| 1. |
- Agåker, Marcus, et al.
(författare)
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A five-axis parallel kinematic mirror unit for soft X-ray beamlines at MAX IV
- 2020
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Ingår i: Journal of Synchrotron Radiation. - : INT UNION CRYSTALLOGRAPHY. - 0909-0495 .- 1600-5775. ; 27, s. 262-271
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Tidskriftsartikel (refereegranskat)abstract
- With the introduction of the multi-bend achromats in the new fourth-generation storage rings the emittance has decreased by an order of magnitude resulting in increased brightness. However, the higher brightness comes with smaller beam sizes and narrower radiation cones. As a consequence, the requirements on mechanical stability regarding the beamline components increases. Here an innovative five-axis parallel kinematic mirror unit for use with soft X-ray beamlines using off-axis grazing-incidence optics is presented. Using simulations and measurements from the HIPPIE beamline at the MAX IV Laboratory it is shown that it has no Eigen frequencies below 90 Hz. Its positioning accuracy is better than 25 nm linearly and 17-35 mu rad angularly depending on the mirror chamber dimensions.
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| 2. |
- Agåker, Marcus, et al.
(författare)
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An ultra-high-stability four-axis ultra-high-vacuum sample manipulator
- 2021
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Ingår i: Journal of Synchrotron Radiation. - : International Union Of Crystallography. - 1600-5775 .- 0909-0495. ; 28:Pt 4, s. 1059-1068
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Tidskriftsartikel (refereegranskat)abstract
- A report on a four-axis ultra-high-stability manipulator developed for use at the Veritas and Species RIXS beamlines at MAX IV Laboratory, Lund, Sweden, is presented. The manipulator consists of a compact, light-weight X-Y table with a stiffened Z tower carrying a platform with a rotary seal to which a manipulator rod holding the sample can be attached. Its design parameters have been optimized to achieve high eigen-frequencies via a light-weight yet stiff construction, to absorb forces without deformations, provide a low center of gravity, and have a compact footprint without compromising access to the manipulator rod. The manipulator system can house a multitude of different, easily exchangeable, manipulator rods that can be tailor-made for specific experimental requirements without having to rebuild the entire sample positioning system. It is shown that the manipulator has its lowest eigen-frequency at 48.5 Hz and that long-term stability is in the few tens of nanometres. Position accuracy is shown to be better than 100 nm. Angular accuracy is in the 500 nrad range with a long-term stability of a few hundred nanoradians.
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| 3. |
- Agåker, Marcus, et al.
(författare)
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Double core excitations in LiI : Evidence for multicenter coupling in resonant inelastic soft x-ray scattering spectra
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:24, s. 241105-
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Tidskriftsartikel (refereegranskat)abstract
- Resonances in inelastic soft x-ray scattering spectra of LiI, in which final states with Li 1s as well as I 4d vacancies are populated have been observed. The intermediate states involve both Li 1s double core excitations and I parallel to 4p(-1)+4d(-2)4f > states. It is suggested that the spectra are influenced by multicenter coupling.
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| 4. |
- Agåker, Marcus, et al.
(författare)
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Double Core Excitations in Lithium Halides
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:4, s. 045112-
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering spectra of LiF , LiCl , LiBr , and LiI excited in the vicinity of the Li double core hole resonances are presented. All lithium halides show similar phenomenology, including scattering via states where both excited electrons are localized during the scattering process, as well as states where one electron delocalizes. Also transitions that involve additional band excitations are observed. A strong influence of the chemical surrounding is found, and it is discussed in terms of the ionic character of the chemical bond.
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| 5. |
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| 6. |
- Agåker, Marcus, 1976-
(författare)
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Double Excitations in Helium Atoms and Lithium Compounds
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses the investigation of doubly excited 2l´nl states in helium atoms and double core excitations in solid lithium compounds.Measurements on He are made in field free environments and under the influence of electric and magnetic fields, using synchrotron based inelastic photon scattering. Cross sections for scattering to singly excited final states are directly determined and compared to theoretical results and are found to be in excellent agreement. Radiative and spin-orbit effects are quantified and are shown to play an important role in the overall characterization of highly excited He states below the N =2 threshold. A dramatic electric field dependence is also observed in the flourecence yield already for relatively weak fields. This signal increase, induced by electric as well as magnetic fields, is interpreted in terms of mixing with states of higher fluorescence branching ratios.Double core excitations at the lithium site in solid lithium compounds are investigated using resonant inelastic x-ray scattering (RIXS). The lithium halides LiF, LiCl, LiBr and LiI are studied as well as the molecular compounds Li2O, Li2CO3 and LiBF4. States with one, as well as both, of the excited electrons localized at the site of the bare lithium nucleus are identified, and transitions which involve additional band excitations are observed. A strong influence of the chemical surrounding is found, and it is discussed in terms of the ionic character of the chemical bond.
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| 7. |
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| 8. |
- Agåker, Marcus, et al.
