| 1. |
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| 2. |
- Grumer, Jon, et al.
(författare)
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Hyperfine induced intensity redistribution in In II
- 2010
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:7
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical investigation of the hyperfine structure of the 5s5d D-3(2)-5s4f F-3(2,3)0 transitions in In II. Earlier work has failed in determining hyperfine constants for the upper levels of these transitions. We show that this is due to strong off-diagonal hyperfine interaction, which not only changes the position of the individual hyperfine lines but also introduces large intensity redistributions among the different hyperfine levels. We present hyperfine dependent gf-values and show that off-diagonal hyperfine interaction reduces some of the gf-values by two orders of magnitude, while others are increased by up to more than a factor of 6. We also discuss the influence on the hyperfine structure of an accurate representation of the level-splitting of the 5s4f configuration. We show that the hyperfine interaction in F-3(3)0 and F-1(3)0 is very hard to determine accurately even in a large-scale calculation, and we derive a semi-empirical method for adjusting our results using an experimentally known, diagonal hyperfine constant for 5s4f F-1(3)0. The resulting theoretical synthetic spectra reproduce the experimental values to high accuracy and facilitate the identification of all observed lines.
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| 3. |
- Öhrwall, Gunnar, et al.
(författare)
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Photofragmentation of cyanogen upon carbon and nitrogen K-shell excitation by partial ion yield experiments
- 2010
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:9, s. 095201-
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Tidskriftsartikel (refereegranskat)abstract
- Partial ion yield spectroscopy was used to study fragmentation processes in cyanogen after C 1s and N 1s photoexcitation. The interpretation of the core excitation spectrum mostly follows the literature, but the high resolution has in some cases allowed a more detailed assignment. Using the fact that in Rydberg states there is an intensity increase as the fragmentation process becomes more extensive compared to valence orbitals, we have been able to distinguish resonances with valence and Rydberg character. Furthermore, we have been able to assign features in the ionization continuum as arising from double excitations or shape resonances, by observation of the suppression of anion yield at shape resonances.
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| 4. |
- Andersson, Martin, et al.
(författare)
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Hyperfine dependent lifetimes in Mg-like ions
- 2010
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:9
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical investigations of the hyperfine quenching of the two metastable levels 1s(2)2s(2)2p(6)3s3p P-3(0) and P-3(2) have been performed along the magnesium-like iso-electronic sequence ranging from Z = 12 to Z = 31. It is shown that the lifetime of the latter level is sensitive to hyperfine quenching in the beginning of the sequence, but that this sensitivity decreases going to higher Z. It is also shown that the branching fractions of the 3s(2) S-1(0)-3s3p P-3(2) and 3s3p P-3(1)-3s3p P-3(2) transitions are very sensitive to hyperfine quenching, which could lead to some dramatic effects in the spectrum. Our predicted transition rates of the hyperfine induced 3s(2) S-1(0)-3s3p P-3(0) transition are compared to earlier results and some disagreements are found and explained. The present predicted lifetime of 3s3p P-3(0) in Al-27(+) is slightly longer than the recent measurement, but in better agreement than earlier predictions.
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| 5. |
- Andersson, Martin, et al.
(författare)
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The anomalous hyperfine structure of Al II
- 2012
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 45:13
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Tidskriftsartikel (refereegranskat)abstract
- The hyperfine structure of a large number of transitions in Al II cannot be described using A and B hyperfine constants and the hyperfine structure is therefore said to be anomalous. In this paper, we have studied the hyperfine structure of a few transitions in Al II, 3s5s(3)S-3s5p(3)P, 3s4d(3)D-3s5p(3)P and 3s5p(3)P-3s5d(3)D, by combining theory and experiment. It is shown that the anomalous hyperfine structure is due to strong off-diagonal hyperfine interaction resulting not only in a deplacement of the energies of the hyperfine levels, but also resulting in large intensity redistribution among the individual hyperfine lines. It is shown that the hyperfine mixing in 3s4d(3)D and 3s5d(3)D is very large, whereas small but not negligible in 3s5p(3)P. By combining experimental spectra and theory we could obtain accurate wavefunctions for the 3s4d(3)D and 3s5d(3)D hyperfine levels which were used to calculate the gf-values of all individual hyperfine transitions not only for 3s5p(3)P, but also for 3s3p(3)P and 3s4p(3)P, where the off-diagonal hyperfine interaction leads to negligible intensity redistribution.
