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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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Convergence acceleration method for precision calculation of the Bethe logarithm
In this article we propose a simple approach for the precision calculation of the Bethe logarithm. In this approach, the Bethe logarithm is recast into a more flexible form that includes a free parameter λ. The leading contributions are obtained from specific operators, while the remaining terms are eliminated by adjusting λ. Through the use of dimensional regularization, singular divergences are algebraically canceled. Our approach notably reduces the complexity of Bethe logarithm calculations. Using this approach, we obtain a highly precise result for the Bethe logarithm for the ground state of hydrogen, achieving 49 significant digits. In the case of helium, this approach retains its simplicity and efficiency.
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The role of buffer gas in shaping the D1 line spectrum of potassium vapour
In this study, we investigate the effect of buffer gas and magnetic field on the spectral line shapes of the potassium D1 transition using sealed vapour cells filled with varying amounts of neon as a buffer gas. Employing a dual-temperature control system, we independently manipulate the cell body and stem temperatures to explore Doppler and collisional effects on the spectrum. Our results show how the Voigt spectral profile changes from Gaussian- to Lorentzian-dominated forms due to pressure broadening and shifts caused by collisions between potassium atoms and neon. Our measurements are in excellent agreement with the literature values for potassium-neon collisions. For the first time we were able to incorporate the buffer-gas shift and broadening into the modified Voigt profile via the ElecSus code, and found excellent agreement between the predicted and measured line profiles. We also analyse the potassium D1 spectral lines in the hyperfine Paschen–Back regime using strong magnetic fields, demonstrating how Zeeman splitting modifies the pressure-broadened line shape. This work provides valuable insights into collision-induced broadening and shifts, enhancing our understanding of potassium spectroscopy and its application in the development of advanced magneto-optical filters for solar physics and other applications.
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Quantitative uncertainty analysis of extracting attosecond delays from spectrally overlapping RABBIT experiments
A two-dimensional spectrogram with oscillations along the temporal dimension and partially overlapping peaks along the spectral dimension is the typical outcome of interferometric measurements, e.g. the reconstruction of attosecond beating by interference of two-photon transitions experiment of complex systems. It is necessary to retrieve the oscillation phases of the individual components in order to extract the attosecond photoionisation time delays. One can use either the global-fit method (simulating the oscillations of each component and adding them together) or the complex-fit method (first Fourier transforming along the temporal dimension and then fitting the Fourier coefficients at the relevant frequency in the spectral dimension). Here, we prove that the two methods are mathematically equivalent in the frame of least-squares fitting, and we derive the formula for the variance of the extracted phases based on the Poisson distribution. The fitting and the uncertainty formula are not limited to specific peak shapes. For the special case of two Gaussian peaks, there is a relatively simple expression for the phase uncertainty. The method can be further extended to fitting with peaks that have known phase structures or peaks with relative phase constraints. The uncertainty formula (with multiple peaks and a background) is verified by numerical simulations, and the results show that phase retrieval is possible as long as the peaks do not fully overlap (having exactly the same shape, position and phase structure), although the uncertainty rises with the degree of overlap. We also find that the correctness of fitting relies on properly assigning all the peaks in the energy domain, which is particularly important for extracting the phase from a relatively weak peak overlapped with other peaks.
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Optimizing frequency conversion based on three-wave mixing in a microring with pulse driving
High-quality Kerr-nonlinear optical microresonators driven by continuous-wave lasers have enabled the generation of coherent frequency conversion. Here, we take an alternative approach by using different types of pulses to drive a nonlinear microring resonator and leveraging the three-wave mixing process to generate and shape the converted pulses. The results reveal that the conversion efficiency and the shape quality of the converted pulse are collectively determined by the pump pulse profile, the external coupling rate between the resonator and waveguide, and the temporal offset between the two driving pulses. For a given pump energy, the optimized pump pulse that achieves the highest shape quality in the converted pulses does not necessarily yield the maximum conversion efficiency. Furthermore, we propose a genetic iterative algorithm to determine the optimal pump pulse shape for maximizing conversion efficiency under fixed coupling and signal light conditions. Meanwhile, this scheme, proposed to determine the optimal conditions for achieving maximum conversion efficiency, can be extended to investigate other pulse-driven nonlinear optical processes.
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Electron–molecule elastic scattering: a study using the configuration interaction method and model potentials
In this work, the theory of electron–molecule scattering and the influence of model potentials on improving differential cross-section (DCS) results are addressed. Unlike the treatment that uses the Hartree–Fock (HF) approximation, the configuration interaction method (CI) is employed to treat the target and obtain the static and exchange potentials. Using CI, the influence and behavior of the correlation-polarization model potential proposed by Padial and Norcross, as well as the potential called free parameter B, are analyzed in the calculation of DCS for elastic scattering, within the energy range of 5 eV – 20 eV. By comparing the results with experimental data and other theoretical results, it is shown that, although the Padial and Norcross potential is widely used in conjunction with HF and leads to satisfactory results in this case, its use with the CI method leads to unsatisfactory results, particularly for low scattering angles. On the other hand, the free parameter B potential appears to be more appropriate for including polarization effects, with no need for corrections related to electron correlation. The Lippmann–Schwinger equation, applied to scattering theory, is solved using the iterative variational method of Schwinger variational iterative method (SVIM), and in the CI calculation, single and double excitations are included.