| 1. |
- Sondhauss, Peter, et al.
(författare)
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Picosecond x-ray studies of coherent folded acoustic phonons in a periodic semiconductor heterostructure
- 2006
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 1996-756X .- 0277-786X. ; 6118, s. 1180-1180
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Konferensbidrag (refereegranskat)abstract
- Zone folded coherent acoustic phonons were generated in a multilayered GaSb/InAs epitaxial heterostructure via rapid heating by femtosecond laser pulses. These phonons were probed by means of ultrafast x-ray diffraction. Phonons both from the fundamental acoustic branch and the first back-folded branch were detected. This represents the first clear evidence for phonon branch folding based directly on the atomic motion to which x-ray diffraction is sensitive. From a comparison of the measured phonon-modulated x-ray reflectivity with simulations, evidence was found for a reduction of the laser penetration depth. This reduction can be explained by the self-modulation of the absorption index due to photogenerated free carriers.
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| 2. |
- Fang, Jun, et al.
(författare)
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Functional characterization of a multi-cancer risk locus on chr5p15.33 reveals regulation of TERT by ZNF148
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Genome wide association studies (GWAS) have mapped multiple independent cancer susceptibility loci to chr5p15.33. Here, we show that fine-mapping of pancreatic and testicular cancer GWAS within one of these loci (Region 2 in CLPTM1L) focuses the signal to nine highly correlated SNPs. Of these, rs36115365-C associated with increased pancreatic and testicular but decreased lung cancer and melanoma risk, and exhibited preferred protein-binding and enhanced regulatory activity. Transcriptional gene silencing of this regulatory element repressed TERT expression in an allele-specific manner. Proteomic analysis identifies allele-preferred binding of Zinc finger protein 148 (ZNF148) to rs36115365-C, further supported by binding of purified recombinant ZNF148. Knockdown of ZNF148 results in reduced TERT expression, telomerase activity and telomere length. Our results indicate that the association with chr5p15.33-Region 2 may be explained by rs36115365, a variant influencing TERT expression via ZNF148 in a manner consistent with elevated TERT in carriers of the C allele.
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| 3. |
- Fullagar, Wilfred, et al.
(författare)
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A broadband laser plasma X-ray source for application in ultrafast chemical structure dynamics
- 2007
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 78:11, s. 1-115105
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Tidskriftsartikel (refereegranskat)abstract
- A plasma source free from characteristic emission lines is described, based on laser irradiation of a water jet in a helium atmosphere. Various key aspects of the laser interaction are presented along with practical characterization of the observed isotropic ~4–10 keV x-ray emissions, measurements of which indicate subpicosecond duration. Observations are consistent with a vacuum heating plasma mechanism at the helium-water interface and indicate strong potential for in-house ultrafast chemical structure dynamics application when coupled to contemporary detector developments.
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| 4. |
- Harbst, Michael
(författare)
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Generation and Applications of Short-Pulse X-ray Radiation
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis summarizes work using hard X-ray radiation on nanosecond and picosecond timescales. The focus is on the experimental part including detailed descriptions of setups for laser pumped - X-ray probe experiments. X-ray diffraction is sensitive to structural properties on the length scale of chemical bonds. The greatest success of X-ray diffraction lies in the determination of crystal structures, but many other application of X-ray diffraction exist. In this work, this structural probe was used to detect changes in the crystal structure in the form of lattice perturbations and phase transitions. The field of time-resolved X-ray diffraction employs subpicosecond temporal resolution to study ultra-fast processes such as non-thermal melting and coherent optical phonons. This requires rather specialized equipment and setups. An introduction to this and to the time-resolved X-ray diffraction method is provided together with a description of the synchrotron radiation facility beam-line D611 at MAX-lab in Lund, which is dedicated to such experiments. This thesis also describes studies on laser produced plasma at the Lund High-Power Laser Facility. Work with this source started at the High-Power Laser Facility already in 1992. The source was developed as a potential X-ray source for medical applications. This thesis focuses on the laser produced plasma source as a femtosecond source and its characterization. The thesis also contains theory on the phenomena encountered. The theoretical description are intended to provide a basic understanding and guidelines for further reading if the reader is interested in expanding his or her knowledge on the subject.
