In this work, two different atomic models (ANALOP based on parametric potentials and IDEFIX based on the dicenter model) are used to calculate the opacities for bound–bound transitions in hot dense, low Z plasmas, and the results are compared to each other. In addition, the ANALOP code has been used to compute free–bound cross sections for hydrogen-like ions.

We present here experimental studies of broadened bound‐bound emissivities and opacities of low Z plasmas that are the best candidates for exhibiting ion and electron correlations. First we report on an emission experiment where a new target design is used to access the highest densities. Such targets irradiated by an intense long laser pulse generate plasmas well adapted to model and extract opacities. The measurements are compared to theoretical results obtained from simulations involving new atomic/molecular physics models that take into account detailed line profiles. We end up with the description of an absorption experiment in progress, this experiment using the same targets.

We present an advanced theory of x‐dips in spectral lines emitted from laser‐produced plasmas. We compare predictions of this theory with our previous experimental results where, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two dips in the Lyγ aluminum line perturbed by fully stripped carbon. Our theory gives a reasonable agreement with our experimental results. The results are of importance for the diagnostics of fundamental processes as it opens up a way to experimentally produce not‐yet‐available fundamental data on charge exchange between multi‐charged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the x‐dips are the only one signature of charge exchange in profiles of spectral lines emitted by plasmas and they are the only one quasi‐molecular phenomenon that could be observed at relatively “low” densities of laser‐produced plasmas, all those aspects emphasize the interest for studying heterogeneous plasma emission.

In this work two atomic physics models (the IDEFIX code using the dicenter model and the code based on parametric potentials ANALOP) have been used to calculate the opacities for bound-bound transitions in hot ultra-dense, low Z plasmas. These simulations are in connection with experiments carried out at LULI during the last two years, focused on bound-bound radiation. In this paper H-like opacities for aluminum and fluorine plasmas have been simulated, using both theoretical models, in a wide range of densities and temperatures higher than 200 eV.

A nonperturbative approach to the description of spectral line shapes of Ly-alpha radiation produced by multicharge ion-pair collisions is proposed. A closed expression that describes the central part of the line as well as the wings with an oscillation structure due to the extremum in the difference between the potential-energy curves has been obtained. It has been found that the exchange interaction leads to the formation of two satellites in the red and blue wings of the Ly-alpha perpendicular transitions.

We present an advanced theory of charge-exchange-caused dips (also called X-dips) in spectral lines from laser-produced plasmas. We compare predictions of this advanced theory with our previously published experimental results where, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two X-dips in the Lγ line of Al XIII perturbed by fully stripped carbon. We show that our advanced theory is in excellent agreement with our experimental results. From the practical point of view, our results open up a way to experimentally produce not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the results are important because the X-dips are the only one signature of charge exchange in profiles of spectral lines emitted by plasmas and they are the only one quasimolecular phenomenon that could be observed at relatively “low” densities of laser-produced plasmas.

A model approach to describing the shape of Lyman transition lines in pair collisions of multicharged ions was suggested. The approach was not based on perturbation theory. A closed equation for both the central line region and the oscillation structure caused by an extremum in the difference of energy terms was obtained. Exchange interaction was shown to cause the formation of two spectral satellites in the red and blue wings of perpendicular Lyman-alpha transitions. The obtained spectral formula was generalized to transitions asymptotically forbidden in the limit of large distances.

A formula was obtained that describes asymptotically forbidden quasimolecular optical transitions in the frame of the semiclassical approach. It is particularly relevant for the weak extrema in the difference between the ground- and excited-state interaction potentials. When averaged over impact parameters and velocity distribution the formula agreed reasonably well with the recent experimental data for the Ca(41S→31D) + He transition.

The transmission function and the resulting emissivity and opacity of bound-bound transitions in hot ultra-dense, low Z (aluminum or fluorine) plasmas are investigated in this paper. It is shown that the treatment of both the area-normalized line profiles and the absorption oscillator strengths involved are crucial. Taking account, self-consistently, of all the interactions inside a radiating transient molecule, as proposed in the dicenter code IDEFIX, we computed the photo-excitation cross-sections, the emissivities, the opacities, and then compare the results with those from standard codes. We emphasize the strong dependence of the above quantities with the ionic correlations. A first experiment, devoted to measure opacities and emissivities of hot and ultra-dense aluminum plasmas, has been designed. The interpretation of the results shows the adaptability of the dicenter model for these extreme conditions. (C) 2001 Elsevier Science Ltd. All rights reserved.

Since its creation, LULI has given an important contribution to laser plasma physics and Inertial Confinement Fusion studies. We will review some major results obtained these last two years with a 600 ps laser chain and with the recent 100-TW, 300fs ultra-intense laser chain. These result cover a wide spectrum of laser plasma physics research such as laser plasma interaction, laser plasma acceleration, fast ignitor, atomic processes in dens plasmas, shock waves generation and x-rays laser.

In previous work of the dicenter model, used to take into account the ionic correlation effects in hot dense plasmas, only considered a single perturbing ion (i.e., the nearest neighbor ion) thus limiting its range of applicability. The improvement proposed in the present work includes the effect of all perturbing ions through a quasistatic external microfield acting on a “quasi-molecule”. This enlarges the domain of validity of the dicenter model. For low densities this new alternative model gives line widths in agreement with standard “monocenter” profiles without artificially reducing the electron screening inside the dicenter emitting cell. This reduced screening, which had been employed to treat the repulsive interactions between the quasi-molecule and the other perturbing ions, is removed in the present work.

