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International audience; We present an experiment performed in 2016 at the LULI2000 laser facility in which X-ray and XUV absorption structures of nickel hot plasmas were measured simultaneously. Such experiments may provide stringent tests of the accuracy of plasma atomic-physics codes used to the modeling of plasmas close to local thermodynamic equilibrium. The experimental setup relies on a symmetric heating of the sample foil by two gold hohlraums in order to reduce the spatial gradients. The plasma conditions are characterized by temperatures between 10 and 20 eV and densities of the order of 10$^{−3}$ g/cm $^3$-10$^{−2}$ g/cm$^3$. For the X-ray part, we investigate the 2p-3d and 2p-4d transitions, and for the XUV part, we recorded the $\Delta$n = 0 (n = 3) transitions, which present a high sensitivity to plasma temperature. These latter transitions are of particular interest because, in mid-Z plasmas, they dominate the Planck and Rosseland mean opacities. Measured spectra are compared to calculations performed using the hybrid opacity code SCO-RCG and the Flexible Atomic Code (FAC). The influence of a spectator electron on the calculated spectra is analyzed using the latter code.

International audience; A good knowledge of absorption properties of plasmas at temperature of few tens of eV is essential in several domains such as astrophysics and inertial fusion science. For instance the description of stellar envelopes or the analysis of beta-Cephei pulsation requires an accurate determination of the Rosseland absorption coefficient, which strongly depends on the radiative properties of plasmas in the extreme-UV (XUV) range. Contrary to measurements in X-ray range, the literature on the absorption properties of plasmas of mid-Z elements in XUV domain is less abundant. Furthermore the theoretical interpretation of such spectra represents a theoretical challenge since this energy range involves transition arrays from n equal 3 to 3 with an approximately half-open 3d subshell and possibly other open spectator subshells which contain a huge number of lines. The aim of this paper is to describe an experiment recently performed on the LULI 2000 laser facility mostly devoted to measurements of the absorption in the 60-180 eV spectral region in a copper plasma at a temperature of 10 to 30 eV and a density of few mg/cm$^3$. The experimental scheme is based on an indirect heating of multilayer thin foils by two gold cavities irradiated by two nanosecond doubled-frequency beams with an energy of several hundreds of J. This scheme allows one to obtain moderate temperature-and density-gradients and ensures conditions close to local thermodynamic equilibrium. The self-emission of cavities in XUV range is tentatively eliminated by the use of a time-dependent detection. A preliminary interpretation of these measurements is proposed. This analysis relies on three different codes: the hybrid code SCO-RCG, the Flexible Atomic Code in detailed or configuration-average mode, and the HULLAC code in level or configuration mode. A partial agreement is obtained between theory and experiment, though the account for temperature gradients is probably necessary to accurately describe the present measurements.

Collisional-radiative atomic models are widely used to help diagnose experimental plasma conditions through fitting and interpreting measured spectra. Here we present the results of a code comparison in which a variety of models determined plasma temperatures and densities by finding the best fit to an experimental L-shell Kr spectrum from a well characterized, but not benchmarked, laser plasma. While variations in diagnostic strategies and qualities of fit were significant, the results generally confirmed the typically quoted uncertainties for such diagnostics of ±20% in electron temperature and factors of about two in density. The comparison also highlighted some model features important for spectroscopic diagnostics: fine structure was required to match line positions and relative intensities within each charge state and for density diagnostics based on emission from metastable states; an extensive configuration set was required to fit the wings of satellite features and to reliably diagnose the temperature through the inferred charge state distribution; and the inclusion of self-consistent opacity effects was an important factor in the quality of the fit.

We discuss the role of Configuration Interaction (CI) and the influence of the number of configurations taken into account in the calculations of nickel and iron spectral opacities provided by the OPAC international collaboration, including statistical approaches (SCO, CASSANDRA, STA), detailed accounting (OPAS, LEDCOP, OP, HULLAC-v9) or hybrid method (SCO-RCG). Opacity calculations are presented for a temperature T of 27.3 eV and a density of 3.4 mg/cm 3 , conditions relevant for pulsating stellar envelopes.

