Search Results (785)

A theoretical scheme for precise measurement of microwave (MW) electric fields is proposed using a structured control field in Rydberg atoms. We use a Bessel–Gauss (BG) beam to drive the excited-state transition, its spatial structure characteristics result in a narrow linewidth of probe transmission, which benefits MW electric field measurement. It is interesting that the spectral linewidth could be further narrowed by increasing the azimuthal index. The minimum detectability of the MW field is about one-tenth of the common electromagnetically induced transparency scheme, and the spectrum resolution could be improved by about 40 times from simulation. Moreover, the system has good robustness. Full article

Using the Multiconfiguration Dirac–Hartree–Fock method as implemented in the General Relativistic Atomic Structure Package, the magnetic dipole and electric quadrupole hyperfine structure constants were determined for the ground and first excited levels of ^135,137Ba II isotopes, as well as for ¹³⁷Ba I and ⁸⁷Sr II, to assess the robustness of the developed model. This study builds upon and extends previous investigations by examining the levels involved in resonance lines, with the aim of resolving persistent discrepancies in the hyperfine structure of ¹³⁷Ba II and ⁸⁷Sr II. New code developments such as the use of natural orbitals, as well as the addition of polarization effects and Configuration State Function Generators, as implemented in GRASPG, were tested for these heavy elements. The developed strategy allowed us to achieve encouraging results that satisfactorily agree with experiments for all studied levels but ${}^{2}D_{5/2}$ in the ¹³⁷Ba II isotope. This disagreement was also observed in ¹³⁵Ba II isotope as well as in ⁸⁷Sr II. With two valence electrons, ¹³⁷Ba I is definitely more complex, requiring a multireference approach. Even with the latter, the theory–observation disagreement observed for the hyperfine structure of the low-lying levels remains large in comparison with the alkali-like systems. Possible ongoing developments to remediate this issue are discussed in the conclusions. Full article

The food processing industry is seeking new technologies to enhance product safety, extend shelf life, and optimise food quality in response to growing consumer demand for high-quality products. Since the discovery of plasma technology, its potential applications in food processing have been numerous. For most of these applications, plasma characterisation is key to successfully scaling up from laboratory to industrial settings. A highly valuable tool for plasma characterisation is optical emission spectroscopy (OES), which serves as a non-invasive diagnostic method to monitor reactive species, specifically excited atoms and molecules (reactive oxygen and nitrogen species—RONS) that are critical for food treatment. The main role of OES in food control is to enable species identification and real-time process monitoring, providing feedback on electron temperature and density to prevent thermal damage to sensitive food products. It also facilitates optimisation by adjusting voltage and gas flow rates to maximise the production of antimicrobial species. These results ensure that processes are reliable and repeatable, supporting the transition from laboratory-scale to industrial applications. The paper provides an overview of the use of optical emission spectroscopy in various applications of plasma technology in food processing, including the determination of the elemental composition of raw materials and final products, detection of contaminants, quality control, determination of characteristic plasma parameters, and ensuring compliance with food safety regulations. Full article

By numerically solving the time-dependent Schrödinger equation (TDSE), we study the elementary excitation and ionization processes of atomic hydrogen on the same footing, which is irradiated by the two-color laser fields composed of a strong 400 nm pulse and a weak 800 nm pulse. We find that under different intensities of the 400 nm laser, the ionization and excitation probabilities exhibit completely distinct modulations with the variation in the intensity of the 800 nm laser. Electron energy spectra (EESs), including above-threshold ionization (ATI) peaks and below-threshold bound states, indicate that the involvement of Rydberg states and the shift of low-energy ATI peaks due to the increase in the ponderomotive energy are the primary causes of the above-mentioned modulation behavior. By virtue of a quantum-state-resolved numerical method, the angular-momentum-resolved EES reveal how the addition of the 800 nm laser field perturbs and modifies the strong, 400 nm dominated multiphoton excitation and ionization channels. Our study provides a flexible control strategy for multiphoton excitation and ionization in atoms and even molecules and further advances the understanding of the complex ultrafast dynamics driven by two-color femtosecond laser fields. Full article

