X-ray broadband Ni/SiC multilayers: improvement with W barrier layers

International audienceWe present an experimental study and performance improvement of periodic and aperiodic Ni/SiC multilayer coatings. Periodic Ni/SiC multilayer mirrors have been coated and characterized by grazing incidence X-ray reflectometry at 8.048 keV (Cu Kα radiation) and by measurements at 3 keV and 5 keV on synchrotron radiation facilities. An interdiffusion effect is found between Ni and SiC layers. A two-material model, NixSiy/SiC, using a silicide instead of Ni, was used to fit the measurements. The addition of 0.6 nm W barrier layers at the interfaces allows a significant reduction of the interdiffusion between Ni and SiC. In order to obtain a specific reflectivity profile in the 2 – 8 keV energy range, we have designed and coated aperiodic multilayer mirrors by using Ni/SiC with and without W barrier layers. The experimental reflectivity profiles as a function of the photon energy were measured on a synchrotron radiation facility in both cases. Adding W barrier layers in Ni/SiC multilayers provides a better precision on the layer thicknesses and a very good agreement between the experimental data and the targeted spectral profile

Adaptive shaping of a focused intense laser beam into a doughnut mode

International audienceWe present a method to shape the intensity distribution of an intense laser beam in the focal region, by means of a bimorph adaptive mirror. We emphasize the advantages in terms of flexibility with respect of previous methods making use of specially designed retarding phase plates; however, the nature of the mirror imposes constraints on the accessible wavefronts, whose consequences are analyzed. We present an experimental demonstration of the feasibility of the scheme on a high intensity femtosecond laser system

Study of the X-ray scattering in the silicon and CdTe XPAD

The XPAD3, a photon counting hybrid pixel detector developed in collaboration by SOLEIL Synchrotron, the Institut Néel and the Centre de Physique des Particules de Marseille (CPPM) [1], is now successfully used for a large variety of X-ray experiments on third generation synchrotron light sources [2]. Several 7.3 cm x 12.5 cm imagers composed of 8 silicon modules (7 chips per module, 9600 pixel of 130μm side per chip) are routinely used on different synchrotron beamlines at Soleil and on the CRG beamline D2AM at ESRF. Detector performances such as noiseless detection, high dynamic (27 bits) and fast framing rate (640 fps) have opened up the possibility of new or improved types of measurements. Nevertheless, above 15 keV, besides the loss of efficiency [2], the X-ray scattering in silicon sensor and the material located behind significantly increases the shape and the width of thepoint-spread function at 0.01% of the maximum. This effect prevents the study of low intensity phenomena such as diffuse scattering, which would be observed at the foot of theBragg peak and theoretically measurable with the large dynamic of the detector. This effect has been measured at different energies with monochromatic synchrotron beam (on CRISTAL and METROLOGIE Soleil beamlines) on a mono module Silicon XPAD and then compared with a Quad CdTe XPAD prototype (cf. figure 1). The results, which will be presented, demonstrate the superiority of the high Z sensor and push the investigation of the CdTe as a material sensor even at mid energy

Multi-Lateral Shearing Interferometry: Principle and Application to X-Ray Phase Imaging

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Optimization of the focused flux of high harmonics

Following the theoretical predictions [1], the observation of two-photon processes by interaction of vacuum ultraviolet (VUV) radiation with inner-shell levels of atoms requires focused intensities in the $10^{13}{-}10^{14}$ W/cm2 range. Our aim is to reach this regime in order to study non-linear optics at these wavelengths. We first optimized the high harmonic conversion efficiency in argon by studying the best experimental conditions for phase-matching, concentrating on focus geometry related to laser energy, cell length and position relative to the focus. We then studied the resulting harmonic beam focusability by a toroidal mirror (f=10 cm) and made an image of the harmonic focus. We conclude with an evaluation of the focused intensity that we are able to reach experimentally

Optimization of the wave front of high order harmonics

We present a full optimization of the high harmonics wave front owing to the use of a soft X-ray Hartmann sensor. The sensor was calibrated using a high harmonic source with an accuracy of λ/50 root-mean-square (rms) with λ around 30 nm. We observed a high harmonic wave front of λ/7 rms, which is two times the diffraction-limit, astigmatism being the dominant aberration for every condition of generation. By clipping slightly the unfocused high harmonic beam, it is possible to produce a diffraction-limited beam containing approximately 90% of the incident energy

Wavefront analysis of nonlinear self-amplified spontaneous-emission free-electron laser harmonics in the single-shot regime

International audienceThe single-shot spatial characteristics of the vacuum ultraviolet self-amplified spontaneous emission of a free electron laser (FEL) is measured at different stages of amplification up to saturation with a Hartmann wavefront sensor. We show that the fundamental radiation at 61.5 nm tends towards a single-mode behavior as getting closer to saturation. The measurements are found in good agreement with simulations and theory. A near diffraction limited wavefront was measured. The analysis of Fresnel diffraction through the Hartmann wavefront sensor hole array also provides some further insight for the evaluation of the FEL transverse coherence, of high importance for various applications. © 2011 American Physical Society

Backside-illuminated scientific CMOS detector for soft X-ray resonant scattering and ptychography

International audienceHuge progress have been done with the 3 rd generation storage ring, and more recently the ultimate storage ring under development suggest an unprecedent increase of x-ray brightness. Unfortunately, as far as the detectors are concerned, progress has not been as fast and even more so in the range of soft x-rays. In particular for 2D detector the most commonly used detector are based on old CCD technology and the recent development of CMOS detector will be certainly crucial for 2D detector in the soft x-rays. With this goal we explore the possibilities and the the performance of a camera equipped with new mass-marketed scientific Complementary Metal Oxide Semiconductor Back Side Illuminated (sCMOS-BSI) integrated in vacuum environment for soft X-ray experiment at synchrotron. The 4 Mpix sensor reaches a frame rate up to 48 fps while suiting the necessary performances needed for X-ray experiments, in term of linearity (98 %), homogeneity (PRNU <1%) charge capacity (up to 80 ke-), readout noise (down to 2 e-rms) and adequate dark current (3 e-/s/px). The sensor performances tests in the X-ray range have been performed at the SOLEIL METROLOGIE beamline. The Quantum Efficiency, the spatial resolution (24 lp/mm), the energy resolution (< 100 eV) and the radiation damage versus the X-ray dose (< 200 Gy) have been evaluated in the energy range from 40 eV to 2000 eV. In order to illustrate the capabilities of this new sCMOS-BSI sensor, several experiments have been performed at three soft x-ray beamline of the SOLEIL synchrotron: diffraction pattern from a pinhole at 186 eV, scattering experiment from nanostructured Co/Cu multilayer at 700 eV and Ptychoraphy imaging in transmission at 706 eV