O. Peyrusse

Kinetic to thermal energy transfer and interpenetration in the collision of laser-produced plasmas

An experimental and numerical analysis of the collision of two plasmas produced from laser-exploded Al/Al and Al/Mg pairs of foils is presented. Various imaging and spectroscopic x-ray techniques have been used to diagnose the collision over a broad range of intertarget distances and laser intensities. Ion temperatures in the 10 keV range have been measured from Doppler broadening. Electron temperatures and densities have been deduced from line ratios and interpenetration distances have been determined by the spatial extent of Mg and Al x-ray lines. Eulerian multifluid simulations have been developed and coupled to atomic physics postprocessing. The comparison of the measurements with these simulations shows that interpenetration prevails at large intertarget distances and high laser intensities; kinetic to thermal energy transfer then takes place on a ∼200-μm wide region and during ∼150 ps.

High-power 1 kHz laser-plasma x-ray source for ultrafast x-ray absorption near-edge spectroscopy in the keV range

A high average power broadband x-ray source is developed in the multi-keV range, based on the thermal emission of plasmas produced with a 1 kHz fs laser focused on high Z element target. This compact ultrafast x-ray source is used to measure the x-ray absorption near-edge spectroscopy of aluminum K-edge (1.559 keV) with noise lower than 1% of the absorption edge when accumulating laser shots over a few tens of seconds. That demonstrates its suitability to study atomic and electronic structures of matter during ultrafast phase transitions among solid, liquid, or higher energy density states.

X-ray absorption for the study of warm dense matter

A time-resolved ultrafast x-ray spectrometer is developed in order to extract the x-ray absorption near-edge spectroscopy (XANES) structure of an Al sample in the warm dense matter regime. In this context, an intense, broadband, short (ps) x-ray source based on the M-band emission from high-Z plasmas is optimized to maximize the photon flux around the Al K-edge. An experiment is reported, devoted to probe a solid Al foil isochorically heated by laser-produced protons up to 3?eV. The experimental x-ray spectra lead to an estimation of the electron temperature with an accuracy of 15%. In good agreement with two different theoretical approaches, the observed progressive smoothing of the XANES structures is clearly related to a significant loss of ion?ion correlation.

Effective superconfiguration temperature and the radiative properties of nonlocal thermodynamical equilibrium hot dense plasma

The model of superconfiguration (SC) temperatures has been used extensively for computing the population dynamics of very large systems in hot dense plasmas. Plasmas of Ge, Xe, and Au have been studied for a wide range of values of Te and Ne. For plasmas containing a distribution of a dozen of ionization states, two systems of a few hundreds of linear equations are solved, with one equation per SC. The power of the method lies in the possibility of determining the populations of all the electronic configurations belonging to those SCs. This opens the way to detailed modeling of complex spectra and to calculations of emissivities and opacities in laser-plasma simulations and experiments.

Temperature and electron density measurements on laser driven radiative shocks

In this paper, new results on radiative shocks generated by a high power laser in a xenon gas cell are presented. Several shock parameters were measured: temperature, radial expansion and velocity, as well as the electron density in the radiative precursor and its velocity. Multiple laser shot allowed the investigation of physical trends changing initial conditions (laser energy and initial gas pressure). Results are compared with one- and two-dimensional radiative hydrodynamic simulations. The experiments were carried out at the LULI Laboratory.

Broad M-band multi-keV x-ray emission from plasmas created by short laser pulses

The investigation of the broad M-band x-ray emission from high-Z plasmas created by a laser, with a 30 fs to 3 ps pulse duration and achieving 1015–17 W/cm2 on target, is reported. Experimental emission spectra are measured in the energy range from 1.50 to 1.75 keV and discussed as potential backlighting x-ray sources for time-resolved x-ray absorption spectroscopy studies. They are compared with theoretical nonlocal thermodynamic equilibrium calculations of x-ray emission.

Density and Temperature Measurements on Laser Generated Radiative Shocks

This paper presents some recent measurements on radiative shocks generated in a xenon gas cell using high power laser. We show new results on temperature and electronic density, and on radial expansion of the shock at various initial conditions (laser energy and gas pressure). The data obtained are compared with one-dimensional and two-dimensional hydro simulations.

EXPERIMENTAL AND NUMERICAL ANALYSIS OF A PLASMA COLLISION BY X-RAY SPECTROSCOPY AND IMAGING

Abstract The collision of two counter-streaming plasmas produced with laser-exploded thin foils has been diagnosed by x-ray imaging and spectroscopy. The time-history of the emission of the aluminium (1s2-1s3p) Heβ line has been measured for different inter-target distances and laser intensities. Interpenetration has been observed for different plasma conditions by following the spatial extent of Mg and Al x-ray lines. Doppler broadening of the Al Heβ line has been measured and is under analysis for ion temperature determination, taking into account reabsoption along the line of sight of the spectrograph. Comparison of the experimental data with a hydrodynamic code describing the interpenetrating plasmas and coupled with a radiative atomic package gives good overall agreement with the measurements of interpenetration and the history of the collision.

Polarization induced modification of thermal radiative properties of solid density plasmas produced by subpicosecond laser

Near solid density plasmas have been obtained by the interaction of ultraintense (2×1018 W cm−2) clean laser pulses with targets composed of different thickness of Al on a Si substrate. The depth of the x-ray emission and spectral shapes were measured using x-ray spectroscopy, which simultaneously characterized the emitting plasma and the suprathermal electron distribution. Strong modifications of the plasmas thermal radiative properties have been observed, for the first time, by changing the laser polarization from S to P. This correlates with an increase of suprathermal electrons production.

X-ray Spectroscopy of Hot Dense Plasmas: Experimental Limits^ Line Shifts & Field Effects

High‐resolution x‐ray spectroscopy is capable of providing complex information on environmental conditions in hot dense plasmas. Benefiting from application of modern spectroscopic methods, we report experiments aiming at identification of different phenomena occurring in laser‐produced plasma. Fine features observed in broadened profiles of the emitted x‐ray lines and their satellites are interpreted using theoretical models predicting spectra modification under diverse experimental situations.