Atoms, Volume 6, Issue 3 (September 2018) – 19 articles

Molecular overtone transitions provide optical frequency transitions sensitive to variation in the proton-to-electron mass ratio ( $\mu \equiv m_p/m_e$ ). However, robust molecular state preparation presents a challenge critical for achieving high precision. Here, we characterize infrared and optical-frequency broadband laser cooling schemes for TeH ${}^{+}$ , a species with multiple electronic transitions amenable to sustained laser control. Using rate equations to simulate laser cooling population dynamics, we estimate the fractional sensitivity to $\mu$ attainable using TeH ${}^{+}$ . We find that laser cooling of TeH ${}^{+}$ can lead to significant improvements on current $\mu$ variation limits. Full article

Semi-empirical transition probabilities for magnetic dipole (M1) and electric quadrupole (E2) emission lines have been derived from parametric studies of experimental energy levels in Tm³⁺ (Tm IV), Yb⁴⁺ (Yb V), and Er³⁺ (Er IV), using Cowan codes. Results are compared with those existing from ab initio calculations or from more sophisticated semi-empirical calculations. Satisfactory agreements show that simple parametric calculations can provide good predictions on line intensities, provided that experimental levels are available, allowing reliable fits of energy parameters. Full article

Neutral Chromium (Cr I) is an important element in many laboratory plasma applications. In this work, expectation values of the radius for Cr I are calculated. These atomic data are calculated with three different atomic codes: Cowan code using the Hartree–Fock Relativistic approximation, SUPERSTRUCTURE and AUTOSTRUCTURE codes using scaled Thomas–Fermi–Dirac–Amaldi potential. Relativistic corrections are introduced according to the Breit–Pauli approach. The $3d^{5}4s$ , $3d^{4}4s^2,$ $3d^{5}4d,3d^{5}4p$ and $3d^{4}4s4p$ configurations are included to obtain the expectation values of radius of Cr I and compared with available data. The novelty of our work is to obtain new values of $<\frac{1}{r}>,<r>,$ and $<r^2>$ for the configuration of $4p$ and $4d$ and the values of $<r^3>$ for all orbitals configurations considered in this work. Full article

There is presented an overview of the latest advances in the analytical theory of Stark broadening of hydrogenic spectral lines in various types of laboratory and astrophysical plasmas. They include: (1) advanced analytical treatment of the Stark broadening of hydrogenic spectral lines by plasma electrons; (2) center-of-mass effects for hydrogen atoms in a nonuniform electric field: applications to magnetic fusion, radiofrequency discharges, and flare stars; (3) penetrating-ions-caused shift of hydrogenic spectral lines in plasmas; (4) improvement of the method for measuring the electron density based on the asymmetry of hydrogenic spectral lines in dense plasmas; (5) Lorentz–Doppler broadening of hydrogen/deuterium spectral lines: analytical solution for any angle of observation and any magnetic field strength, and its applications to magnetic fusion and solar physics; (6) Revision of the Inglis-Teller diagnostic method; (7) Stark broadening of hydrogen/deuterium spectral lines by a relativistic electron beam: analytical results and applications to magnetic fusion; (8) Influence of magnetic-field-caused modifications of the trajectories of plasma electrons on shifts and relative intensities of Zeeman components of hydrogen/deuterium spectral lines: applications to magnetic fusion and white dwarfs; (9) Influence of magnetic-field-caused modifications of trajectories of plasma electrons on the width of hydrogen/deuterium spectral lines: applications to white dwarfs; (10) Stark broadening of hydrogen lines in plasmas of electron densities up to or more than N_e~10²⁰ cm⁻³; and, (11) The shape of spectral lines of two-electron Rydberg atoms/ions: a peculiar Stark broadening. Full article

Cross sections for rotational excitation and de-excitation of the HeH⁺ ion by an electron impact are computed using a theoretical approach that combines the UK R-matrix code and the multi-channel quantum defect theory. The thermally-averaged rate coefficients derived from the obtained cross sections are fitted to an analytical formula valid for a wide range of temperatures. Full article

This brief review highlights some current issues in Galactic stellar nucleosynthesis, and some recent laboratory studies by the Wisconsin atomic physics group that have direct application to stellar spectroscopy to advance our understanding of the chemical evolution of our Galaxy. The relevant publication history of the lab studies are summarized, and investigations into the abundances of neutron-capture and iron-peak elements in low metallicity stars are described. Finally, new initiatives in near-infrared spectroscopy are briefly explored. Full article

