Atoms

8 pages, 287 KiB

Open AccessArticle

Dataset for Optical Processes in Dense Astrophysical and Laboratory Plasmas

by Nenad M. Sakan, Vladimir A. Srećković, Zoran J. Simić and Momchil Dechev

Atoms 2024, 12(11), 59; https://doi.org/10.3390/atoms12110059 - 14 Nov 2024

The interest in the modeling of laboratory and astrophysical plasma behavior from mid up to strong non-ideality (NI), e.g., plasma in which a Coulomb interaction becomes dominant, led us to further investigate the optical properties of such systems. An expanded set of results [...] Read more.

The interest in the modeling of laboratory and astrophysical plasma behavior from mid up to strong non-ideality (NI), e.g., plasma in which a Coulomb interaction becomes dominant, led us to further investigate the optical properties of such systems. An expanded set of results and properties like wave functions, dipole matrix elements, etc., for such systems is presented in this submission. The methodologies of our research, as well as the current and future elements of their applications, are explained. In addition to being helpful to other researchers for achieving a variety of goals, the data from this study could be useful the interdisciplinary fields of machine learning, astrochemistry and fusion physics. The dataset is available online at the repository Figshare. Full article

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9 pages, 430 KiB

Open AccessArticle

On Resonance Enhancement of E1-E2 Nondipole Photoelectron Asymmetries in Low-Energy Ne 2p Photoionization

by Valeriy K. Dolmatov and Steven T. Manson

Atoms 2024, 12(11), 58; https://doi.org/10.3390/atoms12110058 - 7 Nov 2024

Abstract

Earlier, a significant enhancement of the nondipole parameters

γ_{2 p}

,

δ_{2 p}

, and

ζ_{2 p} = γ_{2 p} + 3 δ_{2 p}

in the photoelectron angular distribution for Ne

2 p

photoionization was predicted, owing to [...] Read more.

Earlier, a significant enhancement of the nondipole parameters

γ_{2 p}

,

δ_{2 p}

, and

ζ_{2 p} = γ_{2 p} + 3 δ_{2 p}

in the photoelectron angular distribution for Ne

2 p

photoionization was predicted, owing to resonance interference between dipole (

E 1

) and quadrupole (

E 2

) transitions. This enhancement manifests as narrow resonance spikes in the parameters due to the low-energy

2 s \to 3 p

and

2 s \to 4 p

dipole, as well as the

2 s \to 3 d

quadrupole autoionizing resonances. Given the unique nature of this predicted enhancement, it requires further validation, specifically regarding whether these narrow spikes in

γ_{2 p}

,

δ_{2 p}

and

ζ_{2 p}

will or will not retain their values for experimental observation if one accounts for a typical finite frequency spread in the ionizing radiation. To address this, we revisit the previous study, now incorporating the effect of frequency spread in the ionizing radiation, assuming a spread as large as 5 meV at the half-maximum of the radiation’s intensity. In the present paper we demonstrate that while the frequency spread does affect the resonance enhancement of

γ_{2 p}

,

δ_{2 p}

and

ζ_{2 p}

, these parameters still retain quantitatively significant values to be observed experimentally. The corresponding calculations were performed using the random phase approximation with exchange, which accounts for interchannel coupling in both dipole and quadrupole photoionization amplitudes. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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11 pages, 426 KiB

Open AccessArticle

Excitation of Helium by Proton and Antiproton Impact

by Zsuzsánna Bálint, Sándor Borbély and Ladislau Nagy

Atoms 2024, 12(11), 57; https://doi.org/10.3390/atoms12110057 - 3 Nov 2024

Abstract

The electron transitions in atoms caused by charged particle impact are benchmarks for the study of electron dynamics. In the present paper we focus on the excitation of helium by proton and antiproton impact. We perform both ab initio and perturbational calculations, revealing [...] Read more.

The electron transitions in atoms caused by charged particle impact are benchmarks for the study of electron dynamics. In the present paper we focus on the excitation of helium by proton and antiproton impact. We perform both ab initio and perturbational calculations, revealing the importance of electron correlations and higher-order effects. The influence of the projectile charge sign on the excitation cross section is also studied. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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14 pages, 361 KiB

Open AccessArticle

On a Study of Photoionization of Atoms and Ions from Endohedral Anions

by Valeriy K. Dolmatov, Larissa V. Chernysheva and Victor G. Yarzhemsky

Atoms 2024, 12(11), 56; https://doi.org/10.3390/atoms12110056 - 30 Oct 2024

Abstract

We study the relationship between the results of two qualitatively different semi-empirical models for photoionization cross sections,

σ_{n ℓ}

, of neutral atoms (A) and their cations (

A^{+}

) centrally encapsulated inside a fullerene anion,

C_{N}^{q}

[...] Read more.

