| 1. |
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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
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| 6. |
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| 7. |
- Banerjee, Ambar, 1985-, et al.
(författare)
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Simulating fluorine K -edge resonant inelastic x-ray scattering of sulfur hexafluoride and the effect of dissociative dynamics
- 2023
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 108:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on a computational study of resonant inelastic x-ray scattering (RIXS), at different fluorine K-edge resonances of the SF6 molecule, and corresponding nonresonant x-ray emission. Previously measured polarization dependence in RIXS is reproduced and traced back to the local σ and π symmetry of the molecular orbitals and corresponding states involved in the RIXS process. Also electron-hole coupling energies are calculated and related to experimentally observed spectator shifts. The role of dissociative S-F bond dynamics is explored to model detuning of RIXS spectra at the |F1s-16a1g1) resonance, which shows challenges to accurately reproduce the required steepness for core-excited potential energy surface. We show that the RIXS spectra can only be properly described by considering breaking of the global inversion symmetry of the electronic wave function and core-hole localization, induced by vibronic coupling. Due to the core-hole localization we have symmetry forbidden transitions, which lead to additional resonances and changing width of the RIXS profile.
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| 8. |
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| 9. |
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| 10. |
- Couto, Rafael C., et al.
(författare)
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Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing
- 2016
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The unique opportunity to study and control electron-nuclear quantum dynamics in coupled potentials offered by the resonant inelastic X-ray scattering (RIXS) technique is utilized to unravel an anomalously strong two-electron one-photon transition from core-excited to Rydberg final states in the CO molecule. High-resolution RIXS measurements of CO in the energy region of 12-14 eV are presented and analyzed by means of quantum simulations using the wave packet propagation formalism and ab initio calculations of potential energy curves and transition dipole moments. The very good overall agreement between the experimental results and the theoretical predictions allows an in-depth interpretation of the salient spectral features in terms of Coulomb mixing of "dark" with "bright" final states leading to an effective two-electron one-photon transition. The present work illustrates that the improved spectral resolution of RIXS spectra achievable today may call for more advanced theories than what has been used in the past.
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| 11. |
- Couto, Rafael C., et al.
(författare)
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Coupled electron-nuclear dynamics in resonant 1σ→2π x-ray Raman scattering of CO molecules
- 2016
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed experimental-theoretical analysis of O K-edge resonant 1σ-2π inelastic x-ray scattering (RIXS) from carbon monoxide with unprecedented energy resolution. We employ high-level ab initio calculations to compute the potential energy curves of the states involved in the RIXS process and simulate the measured RIXS spectra using the wave-packet-propagation formalism, including Coulomb coupling in the final-state manifold. The theoretical analysis allows us to explain all the key features of the experimental spectra, including some that were not seen before. First, we clearly show the interference effect between different RIXS channels corresponding to the transition via orthogonal Πx1 and Πy1 core-excited states of CO. Second, the RIXS region of 13 eV energy loss presents a triple structure, revealed only by the high-resolution measurement. In previous studies, this region was attributed solely to a valence state. Here we show a strong Coulomb mixing of the Rydberg and valence final states, which opens the forbidden RIXS channels to the "dark" final Rydberg states and drastically changes the RIXS profile. Third, using a combination of high-resolution experiment and high-level theory, we improve the |4σ-12π1) final-state potential-energy curve by fitting its bottom part with the experiment. Also, the coupling constants between Rydberg and valence states were refined via comparison with the experiment. Our results illustrate the large potential of the RIXS technique for advanced studies of highly excited states of neutral molecules.
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| 12. |
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| 13. |
- 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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| 14. |
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| 15. |
- Hellgren, Niklas, et al.