A pulsed discharge light source was used to study the two and three times ionized argon (Ar II, Ar III) spectra in the 480–6218 Å region. A set of 129 transitions of Ar III and 112 transitions of Ar IV were classified for the first time. We extended the analysis of Ar III to five new energy levels belonging to 3s²3p³4d, 3s²3p³5s odd configurations. For Ar IV, 10 new energy levels of the 3s²3p²3d and 3s²3p²4p even and odd configurations, respectively, are presented. For the prediction of energy levels, line transitions, and transition probabilities, relativistic Hartree–Fock calculations were used. Full article

Micro-plasma is generated in ultra-high-pure hydrogen gas, which fills the inside of a cell at a pressure of (1.08 ± 0.033) × 10⁵ Pa by using a Q-switched neodymium-doped yttrium-aluminum-garnet (Nd:YAG) laser device operated at a fundamental wavelength of 1064 nm and a pulse duration of 14 ns. The micro-plasma emission spectra of the hydrogen Balmer alpha line, H_α, are recorded with a Czerny–Turner type spectrometer and an intensified charge-coupled device. The spectra are calibrated for wavelength and corrected for detector sensitivity. During the first few tens of nanoseconds after the initiation of optical breakdown, the significant Stark-broadened and Stark-shifted H_α lines mark the well-above hypersonic outward expansion. The vertical diameters of the spectrally resolved plasma images are measured for the determination of expansion speeds, which were found to decrease from 100 to 10 km/s for time delays of 10 to 35 ns. For time delays of 0.5 µs to 1 µs, the expansion speed of the plasma decreases to the speed of sound of 1.3 km/s in the near ambient temperature and pressure of the hydrogen gas. Full article

Intra-Stark spectroscopy (ISS) is the spectroscopy within the quasi-static Stark profile of a spectral line. The present paper reviews the X-ray ISS-based studies recently advanced for the diagnostics of the relativistic laser–plasma interactions. By improving experiments performed on the Vulcan Petawatt (PW) laser facility at the Rutherford Appleton Laboratory (RAL), the simultaneous production of the Langmuir waves and of the ion acoustic turbulence at the surface of the relativistic critical density gave the first probe by ISS of the parametric decay instability (PDI) predicted by PIC simulations. The reliable reproducibility of the experimental signatures of PDI—i.e., the Langmuir-wave-induced dips—allowed measurements of the fields of the Langmuir and ion acoustic waves. The parallel theoretical study based on a rigorous condition of the dynamic resonance depending on the relative values of the ion acoustic and the Langmuir fields could explain the disappearance of the Langmuir dips as the Langmuir wave field increases. The ISS used for the diagnostic of the PDI process in relativistic laser–plasma interactions has reinforced the reliability of the spectral line shape while allowing for all broadening mechanisms. The results can be used for a better understanding of intense laser–plasma interactions and for laboratory modelling of physical processes in astrophysical objects. Full article

This work communicates results from optical emission spectroscopy following laser-induced optical breakdown at or near nanomaterial. Selected atomic lines of silver are evaluated for a consistent determination of electron density. Comparisons are presented with Balmer series hydrogen results. Measurements free of self-absorption effects are of particular interest. For several silver lines, asymmetries are observed in the recorded line profiles. Electron densities of interest range from 0.5 to 3 × 10¹⁷ cm⁻³ for five nanosecond Q-switched Nd:YAG radiation at wavelengths of 1064 nm, 532 nm, and 355 nm and for selected silver emission lines including 328.06 nm, 338.28 nm, 768.7 nm, and 827.3 nm and the hydrogen alpha Balmer series line at 656.3 nm. Line asymmetries are presented for the 328.06-nm and 338.28-nm Ag I lines that are measured following generation of the plasma due to multiple photon absorption. This work explores electron density variations for different irradiance levels and reports spectral line asymmetry of resonance lines for different laser fluence levels. Full article

The accuracy of approximate automodel solutions for the Green’s function of the Biberman-Holstein equation for the Stark broadening of spectral lines is analyzed using the distributed computing. The high accuracy of automodel solutions in a wide range of parameters of the problem is shown. Full article

This work reports measurements of calcified gallstone elemental compositions using laser-induced optical emission spectroscopy. The experimental results support the importance of the magnesium concentration in gallstone growth. Granular stones reveal an increased magnesium concentration at the periphery of the granules, suggesting the inhibition of further growth. Non-granular gallstones reveal lower overall magnesium concentrations, but with higher values near the center. Full article

