X-ray imaging with off-axis Bragg Fresnel multilayer lenses

We analyse the possibilities of using a new kind of Bragg Fresnel Multilayer Lens that we have designed in order to improve image contrast[1]. We discuss the aberrations and the dynamical properties of this lens on the base of a recently developed dynamical theory[2] and of the data from the first imaging tests that we have performed. The principle of the optimal configuration for utilisation of these lenses is given

Submicrometre resolution phase-contrast radiography with the beam from an X-ray waveguide

Experimental data with unprecedented submicrometre resolution obtained in a phase-contrast radiography experiment in a magnifying configuration are presented. The term `phase contrast' here indicates that the phase retardation of coherent light in matter was utilized as the contrast mechanism. The coherent and divergent beam exiting an X-ray waveguide was used in a lensless configuration to magnify spatial variations in optical path length up to several hundred times. The defocused image of a nylon fibre was measured with a resolution of 0.14 µm at the object. Sufficient contrast was found for exposure times of 0.1 s, i.e. in the regime for real-time studies

Supersonic-to-subsonic transition of a radiation wave observed at the LMJ

International audienceWe detail results of an experiment performed at the Laser Mégajoule (LMJ) facilityaimed at studying transition from supersonic radiation front to shock front in a lowdensity CHOBr foam enclosed in a plastic tube driven by thermal emission producedin a laser heated spherical gold cavity. Time resolved 2D hard x-ray radiographyimaging using a Sc source (photon energy at ~ 4.3 keV) is employed to measure thedensity perturbation front position, absorption, curvature and shocked materialcompression (defined as the compressed foam density normalized to its nominal value)from the supersonic to the subsonic regimes of propagation. Between these two regimeswhere compression goes from 1 (limited hydrodynamics) to 4 (strong shock formed), aquick increase of the foam compression is observed at the transition time tHS =6.75±0.75 ns, corresponding to the transient transonic regime (HS means“hydrodynamically separated” and refers to the instant when the shock and the radiationfront physically separate). This time is associated to a foam compression ratio of ~2and a Mach number of the slowing down front below M < 2. Experimental results aresuccessfully compared to 3D hydrodynamics simulations; comparisons never presentedfor that regime in past similar studies to our knowledge. Simulations show that thetransition time tHS is sensitive to the radiation closure of the tube entrance. This closure, which occurs in 3D, affects the amount of x-ray energy coupled from the laser heatedcavity to the CHOBr foam, and consequently the transient transonic regime dynamics

Extensive characterization of Marshak waves observed at the LIL laser facility

International audienceWe detail results of an experiment performed at the Ligne d'Intégration Laser (LIL) facility aimed at studying supersonic and diffusive radiation front propagation in low density SiO2 aerogel (20 and 40 mg/cm 3) enclosed in a gold tube, driven by thermal emission from a laserheated spherical gold cavity. Evolution of the front is studied continuously by measuring its self-emission with a 1D (1 dimensional) time resolved soft-x-ray imager. Measurement is performed along (through a 200 µm wide observation slit) and at the exit of the tube giving access to the dynamics and the curvature of the front. Experimental results are then compared successfully to results from the 3D (3 dimensional) radiation hydrodynamics code TROLL which shows that if continuous tracking of the front position is accessible with this experimental scheme, measurement of its maximum radiation temperature is on the contrary affected by radiation closure of the observation slit. 3D simulations also indicate that this effect can even be worsened if one includes pointing errors of the x-ray imager. Radiation temperature along the tube was then inferred by combining results from the imager to a wall shock breakout time measurement using a VISAR and results from a broadband x-ray spectrometer used to determine the temperature at the exit of the tube. A decrease of the radiation temperature along the tube is observed, the decrease being more important for the higher SiO2 aerogel density

Testing of submicrometer fluorescence microprobe based on Bragg-Fresnel crystal optics at the ESRF

International audienceHard x-ray phase zone plate fabricated by lithographic techniques Applied Physics Letters 61, 1877 (1992); https://doi. Hard x-ray microprobe with total-reflection mirrors Review of Scientific Instruments 63, 578 (1992); https://doi.org/10.1063/1.1142710 The recent development of Bragg-Fresnel crystal optics. Experiments and applications at the ESRF (invited) Review of Scientific Instruments 66, 2053 (1995); https://doi. An x-ray fluorescence microprobe with circular Bragg-Fresnel lens was tested at the European Synchrotron Radiation Facility Microfocus beamline. A focal spot of 0.7 ,um was observed using the knife-edge technique at the energy 7.6 keV (wavelength 1.6 A). The intensity in the focal spot was measured to lo* ph/s in energy bandwidth of 10m5. The fluorescence microprobe was applied for mapping 100 pm size micrometeorite at 13.5 keV. 0 1995 American Znstitute ofPhysics

Laser Smoothing and Imprint Reduction with a Foam Layer in the Multikilojoule Regime

International audienceThis Letter presents first experimental results of the laser imprint reduction in fusion scale plasmas using a low-density foam layer. The experiments were conducted on the LIL facility at the energy level of 12 kJ with millimeter-size plasmas, reproducing the conditions of the initial interaction phase in the direct-drive scheme. The results include the generation of a supersonic ionization wave in the foam and the reduction of the initial laser fluctuations after propagation through 500  μm of foam with limited levels of stimulated Brillouin and Raman scattering. The smoothing mechanisms are analyzed and explained

Overview of on-going LIL experiments

The Ligne d'Integration Laser (LIL) facility has been designed as a prototype for the Laser MegaJoule (LMJ) which is a cornerstone of the French 'Simulation Program'. This laser has been intensively used to test and improve the LMJ components. In addition, a large panel of plasma diagnostics has been installed and is currently used to perform laser-plasma experiments. After a brief discussion about the LIL design, we present the last results in various plasma physics domains.</p