Artifacts reduction in high-acutance phase images for X-ray grating interferometry.

X-ray grating-based techniques often lead to artifacts in the phase retrieval process of phase objects presenting very fast spatial transitions or sudden jumps, especially in the field of non-destructive testing and evaluation. In this paper, we present a method that prevents the emergence of artifacts by building an interferogram corrected from any variations of the object intensity and given as input in the phase retrieval process. For illustration, this method is applied to a carbon fiber specimen imaged by a microfocus X-ray tube and a single 2D grating. A significant reduction of artifacts has been obtained, by a factor higher than 10. This evaluation has been performed experimentally thanks to the Confidence Map tool, a recently developed method that estimates the error distribution from the phase gradient information.

Confidence map tool for gradient-based X-ray phase contrast imaging.

We present a graphical tool that we call a "confidence map". It allows to evaluate locally the quality of a phase image retrieved from the measurement of its gradients. The tool is primarily used to alert the observer to the presence of artifacts that could affect his interpretation of the image. It can also be used to optimize a phase imager since it associates a cause with the creation of each artifact: dislocation, under-sampling and noise. An illustration of the use of the confidence map tool is presented, based on a microfocus X-ray tube using multilateral shearing interferometry, a gradient based phase contrast technique employing a single 2D-grating.

First pump-probe-probe hard X-ray diffraction experiments with a 2D hybrid pixel detector developed at the SOLEIL synchrotron.

A new photon-counting camera based on hybrid pixel technology has been developed at the SOLEIL synchrotron, making it possible to implement pump-probe-probe hard X-ray diffraction experiments for the first time. This application relies on two specific advantages of the UFXC32k readout chip, namely its high frame rate (50 kHz) and its high linear count rate (2.6 × 106 photons s-1 pixel-1). The project involved the conception and realization of the chips and detector carrier board, the data acquisition system, the server with its specific software, as well as the mechanical and cooling systems. This article reports on in-laboratory validation tests of the new detector, as well as on tests performed at the CRISTAL beamline within the targeted experimental conditions. A benchmark experiment was successfully performed, showing the advantages of the pump-probe-probe scheme in correcting for drifts of the experimental conditions.

FemtoMAX - an X-ray beamline for structural dynamics at the short-pulse facility of MAX IV.

The FemtoMAX beamline facilitates studies of the structural dynamics of materials. Such studies are of fundamental importance for key scientific problems related to programming materials using light, enabling new storage media and new manufacturing techniques, obtaining sustainable energy by mimicking photosynthesis, and gleaning insights into chemical and biological functional dynamics. The FemtoMAX beamline utilizes the MAX IV linear accelerator as an electron source. The photon bursts have a pulse length of 100 fs, which is on the timescale of molecular vibrations, and have wavelengths matching interatomic distances (Å). The uniqueness of the beamline has called for special beamline components. This paper presents the beamline design including ultrasensitive X-ray beam-position monitors based on thin Ce:YAG screens, efficient harmonic separators and novel timing tools.

Underwater acoustic wave generation by filamentation of terawatt ultrashort laser pulses.

Acoustic signals generated by filamentation of ultrashort terawatt laser pulses in water are characterized experimentally. Measurements reveal a strong influence of input pulse duration on the shape and intensity of the acoustic wave. Numerical simulations of the laser pulse nonlinear propagation and the subsequent water hydrodynamics and acoustic wave generation show that the strong acoustic emission is related to the mechanism of superfilamention in water. The elongated shape of the plasma volume where energy is deposited drives the far-field profile of the acoustic signal, which takes the form of a radially directed pressure wave with a single oscillation and a very broad spectrum.

Underwater acoustic signals induced by intense ultrashort laser pulse.

Acoustic signals generated in water by terawatt (TW) laser pulses undergoing filamentation are studied. The acoustic signal has a very broad spectrum, spanning from 0.1 to 10 MHz and is confined in the plane perpendicular to the laser direction. Such a source appears to be promising for the development of remote laser based acoustic applications.