We study the relationship between the results of two qualitatively different semi-empirical models for photoionization cross sections,

σ_{n ℓ}

, of neutral atoms (A) and their cations (

A^{+}

) centrally encapsulated inside a fullerene anion,

C_{N}^{q}

, where q represents the negative excess charge on the shell. One of the semi-empirical models, broadly employed in previous studies, assumes a uniform excess negative charge distribution over the entire fullerene cage, by analogy with a charged metallic sphere. The other model, presented here, considers the quantum states of the excess electrons on the shell, determined by specific n and ℓ values of their quantum numbers. Remarkably, both models yield similar photoionization cross sections for the encapsulated species. Consequently, we find that the photoionization of the encapsulated atoms or cations inside the

C_{N}^{q}

anion is influenced only slightly by the quantum states of the excess electrons on the fullerene cage. Furthermore, we demonstrate that the influence decreases even further as the size of the fullerene cage increases. All this holds true at least under the assumption that the encapsulated atom or cation is compact, i.e., its electron density remains primarily within itself rather than being drawn into the fullerene shell. This remarkable finding results from Hartree–Fock calculations combined with a popular modeling of the fullerene shell which is simulated by an attractive spherical annular potential. Full article

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12 pages, 5333 KiB

Open AccessArticle

Impact of Calcium Doping on the Electronic and Optical Characteristics of Strontium Hydride (SrH₂): A DFT Study

by Hamza Errahoui, Mohamed Karouchi, Abdelkebir Ejjabli, Aymane El haji, Abdelmounaim Laassouli, Omar Ait El Alia, Salah Chaji, Youssef Lachtioui and Omar Bajjou

Atoms 2024, 12(11), 55; https://doi.org/10.3390/atoms12110055 - 29 Oct 2024

Abstract

This study investigates the electronic and optical properties of calcium-doped strontium hydride (SrH₂) using first-principles density functional theory (DFT) calculations via the CASTEP code with generalized gradient approximation (GGA). We explore the impact of calcium (Ca) doping on the electronic band [...] Read more.

This study investigates the electronic and optical properties of calcium-doped strontium hydride (SrH₂) using first-principles density functional theory (DFT) calculations via the CASTEP code with generalized gradient approximation (GGA). We explore the impact of calcium (Ca) doping on the electronic band structure, density of states (DOS), and optical absorption spectra of SrH₂. Our results show that Ca doping significantly alters the electronic properties of SrH₂, notably increasing the indirect bandgap from 1.3 eV to 1.6 eV. The DOS analysis reveals new states near the Fermi level, primarily from Ca 3d orbitals. Moreover, the optical absorption spectra display enhanced absorption in the visible range, suggesting the potential for optoelectronic applications. This research highlights the feasibility of tuning the electronic and optical characteristics of SrH₂ through Ca doping, thus opening the way for the generation of advanced materials with tailored properties. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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17 pages, 354 KiB

Open AccessArticle

Gordon Decomposition of the Magnetizability of a Dirac One-Electron Atom in an Arbitrary Discrete Energy State

by Patrycja Stefańska

Atoms 2024, 12(11), 54; https://doi.org/10.3390/atoms12110054 - 25 Oct 2024

Abstract

We present a Gordon decomposition of the magnetizability of a Dirac one-electron atom in an arbitrary discrete energy eigenstate, with a pointlike, spinless, and motionless nucleus of charge

Z e

. The external magnetic field, by which the atomic state is perturbed, is [...] Read more.

We present a Gordon decomposition of the magnetizability of a Dirac one-electron atom in an arbitrary discrete energy eigenstate, with a pointlike, spinless, and motionless nucleus of charge

Z e

. The external magnetic field, by which the atomic state is perturbed, is assumed to be weak, static, and uniform. Using the Sturmian expansion of the generalized Dirac–Coulomb Green function proposed by Szmytkowski in 1997, we derive a closed-form expressions for the diamagnetic (

χ_{d}

) and paramagnetic (

χ_{p}

) contributions to

χ

. Our calculations are purely analytical; the received formula for

χ_{p}

contains the generalized hypergeometric functions ₃F₂ of the unit argument, while