(författare)
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Electronic structure of carbon nitride thin films studied by X-ray spectroscopy techniques
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 471:02-jan, s. 19-34
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Tidskriftsartikel (refereegranskat)abstract
- Magnetron-sputtered carbon nitride thin films with different structures and compositions were analyzed by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), as well as X-ray emission spectroscopy (XES). In all techniques, the carbon spectra are broad and featureless with little variation depending on growth conditions. The nitrogen spectra, on the other hand, show more distinct features, providing a powerful tool for structural characterization. By comparing the experimental spectra with calculations on different model systems, we are able to identify three major bonding structures of the nitrogen-N1: nitrile (C equivalent to N) bonds; N2: Pyridine-like N, i.e., N bonded to two C atoms; and N3: graphite-like N, i.e., N bonded to three C atoms as if substituted in a graphitic network, however, possibly positioned in a pentagon and/or with sp(3) carbon neighbors. The presence of N2 and N3 are best detected by XPS, while N1 is better detected by NEXAFS. The calculated XES spectra also give good indications how valence band spectra should be interpreted. Films grown at the higher temperatures ( greater than or equal to 350 degreesC) show a pronounced angular dependence of the incoming photon beam in NEXATS measurements, which suggests a textured microstructure with standing graphitic basal planes, while amorphous films grown at low temperatures show isotropic properties.
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| 16. |
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| 17. |
- John Mukkattukavil, D., et al.
(författare)
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Resonant inelastic soft x-ray scattering on LaPt 2 Si 2
- 2022
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Ingår i: Journal of physics. Condensed matter : an Institute of Physics journal. - 1361-648X .- 0953-8984. ; 34:32
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt2Si2single crystal at the Si 2pand La 4dedges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Sisanddlocal partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4fexcitations. Calculations show that Ptd-LPDOS dominates the occupied states, and a sharp localized Lafstate is found in the unoccupied states, in line with the observations.
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| 18. |
- 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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| 19. |
- 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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| 20. |
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| 21. |
- 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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| 22. |
- 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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| 23. |
- Kokkonen, Esko, et al.
(författare)
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Upgrade of the SPECIES beamline at the MAX IV Laboratory
- 2021
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Ingår i: Journal of Synchrotron Radiation. - 1600-5775. ; 28, s. 588-601
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Tidskriftsartikel (refereegranskat)abstract
- The SPECIES beamline has been transferred to the new 1.5 GeV storage ring at the MAX IV Laboratory. Several improvements have been made to the beamline and its endstations during the transfer. Together the Ambient Pressure X-ray Photoelectron Spectroscopy and Resonant Inelastic X-ray Scattering endstations are capable of conducting photoelectron spectroscopy in elevated pressure regimes with enhanced time-resolution and flux and X-ray scattering experiments with improved resolution and flux. Both endstations offer a unique capability for experiments at low photon energies in the vacuum ultraviolet and soft X-ray range. In this paper, the upgrades on the endstations and current performance of the beamline are reported.
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| 24. |
- Kuiper, Pieter, 1960-, et al.
(författare)
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Resonant X-Ray raman spectra of Cu dd excitations in Sr2CuO2Cl2
- 1998
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Ingår i: Physical Review Letters. - College Park, MD : American Physical Society. - 0031-9007 .- 1079-7114. ; 80:23, s. 5204-5207
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Tidskriftsartikel (refereegranskat)abstract
- We present resonant x-ray Raman scattering results on Sr2CuO2Cl2, a model compound for high- Tc superconductors. We demonstrate that the dd excitations can be observed and show that the polarization dependence can be used to identify the dd excitations. We find the transition from the dx2−y2 ground state to the dxy excited state at 1.35 eV and to the degenerate dxz and dyz excited states at 1.7 eV. From analysis of the polarization dependence we conclude that the d3z2−r2 orbital energy is at 1.5 eV and not in the midinfrared (0.5 eV) as recently suggested. We use recent theoretical arguments to show that the d3z2−r2 excitation is accompanied by a local spin flip resulting in a shift upwards of 0.2 eV due to the exchange interaction with the neighboring spins. ©1998 American Physical Society.
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| 25. |
- Magnuson, Martin, et al.
(författare)
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Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:6, s. 4281-4287
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Tidskriftsartikel (refereegranskat)abstract
- We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.
