Ion emission from warm dense matter produced by irradiation with a soft x-ray free-electron laser

We report on an experiment performed at the FLASH2 free-electron laser(FEL)aimed at producing warm dense matter via soft x-ray isochoric heating.In the experiment,we focus on study of the ions emitted during the soft x-ray ablation process using time-of-flight electron multipliers and a shifted Maxwell–Boltzmann velocity distribution model.We find that most emitted ions are thermal,but that some impurities chemisorbed on the target surface,such as protons,are accelerated by the electrostatic field created in the plasma by escaped electrons.The morphology of the complex crater structure indicates the presence of several ion groups with varying temperatures.We find that the ion sound velocity is controlled by the ion temperature and show how the ion yield depends on the FEL radiation attenuation length in different materials.

Dynamically pre-compressed hydrocarbons studied by self-impedance mismatch

Using the SG-III prototype laser at China Academy of Engineering Physics,Mianyang,we irradiated polystyrene(CH)samples with a thermal radiation drive,reaching conditions on the principal Hugoniot up to P≈1 TPa(10 Mbar),and away from the Hugoniot up to P≈300 GPa(3 Mbar).The response of each sample was measured with a velocity interferometry diagnostic to determine the material and shock velocity,and hence the conditions reached,and the reflectivity of the sample,from which changes in the conductivity can be inferred.By applying the selfimpedance mismatch technique with the measured velocities,the pressure and density of thermodynamic points away from the principal Hugoniot were determined.Our results show an unexpectedly large reflectivity at the highest shock pressures,while the off-Hugoniot points agree with previous work suggesting that shock-compressed CH conductivity is primarily temperature-dependent.

Alignment of solid targets under extreme tight focus conditions generated by an ellipsoidal plasma mirror

The design of ellipsoidal plasma mirrors(EPMs)for the PEARL laser facility is presented.The EPMs achieve a magnification of 0.32 in focal spot size,and the corresponding increase in focused intensity is expected to be about 8.Designing and implementing such focusing optics for short-pulse(<100 fs)systems paves the way for their use in future high-power facilities,where they can be used to achieve intensities beyond 1023W/cm^(2).A retro-imaging-based target alignment system is also described,which is used to align solid targets at the output of the ellispoidal mirrors(with a numerical aperture of 0.75 in this case).

Morphology and Properties of Hybrid Systems Comprising Gold Nanoparticles in CuPc Matrices

Transmission electron microscopy and surface- and bulk-sensitive spectroscopic methods were used to study the morphology and the electronic structure of a hybrid organic-inorganic system composed of gold nanoparticles （NP＇s） which were distributed in an organic matrix. Au atoms deposited onto a copper phthalocyanine （CuPc） surface diffuse into the organic matrix and self-assemble in well defined NP＇s with metallic properties. No formation of a continuous metallic Au film on top of the CuPc film is observed up to nominal coverages as large as 130 A.

Morphology and Electronic Properties of Hybrid Organic-Inorganic System: Ag Nanoparticles Embedded into CuPc Matrix

Materials with a high on-off resistance ratio could become the basis for resistive random-access memory (RRAM). It is assumed that one of RRAM types can be based on hybrid organic-inorganic systems, while particular attention is focused on hybrid systems consisting of metal nanoparticles (NP) embedded in organic matrix (OM). In this investigation we created and studied the hybrid organic-inorganic systems made of metal (Ag) nanoparticles embedded in organic semiconductor material CuPc. The LEED patterns and NEXAFS data demonstrate that the CuPc films deposited on Au(001) substrate are highly ordered and molecular planes lie parallel to the gold surface. The metal atoms were deposited on the outer surface of the organic molecular film and self-assembled into nanoparticles due to surface and bulk diffusion. The properties of nano-composite materials seem to be significantly dependent on the microstructure, i.e. the size, concentration, bulk- and size-distribution of nanoparticles;therefore we have studied by high resolution transmission electron microscopy the evolution of morphology of nano-composite films as a function of nominal metal deposition. The filled and empty electronic states of the hybrid organic-inorganic systems, energy level alignment at interfaces formed between metal nanoparticles and the organic semiconductor CuPc as well as the chemical interaction at the NP/OM interface were studied by UPS, XPS and NEXAFS methods.

