| 1. |
- Allaf Navirian, Hengameh, et al.
(författare)
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Acoustically driven ferroelastic domain switching observed by time-resolved x-ray diffraction
- 2010
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 81:2
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Tidskriftsartikel (refereegranskat)abstract
- Domain polarization switching in potassium dihydrogen phosphate (KH2PO4, KDP) induced by a propagating strain wave has been observed with time-resolved x-ray diffraction. A pulsed electric field with amplitude of 6 kV/cm and duration of 1 mu s was applied along the crystallographic c axis. The field-induced strain waves emanating from the sample surfaces are the result of the converse piezoelectric effect. In the center of the probed surface two waves interfered constructively inducing ferroelastic domain switching, in the absence of an external electric field, at a delay of 3 mu s, corresponding to acoustic propagation at a velocity found to be 1500 m/s.
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| 2. |
- Allaf Navirian, Hengameh, et al.
(författare)
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Repetitive ultrafast melting of InSb as an x-ray timing diagnostic
- 2008
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 103:10, s. 6-103510
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Tidskriftsartikel (refereegranskat)abstract
- We have demonstrated the possibility of using repetitive ultrafast melting of InSb as a timing diagnostic in connection with visible-light pump/x-ray probe measurements at high-repetition-rate x-ray facilities. Although the sample was molten and regrown approximately 1x10(6) times, a distinct reduction in time-resolved x-ray reflectivity could be observed using a streak camera with a time resolution of 2.5 ps. The time-resolved x-ray reflectivity displayed this distinct decrease despite the fact that the average reflectivity of the sample had fallen to approximately 50% of its original value due to accumulated damage from the prolonged laser exposure. The topography of the laser-exposed sample was mapped using an optical microscope, a stylus profilometer, photoelectron microscopy, and a scanning tunneling microscope. Although the surface of the sample is not flat following prolonged exposure at laser fluences above 15 mJ/cm(2), the atomic scale structure regrows, and thus, regenerates the sample on a nanosecond timescale. In the fluence range between 15 and 25 mJ/cm(2), the laser power is sufficient to melt the sample, while regrowth occurs with a sufficiently good structure to allow the extraction of timing information via ultrafast time-resolved x-ray measurements. This can be applied for timing purposes at synchrotron radiation and x-ray free-electron laser facilities. It is also noteworthy that we were able to reproduce the fluence dependencies of melting depth and disordering time previously obtained in single-shot, nonthermal melting experiments with higher temporal resolution.
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| 3. |
- Enquist, Henrik, et al.
(författare)
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Large acoustic transients induced by non-thermal melting of InSb
- 2007
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Ingår i: Physical Review Letters. - 1079-7114. ; 98
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Tidskriftsartikel (refereegranskat)abstract
- We have observed large-amplitude strain waves following a rapid change in density of InSb due to nonthermal melting. The strain has been measured in real time via time-resolved x-ray diffraction, with a temporal resolution better than 2 ps. The change from the solid to liquid density of the surface layer launches a high-amplitude strain wave into the crystalline material below. This induces an effective plane rotation in the asymmetrically cut crystal leading to deflection of the diffracted beam. The uniform strain in the layer below the molten layer is 2.0(±0.2)%. A strain of this magnitude develops within 5 ps of the incident pulse showing that the liquid has reached the equilibrium density within this time frame. Both the strain amplitude and the depth of the strained material in the solid can be explained by assuming a reduction in the speed of sound in the nonequilibrium liquid compared to measured equilibrium values.
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| 4. |
- Enquist, Henrik, et al.
(författare)
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Subpicosecond hard x-ray streak camera using single-photon counting.
- 2010
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Ingår i: Optics Letters. - 1539-4794. ; 35:19, s. 3219-3221
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Tidskriftsartikel (refereegranskat)abstract
- We have developed and characterized a hard x-ray accumulating streak camera that achieves subpicosecond time resolution by using single-photon counting. A high repetition rate of 2 kHz was achieved by use of a readout camera with built-in image processing capabilities. The effects of sweep jitter were removed by using a UV timing reference. The use of single-photon counting allows the camera to reach a high quantum efficiency by not limiting the divergence of the photoelectrons.
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| 5. |
- Harbst, Michael, et al.