χ_{d}

is of an elementary form. For the atomic ground state, both results reduce to the formulas obtained earlier by other author. This work is a prequel to our recent article, where the numerical values of

χ_{d}

and

χ_{p}

for some excited states of selected hydrogenlike ions with

1 ⩽ Z ⩽ 137

were obtained with the use of the general formulas derived here. Full article

8 pages, 1199 KiB

Open AccessArticle

CO Dissociation Induced by 1 keV/u Ar²⁺ Ion

by Chijun Zhang, Ruitian Zhang, Shaofeng Zhang and Xinwen Ma

Atoms 2024, 12(10), 53; https://doi.org/10.3390/atoms12100053 - 18 Oct 2024

Abstract

CO is one of the important molecules in dense molecular clouds, and its dissociation induced by cosmic ray heavy ions is a fundamental process for molecular breaking up and rearrangement in astronomical networks. Extensive laboratory simulations are required to understand molecular evolution in [...] Read more.

CO is one of the important molecules in dense molecular clouds, and its dissociation induced by cosmic ray heavy ions is a fundamental process for molecular breaking up and rearrangement in astronomical networks. Extensive laboratory simulations are required to understand molecular evolution in astrophysical contexts. Here, we investigate the CO dissociation induced by 1 keV/u

{Ar}^{2 +}

using cold target recoil ion momentum spectroscopy. Kinetic energy release for double electron capture

{Ar}^{2 +} + CO \to {Ar}^{0} + C^{+} + O^{+}

and transfer ionization

{Ar}^{2 +} + CO \to {Ar}^{+} + C^{+} + O^{+} + e^{-}

was obtained. The dissociation mechanisms are attributed to different KER distributions. The autoionization process is identified below the

{CO}^{2 +}

double ionization threshold. Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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9 pages, 532 KiB

Open AccessArticle

An Extensive Analysis of Tsallis Statistics: π^±, K^± Mesons, and

p \bar{p}

Baryon in Inelastic pp Collisions

by Uzma Tabassam, Zain Ul Abidin, Khadija Gul and Irfan Siddique

Atoms 2024, 12(10), 52; https://doi.org/10.3390/atoms12100052 - 15 Oct 2024

Abstract

This study explores the inelastic doubly differential transverse momentum spectra of the primary charged particles,

(π^{+} + π^{-})

,

(K^{+} + K^{-})

and

(p \bar{p})

, as a function of observables associated [...] Read more.

This study explores the inelastic doubly differential transverse momentum spectra of the primary charged particles,

(π^{+} + π^{-})

,

(K^{+} + K^{-})

and

(p \bar{p})

, as a function of observables associated with underlying event (UE) at

\sqrt{s} = 13 T e V

. The particle production is measured on the basis of different angular regions like toward, transverse and away, elucidated with respect to the direction of leading particle of an event. To study the thermal freeze-out parameters, the non-extensive Tsallis distribution function is used to extract the temperature

T_{e f f}

and chemical potential

μ

, which provide a basis to explain the QCD matter. The Tsallis distribution function describes transverse momentum spectra in pseudorapidity region of

| η | < 0.8

. It is observed that effective temperature

T_{e f f}

changes from away to towards and forward region. Full article

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10 pages, 4757 KiB

Open AccessReview

High-Precision Experiments with Trapped Radioactive Ions Produced at Relativistic Energies

by Timo Dickel, Wolfgang R. Plaß, Emma Haettner, Christine Hornung, Sivaji Purushothaman, Christoph Scheidenberger and Helmut Weick

Atoms 2024, 12(10), 51; https://doi.org/10.3390/atoms12100051 - 8 Oct 2024

Abstract

Research on radioactive ion beams produced with in-flight separation of relativistic beams has advanced significantly over the past decades, with contributions to nuclear physics, nuclear astrophysics, atomic physics, and other fields. Central to these advancements are improved production, separation, and identification methods.The FRS [...] Read more.