The European X-ray Free-Electron Laser: toward an ultra-bright, high repetition-rate x-ray source

The status of the European X-ray Free-Electron Laser(European XFEL), under construction near Hamburg, Germany, is described. The start of operations of the LCLS at SLAC and of SACLA in Japan has already produced impressive scientific results. The European XFEL facility is powered by a 17.5 Ge V superconducting linear accelerator that,compared to these two operating facilities, will generate two orders of magnitude more pulses per second, up to 27 000.It can therefore support modes of operation switching the beam up to 30 times per second among three different experiments, providing each of them with thousands of pulses per second. The scientific possibilities opened up by these capabilities are briefly described, together with the current instrumental developments(in optics, detectors, lasers,etc.) that are necessary to implement this program.

Phase imaging of irradiated foils at the OMEGA EP facility using phase-stepping X-ray Talbot–Lau deflectometry

Diagnosing the evolution of laser-generated high energy density(HED)systems is fundamental to develop a correct understanding of the behavior of matter under extreme conditions.Talbot–Lau interferometry constitutes a promising tool,since it permits simultaneous single-shot X-ray radiography and phase-contrast imaging of dense plasmas.We present the results of an experiment at OMEGA EP that aims to probe the ablation front of a laser-irradiated foil using a Talbot–Lau X-ray interferometer.A polystyrene(CH)foil was irradiated by a laser of 133 J,1 ns and probed with 8 keV laser-produced backlighter radiation from Cu foils driven by a short-pulse laser(153 J,11 ps).The ablation front interferograms were processed in combination with a set of reference images obtained ex situ using phase-stepping.We managed to obtain attenuation and phase-shift images of a laser-irradiated foil for electron densities above 1022 cm−3.These results showcase the capabilities of Talbot–Lau X-ray diagnostic methods to diagnose HED laser-generated plasmas through high-resolution imaging.

An accelerator scenario for a hard X-ray free electron laser combined with high energy electron radiography

In order to study the dynamic response of the material and the physical mechanism of fluid dynamics, an accelerator scenario which can be applied to both hard X-ray free electron laser and high energy electron radiography is proposed. This accelerator is mainly composed of a 12 GeV linac, an undulator branch and an eRad beamline. In order to characterize a sample＇s dynamic behavior in situ and real-time with XFEL and eRad simultaneously, the linac should be capable of accelerating the two kinds of beam within the same operation mode. Combining in-vacuum and tapering techniques, the undulator branch can produce more than 10zl photons per pulse in 0.1% bandwidth at 42 keV. Finally, an eRad amplifying beamline with 1：10 ratio is proposed as an important complementary tool for the wider view field and density identification ability.

Modeling of ultrafast X-ray induced magnetization dynamics in magnetic multilayer systems

In this work,we report on modeling results obtained with our recently developed simulation tool enabling nanoscopic description of electronic processes in X-ray irradiated ferromagnetic materials.With this tool,we have studied the response of Co/Pt multilayer system irradiated by an ultrafast extreme ultraviolet pulse at the M-edge of Co(photon energy~60 eV).It was previously investigated experimentally at the FERMI free-electron-laser facility,using the magnetic small-angle X-ray scattering technique.Our simulations show that the magnetic scattering signal from cobalt decreases on femtosecond timescales due to electronic excitation,relaxation,and transport processes both in the cobalt and in the platinum layers,following the trend observed in the experimental data.The confirmation of the predominant role of electronic processes for X-ray induced demagnetization in the regime below the structural damage threshold is a step toward quantitative control and manipulation of X-ray induced magnetic processes on femtosecond timescales.