| 1. |
- Sörngård, Johanna, et al.
(författare)
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Study of the possibilities with combinations of circularly and linearly polarized light for attosecond delay investigations
- 2020
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:13
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Tidskriftsartikel (refereegranskat)abstract
- We present calculations on the atomic delay in photoionzation obtained with different combinations of linearly and circularly polarized light, and show how a tensor operator approach can be used to readily obtain results for any combination from a single calculation of the radial integrals. We find that for certain choices of polarization and detection geometry a single time-delay measurement is enough to extract the atomic delay since the relative phase in a RABBIT type measurement will be imprinted on the photo electron anisotropy. We show further that the full angular dependence can be qualitatively understood from a plane wave analysis. The results are illustrated by many-body calculations of two-photon above threshold ionization on argon.
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| 2. |
- Bertolino, Mattias, et al.
(författare)
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Propensity rules and interference effects in laser-Assisted photoionization of helium and neon
- 2020
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:14
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the angle-resolved photoelectron spectra from laser-Assisted photoionization for helium and neon atoms using an ab initio method based on time-dependent surface flux and configuration interaction singles. We find that the shape of the distributions can be interpreted using a propensity rule, an intrinsic difference in the absorption and the emission processes, as well as interference effects between multiple paths to the final angular momentum state. The difference between absorption and emission is hidden in the first sideband in neon due to the multiple competing m channels, while in the second sideband a qualitative difference between absorption and emission is observed. In the m-resolved case, a clear difference is observed already in the first sideband, as exemplified in helium and m-resolved neon.
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| 3. |
- Cheng, Yu Chen, et al.
(författare)
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Imaging multiphoton ionization dynamics of CH3I at a high repetition rate XUV free-electron laser
- 2021
-
Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:1
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Tidskriftsartikel (refereegranskat)abstract
- XUV multiphoton ionization of molecules is commonly used in free-electron laser experiments to study charge transfer dynamics. However, molecular dissociation and electron dynamics, such as multiple photon absorption, Auger decay, and charge transfer, often happen on competing time scales, and the contributions of individual processes can be difficult to unravel. We experimentally investigate the Coulomb explosion dynamics of methyl iodide upon core-hole ionization of the shallow inner-shell of iodine (4d) and classically simulate the fragmentation by phenomenologically introducing ionization dynamics and charge transfer. Under our experimental conditions with medium fluence and relatively long XUV pulses (similar to 75 fs), we find that fast Auger decay prior to charge transfer significantly contributes to the charging mechanism, leading to a yield enhancement of higher carbon charge states upon molecular dissociation. Furthermore, we argue for the existence of another charging mechanism for the weak fragmentation channels leading to triply charged carbon atoms. This study shows that classical simulations can be a useful tool to guide the quantum mechanical description of the femtosecond dynamics upon multiphoton absorption in molecular systems.
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| 4. |
- Ekholm, V., et al.
(författare)
-
Core-hole localization and ultra-fast dissociation in SF6
- 2020
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:18
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering spectra excited at the fluorine K resonances of SF(6)have been recorded. While a small but significant propensity for electronically parity-allowed transitions is found, the observation of parity-forbidden electronic transitions is attributed to vibronic coupling that breaks the global inversion symmetry of the electronic wavefunction and localizes the core hole. The dependence of the scattering cross section on the polarization of the incident radiation and the scattering angle is interpreted in terms of local pi/sigma symmetry around the S-F bond. This symmetry selectivity prevails during the dissociation that occurs during the scattering process.
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| 5. |
- Forbes, Ruaridh, et al.