We analyzed the spectra of X-ray transmission through radiatively heated medium-Z plasma (Fe, Ni, Cu and Ge) measured at LULI2000 facility in the wavelength range of 2p–nd transitions. The analysis was performed using the statistical superconfiguration code SCO, two line-by-line opacity codes based on the HULLAC and FAC packages and a new hybrid statistical-detailed code SCORCG. The temperature and mass density of the samples were estimated from hydrodynamic simulations based on the cavity radiative temperature measurements. The theory–experiment agreement is relatively good in the wavelength range corresponding to the 2p–3d transitions except in the germanium case. In the wavelength range of the 2p–2d, n > 3 transitions a relatively good theory–experiment agreement was found in the copper case. As predicted by calculations the separation of the characteristic spin-orbit-split 2p–3d structures, absent in the iron measured spectrum, appears in the nickel spectrum and is visible in the copper and germanium spectra. Comparisons of the experimental transmission with calculations confirm the importance of the relativistic configuration interaction. The absorption strength of the measured germanium 2p–3d transition is much larger than that obtained from the codes. Spatial temperature and density gradients, relatively high in the germanium sample, may be at the origin of this discrepancy.

Opacity is an important ingredient of the evolution of stars. The calculation of opacity coefficients is complicated by the fact that the plasma contains partially ionized heavy ions that contribute to opacity dominated by H and He. Up to now, the astrophysical community has greatly benefited from the work of the contributions of Los Alamos [1], Livermore [2] and the Opacity Project (OP) [3]. However unexplained differences of up to 50% in the radiative forces and Rosseland mean values for Fe have been noticed for conditions corresponding to stellar envelopes. Such uncertainty has a real impact on the understanding of pulsating stellar envelopes, on the excitation of modes, and on the identification of the mode frequencies. Temperature and density conditions equivalent to those found in stars can now be produced in laboratory experiments for various atomic species. Recently the photo-absorption spectra of nickel and iron plasmas have been measured during the LULI 2010 campaign, for temperatures between 15 and 40 eV and densities of ~3 mg/cm3. A large theoretical collaboration, the "OPAC", has been formed to prepare these experiments. We present here the set of opacity calculations performed by eight different groups for conditions relevant to the LULI 2010 experiment and to astrophysical stellar envelope conditions., 15 pages, 10 figures

Opacities of four medium Z element plasmas (iron, nickel, copper and germanium) have been measured at the LULI-2000 facility in similar conditions: temperatures between 15 and 25 eV and densities between 2 and 10 mg/cm3, in a wavelength range (8–18 A) including the strong 2p–3d structures. Two laser beams from the LULI facility were used in the nanosecond-picosecond configuration. The NANO-2000 beam (at λ = 0.53 μm) heated a gold hohlraum with an energy between 30 and 150 J with a duration of 0.6 ns. Samples covering half a hohlraum hole were thus radiatively heated. The picosecond pulse PICO-2000 beam (at λ = 1.053 μm) has been used to produce a short (about 10 ps) X-ray backlighter in order to reduce time variations of temperatures and densities during the measurement. A crystal high-resolution spectrometer was used as the main diagnostic to record at the same time the non-absorbed and the absorbed backlighter spectra. Radiation temperatures were measured using a broadband spectrometer. 1D and 2D simulations have been performed in order to estimate hydrodynamic plasmas parameters. The measured spectra have been compared with theoretical ones obtained using either the superconfiguration code SCO or the detailed term accounting code HULLAC. These comparisons allow us to check the modeling of the statistical broadening and of the spin-orbit splitting of the 2p–3d transitions and related effects such as the interaction between relativistic subconfigurations belonging to the same non-relativistic configuration.

Conversion efficiencies of laser light into K x-ray radiation are used to characterize laser-solid interactions e.g. in measurements with back-lighter targets in Inertial Confinement Fusion research or in ultra short x-ray science where ultra short laser pulses are used to create x-rays for investigation of dynamic processes. In our measurements we observed high energy (few tens of keV) K x-ray radiation of element pairs created upon impact of a 1 ps, 100 J laser pulse on the target surface. The high-energy electrons created in this interaction ionise and excite the target material. We have used high purity alloy foils of Pd and Ag, as well as In and Sn and crystals of CsI and rare earth molybdates as target materials. Both constituents of these targets were simultaneously excited in one shot. The K x-ray radiation was dispersed and detected with the LCS (LULI Crystal Spectrometer), a Cauchois-type cylindrically bent transmission-crystal spectrometer. Measuring ratios in the x-ray spectra permits determination of relative conversion efficiencies for pairs of elements under identical laser-target interaction conditions.

