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Abstract: The Collisional-Radiative model CoRaM-Al is implemented in a 0D numerical code in the purpose of describing the formation of the plasma resulting from the interaction between a 4ns Nd:YAG laser pulse and an aluminum sample in vacuum. The influence of the first three harmonics at 355nm, 532nm and 1064nm is studied. In each case, the fluence value is set equal to the threshold above which a phase explosion takes place. The sample surface temperature is therefore limited to the critical temperature (6700K). The solid→gas transition is classically treated by using the Hertz–Knudsen law. The species considered in CoRaM-Al are Al, Al+, Al2+, Al3+ and free electrons. They are in thermochemical non-equilibrium at different temperatures. Each state behaves freely owing to electron impact induced excitation and ionization, elastic collisions, Multiphoton Ionization (MPI), Inverse Bremsstrahlung (IB), thermal Bremsstrahlung, and spontaneous emission. The results show that MPI and IB play a complementary role in the heating process of electrons. In the ultraviolet and visible cases, the increase in electron temperature is mainly due to multiphoton ionization before the maximum irradiance. The electron temperature does not exceed 9000K. The heavy particle temperature mainly results from the surface temperature. Conversely, in the infrared case, electron temperature strongly increases after the maximum irradiance owing to inverse Bremsstrahlung. Electrons then give a part of their energy for the benefit of heavy particles, which leads to the increase in their temperature. The electron number density reaches its maximum during the laser pulse with a value of the order of 1025 m−3 and the electron temperature exceeds 13,000K. A maximum of the ionization degree close to 0.2 is thus obtained at 1064nm. [Copyright &y& Elsevier]

This paper presents the results of relativistic calculation intended specifically to investigate the dominant states for dielectronic recombination of Li-like into Be-like Al ions in short-pulse laser produced plasmas. The relativistic Dirac R-matrix calculation is performed to output resonance energy levels and rates. The target energies and orbitals are calculated with the extended average level multi-configurational Dirac-Fock method in the general-purpose relativistic atomic structure package. This type of calculation gives a set of 13 bound orbitals that is optimized over all the levels included. The resulting 13 relativistic orbitals produced 74 Jπ levels, all of which are to be used in the close-coupling expansion. To the best of our knowledge, the work reported herein describes for the first time such detailed calculation for this atomic system and the results are relevant to the short-pulse laser produced plasma modeling. [ABSTRACT FROM AUTHOR]

Abstract: A zero-dimensional collisional–radiative (CR) model, coupled self-consistently with the electron Boltzmann equation, has been applied to the description of a metallic-laser induced plasma at experimental conditions typical of LIBS experiment. To take in account expansion effects, the experimental temperature and total number density as function of time have been used as input data. Plasma composition and the simultaneous time evolution of both heavy particle level distributions and the electron energy distribution function have been calculated by taking into account the most relevant collisional and radiative processes. This approach estimates the hierarchy of the elementary processes during the expansion and possible deviations from LTE conditions. The comparison of the experimental and theoretical results shows a good agreement, but at the same time new questions arise on the analysis of spectroscopic results and on the assumption generally made in LIBS. [ABSTRACT FROM AUTHOR]

Abstract: We present the development of population kinetics models for tin plasmas that can be employed to design an EUV source for microlithography. The atomic kinetic code is constrained for the requirement that the model must be able to calculate spectral emissivity and opacity that can be used in radiation hydrodynamic simulations. Methods to develop compact and reliable atomic model with an appropriate set of atomic states are discussed. Specifically, after investigation of model dependencies and comparison experiment, we improve the effect of configuration interaction and the treatment of satellite lines. Using the present atomic model we discuss the temperature and density dependencies of the emissivity, as well as conditions necessary to obtain high efficiency EUV power at λ =13.5nm. [Copyright &y& Elsevier]