(författare)
-
Time-resolved site-selective imaging of predissociation and charge transfer dynamics : The CH3I B-band
- 2020
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:22
-
Tidskriftsartikel (refereegranskat)abstract
- The predissociation dynamics of the 6s (B2E) Rydberg state of gas-phase CH3I were investigated by time-resolved Coulomb-explosion imaging using extreme ultraviolet (XUV) free-electron laser pulses. Inner-shell ionization at the iodine 4d edge was utilized to provide a site-specific probe of the ensuing dynamics. The combination of a velocity-map imaging (VMI) spectrometer coupled with the pixel imaging mass spectrometry (PImMS) camera permitted three-dimensional ionic fragment momenta to be recorded simultaneously for a wide range of iodine charge states. In accord with previous studies, initial excitation at 201.2 nm results in internal conversion and subsequent dissociation on the lower-lying A-state surface on a picosecond time scale. Examination of the time-dependent yield of low kinetic energy iodine fragments yields mechanistic insights into the predissociation and subsequent charge transfer following multiple ionization of the iodine products. The effect of charge transfer was observed through differing delay-dependencies of the various iodine charge states, from which critical internuclear distances for charge transfer could be inferred and compared to a classical over-the-barrier model. Time-dependent photofragment angular anisotropy parameters were extracted from the central slice of the Newton sphere, without Abel inversion, and highlight the effect of rotation of the parent molecule before dissociation, as observed in previous
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| 6. |
- Kiselev, M. D., et al.
(författare)
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An experimental and theoretical study of the Kr 3d correlation satellites
- 2022
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55:5
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Tidskriftsartikel (refereegranskat)abstract
- The Kr 3d correlation satellites have been studied experimentally by using plane polarized synchrotron radiation to record polarization dependent photoelectron spectra (PES), and theoretically by employing the R-matrix method to calculate photoionization cross sections, PES and angular distributions. The experimental spectra have allowed the photoelectron anisotropy parameters characterizing the angular distributions, and the intensity branching ratios, related to the photoionization partial cross sections, to be evaluated. The results are discussed in terms of normal and conjugate shake-up processes. The experimental and calculated photoelectron angular distributions associated with those correlation satellites that arise predominantly through conjugate shake-up mechanisms are shown to be isotropic. In contrast, the anisotropy parameters associated with satellites due to normal shake-up processes exhibit a dependence on electron kinetic energy similar to that of the anisotropy parameters corresponding to the Kr 3d main lines. The theoretical results include an analysis of the partial waves representing the emitted photoelectron and, for certain correlation satellites, show that a particular ionization continuum dominates. This, in turn, may allow the dominant normal or conjugate shake-up mechanism forming the satellite to be identified.
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| 7. |
- Kockert, Hansjochen, et al.
(författare)
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UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses
- 2022
-
Ingår i: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55:1
-
Tidskriftsartikel (refereegranskat)abstract
- The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH2BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump-XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH2Br radicals produced by C-I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH2BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.
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| 8. |
- Olofsson, Edvin, et al.
(författare)
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Frustrated tunneling dynamics in ultrashort laser pulses
- 2021
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:15
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Tidskriftsartikel (refereegranskat)abstract
- We study a model for frustrated tunneling ionization using ultrashort laser pulses. The model is based on the strong field approximation and it employs the saddle point approximation to predict quasiclassical trajectories that are captured on Rydberg states. We present a classification of the saddle-point solutions and explore their behavior as functions of angular momentum of the final state, as well as the carrier-envelope phase (CEP) of the laser pulse. We compare the final state population computed by the model to results obtained by numerical propagation of the time-dependent Schrödinger equation (TDSE) for the hydrogen atom. While we find qualitative agreement in the CEP dependence of the populations in principal quantum numbers, n, the populations to individual angular momentum channels, ℓ, are found to be inconsistent between model and TDSE. Thus, our results show that improvements of the quasiclassical trajectories are in order for a quantitative model of frustrated tunneling ionization.
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| 9. |
- Si, Ran, et al.