Thanks to their high dynamic range and ability to withstand electromagnetic pulse, imaging plates (IPs) are commonly used as passive detectors in laser-plasma experiments. In the framework of the development of the diagnostics for the Petawatt Aquitaine Laser facility, we present an absolute calibration and spatial resolution study of five different available types of IP (namely, MS-SR-TR-MP-ND) performed by using laser-induced K-shell X-rays emitted by a solid silver target irradiated by the laser ECLIPSE at CEntre Lasers Intenses et Applications. In addition, IP sensitivity measurements were performed with a 160 kV X-ray generator at CEA DAM DIF, where the absolute response of IP SR and TR has been calibrated to X-rays in the energy range 8-75 keV with uncertainties of about 15%. Finally, the response functions have been modeled in Monte Carlo GEANT4 simulations in order to reproduce experimental data. Simulations enable extrapolation of the IP response functions to photon energies from 1 keV to 1 GeV, of interest, e.g., for laser-driven radiography. © 2016 AIP Publishing LLC.

Point-projection K-shell absorption spectroscopy has been used to measure absorption spectra of transient aluminum plasma created by an ultra-short laser pulse. The 1s-2p and 1s-3p absorption lines of weakly ionized aluminum were measured for an extended range of densities in a low-temperature regime. Independent plasma characterization was obtained using frequency domain interferometry diagnostic (FDI) that allows the interpretation of the absorption spectra in terms of spectral opacities. A detailed opacity code using the density and temperature inferred from the FDI reproduce the measured absorption spectra except in the last stage of the recombination phase.

X and XUV spectra of Xe and Kr were measured in a gas jet irradiated by a 400 J energy, 1.5 ns duration laser pulse. Simultaneously, the plasma was diagnosed by electronic and ionic Thomson scattering. The XUV spectra were time-resolved with a differentially pumped streak camera. Experimental spectra are compared with simulations performed with a NLTE atomic physics model.

The ionization and recombination dynamics of transient aluminum plasmas was measured using point projection K-shell absorption spectroscopy. An aluminum plasma was produced with a subpicosecond beam of the 100-TW laser at the LULI facility and probed at different times with a picosecond X-ray backlighter created with a synchronized subpicosecond laser beam. Fourier-Domain-Interferometry (FDI) was used to measure the electron temperature at the peak of the heating laser pulse. Absorption X-ray spectra at early times are characteristic of a dense and rather homogeneous plasma, with limited longitudinal gradients as shown by hydrodynamic simulations. The shift of the Al K-edge was measured in the cold dense plasma located at the edge of the heated plasma. From the 1s–2p absorption spectra, the average ionization was measured as a function of time and was also modeled with a collisional-radiative atomic physics code coupled with hydrodynamic simulations.

Nous avons mesure le spectre d'absorption en couche K de plasmas d'aluminium a haute densite. Deux faisceaux de la chaine laser femtoseconde 100 TW du LULI (de duree 300 fs) ont ete utilises pour produire le plasma absorbant sur une feuille mince d'Al (830 A ou 500 A), et la source de radiographie sur du samarium massif. Les spectres X etaient resolus spatialement dans une direction perpendiculaire a la direction de la dispersion spectrale. Les spectres ont ete mesures pour differents retards entre la source de radiographie et le plasma d'Al. Des simulations des spectres et de l'ionisation en fonction du temps et de l'intensite, obtenues au moyen de codes hydrodynamiques et de structure atomique, montrent un bon accord avec les resultats experimentaux.

Recent experimental results on ion beams produced in high-intensity laser–solid interactions indicate the presence of very intense electric fields in the target. This suggests the possibility of efficiently heating a solid material by means of the fast electrons created during the laser–solid interactions and trapped in the target, rather than by the laser photons themselves. We tested this mechanism by irradiating very small cubic aluminum targets with the LULI 100-TW, 300-fs laser at 1.06-μm wavelength. X-ray spectra were measured with an ultra-fast streak camera, coupled to a conical Bragg crystal, providing spectra in the 1.5-keV range with high temporal and spectral resolution. The results indicate the creation of a hot plasma, but a very low coupling between the rapid electrons and the solid. A tentative explanation, in agreement with other experimental results and with preliminary particle-in-cell (PIC) simulations, points out the fatal role of the laser prepulse.