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| 6. |
- Bäckström, Erik, et al.
(författare)
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Experimentally determined oscillator strengths in Rh II
- 2013
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:20, s. 205001-
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents new experimentally determined branching fractions and oscillator strengths (log gf) for lines originating from 17 levels belonging to 5 terms of the first excited odd configuration 4d(7)(D-4) 5p in Rh II. The intensity calibrated spectra of Rh II have been recorded with a Fourier transform spectrometer between 25000 and 45000 cm(-1) (2200-4000 angstrom). In this region, 49 lines have been identified and measured. By combining the branching fractions obtained from the spectra with previously measured lifetimes, log gf values are reported. The new results are compared with previous theoretical work.
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| 7. |
- Cattani, F., et al.
(författare)
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Co-propagating Bose-Einstein condensates and electromagnetic radiation: formation of mutually localized structures
- 2010
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 1361-6455 .- 0953-4075. ; 43:8
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Tidskriftsartikel (refereegranskat)abstract
- A semi-classical model is derived for describing the interaction between coherent electromagnetic radiation and a Bose-Einstein condensate in the limit of zero temperature, including the back action of the atoms on the radiation. This model is used to analyse the problem of the self-consistent evolution of a laser beam and a BEC atomic beam. The mutual propagation is studied numerically and demonstrates not only the possibility of a stationary regime of mutual guiding, but also of generating a collapse-like phenomenon.
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| 8. |
- Clementson, Joel, et al.
(författare)
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Tungsten spectroscopy relevant to the diagnostics of ITER divertor plasmas
- 2010
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:14
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of using extreme ultraviolet emission from low charge states of tungsten ions to diagnose the divertor plasmas of the ITER tokamak has been investigated. Spectral modelling of Lu-like W3+ to Gd-like W10+ has been performed by using the Flexible Atomic Code, and spectroscopic measurements have been conducted at the Sustained Spheromak Physics Experiment (SSPX) in Livermore. To simulate ITER divertor plasmas, tungsten was introduced into the SSPX spheromak by prefilling it with tungsten hexacarbonyl prior to the usual hydrogen gas injection and initiation of the plasma discharge. The tungsten emission was studied using a grazing-incidence spectrometer.
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| 9. |
- Cryan, J P, et al.
(författare)
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Molecular frame Auger electron energy spectrum from N2
- 2012
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 45:5, s. 055601-
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Tidskriftsartikel (refereegranskat)abstract
- Here we present the first angle-resolved, non-resonant (normal) Auger spectra for impulsively aligned nitrogen molecules. We have measured the angular pattern of Auger electron emission following K -shell photoionization by 1.1 keV photons from the Linac Coherent Light Source (LCLS). Using strong-field-induced molecular alignment to make molecular frame measurements is equally effective for both repulsive and quasi-bound final states. The capability to resolve Auger emission angular distributions in the molecular frame of reference provides a new tool for spectral assignments in congested Auger electron spectra that takes advantage of the symmetries of the final diction states. Based on our experimental results and theoretical predictions, we propose the assignment of the spectral features in the Auger electron spectrum.
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| 10. |
- Dahlström, J. Marcus, et al.
(författare)
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Introduction to attosecond delays in photoionization
- 2012
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 45:18, s. 183001-
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Tidskriftsartikel (refereegranskat)abstract
- This tutorial presents an introduction to the interaction of light and matter on the attosecond timescale. Our aim is to detail the theoretical description of ultra-short time delays and to relate these to the phase of extreme ultraviolet (XUV) light pulses and to the asymptotic phaseshifts of photoelectron wave packets. Special emphasis is laid on time-delay experiments, where attosecond XUV pulses are used to photoionize target atoms at well-defined times, followed by a probing process in real time by a phase-locked, infrared laser field. In this way, the laser field serves as a 'clock' to monitor the ionization event, but the observable delays do not correspond directly to the delay associated with single-photon ionization. Instead, a significant part of the observed delay originates from a measurement induced process, which obscures the single-photon ionization dynamics. This artefact is traced back to a phaseshift of the above-threshold ionization transition matrix element, which we call the continuum-continuum phase. It arises due to the laser-stimulated transitions between Coulomb continuum states. As we shall show here, these measurement-induced effects can be separated from the single-photon ionization process, using analytical expressions of universal character, so that eventually the attosecond time delays in photoionization can be accessed.
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