(författare)
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Proposal for observation of transitions induced by external magnetic fields mixing in the lower states : with an example from Fe X
- 2020
-
Ingår i: Journal of Physics B. - : Institute of Physics (IOP). - 0953-4075 .- 1361-6455. ; 53:9
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Tidskriftsartikel (refereegranskat)abstract
- It is normally assumed that induced transitions, by e.g. hyperfine, magnetic field or spin interaction, arise due to mixing in the upper levels. In this paper we discuss an example when mixing in the lower levels through an externally applied magnetic field gives rise to a magnetic field induced transition. We discuss the theory for such a transition and give an example from Fe X, which is relevant for the determination of the magnetic field of the solar corona. To make this possible, it is important to determine the energy difference between the 3p(4)3d D-4(5/2) and D-4(7/2), which are accidentally very close in energy in Fe X. The splitting of these levels is expected to be around 3.5 cm(-1) whereas their excitation energies are about 388 709 cm(-1). We discuss how this fine structure can be determined, by observing transitions from levels that decay into this pair which have a longer wavelength than the resonance transition. Finally we discuss an experimental scenario based on an electron beam ion trap and a Fabry-Perot interferometer, to perform the measurement of this interval.
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| 10. |
- Sorensen, S. L., et al.
(författare)
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From synchrotrons for XFELs : The soft x-ray near-edge spectrum of the ESCA molecule
- 2020
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:24
-
Tidskriftsartikel (refereegranskat)abstract
- A predictive understanding of soft x-ray near-edge absorption spectra of small molecules is an enduring theoretical challenge and of current interest for x-ray probes of molecular dynamics. We report the experimental absorption spectrum for the electron spectroscopy for chemical analysis (ESCA) molecule (ethyl trifluoroacetate) near the carbon 1s absorption edge between 285-300 eV. The ESCA molecule with four chemically distinct carbon sites has previously served as a theoretical benchmark for photoelectron spectra and now for photoabsorption spectra. We report a simple edge-specific approach for systematically expanding standard basis sets to properly describe diffuse Rydberg orbitals and the importance of triple excitations in equation-of-motion coupled-cluster calculations of the energy interval between valence and Rydberg excitations.
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| 11. |
- Turconi, M., et al.
(författare)
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Spin-orbit-resolved spectral phase measurements around a Fano resonance
- 2020
-
Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:18
-
Tidskriftsartikel (refereegranskat)abstract
- We apply a spectrally-resolved electron interferometry technique to the measurement of the spectral phase in the vicinity of the 3s(1)3p(6)4p Fano resonance of argon. We show that it allows disentangling the phases of the two nearly-overlapping electron wavepackets corresponding to different spin-orbit final states. Using simple assumptions, it is possible to process the experimental data and numerically isolate each component in a self-consistent manner. This in turn allows reconstructing the autoionization dynamics of the dominant channel.
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| 12. |
- Ingle, R. A., et al.
(författare)
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Carbon K-edge x-ray emission spectroscopy of gas phase ethylenic molecules
- 2022
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55:4
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the C K-edge x-ray absorption spectra and the resonant (RXES) and non-resonant (NXES) x-ray emission spectra of ethylene, allene and butadiene in the gas phase. The RXES and NXES show clear differences for the different molecules. Overall both types of spectra are more structured for ethylene and allene, than for butadiene. Using density functional theory–restricted open shell configuration interaction single calculations, we simulate the spectra with remarkable agreement with the experiment. We identify the spectral features as being due to transitions involving localised 1s orbitals. For allene, there are distinct spectral bands that reflect transitions predominantly from either the central or terminal carbon atoms. These results are discussed in the context of ultrafast x-ray studies aimed at detecting the passage through conical intersections in polyatomic molecules.
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| 13. |
- Caliskan, Sema, et al.