X-ray transmission spectra of copper, nickel and aluminum laser produced plasmas were measured at the LULI2000 laser facility with an improved target design of indirect heating. Measurements were performed in plasmas close to local thermodynamic equilibrium at temperatures around 25 eV and densities between 10−3 g/cm3 and 10−2 g/cm3. This improved design provides several advantages, which are discussed in this paper. The sample is a thin foil of mid-Z material inserted between two gold cavities heated by two 300J, 2ω, nanosecond laser beams. A third laser beam irradiates a gold foil to create a spectrally continuous X-ray source (backlight) used to probe the sample. We investigate 2p–3d absorption structures in Ni and Cu plasmas as well as 1s–2p transitions in an additional Al plasma layer to infer the in-situ plasma temperature. Geometric and hydrodynamic calculations indicate that the improved geometry reduces spatial gradients during the transmission measurements. Experimental absorption spectra are in good agreement with calculations from the hybrid atomic physics code SCO-RCG.

Transmission crystal spectrometers (TCS) are used on many laser facilities to record hard X-ray spectra. During experiments, signal recorded on imaging plates is often degraded by a background noise. Monte-Carlo simulations made with the code GEANT4 show that this background noise is mainly generated by diffusion of MeV electrons and very hard X-rays. An experiment, carried out at LULI2000, confirmed that the use of magnets in front of the diagnostic, that bent the electron trajectories, reduces significantly this background. The new spectrometer SPECTIX (Spectrometre PETAL a Cristal en TransmIssion X), built for the LMJ/PETAL facility, will include this optimized shielding.

The international OPAC consortium consists of astrophysicists, plasma physicists and experimentalists who examine opacity calculations used in stellar physics that appear questionable and perform new calculations and laser experiments to understand the differences and improve the calculations. We report on iron and nickel opacities for envelopes of stars from 2 to 14 M ⊙ and deliver our first conclusions concerning the reliability of the used calculations by illustrating the importance of the configuration interaction and of the completeness of the calculations for temperatures around 15–27 eV.

Nous presentons les premiers resultats d'une experience realisee sur l'installation LULI2000 du Laboratoire pour l'Utilisation des Lasers Intenses. Au cours de celle-ci, nous avons etudie l'emission X de plasmas de niobium, tantale et tungstene, dans des conditions hors equilibre thermodynamique local (de l'ordre de 1,5 keV en temperature, et 1020 cm−3 en densite electronique). Nous avons mesure le spectre X emis dans la gamme 2,4-2,9 keV a l'aide d'un spectrometre a cristal tronconique. Nous avons egalement mis en place des diagnostics hydrodynamiques (diffusion Thomson et emission propre resolues en temps) afin de bien caracteriser le plasma etudie. Une etude est en cours afin de comparer les mesures aux simulations. Nous comparons les mesures hydrodynamiques au code MULTI pour ajuster certains parametres experimentaux mal connus et determiner l'evolution du plasma, puis utilisons ces resultats dans les calculs de spectres effectues a l'aide du code FLYCHK.

The first experiments on the National Ignition Facility (NIF) in the US started and will be followed by the Laser MegaJoule (LMJ) in France. Such facilities will provide unique tools for inertial confinement fusion (ICF) physics & for basic science. A petawatt short pulse laser (ps) is being added to the ns pulse beams of the LMJ. This is PETAL (PETawatt Aquitaine Laser), under construction on the LMJ site near Bordeaux (France). The Petal+ project is aiming at the design and construction of diagnostics dedicated to experiments with PETAL and LMJ laser beams. Within Petal+, three types of diagnostics are under study: a proton spectrometer, an electron spectrometer and a large-band X-ray spectrometer. The first goal of these diagnostics will be to characterize the secondary radiation and particle sources produced with PETAL. They will also be used for experiments using both ns and ps beams. In the present paper emphasis is put on the charged-particle diagnostics.