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| 26. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Magnetic circular dichroism in X-ray fluorescence of Heuseler alloys at threshold excitation
- 2001
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Ingår i: Solid State Communications. - 0038-1098 .- 1879-2766. ; 117:2, s. 79-82
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Tidskriftsartikel (refereegranskat)abstract
- The results of fluorescence measurements of magnetic circular dichroism (MCD) in Mn L2,3 X-ray emission and absorption for Heusler alloys NiMnSb and Co2MnSb are presented. Very intense resonance Mn L3 emission is found at the Mn 2p3/2 threshold and attributed to a peculiarity of the threshold excitation in materials with a half-metallic character of the electronic structure. The excitation energy dependence of Mn L2,3 X-ray emission spectra (XES) was measured at beamline ID12B at the European Synchrotron Radiation Facility (ESRF, Grenoble) using 83% circularly polarized X-rays. A very large MCD effect found in XES is attributed to strong exchange splitting of spin-up and spin-down Mn 3d states. The anomalously high ratio of L2 emission intensity to L3 emission intensity is found.
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| 27. |
- Magnuson, Martin, et al.
(författare)
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Resonant and nonresonant x-ray emission spectroscopy of poly(pyridine-2,5-diyl)
- 1998
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Ingår i: Advance Light Source. - Berkeley : University of California. ; , s. 135-138
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Conjugated polymers have been the subject of much interest owing to their unique electronic properties which can be technically exploited e.g., as doping induced electrical conductors and light emitting diodes [ I]. Detailed experimental studies of the uppermost 7t-orbital levels at the valence band edges of these polymers are important to gain an understanding of their properties. Such studies have been carried out by many techniques including photoelectron spectroscopy using photon excitation in both the x-ray and ultraviolet wavelength regimes....
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| 28. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Resonant inelastic soft X-ray scattering spectra at the nitrogen and carbon K-edges of poly(pyridine-2,5-diyl)
- 1999
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 101-103, s. 573-578
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic scattering measurements of the conjugated polymer, poly(pyridine-2,5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of σ symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer.
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| 29. |
- Magnuson, Martin, et al.
(författare)
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Spin transition in LaCoO3 investigated by resonant soft X-ray emission spectroscopy
- 2004
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 68:2, s. 289-295
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Tidskriftsartikel (refereegranskat)abstract
- The spin transition in LaCoO3 is investigated by temperature-dependent resonant soft X-ray emission spectroscopy near the Co 2p absorption edges. This element-specific technique is more bulk sensitive with respect to the temperature-induced spin state of the Co3+ ions in LaCoO3 than other high-energy spectroscopic methods. The spin transition is interpreted and discussed with ab initio density-functional theory within the fixed-spin moment method, which is found to yield consistent spectral functions to the experimental data. The spectral changes for LaCoO3 as a function of temperature suggest a change in spin state as the temperature is raised from 85 to 300 K, while the system remains in the same spin state as the temperature is further increased to 510 K.
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| 30. |
- Magnuson, Martin, 1965-, et al.
(författare)
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The electronic structure of poly(pyridine-2,5-diyl) investigated by soft X-ray absorption and emission spectroscopies
- 1998
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 237:3, s. 295-304
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and non-resonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the electron bands in line with symmetry selection and momentum conservation rules. The effect is most visual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of symmetry and are less frequency dependent.
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| 31. |
- Magnuson, Martin, 1965-, et al.
(författare)
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The electronic structure of polyaniline and doped phases studied by soft X-ray absorption and emission spectroscopies
- 1999
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 111:10, s. 4756-4761
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the conjugated polymer, polyaniline, has been studied by resonant and nonresonant soft x-ray emission spectroscopy using synchrotron radiation for the excitation. The measurements were made on polyaniline and a few doped (protonated) phases for both the carbon and nitrogen contents. The resonant x-ray emission spectra show depletion of the π electron bands due to the selective excitation which enhances the effect of symmetry selection rules. The valence band structures in the x-ray emission spectra attributed to the π bands show unambiguous changes of the electronic structure upon protonation. By comparing to x-ray absorption measurements, the chemical bonding and electronic configuration is characterized.
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| 32. |
- Mukkattukavil, Deepak John, 1993-, et al.
(författare)
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Resonant inelastic soft x-ray scattering on LaPt2Si2
- 2022
-
Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 34:32
-
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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| 33. |
- Rubensson, Jan-Erik, et al.
(författare)
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Influence of the Radiative Decay on the Cross Section for Double Excitations in Helium
- 1999
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 83:5, s. 947-950
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Tidskriftsartikel (refereegranskat)abstract
- The fluorescence yield spectrum of the double excitations in helium has been measured. All three Rydberg series converging to the N = 2 threshold are resolved, and the intensity of the individual lines is determined. The intensity variation through each series indicates that the radiative decay channel cannot be neglected when discussing the double excitations in helium. This calls for a revision of the interpretation of the absorption spectrum, and sets the limit for using the ion yield method to monitor the absorption probability.