(författare)
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Studies of resolidification of non-thermally molten InSb using time-resolved X-ray diffraction
- 2005
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Ingår i: APPLIED PHYSICS A: MATERIALS SCIENCE & PROCESSING. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 81:5, s. 893-900
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Tidskriftsartikel (refereegranskat)abstract
- We have used time-resolved X-ray diffraction to monitor the resolidification process of molten InSb. Melting was induced by an ultra-short laser pulse and the measurement conducted in a high-repetition-rate multishot experiment. The method gives direct information about the nature of the transient regrowth and permanently damaged layers. It does not rely on models based on surface reflectivity or second harmonic generation (SHG). The measured resolidification process has been modeled with a 1-D thermodynamic heat-conduction model. Important parameters like sample temperature, melting depth and amorphous surface layer thickness come directly out of the data, while mosaicity of the sample and free carrier density can be quantified by comparing with models. Melt depths up to 80 nm have been observed and regrowth velocities in the range 2-8 m/s have been measured.
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| 6. |
- Jurgilaitis, Andrius, et al.
(författare)
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X-ray diffraction from the ripple structures created by femtosecond laser pulses
- 2010
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Ingår i: Applied Physics A: Materials Science & Processing. - : Springer Science and Business Media LLC. - 1432-0630. ; 100:1, s. 105-112
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the investigation and characterization of the laser-induced surface structure on an asymmetrically cut InSb crystal. We describe diffraction from the ripple surface and present a theoretical model that can be used to simulate X-ray energy scans. The asymmetrically cut InSb sample was irradiated with short-pulse radiation centred at 800 nm, with fluences ranging from 10 to 80 mJ/cm(2). The irradiated sample surface profile was investigated using optical and atomic force microscopy. We have investigated how laser-induced ripples influence the possibility of studying repetitive melting of solids using X-ray diffraction. The main effects arise from variations in local asymmetry angles, which reduce the attenuation length and increase the X-ray diffraction efficiency.
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| 7. |
- 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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| 8. |
- Nüske, Ralf, et al.
(författare)
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Time-resolved x-ray scattering from laser-molten indium antimonide.
- 2010
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 81:1
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a concept to study transient liquids with picosecond time-resolved x-ray scattering in a high-repetition-rate configuration. Femtosecond laser excitation of crystalline indium antimonide (InSb) induces ultrafast melting, which leads to a loss of the long-range order. The remaining local correlations of the liquid result in broad x-ray diffraction rings, which are measured as a function of delay time. After 2 ns the liquid structure factor shows close agreement with that of equilibrated liquid InSb. The measured decay of the liquid scattering intensity corresponds to the resolidification rate of 1 m/s in InSb.
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| 9. |
- Sheppard, J M H, et al.
(författare)
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Simulations of the phonon Bragg switch in GaAs
- 2005
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Ingår i: Solid State Communications. - : Elsevier BV. - 1879-2766 .- 0038-1098. ; 136:3, s. 181-185
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Tidskriftsartikel (refereegranskat)abstract
- It has recently been proposed that X-rays can be switched on sub-picosecond time-scales by using laser-generated coherent optical phonons: The so called phonon Bragg switch. We present here detailed simulations of the efficiency of such a switch by solving the time-dependent generalized Takagi-Taupin equations utilizing a perturbative approach. We explore the switching efficiency in diffraction from the (004) planes of GaAs as a function of both excited phonon wave vector and amplitude.
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| 10. |
- Sondhauss, Peter
(författare)
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MASH, a Framework for the Automation of X-ray Optical Simulations
- 2014
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Ingår i: Advances in Computational Methods for X-Ray Optics III. - : SPIE. - 1996-756X .- 0277-786X. ; 9209, s. 92090-92090
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Konferensbidrag (refereegranskat)abstract
- MASH stands for "Macros for the Automation of SHadow". It allows to run a set of ray-tracing simulations, for a range of photon energies for example, fully automatically. Undulator gaps, crystal angles etc. are tuned automatically. Important output parameters, such as photon flux, photon irradiance, focal spot size, bandwidth, etc. are then directly provided as function of photon energy. A photon energy scan is probably the most commonly requested one, but any parameter or set of parameters can be scanned through as well. Heat load calculations with finite element analysis providing temperatures, stress and deformations (Comsol) are fully integrated. The deformations can be fed back into the ray-tracing process simply by activating a switch. MASH tries to hide program internals such as file names, calls to pre-processors etc., so that the user (nearly) only needs to provide the optical setup. It comes with a web interface, which allows to run it remotely on a central computation server. Hence, no local installation or licenses are required, just a web browser and access to the local network. Numerous tools are provided to look at the ray-tracing results in the web-browser. The results can be also downloaded for local analysis. All files are human readable text files, that can be easily imported into third-party programs for further processing. All set parameters are stored in a single human-readable file in XML format.
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