| 1. |
- Hartmann, N., et al.
(författare)
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Attosecond time-energy structure of X-ray free-electron laser pulses
- 2018
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 12:4, s. 215-220
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Tidskriftsartikel (refereegranskat)abstract
- The time-energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science. © 2018 The Author(s).
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| 2. |
- Heider, R., et al.
(författare)
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Megahertz-compatible angular streaking with few-femtosecond resolution at x-ray free-electron lasers
- 2019
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Ingår i: Physical Review A. - 2469-9926. ; 100:5
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Tidskriftsartikel (refereegranskat)abstract
- Highly brilliant, coherent, femtosecond x-ray pulses delivered by free-electron lasers (FELs) constitute one of the pillars of modern ultrafast science. Next generation FEL facilities provide up to megahertz repetition rates and pulse durations down to the attosecond regime utilizing self-amplification of spontaneous emission. However, the stochastic nature of this generation mechanism demands single-shot pulse characterization to perform meaningful experiments. Here we demonstrate a fast yet robust online analysis technique capable of megahertz-rate mapping of the temporal intensity structure and arrival time of x-ray FEL pulses with few-femtosecond resolution. We performed angular streaking measurements of both neon photo- and Auger electrons and show their applicability for a direct time-domain feedback system during ongoing experiments. The fidelity of the real-time pulse characterization algorithm is corroborated by resolving isolated x-ray pulses and double pulse trains with few-femtosecond substructure, thus paving the way for x-ray-pump-x-ray-probe FEL science at repetition rates compatible with the demands of LCLS-II and European XFEL.
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| 3. |
- Lutman, A. A., et al.
(författare)
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Polarization control in an X-ray free-electron laser
- 2016
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 10:7, s. 468-472
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers are unique sources of high-brightness coherent radiation. However, existing devices supply only linearly polarized light, precluding studies of chiral dynamics. A device called the Delta undulator has been installed at the Linac Coherent Light Source (LCLS) to provide tunable polarization. With a reverse tapered planar undulator line to pre-microbunch the beam and the novel technique of beam diverting, hundreds of microjoules of circularly polarized X-ray pulses are produced at 500-1,200 eV. These X-ray pulses are tens of femtoseconds long, have a degree of circular polarization of 0.98(+0.02)(-0.04) at 707 eV and may be scanned in energy. We also present a new two-colour X-ray pump-X-ray probe operating mode for the LCLS. Energy differences of Delta E/E = 2.4% are supported, and the second pulse can be adjusted to any elliptical polarization. In this mode, the pointing, timing, intensity and wavelength of the two pulses can be modified.
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| 4. |
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| 6. |
- Auer, Gerald, et al.
(författare)
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Timing and Pacing of Indonesian Throughflow Restriction and Its Connection to Late Pliocene Climate Shifts
- 2019
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Ingår i: Paleoceanography and Paleoclimatology. - : AMER GEOPHYSICAL UNION. - 2572-4517 .- 2572-4525. ; 34:4, s. 635-657
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Tidskriftsartikel (refereegranskat)abstract
- The Pliocene was characterized by a gradual shift of global climate toward cooler and drier conditions. This shift fundamentally reorganized Earth's climate from the Miocene state toward conditions similar to the present. During the Pliocene, the progressive restriction of the Indonesian Throughflow (ITF) is suggested to have enhanced this shift toward stronger meridional thermal gradients. Reduced ITF, caused by the northward movement of Australia and uplift of Indonesia, impeded global thermohaline circulation, also contributing to late Pliocene Northern Hemisphere cooling via atmospheric and oceanographic teleconnections. Here we present an orbitally tuned high-resolution sediment geochemistry, calcareous nannofossil, and X-ray fluorescence record between 3.65 and 2.97 Ma from the northwest shelf of Australia within the Leeuwin Current. International Ocean Discovery Program Site U1463 provides a record of local surface water conditions and Australian climate in relation to changing ITF connectivity. Modern analogue-based interpretations of nannofossil assemblages indicate that ITF configuration culminated similar to 3.54 Ma. A decrease in warm, oligotrophic taxa such as Umbilicosphaera sibogae, with a shift from Gephyrocapsa sp. to Reticulofenestra sp., and an increase of mesotrophic taxa (e.g., Umbilicosphaera jafari and Helicosphaera spp.) suggest that tropical Pacific ITF sources were replaced by cooler, fresher, northern Pacific waters. This initial tectonic reorganization enhanced the Indian Oceans sensitivity to orbitally forced cooling in the southern high latitudes culminating in the M2 glacial event (similar to 3.3 Ma). After 3.3 Ma the restructured ITF established the boundary conditions for the inception of the Sahul-Indian Ocean Bjerknes mechanism and increased the response to glacio-eustatic variability.
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| 8. |
- Grunert, K.G., et al.
(författare)
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Consumer perceptions of food products involving genetic modification : Results from a qualitative study in four Nordic countries
- 2001
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Ingår i: Food Quality and Preference. - 0950-3293 .- 1873-6343. ; 12:8, s. 527-542
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Tidskriftsartikel (refereegranskat)abstract
- Product descriptions of cheese, candy and salmon products were presented to samples of respondents in four Nordic countries. The descriptions represented various applications of genetic modification (GM), varied along a 'distance' dimension and a 'what is modified' dimension, and were presented along with a conventionally produced product. Respondents ranked the products according to preference, and their perceptions were ascertained by the laddering method. Results indicate that respondents regard 'non-GM' as a value in itself, and associate the use of GM with a host of negative consequences and risks, but mostly with uncertainty and unhealthiness. Benefits of the use of GM were perceived and regarded as relevant, but could not compensate for the negative associations. The 'distance' dimension had a clear impact on consumer preferences, whereas the 'what is modified' dimension had effects which were product specific. © 2001 Elsevier Science Ltd.
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