| 1. |
- Omelkov, S. I., et al.
(författare)
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Recent advances in time-resolved luminescence spectroscopy at MAX IV and PETRA III storage rings
- 2022. - 1
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 2380
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Konferensbidrag (refereegranskat)abstract
- Short-wavelength synchrotron radiation excitation has been an indispensable tool in the studies of the properties of wide gap materials using time-resolved low-temperature luminescence spectroscopy. In recent years, several setups for such investigations have been launched at MAX IV Laboratory and Photon Science at DESY. Two permanently stationed time-resolved luminescence setups at FinEstBeAMS and P66 beamlines are in operation at MAX IV 1.5 GeV and Petra III storage rings, respectively. Mobile luminescence setups have been developed for studies at FemtoMAX and P23 beamlines. FinEstBeAMS, P66 and P23 provide time resolution from ?1/4160 to 100 ps. The FemtoMAX photon source based on an in-vacuum undulator getting an electron beam from the 3 GeV linear accelerator provides an exceptional time resolution of ?1/430 ps, limited by time response of the photodetector. The performance of the setups, achieved milestones and research challenges are discussed for four new luminescence stations available for the research community with the main focus on time-resolved techniques.
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| 2. |
- Jarnac, A., et al.
(författare)
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Communication : Demonstration of a 20 ps X-ray switch based on a photoacoustic transducer
- 2017
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 4:5
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Tidskriftsartikel (refereegranskat)abstract
- We have studied an X-ray switch based on a gold coated indium antimonide crystal using time-resolved X-ray diffraction and demonstrated that the switch could reduce the pulse duration of a 100 ps X-ray pulse down to 20 ps with a peak reflectivity of 8%. We have used a dynamical diffraction code to predict the performance of the switch, which was then confirmed experimentally. The experiment was carried out at the FemtoMAX beamline at the short-pulse facility of the MAX IV laboratory. The performance and limitation of the switch are discussed in terms of acoustic transport properties between the two materials and the electron transport properties of gold.
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| 3. |
- Persson, A. I H, et al.
(författare)
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Studies of electron diffusion in photo-excited Ni using time-resolved X-ray diffraction
- 2016
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 109:20
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Tidskriftsartikel (refereegranskat)abstract
- We show that the heat deposition profile in a laser-excited metal can be determined by time-resolved X-ray diffraction. In this study, we investigated the electron diffusion in a 150 nm thick nickel film deposited on an indium antimonide substrate. A strain wave that mimics the heat deposition profile is generated in the metal and propagates into the InSb, where it influences the temporal profile of X-rays diffracted from InSb. We found that the strain pulse significantly deviated from a simple exponential profile, and that the two-temperature model was needed to reproduce the measured heat deposition profile. Experimental results were compared to simulations based on the two-temperature model carried out using commercial finite-element software packages and on-line dynamical diffraction tools. To reproduce the experimental data, the electron-phonon coupling factor was lowered compared to previously measured values. The experiment was carried out at a third-generation synchrotron radiation source using a high-brightness beam and an ultrafast X-ray streak camera with a temporal resolution of 3 ps.
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| 4. |
- Harb, M., et al.
(författare)
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Phonon-phonon interactions in photoexcited graphite studied by ultrafast electron diffraction
- 2016
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 93:10
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Tidskriftsartikel (refereegranskat)abstract
- We investigated phonon-phonon interactions in photoexcited single-crystalline graphite by ultrafast electron diffraction. Transient electron diffraction profiles from a 35 nm graphite film were observed following laser excitation. Changes in intensities of diffraction spots revealed a two-exponential relaxation process with
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| 5. |
- Wang, Xiaocui, et al.
(författare)
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Generation of a large compressive strain wave in graphite by ultrashort-pulse laser irradiation
- 2019
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- We have studied strain wave generation in graphite induced by an intense ultrashort laser pulse. The study was performed in the intensity regime above the ablation threshold of graphite. The aim was to maximize the strain and, thus, also the internal pressure (stress). Laser pulses with a 1 ps temporal duration melt the surface of graphite resulting in a molten material which initially exists at the solid density. As the molten material expands, a compressive strain wave starts propagating into the crystal below the molten layer. The strain pulse was studied with time-resolved X-ray diffraction. At a temporal delay of 100 ps after laser excitation, we observed >10% compressive strain, which corresponds to a pressure of 7.2 GPa. This strain could be reproduced by hydrodynamic simulations, which also provided a temperature map as a function of time and depth.