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| 34. |
- Rubensson, Jan-Erik, et al.
(författare)
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Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds
- 2015
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 114:13
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.
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| 35. |
- Sanchez-Gonzalez, A., et al.
(författare)
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Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL
- 2015
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Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:23
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Tidskriftsartikel (refereegranskat)abstract
- We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.
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| 36. |
- Savchenko, Viktoriia, et al.
(författare)
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Hydrogen bond effects in multimode nuclear dynamics of acetic acid observed via resonant x-ray scattering
- 2021
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:21
-
Tidskriftsartikel (refereegranskat)abstract
- A theoretical and experimental study of the gas phase and liquid acetic acid based on resonant inelastic x-ray scattering (RIXS) spectroscopy is presented. We combine and compare different levels of theory for an isolated molecule for a comprehensive analysis, including electronic and vibrational degrees of freedom. The excitation energy scan over the oxygen K-edge absorption reveals nuclear dynamic effects in the core-excited and final electronic states. The theoretical simulations for the monomer and two different forms of the dimer are compared against high-resolution experimental data for pure liquid acetic acid. We show that the theoretical model based on a dimer describes the hydrogen bond formation in the liquid phase well and that this bond formation sufficiently alters the RIXS spectra, allowing us to trace these effects directly from the experiment. Multimode vibrational dynamics is accounted for in our simulations by using a hybrid time-dependent stationary approach for the quantum nuclear wave packet simulations, showing the important role it plays in RIXS.
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| 37. |
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| 38. |
- Savchenko, Viktoriia, et al.
(författare)
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Vibrational resonant inelastic X-ray scattering in liquid acetic acid : a ruler for molecular chain lengths
- 2021
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O-H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which however cannot be observed in x-ray absorption but only by means of RIXS. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.
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| 39. |
- Schreck, Simon, et al.
(författare)
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Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering.
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Thermally driven chemistry as well as materials' functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.
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| 40. |
- Sjöblom, Peter, et al.
(författare)
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Motion control system of MAX IV Laboratory soft x-ray beamlines
- 2016
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Ingår i: Proceedings of the 12th International Conference on Synchrotron Radiation Instrumentation, SRI 2015. - : Author(s). - 9780735413986 ; 1741
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Konferensbidrag (refereegranskat)abstract
- At the MAX IV Laboratory, five new soft x-ray beamlines are under development. The first is Species and it will be used to develop and set the standard of the control system, which will be common across the facility. All motion axes at MAX IV will be motorized using stepper motors steered by the IcePAP motion controller and a mixture of absolute and incremental encoders following a predefined coordinate system. The control system software is built in Tango and uses the Python-based Sardana framework. The user controls the entire beamline through a synoptic overview and Sardana is used to run the scans.
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| 41. |
- Ström, Magnus, et al.
(författare)
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Magnetic-field induced enhancement in the fluorescence yield spectrum of doubly excited states in helium
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 97:25, s. 253002-
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Tidskriftsartikel (refereegranskat)abstract
- An influence of static magnetic fields on the fluorescence yield spectrum of He in the vicinity of the N=2 thresholds has been observed. The experimental results are in excellent agreement with predictions based on multichannel quantum defect theory, and it is demonstrated that the Rydberg electron ℓ mixing due to the diamagnetic interaction is essential for the description of the observed fluorescence yield intensity enhancement.
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| 42. |
- Såthe, Conny, 1967-
(författare)
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Applications of Soft X-Ray Spectroscopy
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soft X-ray emission spectroscopy is an old experimental technique that has seen a strong revival since the advent of new high brilliance soft X-ray sources in the shape of synchrotrons. This thesis covers a range of applications where soft x-ray techniques have been applied. I have looked at fluorescence yield from doubly excited helium in field free conditions as well as in the presence of weak electric and magnetic fields. Using soft X-ray emission spectroscopy (SXES) I have explored scattering mechanisms in molecular systems. Quenching of symmetry breaking transitions by detuning of the excitation energy was observed in CO2. Bond-length dependence was seen for symmetry breaking transitions in a series of hydrocarbons. Dissociation dynamics was explored in OCS and HCl. I have also applied SXES to liquid water exploring the properties of hydrogen bonding. Buried layers of AlAs under 100 Å GaAs(100) was studied and thickness dependence and interface effects observed. The technique was also used to study the electronic structure of yttrium and vanadium hydrides. dd-excitations and accompanying spin flip excitations was observed in Cu M resonant x-ray Raman emission from Sr2CuO2Cl2.