• The spectra of molybdenum (Mo) emitted by a nanosecond Nd:YAG laser-produced plasma, have been measured in the 6.7–14.3 nm region using a spatio-temporally resolved laser-produced plasma spectroscopy technique. • The calculations were made for the whole observed distinctive features that arose from the 4s- n p, 4p- n d, and 4p- m s resonance transition arrays of the Mo7+-Mo12+ ions. Double excitations (inner-shell excitations) of Mo12+- Mo14+ ions were also considered. • Numerous previously unidentified lines have been identified with the aid of the Hartree-Fock (HF) method within the pseudo-relativistic corrections (HFR) using Cowan's codes. • The steady-state collisional-radiative (CR) model was devoted to obtain the plasma parameters. • The observed spectrum was compared to a spectrum synthesized with calculated data from HFR. The agreement between the simulated spectra and experimental results is excellent. Spectra of highly-charged Mo ions excited in the 6.7–14.3 nm wavelength region by focusing Nd:YAG laser light pulses (λ =1064 nm, 10 ns) have been recorded and investigated. A spatio-temporally resolved laser-produced plasma spectroscopy technique was used. The observed spectra are composed of many lines that correspond to Mo7+-Mo12+ ions belonging to the 4s- n p, 4p- n d (n = 5–8), and 4p- m s (m = 6–8) transition arrays. Only 4p-(5,6)s and 4p-(5,6)d resonance transition of Mo7+ and Mo8+ were analyzed before. The spectrum investigations were based on the Hartree-Fock (HF) method within the framework of the pseudo-relativistic corrections (HFR) using Cowan's codes. Double excitation in Mo12+, Mo13+, and Mo14+ were also worthy of inclusion because of their important contributions. To obtain the best fitting with the spectral features, the possible contributions from the 4s4p k 4d metastable state ions within the plasma were included. Comprehensive calculations were performed and several previously unclassified lines have been identified for the first time. A steady-state collisional-radiative (CR) model was devoted to obtaining the plasma parameters and interpreting the emitted spectrum. The theoretical simulated spectrum agrees reasonably well with the experimental profile, which can indicate the possibility of use for plasma diagnostics. The results should be beneficial for future assessment and comparisons as well as spectroscopic diagnostics of hot plasmas in tokamak plasmas and fusion research. [ABSTRACT FROM AUTHOR]

• The EUV spectra of the middle and late stage of expansion of laser-produced Cd plasma were measured in the 8.5-12 nm region, using a spatiotemporally resolved laser-produced plasma spectroscopic technique. • The 4p-6s resonance transition arrays from Cd4+ to Cd7+ ions dominate the spectrum, which has been identified with the aid of the Hartree-Fock (HF) method with relativistic corrections (HFR) using the Cowan codes. • Several new spectral features were established for the first time and were tentatively assigned. • Using the steady-state collisional-radiative model (CR), the plasma parameters have been obtained by comparing the experimental and simulated spectra, which have given the best agreement for the relative ion populations consistent with the observed spectra. • The evolution behavior of the rate coefficients with an electron density and an electron temperature have been discussed in detail, and several physical aspects involving in plasma expansion were provided. In this paper, the EUV spectra of the middle and late stage of expansion of laser-produced cadmium (Cd) plasma were measured using a spatiotemporally resolved laser-produced plasma spectroscopic technique. The 4p-6s resonance transition arrays from Cd4+ to Cd7+ ions dominate the spectrum, which has been identified with the aid of the Hartree-Fock (HF) method with relativistic corrections (HFR) using the Cowan suite of codes. Several new spectral lines were demonstrated for the first time and were tentatively assigned. Spectral simulations of the plasma expansion into a vacuum based on the assumption of a normalized Boltzmann distribution among the excited states associated with a steady-state collisional-radiative model were also carried out to obtain the plasma parameters by comparing experimental and simulated spectra. The dominant ion stages and the corresponding ion fractions for different ion stages were obtained. In addition, we have discussed in detail the evolution of the rate coefficients with electron density and electron temperature. Numerous physical aspects, including ion expansion energy, electron-ion thermalization time, plasma sound speed, electron plasma velocity and frequency, skin depth, as well as plasma coupling parameters were investigated. We have also found good agreements between experimental and theoretical synthetic spectra using excitation temperatures of 14 eV and 15.5 eV.,. These results should be helpful for further spectral identifications in the fields of plasma diagnostics and nuclear fusion. [ABSTRACT FROM AUTHOR]