(författare)
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Targeted optimization in small-scale atomic structure calculations : application to Au I
- 2024
-
Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 57:5
-
Tidskriftsartikel (refereegranskat)abstract
- The lack of reliable atomic data can be a severe limitation in astrophysical modelling, in particular of events such as kilonovae that require information on all neutron-capture elements across a wide range of ionization stages. Notably, the presence of non-orthonormalities between electron orbitals representing configurations that are close in energy can introduce significant inaccuracies in computed energies and transition probabilities. Here, we propose an explicit targeted optimization (TO) method that can effectively circumvent this concern while retaining an orthonormal orbital basis set. We illustrate this method within the framework of small-scale atomic structure models of Au I, using the Grasp2018 multiconfigurational Dirac-Hartree-Fock atomic structure code. By comparing to conventional optimization schemes we show how a TO approach improves the energy level positioning and ordering. TO also leads to better agreement with experimental data for the strongest E1 transitions. This illustrates how small-scale models can be significantly improved with minor computational costs if orbital non-orthonormalities are considered carefully. These results should prove useful to multi-element atomic structure calculations in, for example, astrophysical opacity applications involving neutron-capture elements.
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| 14. |
- Grånäs, Oscar, 1979-, et al.
(författare)
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Femtosecond fragmentation of CS2 after sulfur 1s ionization : interplay between Auger cascade decay, charge delocalization, and nuclear motion
- 2020
-
Ingår i: Journal of Physics B. - : IOP PUBLISHING LTD. - 0953-4075 .- 1361-6455. ; 53:24
-
Tidskriftsartikel (refereegranskat)abstract
- We present a combined experimental and theoretical study of the fragmentation of molecular CS2 after sulfur 1s Auger cascade decay, consisting of electron-multi-ion coincidence spectra of charged fragments and theoretical simulations combining density functional theory and molecular dynamics. On the experimental side, a procedure for a complete determination of all sets of ions formed is described. For many of the fragmentation channels, we observed a higher charge in one of the sulfur atoms than the other atoms. Based on these observations and the theoretical simulations where the time scale of the nuclear motion and decay is taken into account, we propose that KLL Auger decay after the 1s core hole creation, via 2p double hole states, results in highly charged and strongly repulsive states with one localized core hole. These localized core holes are sufficiently long-lived that some will decay after fragmentation of the molecular ion, thereby efficiently impeding charge exchange between the fragments.
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| 15. |
- Herdrich, M. O., et al.
(författare)
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Application of a metallic-magnetic calorimeter for high-resolution x-ray spectroscopy of Fe at an EBIT
- 2024
-
Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 57:8
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we present an experiment conducted at the S-EBIT-I ion trap of GSI. It involved the study of ion-electron collisions of Fe and Ba ions in various charge states with the electron beam. Characteristic x-ray radiation emitted during the continuous interaction was recorded utilizing an energy-dispersive maXs-30 detector based on metallic-magnetic calorimeter (MMC) technology. Optimizations to the applied sensitivity-drift correction and energy calibration procedures significantly improved the achieved energy resolution compared to previous applications of a similar detector. This made it possible to individually resolve and identify overlapping x-ray lines of iron and barium in a wide spectral range. As a demonstration of the outstanding detector performance, we used the recorded spectral data to extract an estimate of the charge state distribution of Fe ions in the trap. This experiment campaign marks an important milestone in the ongoing effort to enable the deployment of MMC detectors for future high-precision measurements in fundamental physics experiments.
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| 16. |
- Kaiser, L., et al.
(författare)
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Angular emission distribution of O 1s photoelectrons of uniaxially oriented methanol
- 2020
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:19
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Tidskriftsartikel (refereegranskat)abstract
- The angular distribution of O 1s photoelectrons emitted from uniaxially oriented methanol is studied experimentally and theoretically. We employed circularly polarized photons of an energy ofh nu= 550 eV for our investigations. We measured the three-dimensional photoelectron angular distributions of methanol, with the CH3-OH axis oriented in the polarization plane, by means of cold target recoil ion momentum spectroscopy. The experimental results are interpreted by single active electron calculations performed with the single center method. A comparative theoretical study of the respective molecular-frame angular distributions of O 1s photoelectrons of CO, performed for the same photoelectron kinetic energy and for a set of different internuclear distances, allows for disentangling the role of internuclear distance and the hydrogen atoms of methanol as compared to carbon monoxide.