The present work is devoted to the study of opacities for ultra-dense, hot, low Z plasmas. For those highly correlated plasmas, similar to some astrophysical situations and to implosion experiments, ionic and electronic correlation effects modify drastically the atomic and radiative properties. Up to now the quasi-molecular model has been shown to be efficient for an exact treatment of the spectral line shapes. The aim of this work is to use the same approach for the computation of the photo-excitation cross sections, the opacity and the emissivity characterizing ultra-dense and hot plasmas.

We show that extrema in the transition energy can result not only in satellites, but also in dips in spectral line profiles. Moreover, for a practically important case where the extremum in the transition energy is due to charge exchange, its spectral signature most probably should be a dip rather than a satellite.

We report the first experimental observation of charge-exchange-caused dips (also called x dips) in spectral lines of multicharged ions in laser-produced plasmas. Specifically, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two x dips in the Ly. line of Al xiii perturbed by fully stripped carbon. From the practical point of view. this opens up a way to experimentally produce not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the results are important because the x dips are the only one signature of charge exchange in profiles of spectral lines emitted by plasmas and they are the only one quasimolecular phenomenon that could be observed at relatively "low" densities of laser-produced plasmas.

This paper reports on the spectral line shape of hydrogen and helium-like lines relevant to the quasi-static dicenter model. This treatment is justified for hot dense, moderate Z plasmas. The code IDEFIX developed for the quasi-static dicenter model involves a self-consistent description of the interactions and of the radiative properties. Strong dependence of the transition energies and of the dipole moments on the interionic separation are pointed out and novel density-dependent spectroscopic features such as asymmetries, satellite-like features, molecular transitions are exhibited. The theoretical spectra presented here are discussed in connection with experimental results where these exist.

Electron terms in the field of two stationary Coulomb centres (TCCs) of charges Z and Z' separated by a distance R are a fundamental problem of quantum mechanics, presenting fascinating atomic physics: the terms show crossings and avoided crossings. In the latter situation, the electron has a much larger probability of tunnelling from one well to the other (i.e. of charge exchange) than in the absence of such degeneracy. These rich features of the TCC problem are also manifest in different areas of physics such as plasma spectroscopy. Recently it was shown experimentally that charge exchange, enhanced by the encounter of two TCC terms, can result in an unusual structure (a dip) in the spectral line profile emitted by a Z ion from a plasma consisting of both Z and Z' ions. In this paper we present a detailed quantitative theory of this phenomenon, in which its origin is directly traced to the avoided crossings of terms in the TCC problem. We show that our theory explains quantitatively all the results of the above experiment where such a dip was observed in a hydrogen line. We also consider in detail several prospective `radiator-perturber' pairs for observing these signatures of charge exchange in lines of hydrogen-like ions. Further experimental studies of such dips would serve to produce not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods.

The paper deals with a frequently encountered situation where the energy difference between the terms involved in a radiative transition, being plotted versus the radiator-perturber separation, shows extrema. The paradigm, based on 30 years of theoretical and experimental studies, is that the extrema in the transition energy result in satellites in spectral line profiles. In this Rapid Communication we show that this paradigm breaks down the extrema in the transition energy can also result in dips in spectral line profiles. Moreover, we demonstrate that if the extremum in the transition energy is due to the charge exchange, its spectral signature most probably should be a dip rather than a satellite.

LULI will play an important role as a major laser ICF and IFE support facility in Europe after recent or future changes (ASTERIX-Garching, CEA-Limeil) in large laser system programs. We will review the research activities which have been carried out at LULI during the last 2 years both in the nanosecond regime and in the subpicosecond ultraintense regime. As part of the LULI upgrade project, a new 30-J, 300-fs, 100-TW ultraintense laser chain has been commissioned in 1997. This laser has allowed the first complete demonstration of wakefield electron acceleration and is presently used to study new concepts in laser fusion and laser–plasma interaction experiments in the relativistic regime.

The experimental results we present here concern the time evolution of the main plasma parameters in the region between two thin laser accelerated Teflon foils as deduced from fluorine H-like and recombination continuum emission, as well as the time evolution of Fluorine Lyβ line profile. Two X-ray streak cameras with a time resolution of 10 ps have then been used, recording the emission of a 25 μm sized plasma slice between the foils, to be compared to the initial distance (≈100 μm). To obtain a well resolved spectrum despite of the low streak camera photocathode spatial resolution, a high dispersive TlAP spectrometer has been used to record the Lyβ line profile. In this way we can associate any particular line profile we record to the plasma conditions producing it. In conclusion this experiment allows quantitative comparison with hydrodynamics code results, post-processed by atomic physics and spectra codes.

To assess the accuracy of simplified methods for the treatment of ion dynamics in Stark-broadening theory, we have compared two such methods, the relaxation theory and model microfield method, against benchmark calculations fur the CVI H-alpha line. It is shown that both methods show poor agreement at low densities. [S1063-651X(99)12702-8].