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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. |
- 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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| 7. |
- Sjögren, Anders, et al.
(författare)
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High-repetition-rate, hard x-ray radiation from a laser-produced plasma: Photon yield and application considerations
- 2003
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 74:4, s. 2300-2311
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental study of hard x rays produced in laser-produced plasmas. The laser used is a 1 kHz system, delivering 0.7 mJ for 25 fs onto a solid target. The x-ray spectrum was measured with calibrated germanium detectors, allowing a very good estimate of the absolute number of photons emitted from the plasma over a wide energy range; from 7 keV to 0.5 MeV. Assuming a bi-Maxwellian electron distribution with temperatures of 4.5 and 63 keV, theoretical calculations support the experimental findings. The imaging characteristics of the x-ray source were investigated experimentally employing image plates and theoretically based on the electron distribution. (C) 2003 American Institute of Physics.
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| 8. |
- Sondhauss, Peter, et al.
(författare)
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Picosecond X-ray studies of coherent folded phonons in a multiple quantum well
- 2005
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Ingår i: Physical Review Letters. - Lund Univ, Dept Phys, SE-22100 Lund, Sweden. European Synchrotron Radiat Facil, F-38043 Grenoble, France. Malmo Univ, Sch Technol & Soc, S-20506 Malmo, Sweden. Univ Oxford, Dept Phys, Clarendon Lab, Oxford OX1 3PU, England. : AMERICAN PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 94
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Tidskriftsartikel (refereegranskat)abstract
- Coherent folded acoustic phonons in a multilayered GaSb/InAs epitaxial heterostructure were generated by femtosecond laser pulses and studied by means of ultrafast x-ray diffraction. Coherent phonons excited simultaneously in the fundamental acoustic branch and the first back-folded branch were detected. This represents the first clear evidence for phonon branch folding based directly on the atomic motion to which x-ray diffraction is sensitive. From a comparison of the measured phonon-modulated x-ray reflectivity with simulations, evidence was found for a reduction of the laser penetration depth. This reduction can be explained by the self-modulation of the refractive index due to photogenerated free carriers.
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| 9. |
- Sondhauss, Peter, et al.
(författare)
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Time resolved X-ray diffraction and non-thermal inelastic X-ray scattering
- 2004
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Ingår i: AIP Conference Proceedings. - 1551-7616 .- 0094-243X. ; 705, s. 1387-1390
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Konferensbidrag (refereegranskat)abstract
- Atomic processes like e.g. molecular vibrations, chemical reactions or phase transitions happen on picosecond down to femtosecond time scales. Novel pulsed X-ray sources or alternatively ultrafast X-ray detectors allow the investigation of these processes in real time. A powerful tool for the investigation of the dynamics in crystalline materials is time resolved X-ray diffraction (TRXD). As an example the authors present the measurement of "phonon branch folding" in a GaSb/InAs superlattice by means of TRXD. In the second part we look forward to the near future of TRXD. X-ray scattering from coherent acoustic and optical phonons has recently become describable within the framework of dynamical diffraction theory. This theory provides the means for the detailed modeling of how various lattice dynamical processes manifest themselves in the diffracted X-ray signal. Simulations are presented showing the effects of coherent acoustic and optical phonons on the rocking curve of quartz (010)
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| 10. |
- Synnergren, Ola, et al.
(författare)
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Projecting picosecond lattice dynamics through x-ray topography
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:20, s. 3727-3729
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Tidskriftsartikel (refereegranskat)abstract
- A method for time-resolved x-ray diffraction studies has been demonstrated. As a test case, coherent acoustic phonon propagation into crystalline InSb is observed using a laser plasma x-ray source. An extended x-ray topogram of the semiconductor's surface was projected onto a high spatial resolution x-ray detector and acoustic phonons were excited by rapidly heating the crystal's surface with a femtosecond laser pulse. A correlation between the spatial position on the x-ray detector and the time of arrival of the laser pulse was encoded into the experimental geometry by tilting the incident laser pulse with an optical grating. This approach enabled a temporal window of 200 ps to be sampled in a single topogram, thereby negating the disadvantages of pulse-to-pulse fluctuations in the intensity and spectrum of the laser-plasma source. (C) 2002 American Institute of Physics.
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