• A spatio-temporally resolved laser-produced plasma spectroscopy technique have been used to study the laser-produced zirconium (Zr) plasmas in the 6.7–14.7 nm region. • The Hartree-Fok (HF) method with relativistic corrections (HFR) using the Cowan's codes and Flexible Atomic Code (FAC) were used to calculate and interpret the observed spectral obtained. Accordingly, a number of new spectral lines are identified. • A numerical computation based on the assumption of a normalized Boltzmann distribution among the excited states associated with a steady-state collisional-radiative model (CR), has also been performed to obtain the plasma parameters by comparing the experimental and simulated spectra. • Good agreement between the experimental and theoretical calculations were obtained. • Temporal and spatial evolution behavior about plasma parameters have been analyzed, and the variation of electron plasma frequency and skin depth with plasma temperature were introduced. Extreme ultraviolet radiation of laser-produced zirconium (Zr) plasmas were measured in the 6.7–14.7 nm region using a spatio-temporally resolved laser-produced plasma spectroscopy technique. At shorter wavelengths, the spectrum was dominated by several lines attributed to the 4s-(6p,7p,8p) transition arrays of Zr6+ to Zr10+ ions. For the 4s-5p and 4p-6 s transitions, the spectral lines concentrated near 11.18 nm and smoothly move towards longer wavelengths with decreasing ion-charge-state, which are experimentally and theoretically investigated. The Hartree-Fok (HF) method with relativistic corrections (HFR) using the Cowan's codes and Flexible Atomic Code (FAC) were used to calculate and interpret the observed spectra, respectively. At relatively high temperatures, lines from 3p-3d transitions in Zr13+ and Zr14+ ions have been found to have an important contribution. A number of spectral lines are established in this study for the first time. Besides the atomic structure calculations, a numerical computation based on the assumption of a normalized Boltzmann distribution among the excited states associated with a steady-state collisional-radiative model (CR), has also been performed to obtain the plasma parameters by comparing the experimental and simulated spectra. The corresponding dominant ion stages and ion fractions for different ion stages were obtained. We have also provided the evolution of rate coefficients as a function of electron density and electron temperature. We reproduced synthetic spectra which are in good agreement with the experiment. Temporal and spatial evolution behavior about plasma parameters have been analyzed. The variation of electron plasma frequency and skin depth with plasma temperature were introduced. The results may be beneficial for spectroscopic diagnostics of hot plasmas in tokamak and fusion research. [ABSTRACT FROM AUTHOR]

Plasmas of a variety of types can be described by the collisional radiative (CR) model developed by Colombant and Tonan. From the CR model, the ion distribution of a plasma at a given electron temperature and density can be found. This information is useful for further simulations, and due to this, the employment of a suitable CR model is important. Specifically, ionization bottlenecks, where there are enhanced populations of certain charge states, can be seen in these ion distributions, which in some applications are important in maintaining large amounts of a specific ion. The present work was done by implementing an accepted CR model, proposed by Colombant and Tonon, in Python and investigating the effects of variations in the ionization energy and outermost electron subshell occupancy term on the positions of ionization bottlenecks. Laser Produced Plasmas created using a Nd:YAG laser with an electron density of ∼ne = 1021 cm−3 were the focus of this work. Plots of the collisional ionization, radiative recombination, and three-body recombination rate coefficients as well as the ion distribution and peak fractional ion population for various elements were examined. From these results, it is evident that using ionization energies from the NIST database and removing the orbital occupancy term in the CR model produced results with ionization bottlenecks in expected locations. [ABSTRACT FROM AUTHOR]