHO mission Extreme UV Imaging Telescope (EIT). The EUVI telescopes for the STEREO mission are being proceduced by depositing these new generation of multilayers onto primary and secondary mirrors. The reflectivity measurements on a telescope are presented.

The Extreme Ultraviolet Imager (EUVI) is part of the SECCHI instrument suite currently being developed for the NASA STEREO mission. Identical EUVI telescopes on the two STEREO spacecraft will study the structure and evolution of the solar corona in three dimensions, and specifically focus on the initiation and early evolution of coronal mass ejections (CMEs). The EUVI telescope is being developed at the Lockheed Martin Solar and Astrophysics Lab. The SECCHI investigation is led by the Naval Research Lab. The EUVI’s 2048 x 2048 pixel detectors have a field of view out to 1.7 solar radii, and observe in four spectral channels that span the 0.1 to 20 MK temperature range. In addition to its view from two vantage points, the EUVI will provide a substantial improvement in image resolution and image cadence over its predecessor SOHO-EIT, while complying with the more restricted mass, power, and volume allocations on the STEREO mission.

Grazing X-ray reflectometry allows the analysis of thin layer stacks. The fitting of the reflectivity curve by a trial and error method can be used in order to determine the parameters of the films. In order to facilitate this trial and error method, the Fourier transforms of the Grazing X-ray reflectivity curves have been investigated. After the appropriate transformation of the original reflectivity curve in order to make the signal periodic, rough values of the thicknesses can be found. In first approximation, the Fourier transform leads to the auto correlation function of the derivative of the index profile of the stack. The spectrum can give also rough information about roughness by the widening of the peaks, and the height of the peaks are related to the contrast of the indices. The number of peaks in the spectrum is a function of the number of interfaces in the stack. It is shown how one can use the Fourier transform results to make a preliminary stack model before fitting the experimental data.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Diffusion in Ni-Ti multilayers with a period of 120 angstroms is studied in the temperature range of 293 - 743 K by using the grazing angle unpolarized neutron reflectometry. It was shown that Ni diffuses into Ti in this temperature range. The effective diffusion coefficient Deff of Ni into Ti and its corresponding activation energy Qa are determined by measuring the decay of the reflectivity of first Bragg peak arising from the nuclear scattering length density modulation, as a function of annealing temperature at constant time. Two diffusion regimes separated by a pseudo-transition temperature Tc approximately equals 543 K are observed in this Ni-Ti multilayer. The corresponding activation energy values are 0.21 eV and 0.43 eV respectively. The unpolarized neutron reflectivity measurements are completed by crystalline structure, chemical profiling, and magnetic studies.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High reflectivity neutron mirrors require perfectly smooth, sharp interfaces, uniform layer thicknesses and densities and high stack regularity. For this, the multilayers were deposited on water cooled glass substrates using a D-C low energy (300 - 700 V) triode sputtering unit equipped with an accurate thickness monitoring system. This last one is based on the dependence of the deposition rate on the target current. During deposition, the target current is sampled and converted to a digitalized voltage. This voltage value is then fed to a computer where a real-time numerical integration is made. The target current is integrated and the film thickness is given by the integration time. All sputtering parameters are regulated. A feed- back system between anode current and filament heating supply keeps the plasma current constant. The computer also automatically controls the setting and the timing of the runs. Thicknesses can be controlled to an accuracy of better than 1A. Reproducibility is better than 1%. Therefore, a high stack regularity can be achieved with sharp interfaces as will be shown by the characteristics of a 10[Ni-Ti] neutron monochromator. The experimental and theoretical reflection profiles are in perfect agreement indicating a high stack regularity. This technique is also efficient at producing high reflectivity aperiodic media: supermirrors. A 15[Ni-Ti] supermirror in Hayter-Mook configuration gives a neutron reflectivity of the order of 95% with an effective critical angel of 1.9(theta) cNi. The characteristics of the previous monochromator and supermirror have been measured also using secondary ion mass spectrometry, grazing angle x-rays reflectometry, and resistivity measurements.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.