The screening effects of the interaction potentials on the lowest ${}^{1}S$ doubly-excited states of beryllium-like ions were investigated by calculating the density of resonance states within the framework of the stabilization method. Two types of screened interaction potentials, namely static screened Coulomb potential and exponential cosine screened Coulomb potential, were taken into consideration. A model potential was used to describe the interaction between the core and outer electrons, and the Be-like ions were treated as being effectively three-body systems. Calculations were performed for Be and $B^{+}.$ It was possible to calculate the energy and width of one doubly-excited state of Be and four doubly-excited states of $B^{+}$ lying above the 1$s^{2}2p$ threshold. Significant changes were found to exist in the behaviour of the width with varying screening parameters. To the best of our knowledge, such an investigation on the doubly-excited states of Be-like ions under screened environments is the first reported calculation of this type in the literature. Full article

Earlier beam-foil measurements have targeted 4s-4p intercombination transitions in the Zn-, Ga- and Ge-like ions of Nb ($Z=41$), Mo ($Z=42$), Rh ($Z=44$), Ag ($Z=47$) and I ($Z=53$). At the time, the spectra were calibrated with literature data on prominent lines in the Cu- and Zn-like ions. Corresponding literature data on the intercombination transitions in Ga- and Ge-like ions were largely lacking, which caused some ambiguity in the line identifications. We review the (mostly computational) progress made since. We find that a consistent set of state-of-the-art computations of Ga- and Ge-like ions would be highly desirable for revisiting the beam-foil data and the former line identifications for the elements from Kr ($Z=36$) to Xe ($Z=54$). We demonstrate that the literature data for these two isoelectronic sequences are insufficient, and we contribute reference computations in the process. We discuss the option of electron beam ion trap measurements as an alternative to the earlier use of classical light sources, beam-foil interaction and laser-produced plasmas, with the example of Xe ($Z=54$). Full article

The Dirac–Hartree–Fock plus many-body perturbation theory (DHF + MBPT) method has been used to calculate hyperfine structure constants for Fr. Calculated hyperfine structure anomaly for hydrogen-like ion is in good agreement with analytical expressions. It has been shown that the ratio of the anomalies for s and $p_{1/2}$ states is weakly dependent on the principal quantum number. Finally, we estimate Bohr–Weisskopf corrections for several Fr isotopes. Our results may be used to improve experimental accuracy for the nuclear g factors of short-lived isotopes. Full article

The paper is devoted to the investigation of the absorption of ultrashort laser pulses on atoms in plasmas, accounting for the different broadening mechanisms of atomic resonant transitions. The analysis is made in terms of the absorption probability during the entire interaction between the laser pulse and atom. Attention is mainly given to dependence of probability upon the pulse duration and the carrier frequency of the pulse. The results are presented via dimensionless parameters and functions describing the effect of finite pulse duration on atomic spectra for different broadening mechanisms, namely Doppler, Voigt, Holtsmark and their combinations, as well as the Stark line broadening of Rydberg atomic lines. Full article

We report calculations of collision strengths and effective collision strengths for 26 allowed transitions among the $n\le$ 5 degenerate levels of atomic hydrogen for which the close-coupling (CC) and Born approximations have been used. Results are listed over a wide range of energies (up to 100 Ryd) and temperatures (up to ${10}^7$ K), sufficient for applications over a variety of plasmas, including fusion. Similar results have also been calculated for deuterium, but they negligibly differ with those of hydrogen. Full article

This work communicates a review on Balmer series hydrogen beta line measurements and applications for analysis of white dwarf stars. Laser-induced plasma investigations explore electron density and temperature ranges comparable to white dwarf star signatures such as Sirius B, the companion to the brightest star observable from the earth. Spectral line shape characteristics of the hydrogen beta line include width, peak separation, and central dip-shift, thereby providing three indicators for electron density measurements. The hydrogen alpha line shows two primary line-profile parameters for electron density determination, namely, width and shift. Both Boltzmann plot and line-to-continuum ratios yield temperature. The line-shifts recorded with temporally- and spatially-resolved optical emission spectroscopy of hydrogen plasma in laboratory settings can be larger than gravitational redshifts that occur in absorption spectra from radiating white dwarfs. Published astrophysical spectra display significantly diminished Stark or pressure broadening contributions to red-shifted atomic lines. Gravitational redshifts allow one to assess the ratio of mass and radius of these stars, and, subsequently, the mass from cooling models. Full article

We present opacity calculations with the newly developed STAR code, which implements the Super-Transition-Array (STA), with various improvements. The model is used to calculate and analyze local thermodynamic equilibrium opacities of mid and high Z elements and of the solar interior plasma. We briefly review the underlying computational model and present calculations for iron and neodymium over a wide range of temperature and density. Full article