Research on radioactive ion beams produced with in-flight separation of relativistic beams has advanced significantly over the past decades, with contributions to nuclear physics, nuclear astrophysics, atomic physics, and other fields. Central to these advancements are improved production, separation, and identification methods.The FRS Ion Catcher at GSI/FAIRexemplifies these technological advancements. The system facilitates high-precision experiments by efficiently stopping and extracting exotic nuclei as ions and making these available at thermal energies. High-energy synchrotron beams enhance the system’s capabilities, enabling unique experimental techniques such as multi-step reactions, mean range bunching, and optimized stopping, as well as novel measurement methods for observables such as beta-delayed neutron emission probabilities. The FRS Ion Catcher has already contributed to various scientific fields, and the future with the Super-FRS at FAIR promises to extend research to even more exotic nuclei and new applications. Full article

(This article belongs to the Special Issue Advances in Ion Trapping of Radioactive Ions)

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19 pages, 2533 KiB

Open AccessArticle

Fisher Information-Based Optimization of Mapped Fourier Grid Methods

by Sotiris Danakas and Samuel Cohen

Atoms 2024, 12(10), 50; https://doi.org/10.3390/atoms12100050 - 8 Oct 2024

Abstract

The mapped Fourier grid method (mapped-FGM) is a simple and efficient discrete variable representation (DVR) numerical technique for solving atomic radial Schrödinger differential equations. It is set up on equidistant grid points, and the mapping, a suitable coordinate transformation to the radial variable, [...] Read more.

The mapped Fourier grid method (mapped-FGM) is a simple and efficient discrete variable representation (DVR) numerical technique for solving atomic radial Schrödinger differential equations. It is set up on equidistant grid points, and the mapping, a suitable coordinate transformation to the radial variable, deals with the potential energy peculiarities that are incompatible with constant step grids. For a given constrained number of grid points, classical phase space and semiclassical arguments help in selecting the mapping function and the maximum radial extension, while the energy does not generally exhibit a variational extremization trend. In this work, optimal computational parameters and mapping quality are alternatively assessed using the extremization of (coordinate and momentum) Fisher information. A benchmark system (hydrogen atom) is employed, where energy eigenvalues and Fisher information are traced in a standard convergence procedure. High-precision energy eigenvalues exhibit a correlation with the extrema of Fisher information measures. Highly efficient mapping schemes (sometimes classically counterintuitive) also stand out with these measures. Same trends are evidenced in the solution of Dalgarno–Lewis equations, i.e., inhomogeneous counterparts of the radial Schrödinger equation occurring in perturbation theory. A detailed analysis of the results, implications on more complex single valence electron Hamiltonians, and future extensions are also included. Full article

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15 pages, 279 KiB

Open AccessReview

Plasmas Containing Quasimonochromatic Electric Fields (QEFs): Review of the General Principles of Their Spectroscopy and Selected Applications

by Eugene Oks

Atoms 2024, 12(10), 49; https://doi.org/10.3390/atoms12100049 - 27 Sep 2024

Abstract

We review the general principles of the spectroscopy of plasmas containing quasimonochromatic electric fields (QEFs). We demonstrate that the underlying physics is very rich due to the complicated entanglement of four characteristic times: the typical time required for the formation of the quasienergy [...] Read more.

We review the general principles of the spectroscopy of plasmas containing quasimonochromatic electric fields (QEFs). We demonstrate that the underlying physics is very rich due to the complicated entanglement of four characteristic times: the typical time required for the formation of the quasienergy states, the lifetime of the excited state of the radiator, the typical time of the formation of the homogeneous Stark broadening by the electron microfield, and the typical time of the formation of the homogeneous Stark broadening by the dynamic part of the ion microfield. We exemplified how the shape and shift of spectral lines are affected by the mutual interactions of the three subsystems. Specifically, the interaction of the radiator with the plasma can be substantially influenced by the interaction of the radiator with the QEF, and vice versa, as well as by the interaction of the QEF and the plasma with each other. We also provide some applications of these various effects. Finally, we outline directions for future research. Full article

(This article belongs to the Special Issue Spectral Line Shapes in Plasmas, Including Cases with External Electric and Magnetic Fields and Laser Plasma Interaction)

5 pages, 196 KiB

Open AccessArticle

Measurement and Flexible Atomic Code (FAC) Computation of Extreme Ultraviolet (EUV) Spectra of Eu

by Joel H. T. Clementson, Peter Beiersdorfer, Gregory V. Brown, Natalie Hell and Elmar Träbert

Atoms 2024, 12(10), 48; https://doi.org/10.3390/atoms12100048 - 27 Sep 2024

Abstract

A group of EUV lines of H- and He-like ions of C provides excellent wavelength calibrations for a position-sensitive multichannel detector at a high-resolution spectrograph. We have exploited this setting for a series of spectra of highly charged Eu ions recorded at the [...] Read more.

