| 1. |
- Larsson, Jörgen, et al.
(författare)
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Opportunities and challenges using short-pulse X-ray sources.
- 2005
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Ingår i: Second International Conference on Photo-Induced Phase Transitions: Cooperative, Nonlinear and Functional Properties. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 21, s. 87-94
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Konferensbidrag (refereegranskat)abstract
- Free-electron lasers will change the way we carry out time-resolved X-ray experiments. At present date, we use laser-produced plasma sources or synchrotron radiation. Laser-produced plasma sources have short pulses, but unfortunately large pulse-to-pulse fluctuations and large divergence. Synchrotron radiation from third generation source provide collimated and stable beams, but unfortunately long pulses. This means that either the time-resolution is limited to 100 ps or rather complex set-ups involving slicing or streak cameras are needed. Hard X-ray free-electron lasers will combine the best properties of present-day sources and increase the number of photons by many orders of magnitude. Already today, a precursor to the free-electron lasers has been built at Stanford Linear Accelerator Centre (SLAC). The Sub-Picosecond Photon Source (SPPS) has already shown the opportunities and challenges of using short-pulse X-ray sources.
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| 2. |
- Larsson, Jörgen, et al.
(författare)
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Picosecond X-ray diffraction studies of laser-excited acoustic phonons in InSb
- 2002
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Ingår i: Applied Physics A: Materials Science & Processing. - : Springer Science and Business Media LLC. - 1432-0630 .- 0947-8396. ; 75:4, s. 467-478
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Tidskriftsartikel (refereegranskat)abstract
- We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent acoustic phonons were excited in the crystals by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm(2). The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated, monochromatic pulses Of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the unperturbed rocking-curve peak.
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| 3. |
- Larsson, Jörgen, et al.
(författare)
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Time-resolved X-ray diffraction study of the ferroelectric phase-transition in DKDP
- 2004
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 299:2-3, s. 157-161
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Tidskriftsartikel (refereegranskat)abstract
- We have performed experiments where DKDP has been irradiated by short (100 fs), laser pulses. Subsequently X-ray pulses with a duration of 100 ps were used as a probe. Time-resolved X-ray diffraction enables monitoring of the transitions between the paraelectric and ferroelectric phases. By recording the intensity of a peak only present in the paraelectric phase, we observe indications of a phase-transition following laser-irradiation of DKDP in the ferroelectric phase. We have estimated the laser heating effect, by measuring the strain (peak shifts) in the diffraction patterns. Furthermore, the orientation of the ferroelectric domains has been observed. In spite of the fact that the temperature did not rise above the Curie temperature, following interaction with this radiation, the polarization of ferroelectric domains was modified. This indicates a mechanism where short pulses impulsively excite phonons. which enable either reversal of entire domains, the shift of domain walls and/or the broadening of the domain wall widths. (C) 2003 Elsevier B.V. All rights reserved.
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| 4. |
- Lindenberg, AM, et al.
(författare)
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Atomic-scale visualization of inertial dynamics
- 2005
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 308:5720, s. 392-395
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Tidskriftsartikel (refereegranskat)abstract
- The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics of liquids and solids. An accelerator-based source of femtosecond x-ray pulses allowed us to follow directly atomic displacements on an optically modified energy landscape, leading eventually to the transition from crystalline solid to disordered liquid. We show that, to first order in time, the dynamics are inertial, and we place constraints on the shape and curvature of the transition-state potential energy surface. Our measurements point toward analogies between this nonequilibrium phase transition and the short-time dynamics intrinsic to equilibrium liquids.
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