Pascal Mercère

A high-intensity highly coherent soft X-ray femtosecond laser seeded by a high harmonic beam

Synchrotrons have for decades provided invaluable sources of soft X-rays, the application of which has led to significant progress in many areas of science and technology. But future applications of soft X-rays—in structural biology, for example—anticipate the need for pulses with much shorter duration (femtoseconds) and much higher energy (millijoules) than those delivered by synchrotrons. Soft X-ray free-electron lasers should fulfil these requirements but will be limited in number; the pressure on beamtime is therefore likely to be considerable. Laser-driven soft X-ray sources offer a comparatively inexpensive and widely available alternative, but have encountered practical bottlenecks in the quest for high intensities. Here we establish and characterize a soft X-ray laser chain that shows how these bottlenecks can in principle be overcome. By combining the high optical quality available from high-harmonic laser sources (as a seed beam) with a highly energetic soft X-ray laser plasma amplifier, we produce a tabletop soft X-ray femtosecond laser operating at 10 Hz and exhibiting full saturation, high energy, high coherence and full polarization. This technique should be readily applicable on all existing laser-driven soft X-ray facilities.

Hartmann wave-front measurement at 13.4 nm with λ EUV /120 accuracy

We report, for the first time to our knowledge, experimental demonstration of wave-front analysis via the Hartmann technique in the extreme ultraviolet range. The reference wave front needed to calibrate the sensor was generated by spatially filtering a focused undulator beam with 1.7- and 0.6-microm-diameter pinholes. To fully characterize the sensor, accuracy and sensitivity measurements were performed. The incident beams wavelength was varied from 7 to 25 nm. Measurements of accuracy better than lambdaEUV/120 (0.11 nm) were obtained at lambdaEUV = 13.4 nm. The aberrations introduced by an additional thin mirror, as well as wave front of the spatially unfiltered incident beam, were also measured.

Development of fast, simultaneous and multi-technique scanning hard X-ray microscopy at Synchrotron Soleil

A distributed fast-acquisition system for synchronized multi-technique experiments is presented, in which the collection of metadata and the asynchronous merging of large data volumes from multiple detectors are managed as part of the data collection process. This fast continuous scanning scheme, named FLYSCAN, enables measurement of microscopy data on a timescale of milliseconds per pixel. Proof-of-principle multi-technique experiments, namely scanning X-ray fluorescence spectrometry combined with absorption, differential phase contrast and dark-field imaging, have been performed on biological and geological samples.

Quadriwave lateral shearing interferometry in an achromatic and continuously self-imaging regime for future x-ray phase imaging

We present in this Letter a type of quadriwave lateral shearing interferometer for x-ray phase imaging. This device is based on a phase chessboard, and we take advantage of the large spectrum of the source to produce interferograms with a propagation-invariant contrast. Such a grating has been created for hard x-ray interferometry and experimentally tested on a synchrotron beamline at Soleil.

Automatic alignment of a Kirkpatrick-Baez active optic by use of a soft-x-ray Hartmann wavefront sensor.

We present what we believe to be the first automatic alignment of a synchrotron beamline by the Hartmann technique. Experiments were performed, in the soft-x-ray range (E=3 keV, lambda=0.414 nm), by using a four-actuator Kirkpatrick-Baez (KB) active optic. A system imaging the KB focal spot and a soft-x-ray Hartmann wavefront sensor were used alternatively to control the KB optic. The beam corrected with the help of the imaging system was used to calibrate the wavefront sensor. With both closed loops, we focused the beam into a 6.8 microm x 9 microm FWHM focal spot.

High-efficiency zone-plate optics for multi-keV X-ray focusing

High-efficiency nanofocusing of hard X-rays using stacked multilevel Fresnel zone plates with a smallest zone width of 200 nm is demonstrated. The approach is to approximate the ideal parabolic lens profile with two-, three-, four- and six-level zone plates. By stacking binary and three-level zone plates with an additional binary zone plate, the number of levels in the optical transmission function was doubled, resulting in four- and six-level profiles, respectively. Efficiencies up to 53.7% focusing were experimentally obtained with 6.5 keV photons using a compact alignment apparatus based on piezoelectric actuators. The measurements have also been compared with numerical simulations to study the misalignment of the two zone plates.

X-ray phase contrast imaging and noise evaluation using a single phase grating interferometer.

In this paper we present some quantitative measurements of X-ray phase contrast images and noise evaluation obtained with a recent grating based X-ray phase contrast interferometer. This device is built using a single phase grating and a large broadband X-ray source. It was calibrated using a reference sample and finally used to perform measurements of a biological fossil: a mosquito trapped in amber. As phase images, noise was evaluated from the measured interferograms.

Energy resolution of the CdTe-XPAD detector: calibration and potential for Laue diffraction measurements on protein crystals.

The XPAD3S-CdTe, a CdTe photon-counting pixel array detector, has been used to measure the energy and the intensity of the white-beam diffraction from a lysozyme crystal. A method was developed to calibrate the detector in terms of energy, allowing incident photon energy measurement to high resolution (approximately 140 eV), opening up new possibilities in energy-resolved X-ray diffraction. In order to demonstrate this, Laue diffraction experiments were performed on the bending-magnet beamline METROLOGIE at Synchrotron SOLEIL. The X-ray energy spectra of diffracted spots were deduced from the indexed Laue patterns collected with an imaging-plate detector and then measured with both the XPAD3S-CdTe and the XPAD3S-Si, a silicon photon-counting pixel array detector. The predicted and measured energy of selected diffraction spots are in good agreement, demonstrating the reliability of the calibration method. These results open up the way to direct unit-cell parameter determination and the measurement of high-quality Laue data even at low resolution. Based on the success of these measurements, potential applications in X-ray diffraction opened up by this type of technology are discussed.

Metrology and Tests beamline at SOLEIL Design and first results

The objectives of this project is install at the 2.75 GeV SOLEIL synchrotron radiation source a calibration and metrology test facility for the R&D of optical components and detectors. We have build, on a bending magnet, two branches to cover an energy range from few eV to 28 keV and give access to white beam. This installation will first address the needs of the SOLEIL experimental groups (Optics and Detectors) and will be used by a large community. This beamline will also be valuable as a general‐purpose beamline to prepare, test and set up a wide range of experiments in the field of Astrophysics, laser plasma etc … A complementary important aspect of this installation is the realization of primary standard: the metrology beamline of SOLEIL could become the national primary standard source in collaboration with the Laboratoire National d’Essais (LNE) and help in the design and characterization of several diagnostics for the Megajoule Laser in Bordeaux in collaboration with the CEA DIF. The beamline has ...

Hartmann wavefront sensor and adaptive X-ray optics developments for synchrotron applications

We report on the design and performances of a test prototype active X-ray mirror developed for the French national synchrotron radiation facility SOLEIL in collaboration with a French company ISP System. The active mirror uses 11 mechanical actuators: one actuator for the main curvature and 10 actuators along the mirror surface for correction of the residual shape errors. Its radius of curvature can be adjusted from infinity down to 50 m, with residual slope errors in correction less than 0.6 μrad RMS over a 300 mm useful length. A dedicated X-ray Hartmann wavefront sensor, based on YAG:Ce wavelength conversion to visible light, was developed for feedback control of the mirror. Closed-loop experiments were performed at 10 keV on the Metrology and Tests Beamline at SOLEIL.