A group of EUV lines of H- and He-like ions of C provides excellent wavelength calibrations for a position-sensitive multichannel detector at a high-resolution spectrograph. We have exploited this setting for a series of spectra of highly charged Eu ions recorded at the Livermore SuperEBIT electron beam ion trap. A variation in the electron beam energy results in spectra with correspondingly staggered highest Eu ion charge states ranging from Na- through to Ni-like Eu ions. A number of spectral features can be identified from the literature, but the majority of line identifications need guidance from computations of simulated spectra on the basis of collisional-radiative models. For ions with more than two electrons in the valence shell, the typical computational results are of a markedly lower accuracy. We have applied the Flexible Atomic Code (FAC), which is capable of handling all our measured ions with reasonable accuracy. We look into the systematics of the deviation of the computed transition energies from the measured ones as a function of the electron number. Full article

(This article belongs to the Special Issue 21st International Conference on the Physics of Highly Charged Ions)

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19 pages, 3564 KiB

Open AccessArticle

Data-Based Kinematic Viscosity and Rayleigh–Taylor Mixing Attributes in High-Energy Density Plasmas

by Snezhana I. Abarzhi and Kurt C. Williams

Atoms 2024, 12(10), 47; https://doi.org/10.3390/atoms12100047 - 24 Sep 2024

Abstract

We explore properties of matter and characteristics of Rayleigh–Taylor mixing by analyzing data gathered in the state-of-the-art fine-resolution experiments in high-energy density plasmas. The eminent quality data represent fluctuations spectra of the X-ray imagery intensity versus spatial frequency. We find, by using the [...] Read more.

We explore properties of matter and characteristics of Rayleigh–Taylor mixing by analyzing data gathered in the state-of-the-art fine-resolution experiments in high-energy density plasmas. The eminent quality data represent fluctuations spectra of the X-ray imagery intensity versus spatial frequency. We find, by using the rigorous statistical method, that the fluctuations spectra are accurately captured by a compound function, being a product of a power law and an exponential and describing, respectively, self-similar and scale-dependent spectral parts. From the self-similar part, we find that Rayleigh–Taylor mixing has steep spectra and strong correlations. From the scale-dependent part, we derive the first data-based value of the kinematic viscosity in high-energy density plasmas. Our results explain the experiments, agree with the group theory and other experiments, and _carve the path for better understanding Rayleigh–Taylor mixing in nature and technology. Full article

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11 pages, 1230 KiB

Open AccessArticle

Solving Time-Dependent Schödinger Equation for Some PT-Symmetric Quantum Mechanical Problems

by Tsin-Fu Jiang

Atoms 2024, 12(9), 46; https://doi.org/10.3390/atoms12090046 - 11 Sep 2024

Abstract

Using a high-precision code, we generate the eigenstates of a PT-symmetric Hamiltonian. We solve the time-dependent Schrödinger equation (TDSE) of the non-Hermitian system based on the eigenset. Since the formulation is relatively new and the observables are calculated differently than conventional quantum mechanics, [...] Read more.

Using a high-precision code, we generate the eigenstates of a PT-symmetric Hamiltonian. We solve the time-dependent Schrödinger equation (TDSE) of the non-Hermitian system based on the eigenset. Since the formulation is relatively new and the observables are calculated differently than conventional quantum mechanics, we justify it with a paradigmatic case in Hermitian quantum mechanics. We present the harmonic generation spectra on some model PT-Hamiltonians driven by an electric pulse. We discuss the physical differences with the harmonic spectra of a pulse-driven atom. Full article

(This article belongs to the Section Atom Based Quantum Technology)

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1 pages, 152 KiB

Open AccessCorrection

Correction: Stambulchik, E. Stark Broadening of Lyman-α in the Presence of a Strong Magnetic Field. Atoms 2023, 11, 120

by Evgeny Stambulchik

Atoms 2024, 12(9), 45; https://doi.org/10.3390/atoms12090045 - 9 Sep 2024

Abstract

In the original publication [...] Full article

16 pages, 7071 KiB

Open AccessArticle

Applicability of Bispectral Analysis to Causality Determination within and between Ensembles of Unstable Plasma Waves

by Renaud Stauber and Mark Koepke

Atoms 2024, 12(9), 44; https://doi.org/10.3390/atoms12090044 - 5 Sep 2024

Abstract

Turbulence implies nonlinear wave–wave coupling, and determining cause and effect of either is important to understand mixing responsible for enhanced number, momentum, or energy (NME) transport. To explain the identification of parent and daughter modes via a look-up table, we sketch the framework [...] Read more.