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| 17. |
- Kosugi, S., et al.
(författare)
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Conjugate photoelectron recapture peaks in the high resolution Auger electron spectra following near-threshold Ar 2p photoionization
- 2020
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:12
-
Tidskriftsartikel (refereegranskat)abstract
- We have observed formation of Rydberg series superimposed on the Ar (L3M2,3M2,3) Auger electron spectral profile with photoexcitation just above the 2p(3/2)(-1) photoionization threshold. This is due to the recapture of photoelectrons induced by post-collision interaction between the Auger electron and photoelectron: Ar+ 2p(3/2)(-1) + e(-) -> Ar+ 3p(-2)ml + e(-). The intensity distribution of the angular momentum state resolved Rydberg peaks revealed prominent conjugate peaks due to angular momentum exchange between photoelectrons and Auger electrons in the process. In addition, we measured the 2p(3/2)(-1)nl -> 3p(-2)ml + e(-) resonant Auger spectra with high resolution below the 2p(3/2)(-1) threshold. Our results showed that conjugate shake-up/down 2p(3/2)(-1)nd -> 3p(-2)mp + e(-) processes are stronger than the direct 2p(3/2)(-1)nd -> 3p(-2)ms, (m-1)d + e(-) processes in the spectator Auger processes, implying a strong angular momentum exchange effect between photoelectron and Auger electron.
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| 18. |
- Kumagai, Yoshiaki, et al.
(författare)
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Suppression of thermal nanoplasma emission in clusters strongly ionized by hard x-rays
- 2021
-
Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 54:4
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Tidskriftsartikel (refereegranskat)abstract
- Using electron and ion spectroscopy, we studied the electron and nuclear dynamics in similar to 50 000-atom large krypton clusters, following excitation with an intense hard x-ray pulse. Beyond the single pulse experiment, we also present the results of a time-resolved, x-ray pump-near-infrared probe measurement that allows one to learn about the time evolution of the system. After core ionization of the atoms by x-ray photons, trapped Auger and secondary electrons form a nanoplasma in which the krypton ions are embedded, according to the already published scenario. While the ion data show expected features, the electron emission spectra miss the expected pump-probe delay-dependent enhancement except for a slight enhancement in the energy range below 2 eV. Theoretical simulations help to reveal that, due to the deep trapping potential of the ions during the long time expansion accompanied by electron-ion recombination, thermal emission from the transient nanoplasma becomes quenched.
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| 19. |
- Lever, F., et al.
(författare)
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Ultrafast dynamics of 2-thiouracil investigated by time-resolved Auger spectroscopy
- 2020
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54
-
Tidskriftsartikel (refereegranskat)abstract
- We present time-resolved ultraviolet-pump x-ray probe Auger spectra of 2-thiouracil. An ultraviolet induced shift towards higher kinetic energies is observed in the sulfur 2p Auger decay. The difference Auger spectra of pumped and unpumped molecules exhibit ultrafast dynamics in the shift amplitude, in which three phases can be recognized. In the first 100 fs, a shift towards higher kinetic energies is observed, followed by a 400 fs shift back to lower kinetic energies and a 1 ps shift again to higher kinetic energies. We use a simple Coulomb-model, aided by quantum chemical calculations of potential energy states, to deduce a C–S bond expansion within the first 100 fs. The bond elongation triggers internal conversion from the photoexcited S2 to the S1 state. Based on timescales, the subsequent dynamics can be interpreted in terms of S1 nuclear relaxation and S1-triplet internal conversion.
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| 20. |
- Li, S., et al.
