In order to design extreme ultraviolet (EUV) sources for nanolithography, xenon EUV emission has been experimentally studied in a plasma generated by the interaction of a high-power laser with a droplet jet. A theoretical model assuming that the resulting plasma is optically thick allows one to find the distribution of the relevant ions and transitions involved in the emission process. Atomic physics computations are performed using the HULLAC code to give a detailed account of the transitions involved. The importance of 4p–4d, 4d–4f, and 4d–5p transitions is stressed, as well as the need for configuration-interaction treatment of the Δn=0 transitions. Comparisons of a modeled local thermodynamical equilibrium spectrum with experiment provides qualitative agreement and permits an estimate of the plasma temperature, density, and dimensions.

This paper is devoted to the autoionization process of large-angular-momentum Rydberg states.After a brief account of autoionization formalism in nonrelativistic theory and single-configuration approximation, we apply it to atomic states with one electron of large angular momentum. The dominant contribution is the direct one and the exchange contribution is ignored. In this framework, the autoionization width varies with the principal quantum number as n ' and exponentially with the angular momentum.When two excited electroris interact with a spherically symmetric core, it is demonstrated that the interaction between the Rydberg electron and the core polarized by the valence electron is proportional to the interaction between the two active electrons. Using newly derived radial matrix elements, we obtain a generally good agreement between our results and experiments on barium and strontium. Large-/ Rydberg states are shown to be stable versus autoionization as soon as I is about 7. Possible refinements of our method are reviewed. IN THE SINGLE-CONFIGURATION APPROACHConsider a diexcited atom, with the outer electron, hereafter called the "Rydberg electron" and labeled 1, much more excited than the inner electron referred to as the "valence electron" and labeled 2. The other electrons are named core electrons, and their influence mill be studied in Sec. IV. At this step of the formalism, we ignore 38 3484 1988 The American Physical Society 38 AUTOIONIZATION OF RYDBERG STATES WITH LARGE . 3485 the spin-dependent part of the Hamiltonian. Following the Heisenberg approximation for helium, we write the atomic Hamiltonian, in Hartree units (e =Pi= m = 1):

A strong blue fluorescence has been observed following orange-yellow laser excitation in the 1D2 multiplet of Pr3+ : LaF3. This blue fluorescence has different time evolution depending on the excitation wavelength within the absorption line. Time resolved excitation techniques have been used to study this time evolution. It is shown that satellite lines, which accompany the main line, are due to ions between which energy transfer is very active. A mechanism is proposed for the observed up-conversion which is in good agreement both with our results and with observations reported by others. The nature of the interaction between the ions of the satellite lines and that of the interaction responsible for the energy transfer are discussed

A collisional-radiative model describing non-local-thermodynamic-equilibrium plasmas is developed. It is based on the HULLAC suite of codes for the transitions rates, in the zero-temperature radiation field hypothesis. Two variants of the model are presented, the first one is configurationaveraged, while the second one is a detailed level version. Comparisons are made between them in the case of a carbon plasma; they show that the configuration-averaged code gives correct results for an electronic temperature T e = 10 eV (or higher) but fails at lower temperatures such as T e = 1 eV. The validity of the configuration-average approximation is discussed: the intuitive criterion requiring that the average configuration-energy dispersion must be less than the electron thermal energy turns out to be a necessary but far from sufficient condition. Another condition based on the resolution of a modified rate-equation system is proposed. Its efficiency is emphasized in the case of low-temperature plasmas. Finally, it is shown that near-threshold autoionization cascade processes may induce a severe failure of the configuration-average formalism. It is now well-known that in highly-charged hot plasmas, emission and absorption spectra usually display broad structures theoretically described as unresolved transition arrays (UTA) [1,2,3], spin-orbit split arrays (SOSA) [4] or supertransition arrays (STA) [5]. Isolated lines may also be present when transitions occur between two configurations of small degeneracy. The UTA formalism consists in expanding the individual transition energies as a function of the various moments < E n > -where the ponderation is performed using line strengths -with the assumption that levels inside a given configuration are distributed according to thermal equilibrium, the validity of this assumption lying on the condition that the configuration width ∆ c must be smaller than the thermal energy k B T e . Due to its numerous applications, the theory of non-LTE plasmas is nowadays a very active subject [19,20]. For instance, laser-produced and discharged-produced plasmas appear as very promising sources of intense extreme-UV light well suited for 13.5 nm-lithography ([21, 22, 23] and other references in the same volume); for such plasmas of moderate density, the non-LTE condition prevail in most cases. Another domain of application is low-density astrophysics plasmas as well as laboratory coronal plasmas.The aim of this paper is first to present a detailed CR model. One essential feature is that it must be based on a reliable atomic code. To this respect, the HULLAC (Hebrew University Lawrence Livermore Atomic Code) parametric-potential code is known to be efficient in applications dealing with ion spectroscopy and collisional rate calculation. A known limitation of several atomic models used in plasma physics [12,13,14,16,17] is that configuration interaction is ignored. However it has been demonstrated that configuration interaction may play a major role in several radiative effects in pla...

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a b s t r a c tOpacity 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 w3 mg/cm 3 . 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.

International audienceDensity effects in plasmas are analyzed using a Thomas-Fermi approach for free electrons. First, scaling properties are determined for the free-electron potential and density. For hydrogen-like ions, the first two terms of an analytical expansion of this potential as a function of the plasma coupling parameter are obtained. In such ions, from these properties and numerical calculations, a simple analytical fit is proposed for the plasma potential, which holds for any electron density, temperature, and atomic number, at least assuming that Maxwell-Boltzmann statistics is applicable. This allows one to analyze perturbatively the influence of the plasma potential on energies, wave functions, transition rates, and electron-impact collision rates for single-electron ions. Second, plasmas with an arbitrary charge state are considered, using a modified version of the Flexible Atomic Code (FAC) package with a plasma potential based on a Thomas-Fermi approach. Various methods for the collision cross-section calculations are reviewed. The influence of plasma density on these cross sections is analyzed in detail. Moreover, it is demonstrated that, in a given transition, the radiative and collisional-excitation rates are differently affected by the plasma density. Some analytical expressions are proposed for hydrogen-like ions in the limit where the Born or Lotz approximation applies and are compared to the numerical results from the FAC