Turbulence implies nonlinear wave–wave coupling, and determining cause and effect of either is important to understand mixing responsible for enhanced number, momentum, or energy (NME) transport. To explain the identification of parent and daughter modes via a look-up table, we sketch the framework of bispectral analysis without repeating the mathematical formalism of earlier bispectrum researchers. We then apply this technique to a test signal and plasma fluctuation data from the WVU-Q machine, where the inhomogeneous energy density-driven spectrum exhibited a degree of coupling to lower frequencies that was absent in the case of the related, single-eigenmode, current-driven spectrum. Full article

(This article belongs to the Special Issue Plasma Physics Highlights: Non-equilibrium Dynamics, Interfaces and Mixing)

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13 pages, 414 KiB

Open AccessArticle

Cooperative Decay of an Ensemble of Atoms in a One-Dimensional Chain with a Single Excitation

by Nicola Piovella

Atoms 2024, 12(9), 43; https://doi.org/10.3390/atoms12090043 - 28 Aug 2024

Abstract

We propose a new expression of the cooperative decay rate of a one-dimensional chain of N two-level atoms in the single-excitation configuration. From it, the interference nature of superradiance and subradiance arises naturally, without the need to solve the eigenvalue problem of the [...] Read more.

We propose a new expression of the cooperative decay rate of a one-dimensional chain of N two-level atoms in the single-excitation configuration. From it, the interference nature of superradiance and subradiance arises naturally, without the need to solve the eigenvalue problem of the atom–atom interaction Green function. The cooperative decay rate can be interpreted as the imaginary part of the expectation value of the effective non-Hermitian Hamiltonian of the system, evaluated over a generalized Dicke state of N atoms in the single-excitation manifold. Whereas the subradiant decay rate is zero for an infinite chain, it decreases as

1 / N

for a finite chain. A simple approximated expression for the cooperative decay rate is obtained as a function of the lattice constant d and the atomic number N. The results are obtained first for the scalar model and then extended to the vectorial light model, assuming all the dipoles aligned. Full article

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9 pages, 2276 KiB

Open AccessArticle

Detection of Optogalvanic Spectra Using Driven Quasi-Periodic Oscillator Dynamics

by Mark Koepke

Atoms 2024, 12(8), 42; https://doi.org/10.3390/atoms12080042 - 19 Aug 2024

Abstract

The narrowband light from a scannable, single-mode dye laser influences the electrical properties of gas discharges. The variation in these properties as the laser wavelength λ is scanned yields the optogalvanic spectrum of the discharge (i.e., electrical conductivity vs. frequency). By connecting a [...] Read more.

The narrowband light from a scannable, single-mode dye laser influences the electrical properties of gas discharges. The variation in these properties as the laser wavelength λ is scanned yields the optogalvanic spectrum of the discharge (i.e., electrical conductivity vs. frequency). By connecting a neon lamp, capacitor, and power supply in parallel, an undriven relaxation oscillator is formed whose natural frequency f₀ is affected by neon-resonant laser light and this λ-dependence of the relaxation oscillator frequency f₀ yields a variant optogalvanic spectrum (i.e., f₀ vs. frequency). In this paper, a driving force is effectively applied to an otherwise undriven oscillator when the incident light is chopped periodically at f_d. For f_d ≈ f₀ and a sufficiently large driving force amplitude (laser intensity and the degree of neon resonance), the relaxation oscillator can be entrained so that f₀ is locked on f_d and is independent of λ. For the new chopped-light technique described here, f_d is adjusted to be the subthreshold of the entrainment range, where the λ-dependence of f₀ is advantageously exaggerated by periodic pulling, and the beat frequency |f_d − f₀| vs. λ provides an optogalvanic spectrum with appealingly amplified signal-to-noise qualities. Beat frequency neon spectra are reported for the cases f_d < f₀ and f_d > f₀ and are compared with spectra obtained using the unchopped-light (i.e., undriven) method. Full article

(This article belongs to the Special Issue Plasma Physics Highlights: Non-equilibrium Dynamics, Interfaces and Mixing)

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5 pages, 2337 KiB

Open AccessObituary

Claudio Mendoza (1951–2024)

by Manuel Bautista Plaza

Atoms 2024, 12(8), 41; https://doi.org/10.3390/atoms12080041 - 9 Aug 2024

Abstract

I met Claudio in 1989 when I was starting the last year of my physics bachelor’s degree [...] Full article

(This article belongs to the Section Atomic, Molecular and Nuclear Spectroscopy and Collisions)

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