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Journal of Physics B: Atomic, Molecular and Optical Physics - latest papers
Latest articles for Journal of Physics B: Atomic, Molecular and Optical Physics
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Parametric cumulant mapping: a multidimensional correlation method for experiments with high and fluctuating event rates
In atomic, molecular, and optical physics experiments investigating photoinduced reactions in the gas phase, methods that determine which of multiple products correlate are crucial. A major challenge is that instabilities in experimental parameters, such as the laser intensity, influence the event rate, so that false correlations are induced. For correlation at high and fluctuating event rate, which is common in experiments employing free-electron lasers, covariance-based methods are widely used. However, they can only infer correlation between two or three reaction products. In higher dimensions, cumulant mapping can be applied, but only if any event rate fluctuations are negligible. There is yet no method valid for correlation in higher dimensions and at high and fluctuating event rate. To fill this gap, we present a new method: parametric cumulant mapping. Parametric cumulant mapping can infer correlation between any number of reaction products and at arbitrary and even unknown event rate fluctuations. It is theoretically deduced as a generalization of cumulant mapping to correct for fluctuations, and its functionality is demonstrated in simulations. A general formula of the parametric cumulant is given, and explicit expressions in up to four dimensions are presented. Python and Matlab code for computing parametric cumulants in any dimension is provided as supplementary data. We also show that the established method of partial covariance, typically used at linear laser-light fluctuations, is a special case of parametric cumulants.
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Unraveling carrier dynamics and intensity-dependent multi-photon absorption of gold nanorods
In this study, we have investigated the hot carrier dynamics and femtosecond (fs) third-order nonlinear optical (NLO) properties of excited plasmonic modes in gold nanorods (Au NRs). Au NRs were synthesized via a seed-mediated growth method, exhibiting an aspect ratio of ∼3.4. The plasmonic local field enhancement of Au NRs was simulated, which undergoes the non-radiative decay to generate hot carriers. The ultrafast dynamics of these generated carriers associated with the longitudinal surface plasmon resonance (LSPR) and transverse surface plasmon resonance (TSPR) bands are investigated using fs transient absorption spectroscopy measurements. The results reveal insight into carrier relaxation after photoexcitation, demonstrating three decay stages: electron–electron scattering in fs, followed by electron–phonon and phonon–phonon interaction in ps, evolving the final energy into the environment. LSPR mode shows higher relaxation times than TSPR mode at three different fluences. Next, the FFT of transient absorption traces revealed that the breathing vibrational frequency of Au NRs decreases with increasing pump fluence. Moreover, the NLO response of these NRs is explored using the fs Z-scan technique at an excitation wavelength of 800 nm at different peak intensities of 17.4–174 GW cm−2. The open-aperture studies revealed a transition in nonlinear absorption behavior from saturable absorption (SA) to reverse SA with increasing incident laser intensity, indicating strong intensity-dependent nonlinear absorption characteristics. The optical limiting threshold of Au NRs was estimated as ∼14 mJ cm−2. The observed NLO response, combined with ultrafast plasmonic dynamics, highlights the potential of this material for applications in nonlinear photonics and optical limiters.
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Statistics of multi-electron states and J-levels in atomic configurations
The number and nature of atomic configurations are cornerstones of atomic spectroscopy, especially for the calculation of hot-plasma radiative properties. The knowledge of the distributions of magnetic quantum number M and angular momentum J for N identical fermions in a subshell with half-integer spin j is a prerequisite to the determination of the structure of such configurations. The problem is rather complicated, since the possible occurrence of a specific values of J is governed by the Pauli exclusion principle. Several methods, such as generating functions, recurrence relations or algebraic number theory—for instance via Gaussian polynomials—have proven effective in addressing this issue. However, up to now, no general formula was known. In the present work, we present exact and compact explicit formulas for the number of atomic configurations and for the distributions of the total magnetic quantum number M and angular momentum J.
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Elastic scattering of twisted electrons by CO2 molecules at high energies
The elastic scattering of a beam of twisted electrons (Bessel beam) by CO2 molecules is studied theoretically at high energies. The molecule’s structure is optimized using coupled cluster theory and density functional theory with correlation-consistent and Pople basis sets. Coulomb potentials are used for the interactions in the static approximation. The differential and total scattering cross-sections are computed in the first Born approximation. All cross-sections are orientation-averaged using a passive rotational averaging technique. The scattering is studied by the impact of the twisted beam with topological charges in the range ml = 1 and ml = 20. The cross sections are, in addition, averaged over the target’s impact parameters, which accounts for the cross sections of a large distribution of CO2 molecules. Finally, the molecule’s total cross-section by plane waves and twisted beams is reported. The proposed methodology can be applied to study any polyatomic molecule, regardless of its structure.
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Exact solutions and quantum defect theory for van der Waals potentials in ultracold molecular systems
In this paper, we have provided exact two-body solutions to the 2D and 3D Schrödinger equations with isotropic van der Waals potentials of the form . Based on these solutions, we developed an analytical quantum defect theory (QDT) applicable to both quasi-2D and 3D geometries, and applied it to study the scattering properties and bound-state spectra of ultracold polar molecules confined in these geometries. Interestingly, we find that in the attractive (repulsive) van der Waals potential case, the short-range interaction can be effectively modeled by an infinite square barrier (finite square well), which leads to narrow and dense (broad and sparse) resonance structures in the quantum defect parameter. In the quasi-2D attractive case, shape resonances can appear in an ordered fashion across different partial waves, characterized by sharp phase jumps as the scattering energy is varied. Furthermore, the low-energy analytical expansions derived from QDT show excellent agreement with the exact numerical results, validating the accuracy and usefulness of our analytical approach in describing two-body physics governed by long-range van der Waals interactions.