The role of self generated magnetic fields in the transport of a heat wave following a nanosecond laser irradiation of a solid target is investigated. Magnetic fields are expected to localize the electron carrying the heat flux but at the same time are affected in their evolution by the heat flux itself. We performed simultaneous measurements of heat wave propagation velocity within the target and magnetic fields developing on the target surface. These were compared to results obtained by numerical magneto-hydrodynamic modeling, including self-generated B fields. The comparison shows that longitudinal heat flow is overestimated in the simulations. Similarly, but most notably, the radial expansion of the magnetic fields is underestimated by the modeling. The two are likely linked, the more pronounced radial drift of B-fields induces a rotation of heat flux in the radial direction, and corresponding longitudinal heat flux inhibition. This suggests the need for improving present modeling of self-generated magnetic fields evolution in high power laser-matter interaction.

This paper will present an experimental platform developed on LULI2000 to measure x-ray emission of non-LTE plasmas in well-defined hydrodynamic conditions thanks to implementation of a whole set of diagnostics, including time-resolved electronic and ionic Thomson scattering and self-optical pyrometry. K-, L- and M-shell spectra will be presented and the methodology, that has been developed to analyze them, discussed.

An x-ray grating spectrometer was built in order to measure opacities in the 50 eV to 250 eV spectral range with an average spectral resolution ⟨E/δE⟩ ∼ 50. It has been used at the LULI-2000 laser facility at Ecole Polytechnique (France) to measure the Δn = 0, n = 3 transitions of several elements with neighboring atomic number: Cr, Fe, Ni, and Cu in the same experimental conditions. Hence a spectrometer with a wide spectral range is required. This spectrometer features one line of sight looking through a heated sample at backlighter emission. It is outfitted with one toroidal condensing mirror and several flat mirrors cutting off higher energy photons. The spectral dispersion is obtained with a flatfield grating. Detection consists of a streak camera sensitive to soft x-ray radiation. Some experimental results showing the performance of this spectrometer are presented.

Seismology of stars is strongly developing. To address this question we have formed an international collaboration OPAC to perform specific experimental measurements, compare opacity calculations and improve the opacity calculations in the stellar codes [1]. We consider the following opacity codes: SCO, CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large differences for Fe and Ni in equivalent conditions of envelopes of type II supernova precursors, temperatures between 15 and 40 eV and densities of a few mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar results and differ from OP ones for the lower temperatures and for spectral interval values [3]. In this work we discuss the role of Configuration Interaction (CI) and the influence of the number of used configurations. We present and include in the opacity code comparisons new HULLAC-v9 calculations [5, 6] that include full CI. To illustrate the importance of this effect we compare different CI approximations (modes) available in HULLAC-v9 [7]. These results are compared to previous predictions and to experimental data. Differences with OP results are discussed., 4 pages, 3 figures, conference Inertial Fusion Sciences and Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences 2012

This paper deals with theoretical studies on the $2p\ensuremath{-}3d$ absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004--0.01 ${\mathrm{g}/\mathrm{cm}}^{3}$. The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of $2p\ensuremath{-}3d$ transitions has been studied with the help of the statistical superconfiguration opacity code sco and with the fine-structure atomic physics codes hullac and fac. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code rcg has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by sco. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the $2p\ensuremath{-}3d$ transitions have been investigated as a function of the atomic number $Z$. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code scric. The sensitivity of the $2p\ensuremath{-}3d$ structures with respect to temperature and density in medium-$Z$ plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the $\ensuremath{\Delta}n=0$ absorption in medium-$Z$ plasmas for astrophysical applications.

We report recent experimental measurements of the duration of a Ni-like Mo transient XUV laser emitted at 18.9 nm and generated under GRIP geometry at the LASERIX facility. These measurements have been performed using an ultra-fast X-ray streak camera (AXIS Photonique). A new trigger line was implemented, yielding a shot-to-shot jitter of less than 10 ps. The KBr photocathode of the streak camera was positioned close to the plane of the magnified near-field image of the XUV laser emitting aperture. Saturation in the streak camera was avoided by carefully adjusting the signal level of the focused image. The sweep speed was calibrated in-situ by generating a double-pulse XUV laser. Finally the temporal resolution of the instrument was measured directly with a femtosecond, high-order harmonic pulse. XUV laser pulse durations as short as 2.8 ps were measured for a 20° GRIP angle and a 0.75 ps GRIP pulse duration. We present and discuss our study of the effect of these two parameters on the measured pulse duration.