(författare)
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Two-dimensional correlation analysis for x-ray photoelectron spectroscopy
- 2021
-
Ingår i: Journal of Physics B. - : Institute of Physics Publishing (IOPP). - 0953-4075 .- 1361-6455. ; 54:14
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) measures the binding energy of core-level electrons, which are well-localised to specific atomic sites in a molecular system, providing valuable information on the local chemical environment. The technique relies on measuring the photoelectron spectrum upon x-ray photoionisation, and the resolution is often limited by the bandwidth of the ionising x-ray pulse. This is particularly problematic for time-resolved XPS, where the desired time resolution enforces a fundamental lower limit on the bandwidth of the x-ray source. In this work, we report a novel correlation analysis which exploits the correlation between the x-ray and photoelectron spectra to improve the resolution of XPS measurements. We show that with this correlation-based spectral-domain ghost imaging method we can achieve sub-bandwidth resolution in XPS measurements. This analysis method enables XPS for sources with large bandwidth or spectral jitter, previously considered unfeasible for XPS measurements.
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| 21. |
- Marchenko, T., et al.
(författare)
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Single and multiple excitations in double-core-hole states of free water molecules
- 2020
-
Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:22
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined experimental and theoretical study of the double-core-hole photoelectron spectrum obtained in isolated water molecules irradiated with hard x-rays above the oxygen K -2 threshold. States of the type O K -2V and multiply excited states are created by single-photon absorption and subsequent one-electron emission. A detailed analysis enabled by high experimental resolution reveals dissociative nuclear dynamics in the K-2V pre-edge states. At the binding energies above the K- 2 double-ionization potential, a complex spectral pattern is observed and attributed to highly excited states involving multiple shake-up excitation processes with the aid of state- of-the-art theoretical calculations. A strong broadening due to the nuclear motion indicates a highly dissociative nature of these multiply excited states, in agreement with the theoretical analysis.
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| 22. |
- Orban, Istvan, 1980-, et al.
(författare)
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Excitation and recombination studies with silicon and sulphur ions at an EBIT
- 2024
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Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 57:9
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of electron-impact excitation and recombination rate coefficients of highly charged Si and S ions at the Stockholm electron beam ion trap are reported. The experimental method was a combination of photon detection from the trapped ions during probing and subsequently extraction and time-of-flight (TOF) charge analysis of these ions. The TOF technique allows to measure recombination rate coefficients separately for every charge state, and together with the photon spectra of these ions also the excitation rate coefficients. In this paper, we present more details of the experimental procedure and summarize the experimental results in comparison with two different state-of-the-art calculations of recombination and excitation rates for Si10+–Si13+ and S12+–S15+ ions. One of these uses a relativistic configuration interaction approach (flexible atomic code) and the other is a relativistic many-body perturbation theory. A good to excellent agreement with both of them is found in energy and resonance strength for the investigated ions.
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| 23. |
- Puttner, R., et al.
(författare)
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Argon 1s(-2) Auger hypersatellites
- 2020
-
Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:2
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Tidskriftsartikel (refereegranskat)abstract
- The 1s(-2) Auger hypersatellite spectrum of argon is studied experimentally and theoretically. In total, three transitions to the final states 1s(-1)2p(-2)(S-2(e),D-2(e)) and 1s(-1)2s(-1)(S-1)2p(-1)(P-2(o)) are experimentally observed. The lifetime broadening of the 1s(-2) -> 1s(-1)2p(-2)(S-2(e),D-2(e)) states is determined to be 2.1(4) eV. For the used photon energy of h nu = 7500 eV a KK/K ionisation ratio of 2.5(3) x 10(-4) is derived. Generally, a good agreement between the experimental and present theoretical energy positions, linewidths, and intensities is obtained.
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| 24. |
- Püttner, R., et al.
(författare)
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Nonstatistical behavior of the photoionization of spin-orbit doublets
- 2021
-
Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:8
-
Tidskriftsartikel (refereegranskat)abstract
- The photoionization branching ratios of spin-orbit doublets are studied both experimentally and theoretically at energies several keV above threshold. The results show significant relativistic effects for Ar 2p in the autoionizing region below the 1s threshold, and large many-body effects for Xe 3d and 4d in the vicinity of the L-shell thresholds. The branching ratios in Xe are also found to vary significantly over very broad multi-keV energy regions both above and below the inner-shell thresholds. In addition, the Ar 2p study confirms experimentally the decades-old theoretical prediction that the nonresonant branching ratio does not approach the statistical (nonrelativistic) value, and, in fact, progressively diverges from statistical with increasing photon energy. © 2021 The Author(s). Published by IOP Publishing Ltd.