Background: Deep vein thrombosis (DVT) is one of the most common cardiovascular diseases and is especially prevalent in areas with environmental pollution. Bioaccumulation of toxic heavy metals may lead to deterioration of homeostasis with cellular change, endothelial dysfunction, DNA impairment and cellular signaling. The reason for this is usually the accumulation of thrombogenic toxins in the body as a result of long-term exposure or a lack of regulatory gene expression. In this study, we aimed to measure the minerals that potentially accumulate in the nail. The measurement method was laser-induced breakdown spectroscopy (LIBS), which is a form of atomic emission spectroscopy. It uses a highly energetic laser source to form a plasma of excited atoms emitting light of characteristic wavelengths. It provides accurate quantification and reveals the relationship between tissue accumulation of toxic heavy metals and DVT formation. Methods: Between January 2020 and December 2021, 100 patients diagnosed with lower-extremity deep vein thrombosis were screened in a single tertiary healthcare center. Among them, 50 patients who met the eligibility criteria and consented to participate were included in the study. An additional 50 age-matched healthy volunteers were enrolled as controls. Demographic and clinical characteristics were recorded. Nail samples were obtained from each participant, and elemental emission intensities were quantitatively analyzed using laser-induced breakdown spectroscopy (LIBS). Results: No difference in clinical characteristics was detected between the groups. While iron, calcium and silicon were found to be high in DVT patients, magnesium was found to be low. Regarding the magnesium emission, ROC analysis showed 76–90% specificity and 69–82% sensitivity, respectively. Conclusions: LIBS is a useful method because it is easy to use and can be used with a small sample. According to the results of our study, information about the pathogenesis of DVT was obtained through nail analysis. Therefore, we believe that LIBS analysis is a method that may be useful in determining the causes and predisposing factors for DVT. Full article

Calcium phosphate–poly(methyl-methacrylate) composite layers have been synthetized on silicon substrates in magnetron sputtering discharge by adjusting the radio-frequency power. The electron energy distribution function measured at holder substrate position shifts to lower energies when the radio-frequency power applied to the magnetron source increases from 50 to 150 W and the poly(methyl-methacrylate) molecule dissociation is augmented. The optical emission spectral analysis indicated the dynamics of the excitation and ionization processes in the Ar–calcium phosphate–poly(methyl-methacrylate) plasma mixture, as well as the dissociation patterning of the polymer molecules. The Ca I, P I, and H_α atomic lines and CaO, PO, POH, CO, CH and C₂ molecular bands characteristic to the calcium phosphate and poly(methyl-methacrylate) decomposition were evidenced. At 150 W radio-frequency power a reduction in the polymer content in the composite layer volume was observed even if the α-CH₃ main chain and the C=O molecular bands are still present. More C-C/C-H, C-OH/C-O-C polymeric bonds were revealed at the layer surface, indicating the formation of plasma polymers. The Ca/P ratio changes from 1.72 to 1.9 at 50 to 150 W, respectively, maintaining the amorphous structure of the layers. In this power range, the transition of layer surface morphologies from grain-like to worm-like plasma polymer characteristics is connected to an increase in plasma ion density and layer thickness. Full article

Quantum dots combine advantages such as strong processability via solution methods, wide color gamut coverage, and precise emission color coordinates, making them highly promising for applications in optoelectronic devices. However, they face limitations such as insufficient fluorescence intensity and low far-field extraction efficiency. Plasmonic nanocavities based on metallic nanostructures offer an efficient platform for regulating light–matter interactions. In this study, we constructed a tilted plasmonic nanocavity structure composed of a silver nanocube, CdSe/CdS nanorods, and a single-crystal silver microplate. An Al₂O₃ isolation layer prepared via atomic layer deposition was used to control the nanocavity gap, precisely matching the plasmonic resonance mode with the 620 nm fluorescence emission of the quantum dots. This coupling system significantly enhances the radiative rate in the emission band and the electric field strength in the excitation band, achieving a 187-fold luminescence enhancement of the quantum dot. Additionally, leveraging the nano-antenna effect, the fluorescence exhibits upward directional emission. Experimental and simulation results confirm the high-efficiency enhancement and directional control of quantum dot fluorescence by the tilted nanocavity, providing new insights for the integrated application of quantum dots in displays, quantum communication, and other fields. Full article

Dielectronic recombination (DR) is widely recognized as a fundamental atomic process in many astrophysical and laboratory plasmas, where it plays a crucial role in determining ionization balance and level populations over a broad temperature range. Reliable DR resonance strengths and plasma rate coefficients for such plasma modeling can be computed using the Jena Atomic Calculator (JAC)—a relativistic code based on the multiconfiguration Dirac–Hartree–Fock (MCDHF) method. In this work, we investigate the DR of Li-like Ar¹⁵⁺ ions in their ground state (2s), focusing on resonances associated with the fine-structure core excitations $2s_{1/2}\to 2p_{1/2,3/2}$. The resulting fine-structure-resolved DR resonance strengths and plasma rate coefficients are in good agreement with recent high-resolution DR measurements of Ar¹⁵⁺ ions performed at the Main Cooler Storage Ring (CSRm) in Lanzhou, China. These results provide a stringent benchmark for JAC calculations and support their applicability in plasma modeling. Full article