This paper deals with theoretical studies on the 2p-3d absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004-0.01 g/cm(3). The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of 2p-3d transitions has been studied with the help of the statistical superconfiguration opacity code SCO and with the fine-structure atomic physics codes HULLAC and FAC. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code RCG has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by SCO. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the 2p-3d transitions have been investigated as a function of the atomic number Z. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code SCRIC. The sensitivity of the 2p-3d structures with respect to temperature and density in medium-Z plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the Δn=0 absorption in medium-Z plasmas for astrophysical applications.

The lifetime of solar-like stars, the envelope structure of more massive stars, and stellar acoustic frequencies largely depend on the radiative properties of the stellar plasma. Up to now, these complex quantities have been estimated only theoretically. The development of the powerful tools of helio- and astero- seismology has made it possible to gain insights on the interiors of stars. Consequently, increased emphasis is now placed on knowledge of the monochromatic opacity coefficients. Here we review how these radiative properties play a role, and where they are most important. We then concentrate specifically on the envelopes of $\beta$ Cephei variable stars. We discuss the dispersion of eight different theoretical estimates of the monochromatic opacity spectrum and the challenges we need to face to check these calculations experimentally., Comment: 6 pages, 5 figures, in press (conference HEDLA 2010)

Proton radiography measurements of self generated magnetic fields developing in long pulse (ns), high‐power laser plasma interactions were employed to investigate the influence of these fields on the propagation of heat flow in dense plasmas. During the experiments, the heat wave propagation speed was measured simultaneously with the fields. These two coupled measurements could give an insight on the limitations of current numerical models of heat transport. They suggest that non locality of heat transport and diffusion of magnetic fields are important to model correctly the interaction.

International audience; We report on a set of experiments in which solid targets of different atomic numbers (Z) were irradiated with laser pulses of time durations ranging from 300 fs to 33 ps, and energies up to 26 J. The time-resolved X-ray emission in the 7.6-8.1 Å spectral range was measured using an ultra-fast X-ray streak camera coupled with a conical Bragg crystal. In this way we were able to follow the dramatic modification of the spectral features as a function of the laser duration. The features evolve from a "ns-type" emission, characterized by narrow and well-defined spectral lines, to very broad spectral features, due not only to the Stark broadening but also to the proliferation of satellites lines. The measured spectra also show strong time dependence, which allows us to follow the time evolution of the hydrodynamic parameters. We then compare the derived parameter with the CHIVAS hydro-radiative simulations. The experimental results are also compared with the AVERROES/TRANSPEC collisional-radiative code, and with precise spectral line shape calculations (PPP and PrismSPECT). The results seem to indicate regimes of interaction where hot electrons play an important role on spectral line formation.

Resume. Nous presentons les resultats d’une experience recente menee sur l’installation laser 100TW du LULI. Dans cette experience, nous avons irradie des cibles solides de differents numeros atomiques avec des impulsions laser d’energie jusqu’a 26 J et de duree allant de 300 fs a 33 ps. Le diagnostic principal etait une camera a balayage de fente, couplee a un cristal de Bragg conique, qui a permis la mesure resolue en temps de l’emission X du plasma cree dans la gamme 7,6–8,1A. Nous avons pu suivre la modification spectaculaire des structures spectrales induite par la diminution de la duree de l’impulsion laser. Le spectre observe evolue d’une forme caracteristique d’une interaction en regime nanoseconde, avec des raies fines et bien resolues, a une forme de type « patatoide », liee a la presence de structures spectrales extremement elargies, soit par effet Stark soit par simple accumulation de raies satellites. Les spectres mesures montrent egalement une tres forte dependance en temps, ce qui permet de determiner l’evolution des parametres hydrodynamiques du plasma emissif et de les comparer aux simulations realisees avec le code d’hydrodynamique radiative CHIVAS. Les resultats experimentaux ont egalement ete confrontes a des simulations faites a l’aide du code collisionnel-radiatif de cinetique atomique AVERROES/TRANSPEC.