(författare)
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Novel instruments for ultra-soft X-ray emission spectroscopy
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 601:1-2, s. 213-219
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Tidskriftsartikel (refereegranskat)abstract
- Two alternative instrument designs to the traditional Rowland grating spectrometer for high resolution ultra-soft X-ray spectroscopy are presented. The first instrument is a plane grating spectrometer using off-axis parabolic mirrors for collection and refocusing, and with a spatially resolving multichannel detector with delay line read-out. The instrument offers substantially higher performance in terms of resolution and sensitivity than traditional instruments. The second instrument is a Fourier transform spectrometer based on a grazing incidence Mach-Zehnder interferometer using wavefront dividing beamsplitters. The path length difference can be scanned over 0.1 mm, which corresponds to a resolution of 12 meV. (C) 2009 Elsevier B.V. All rights reserved.
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| 9. |
- Agåker, Marcus, et al.
(författare)
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Resonant inelastic soft x-ray scattering at double core excitations in solid LiCl
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:24
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Tidskriftsartikel (refereegranskat)abstract
- Inelastic soft x-ray scattering in LiCl, resonantly enhanced at states with two Li 1s vacancies, is investigated. States in which both excited electrons are localized during the double core hole lifetime, in which one of the electrons delocalize, as well as triply excited states in which the double core excitation is accompanied by a valence-to-conduction band excitation, contribute to the scattering. The angular momentum symmetry of the involved states and the vibronic coupling during the scattering process are reflected in the angular anisotropy. The effect on the local electronic structure of multiple core holes is theoretically studied by means of supercell band calculations.
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| 10. |
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| 11. |
- Agåker, Marcus, et al.
(författare)
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Spectroscopy in the vacuum-ultraviolet
- 2011
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 5:5, s. 248-248
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Tidskriftsartikel (refereegranskat)
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| 12. |
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| 13. |
- Brandenburg, T, et al.
(författare)
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The electronic structure of perfluorodecalin studied by soft X-ray spectroscopy and electronic structure calculations
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:42, s. 23379-23385
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Tidskriftsartikel (refereegranskat)abstract
- Fluorine and carbon K absorption and emission spectra of liquid perfluorodecalin are presented and analyzed in terms of density functional calculations-configuration interaction. A comprehensive view of the electronic structure is given, and site-specific intramolecular interactions are investigated in detail. It is found that, while the outer fluorine atoms have excess charge in the ground state, the lowest excitations must be associated with charge transfer towards the inner carbon atoms.
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| 14. |
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| 15. |
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| 16. |
- Eichmann, U., et al.
(författare)
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Photon-recoil imaging : Expanding the view of nonlinear x-ray physics
- 2020
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Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 369:6511, s. 1630-1633
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Tidskriftsartikel (refereegranskat)abstract
- Addressing the ultrafast coherent evolution of electronic wave functions has long been a goal of nonlinear x-ray physics. A first step toward this goal is the investigation of stimulated x-ray Raman scattering (SXRS) using intense pulses from an x-ray free-electron laser. Earlier SXRS experiments relied on signal amplification during pulse propagation through dense resonant media. By contrast, our method reveals the fundamental process in which photons from the primary radiation source directly interact with a single atom. We introduce an experimental protocol in which scattered neutral atoms rather than scattered photons are detected. We present SXRS measurements at the neon K edge and a quantitative theoretical analysis. The method should become a powerful tool in the exploration of nonlinear x-ray physics.
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| 17. |
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| 18. |
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| 19. |
- Ghosh, Anirudha, et al.
(författare)
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Magnetic circular dichroism in the dd excitation in the van der Waals magnet CrI3 probed by resonant inelastic x-ray scattering
- 2023
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 107:11
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Tidskriftsartikel (refereegranskat)abstract
- We report on a combined experimental and theoretical study on CrI3 single crystals by employing the polarization dependence of resonant inelastic x-ray scattering (RIXS). Our investigations reveal multiple Cr 3d orbital splitting (dd excitations) as well as magnetic dichroism (MD) in the RIXS spectra. The dd excitation energies are similar on the two sides of the ferromagnetic transition temperature, T-C similar to 61 K, although MD in RIXS is predominant at 0.4 T magnetic field below TC. This demonstrates that the ferromagnetic superexchange interaction that is responsible for the interatomic exchange field is vanishingly small compared with the local exchange field that comes from exchange and correlation interaction among the interacting Cr 3d orbitals. The recorded RIXS spectra reported here reveal clearly resolved Cr 3d intraorbital dd excitations that represent transitions between electronic levels that are heavily influenced by dynamic correlations and multiconfiguration effects. Our calculations taking into account the Cr 3d hybridization with the ligand valence states and the full multiplet structure due to intra-atomic and crystal field interactions in Oh and D3d symmetry clearly reproduced the dichroic trend in experimental RIXS spectra.
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| 20. |
- Glover, C. J., et al.
(författare)
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Stationary and dispersive features in resonant inelastic soft X-ray scattering at the Ge 3p resonances
- 2009
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 173:2-3, s. 103-107
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic soft X-ray scattering at the 3p resonances in crystalline Ge is presented. Both stationary and dispersive features are observed in a wide energy range above as well as below the ionization limits. These observations are in agreement with theoretical predictions based on a two-step model where the initially excited electron has no influence on the emission step. Excess population of states in the conduction band is found, and discussed in terms of attosecond electron dynamics. (c) 2009 Elsevier B.V. All rights reserved.