The radiation pattern emitted by two atoms, interacting with each other via the vacuum radiation field, has been calculated, including effects of magnetic state degeneracy for atoms with a ground state having $G=0$ angular momentum and an excited state having $H=1$ angular momentum. For an initial condition in which both atoms are inverted, the time-integrated radiation pattern is identical to that for non-interacting atoms if the atoms lie on the z-axis, but differs if the atoms lie on the x-axis. The underlying dynamics giving rise to this behavior are examined. Full article

This paper investigates the different relaxation channels of a single symmetric top NH₃ and a spherical top CH₄ molecule trapped at low temperature in a clathrate hydrate nano-cage in the infrared absorption domain of their vibrational degrees of freedom. The approach utilizes the Born–Oppenheimer approximation and the extended site inclusion model applied to CO₂ in a previous work, which was based on pairwise atom–atom effective interaction potentials. The calculations show that trapping the methane or ammonia molecule is energetically more favorable in a type sI clathrate structure than in an sII one, and entropic considerations show that methane can be released much more easily than ammonia from clathrate hydrate nano-cages. In the small (s) and large (l) nano-cages with the sI structure, the CH₄ molecule exhibits a more or less perturbed rotational motion, while the NH₃ molecule shows a strongly hindered orientational motion that tends to a three-dimension librational motion (oscillation motion) around its orientational equilibrium configuration. The calculated orientational energy level schemes are quite different from those of the molecular free rotation. In the static field inside the cage, degenerate ${\nu }_3$ and ${\nu }_4$ vibrational modes of methane and ammonia molecules are shifted and split. Moreover, for ammonia molecules, the ${\nu }_1$ and ${\nu }_2$ modes are shifted, and the inversion motion is no longer allowed. The non-radiative and radiative relaxation channels of CH₄, NH₃ and CO₂ in clathrate nano-cages are discussed with reference to the matrix isolation spectroscopic results. Upon laser excitation, then, from the energy levels calculated for the different degrees of freedom, NH₃ and CO₂ are expected to fluoresce, while for CH₄, non-radiative relaxation should lead to evaporation at the surface of clathrates. Experimental setups are suggested to localize and study these species underneath ice surfaces on distant planets or planetesimals from mobile detectors such as drones or CubeSats equipped with appropriate laser sources and telescopes with 2D imaging detectors. Full article

A promising route for removing antibiotics such as penicillin from wastewater is photocatalytic degradation under UV irradiation using TiO₂ nanoparticles. However, the microscopic mechanisms governing the initial degradation steps remain poorly understood. In particular, it is still unclear whether degradation preferentially occurs in solution or upon adsorption on the oxide surface, and which molecular sites are most vulnerable to attack in solution compared to those activated on the catalyst. In this work, we introduce a unified density functional theory approach that treats penicillin V (phenoxymethylpenicillin) consistently, both isolated in solution and adsorbed on an anatase TiO₂ nanocluster, enabling a direct comparison between solution-phase and surface-mediated degradation pathways. Within this framework, we analyze the adsorption configurations, energy-level alignment, charge-transfer pathways, UV-Vis absorption properties, local reactivity descriptors, and the initial steps leading to bond breaking. The results show that the direct photoexcitation of PenV followed by electron transfer to the oxide is less likely, due to the high energy of the pollutant’s excited states. In contrast, degradation initiated by the transfer of photogenerated holes from the catalyst to the adsorbed antibiotic appears more probable, driven by the smaller energetic offset and by the hybridization between molecular and oxide states. Overall, adsorption on the oxide surface appears to be more conducive to degradation, with the carbon atom in the β-lactam ring consistently identified as a susceptible site for attack across different environments. Full article

The giant atom paradigm, where a single quantum emitter couples to a continuum at multiple discrete points, has enabled unprecedented control over light-matter interactions, including decoherence-free subspaces and chiral emission. However, realizing these non-local effects beyond the microwave regime remains a significant challenge due to the diffraction limit. Here, we theoretically propose a photonic analog of giant atoms operating at optical frequencies, utilizing a quantum emitter resonantly coupled to a pair of spatially separated single-mode cavities interacting with a common 1D photonic continuum. By rigorously deriving the effective non-Hermitian Hamiltonian and integrating out the bath degrees of freedom, we demonstrate that the interference between cavity-mediated emission pathways leads to the formation of robust Bound States in the Continuum (BICs). These interference-induced dark states allow for the infinite trapping of excitation within the emitter-cavity subsystem, effectively shielding it from radiative decay. Our results extend the giant atom toolbox to the optical domain, offering a scalable architecture for integrated quantum photonics and quantum interconnects. Full article