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| 43. |
- Såthe, Conny, et al.
(författare)
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Double Excitations of Helium in Weak Static Electric Fields
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 96, s. 043002-
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Tidskriftsartikel (refereegranskat)abstract
- A dramatic electric field dependence has been observed in the fluorescence yield spectrum of the doubly excited states in helium, where a rich phenomenology is encountered below the N=2 threshold. Fluorescence yields of certain states can be tuned to zero, while other dipole-forbidden states are significantly enhanced, for fields much weaker than 1 kV/cm. Using an R-matrix multichannel quantum defect theory, spherical-to-parabolic frame transformation method, we are able to reproduce the main features of the observed spectrum, and we discuss the qualitative behavior in terms of weak electric field mixing.
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| 44. |
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| 45. |
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| 46. |
- Söderström, Johan, et al.
(författare)
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Parity violation in resonant inelastic soft x-ray scattering at entangled core holes
- 2024
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 10:7, s. 3114-
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering (RIXS) is a major method for investigation of electronic structure and dynamics, with applications ranging from basic atomic physics to materials science. In RIXS applied to inversion-symmetric systems, it has generally been accepted that strict parity selectivity applies in the sub-kilo-electron volt region. In contrast, we show that the parity selection rule is violated in the RIXS spectra of the free homonuclear diatomic O2 molecule. By analyzing the spectral dependence on scattering angle, we demonstrate that the violation is due to the phase difference in coherent scattering at the two atomic sites, in analogy with Young's double-slit experiment. The result also implies that the interpretation of x-ray absorption spectra for inversion symmetric molecules in this energy range must be revised.
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| 47. |
- Urpelainen, Samuli, et al.
(författare)
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The SPECIES beamline at the MAX IV Laboratory : A facility for soft X-ray RIXS and APXPS
- 2017
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Ingår i: Journal of Synchrotron Radiation. - 1600-5775 .- 0909-0495. ; 24:1, s. 344-353
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Tidskriftsartikel (refereegranskat)abstract
- SPECIES is an undulator-based soft X-ray beamline that replaced the old I511 beamline at the MAX II storage ring. SPECIES is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (APXPS), near-edge X-ray absorption fine-structure (NEXAFS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) experiments. The beamline has two branches that use a common elliptically polarizing undulator and monochromator. The beam is switched between the two branches by changing the focusing optics after the monochromator. Both branches have separate exit slits, refocusing optics and dedicated permanent endstations. This allows very fast switching between two types of experiments and offers a unique combination of the surface-sensitive XPS and bulk-sensitive RIXS techniques both in UHV and at elevated ambient-pressure conditions on a single beamline. Another unique property of the beamline is that it reaches energies down to approximately 27 eV, which is not obtainable on other current APXPS beamlines. This allows, for instance, valence band studies under ambient-pressure conditions. In this article the main properties and performance of the beamline are presented, together with selected showcase experiments performed on the new setup.
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| 48. |
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| 49. |
- Zitnik, M, et al.
(författare)
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High resolution multiphoton spectroscopy by a tunable free-electron-laser light.
- 2014
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 113:19
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Tidskriftsartikel (refereegranskat)abstract
- Seeded free electron lasers theoretically have the intensity, tunability, and resolution required for multiphoton spectroscopy of atomic and molecular species. Using the seeded free electron laser FERMI and a novel detection scheme, we have revealed the two-photon excitation spectra of dipole-forbidden doubly excited states in helium. The spectral profiles of the lowest (-1,0)^{+1} ^{1}S^{e} and (0,1)^{0} ^{1}D^{e} resonances display energy shifts in the meV range that depend on the pulse intensity. The results are explained by an effective two-level model based on calculated Rabi frequencies and decay rates.
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