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| 21. |
- Gorczyca, Thomas, et al.
(författare)
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Radiative and Relativistic Effects in the Decay of Highly Excited States in Helium
- 2000
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 85:6, s. 1202-1205
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Tidskriftsartikel (refereegranskat)abstract
- A recent experimental study [J.-E. Rubensson et al., Phys. Rev. Lett. 83, 947 (1999)] measured a significant fluorescence yield of the He( 2lnl′) photoexcited resonances, showing major qualitative differences from nonrelativistic predictions. We present a further theoretical study of these states, and perform R-matrix multichannel quantum defect theory calculations to extract fluorescence and ionization cross sections. These theoretical results are in excellent agreement with newer, higher-resolution measurements. Radiative and spin-orbit effects are quantified and shown to play an important role in the overall characterization of highly excited states.
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| 22. |
- John Mukkattukavil, Deepak, et al.
(författare)
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Resonant inelastic soft x-ray scattering on LaPt2Si2
- 2022
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 34:32, s. 324003-
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt2Si2 single crystal at the Si 2p and La 4d edges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Si s and d local partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4f excitations. Calculations show that Pt d-LPDOS dominates the occupied states, and a sharp localized La f state is found in the unoccupied states, in line with the observations.
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| 23. |
- John Mukkattukavil, Deepak, 1993-
(författare)
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Resonant Inelastic X-ray Scattering Studies on Quasi-Two-Dimensional Superconducting Materials
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Unconventional superconductivity is one of the many fascinating research areas of condensed matter physics. Understanding the superconducting pairing mechanism and its connection with other competing states remains unclear. This thesis investigates electronic transitions, charge, and spin fluctuations of various single-crystalline superconductors using a combination of x-ray absorption, x-ray emission, and resonant inelastic x-ray scattering techniques. Room temperature x-ray absorption, x-ray emission, and partial fluorescence yield measurements were carried out on LaPt2Si2 single crystal at the Si 2p and La 4d edges. Atomic-like transitions from La 4d to 4f are observed in x-ray absorption and x-ray emission measurements. The x-ray emission spectrum of LaPt2Si2 at the Si 2p edge is compared to the Si p and d local partial density of states. Resonant inelastic x-ray scattering measurements on YFe2Ge2 single crystal are also presented in this thesis. Magnon dispersion in YFe2Ge2 crystal along (h,0) and (h,h) directions are extracted from resonant inelastic x-ray scattering spectra and inelastic neutron scattering experiments. The magnon dispersion is fitted with the dispersion relation for a square lattice using the nearest and next-nearest neighbor exchange interaction. In YFe2Ge2, the ferromagnetic exchange interaction is higher than the antiferromagnetic interaction. High-resolution resonant inelastic x-ray scattering spectra were measured on La1.675Eu0.2Sr0.125CuO4 superconductor at various temperatures. Charge density fluctuations with shorter correlation lengths have been shown to exist above the structural transition up to 200 K in La1.675Eu0.2Sr0.125CuO4. Phonon dispersion relation has also been mapped from high-resolution resonant inelastic x-ray scattering spectra. Softening of optical phonon mode in La1.675Eu0.2Sr0.125CuO4 is observed at low and high temperatures coinciding with the charge density wave vector.
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| 24. |
- Kimberg, Victor, et al.
(författare)
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Stimulated X-ray Raman scattering : a critical assessment of the building block of nonlinear X-ray spectroscopy
- 2016
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Ingår i: Faraday discussions. - : Royal Society of Chemistry. - 1359-6640 .- 1364-5498.
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Tidskriftsartikel (refereegranskat)abstract
- With the invention of femtosecond X-ray free-electron lasers (XFELs), studies of light-induced chemical reaction dynamics and structural dynamics reach a new era, allowing for time-resolved X-ray diffraction and spectroscopy. To ultimately probe coherent electron and nuclear dynamics on their natural time and length scales, coherent nonlinear X-ray spectroscopy schemes have been proposed. In this contribution, we want to critically assess the experimental realisation of nonlinear X-ray spectroscopy at current-day XFEL sources, by presenting first experimental attempts to demonstrate stimulated resonant X-ray Raman scattering in molecular gas targets.
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| 25. |
- Kjellsson, Ludvig, et al.
(författare)
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Resonant inelastic x-ray scattering at the N2 π*-resonance: Lifetime-vibrational interference, radiative electron rearrangement, and wave-function imaging
- 2021
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 103
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering spectra excited at the pi*-resonance of the nitrogen molecule are presented. Well-resolved vibrational excitations in the electronic ground state, and in the 3 sigma g(-1 )1 pi(1)(g) a(1) Pi(g) state are observed. The spectra are analyzed within the Kramers-Heisenberg formalism, and the importance of lifetime-vibrational interference effects is highlighted. In addition, strongly dissociative multiply excited final states populated in radiative electron rearrangement are found in the valence ionization continua. The vibrational wave functions of the core-excited state are imaged on the strongly dissociative final state potentials.
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