A plasma-assisted ammonia jet flame igniter was developed in this study to address the limitations of conventional spark ignition at high pressures. The effect of pressure on plasma discharge characteristics, optical emission spectra, and exhaust gas emission was systematically investigated, providing new insights into the mechanisms of plasma-assisted ammonia ignition under high-pressure conditions. The results indicate that increased chamber pressure elevates gas density, which in turn raises the voltage required to sustain an arc discharge at 0.4 MPa and markedly reduces the frequency of arc drift. Spectral analysis shows that higher pressure inhibits atomic oxygen lines (777.2 nm and 844.6 nm) while intensifying the molecular nitrogen bands between 350–450 nm. A corresponding decrease in electron excitation temperature is also observed. In terms of exhaust composition, hydrogen concentration demonstrates a bifurcated behavior, rising with pressure under fuel-rich conditions (the equivalence ratio φ > 1.2) and falling under fuel-lean conditions (φ ≤ 1). Conversely, NO concentration consistently decreases with increasing pressure across all test conditions. The ammonia concentration in the exhaust gas shows opposite pressure dependencies at different equivalence ratios. It increases with rising pressure for φ ≥ 1, while it decreases with increasing pressure for φ < 1. Full article

Metallaphotoredox catalysis merges the powerful bond-forming abilities of transition metal catalysis with unique electron or energy transfer pathways accessible in photoexcited states, injecting new vitality into organic synthesis. However, most transition metal catalysts cannot be excited by visible light. Thus, prevalent metallaphotoredox catalytic systems require dual catalysts: a transition metal catalyst and a separate photosensitizer. This leads to inefficient electron transfer between these two low-concentration catalytic species, which often limits overall photocatalytic performance. Single-atom site catalysts (SASCs) offer a promising solution, wherein isolated and quasi-homogeneous transition metal sites are anchored on heterogeneous supports. When semiconductors are employed as the support, the photosensitive unit and transition metal catalytic site can be integrated into one system. This integration switches the electron transfer mode from intermolecular to intramolecular, thereby significantly enhancing photocatalytic efficiency. Furthermore, such heterogeneous catalysts are easier to separate and reuse. This review summarizes recent advances in the application of SASCs for photocatalytic organic synthesis, with a particular focus on elucidating structure–activity relationships of the single-atom sites. Full article

Herein, we propose a simple and cost-effective method for fabricating moderate-sensitivity surface-enhanced Raman scattering (SERS) substrates using Cu-plasma polymer fluorocarbon (Cu-PPFC) nanocomposite films fabricated through RF sputtering. The use of a composite target composed of carbon nanotube (CNT), Cu, and polytetrafluoroethylene (PTFE) powders (5:60–80:35–15 wt%) offers the advantage of the simple fabrication of moderate-sensitivity SERS substrates with a single cathode compared to co-sputtering. X-ray photoelectron spectroscopy (XPS) revealed that the film surface was partially composed of metallic Cu with Cu-F bonds and Cu–O bonds, confirming the coexistence of the conducting and plasmon-active domains. UV-VIS spectroscopy revealed a distinct absorption peak at approximately 680 nm, indicating the excitation of localized surface plasmon resonances in the Cu nanoclusters embedded in the plasma polymer fluorocarbon (PPFC) matrix. Atomic force microscopy and grazing incidence small-angle X-ray scattering analyses confirmed that the Cu nanoparticles were uniformly distributed with interparticle distances of 20–35 nm. The Cu-PPFC nanocomposite film with the highest Cu content (80 wt%) exhibited a Raman enhancement factor of 2.18 × 10⁴ for rhodamine 6G, demonstrating its potential as a moderate-sensitivity SERS substrate. Finite-difference time-domain (FDTD) simulations confirmed the strong electromagnetic field localization at the Cu-Cu nanogaps separated by the PPFC matrix, corroborating the experimentally observed SERS enhancement. These results suggest that a Cu-PPFC nanocomposite film, easily fabricated using a composite target, provides an efficient and scalable route for fabricating reproducible, inexpensive, and moderate-sensitivity SERS substrates suitable for practical sensing applications. Full article