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| 25. |
- Syrwid, Andrzej
(författare)
-
Quantum dark solitons in ultracold one-dimensional Bose and Fermi gases
- 2021
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:10
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Tidskriftsartikel (refereegranskat)abstract
- Solitons are ubiquitous phenomena that appear, among others, in the description of tsunami waves, fiber-optic communication and ultracold atomic gases. The latter systems turned out to be an excellent playground for investigations of matter-wave solitons in a quantum world. This tutorial provides a general overview of the ultracold contact interacting Bose and Fermi systems in a one-dimensional space that can be described by the renowned Lieb-Liniger and Yang-Gaudin models. Both the quantum many-body systems are exactly solvable by means of the Bethe ansatz technique, granting us a possibility for investigations of quantum nature of solitonic excitations. We discuss in details a specific class of quantum many-body excited eigenstates called yrast states and show that they are strictly related to quantum dark solitons in the both considered Bose and Fermi systems.
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| 26. |
- Tempest, Kajsa-My, 1986-, et al.
(författare)
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The Faddeev and Schrödinger approaches to Efimov states — a numerical comparison
- 2023
-
Ingår i: Journal of Physics B. - 0953-4075 .- 1361-6455. ; 56:20
-
Tidskriftsartikel (refereegranskat)abstract
- We compare effective hyperspherical three-body potentials calculated using the S-wave part of the Faddeev equations to calculations using the full Schrödinger equation. As two-body model potential we test both a short-range potential and a Lennard-Jones potential with van der Waals tail. In the former case we find excellent agreement between the two methods for the lowest adiabatic state, indicating that the Faddeev method can be a useful tool also for numerical computations. For excited states the two methods show important differences, but agree for hyperradii larger than about five times the range of the potential (independent of the value of the scattering length and of the number of bound states). For the van der Waals potential, we focus on how well the Faddeev method reproduces the so-called van der Waals universality. We find that indeed the universality is manifest also using this method, but at a slightly different value of the universal parameter κ*. We further derive an efficient method to solve the integro-differential equation arising in the Faddeev method.
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| 27. |
- Uhl, D., et al.
(författare)
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Improved stabilization scheme for extreme ultraviolet quantum interference experiments
- 2022
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55
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Tidskriftsartikel (refereegranskat)abstract
- Interferometric pump-probe experiments in the extreme ultraviolet (XUV) domain are experimentally very challenging due to the high phase stability required between the XUV pulses. Recently, an efficient phase stabilization scheme was introduced for seeded XUV free electron lasers (FELs) combining shot-to-shot phase modulation with lock-in detection [A. Wituschek et al., Nat Commun 11, 1 (2020)]. This method stabilized the seed laser beampath on the fundamental ultraviolet wavelength to a high degree. Here, we extend this scheme including the stabilization of the XUV beampath, incorporating phase fluctuations from the FEL high gain harmonic generation process. Our analysis reveals a clear signal improvement with the new method compared to the previous stabilization scheme.
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- Ögren, Magnus, 1977-, et al.
(författare)
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Stationary states of Bose-Einstein condensed atoms rotating in an asymmetric ring potential
- 2021
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:14
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Tidskriftsartikel (refereegranskat)abstract
- We consider a Bose-Einstein condensate, which is confined ina very tight toroidal/annular trap,in the presence of a potential, which breaks the axial symmetry of the Hamiltonian. We investigate the stationary states of the condensate, when its density distribution co-rotates with the symmetry-breaking potential. As the strength of the potential increases, we have a gradual transition from vortex excitation to solid-body-like motion. Of particular importance are states where the system is static and yet it has a nonzero current/circulation, which is a realization of persistentcurrents/reflectionless potentials.
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