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| 6. |
- Wang, Xiaocui, et al.
(författare)
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Role of Thermal Equilibrium Dynamics in Atomic Motion during Nonthermal Laser-Induced Melting
- 2020
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Ingår i: Physical Review Letters. - 1079-7114. ; 124:10
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that initial atomic velocities as given by thermodynamics play an important role in the dynamics of phase transitions. We tracked the atomic motion during nonthermal laser-induced melting of InSb at different initial temperatures. The ultrafast atomic motion following bond breaking can in general be governed by two mechanisms: the random velocity of each atom at the time of bond breaking (inertial model), and the forces acting on the atoms after bond breaking. The melting dynamics was found to follow the inertial model over a wide temperature range.
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| 7. |
- Bengtsson, Å U J, et al.
(författare)
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Repetitive non-thermal melting as a timing monitor for femtosecond pump/probe X-ray experiments
- 2020
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 7:5, s. 054303-054303
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved optical pump/X-ray probe experiments are often used to study structural dynamics. To ensure high temporal resolution, it is necessary to monitor the timing between the X-ray pulses and the laser pulses. The transition from a crystalline solid material to a disordered state in a non-thermal melting process can be used as a reliable timing monitor. We have performed a study of the non-thermal melting of InSb in single-shot mode, where we varied the sample temperature in order to determine the conditions required for repetitive melting. We show how experimental conditions affect the feasibility of such a timing tool.
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| 8. |
- Gaudin, J., et al.
(författare)
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Time-resolved investigation of nanometer scale deformations induced by a high flux x-ray beam
- 2011
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Ingår i: Optics Express. - 1094-4087. ; 19:16, s. 15516-15524
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Tidskriftsartikel (refereegranskat)abstract
- We present results of a time-resolved pump-probe experiment where a Si sample was exposed to an intense 15 keV beam and its surface monitored by measuring the wavefront deformation of a reflected optical laser probe beam. By reconstructing and back propagating the wavefront, the deformed surface can be retrieved for each time step. The dynamics of the heat bump, build-up and relaxation, is followed with a spatial resolution in the nanometer range. The results are interpreted taking into account results of finite element method simulations. Due to its robustness and simplicity this method should find further developments at new x-ray light sources (FEL) or be used to gain understanding on thermo-dynamical behavior of highly excited materials. (C) 2011 Optical Society of America
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| 9. |
- Harb, Maher, et al.
(författare)
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Picosecond dynamics of laser-induced strain in graphite
- 2011
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 84:4
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Tidskriftsartikel (refereegranskat)abstract
- We report on the use of grazing-incidence time-resolved x-ray diffraction to investigate the evolution of strain in natural graphite excited by femtosecond-laser pulses in the fluence range of 6-35 mJ/cm(2). Strains corresponding to up to similar to 2.8% c-axis expansion were observed. We show that the experimental data is in good agreement with calculations based on the Thomsen strain model in conjunction with dynamical diffraction theory. Furthermore we find no evidence of nonthermal lattice expansion as reported in recent ultrafast electron-diffraction studies of laser-excited graphite conducted under comparable excitation conditions.
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| 10. |
- Harb, Maher, et al.
(författare)
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The c-axis thermal conductivity of graphite film of nanometer thickness measured by time resolved X-ray diffraction
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:23
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Tidskriftsartikel (refereegranskat)abstract
- We report on the use of time resolved X-ray diffraction to measure the dynamics of strain in laser-excited graphite film of nanometer thickness, obtained by chemical vapour deposition (CVD). Heat transport in the CVD film is simulated with a 1-dimensional heat diffusion model. We find the experimental data to be consistent with a c-axis thermal conductivity of similar to 0.7 Wm(-1) K-1. This value is four orders of magnitude lower than the thermal conductivity in-plane, confirming recent theoretical calculations of the thermal conductivity of multilayer graphene. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4769214]
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