A frequency-doubled laser beam of the Nd:glass kilojoule nanosecond LULI2000 facility (1.5 ns duration, 200–400 J energy, 0.53 μm wavelength) was focused on a Xe or Kr gas jet. The plasma was simultaneously diagnosed with X-ray (in the wavelength range of 6–8 A for Kr and of 12–15 A for Xe) and time-resolved XUV (20–200 A) emission spectroscopy. Electron density and temperature as well as the ionization charge were measured by time-resolved Thomson scattering of the heating laser pulse. The spectra are compared with the calculations performed with the NLTE collisional-radiative code AVERROES/TRANSPEC. Best fits of the X-ray and XUV spectra obtained are presented. The measured charge distribution and dynamics is analyzed using the simultaneous Thomson scattering diagnostic.

Point‐projection K‐shell absorption spectroscopy has been used to measure absorption spectra of transient plasma created by an ultra‐short laser pulse. The 1s‐2p and 1s‐3p absorption lines of weakly ionized aluminum and the 2p‐3d absorption lines of bromine were measured over an extended range of densities in a low‐temperature regime. Independent plasma characterization was obtained using frequency domain interferometry diagnostic (FDI) that allows the interpretation of the absorption spectra in terms of spectral opacities. Assuming local thermodynamic equilibrium, spectral opacity calculations have been performed using the density and temperature inferred from the FDI diagnostic to compare to the measured absorption spectra. A good agreement is obtained when non‐equilibrium effects due to non‐stationary atomic physics are negligible at the x‐ray probe time.

International audience; Time-resolved absorption of zinc sulfide (ZnS) and aluminum in the XUV-range has been measured. Thin foils in conditions close to local thermodynamic equilibrium were heated by radiation from laser-irradiated gold spherical cavities. Analysis of the aluminum foil radiative hydrodynamic expansion, based on the detailed atomic calculations of its absorption spectra, showed that the cavity emitted flux that heated the absorption foils corresponds to a radiation temperature in the range 55 60 eV. Comparison of the ZnS absorption spectra with calculations based on a superconfiguration approach identified the presence of species Zn6+ - Zn8+ and S5+ - S6+. Based on the validation of the radiative source simulations, experimental spectra were then compared to calculations performed by post-processing the radiative hydrodynamic simulations of ZnS. Satisfying agreement is found when temperature gradients are accounted for.

We have used point-projection K-shell absorption spectroscopy to infer the ionization and recombination dynamics of transient aluminum plasmas. Two femtosecond beams of the 100 TW laser at the LULI facility were used to produce an aluminum plasma on a thin aluminum foil (83 or 50 nm), and a picosecond x-ray backlighter source. The short-pulse backlighter probed the aluminum plasma at different times by adjusting the delay between the two femtosecond driving beams. Absorption x-ray spectra at early times are characteristic of a dense and rather homogeneous plasma. Collisional-radiative atomic physics coupled with hydrodynamic simulations reproduce fairly well the measured average ionization as a function of time.

The 2p − nd absorption structures in medium Z elements present a valuable benchmark for atomic models since they exhibit a complex dependence on temperature and density. For these transitions lying in the X-ray range, one observes a competition between the spin-orbit splitting and the broadening associated to the excitation of complex structures. Detailed opacity codes based on the HULLAC or FAC suites agree with the statistical code SCO; but in iron computations predict higher peak absorption than measured. An addition procedure on opacities calculated with detailed codes is proposed and successfully tested.

We report an experimental study of the temporal duration of a transient pumping extreme ultraviolet (XUV) laser emitted at 18.9 nm, using an ultrafast x-ray streak camera. We have investigated the shot-to-shot reproducibility of the pulse duration, as well as its behaviour as a function of several pumping parameters. Our results show that the pulse duration increases slowly with the pump pulse duration, in agreement with previous observations performed in a different geometry. The angle of the pump laser relative to the target surface also affects the XUV laser duration in a measurable way.

Point projection K-shell absorption spectroscopy has been used to measure absorption spectra of transient aluminum plasma created by an ultra-short laser pulse. 1s-2p and 1s-3p absorption lines of weakly ionized aluminum were measured for an extended range of densities in a relatively low-temperature regime. Independent plasma characterization was obtained from frequency domain interferometry (FDI) diagnostic and allows the interpretation of the absorption spectra in terms of spectral opacities. The experimental spectra are compared with opacity calculations using the density and temperature inferred from the analysis of the FDI data.