36 research outputs found
Damage threshold in pre-heated materials exposed to intense X-rays
Materials exposed to ultrashort intense x-ray irradiation may experience
various damaging conditions depending on the in-situ temperature. A pre-heated
target exposed to intense x-rays plays a crucial role in numerous systems of
physical-technical importance, ranging from the heavily-, and repeatedly
radiation-loaded optics at x-ray free-electron laser facilities, to the first
wall of prospective inertial fusion reactors. We study theoretically the damage
threshold dependence on the temperature in different classes of materials: an
insulator (diamond), a semiconductor (silicon), a metal (tungsten), and an
organic polymer (PMMA). The numerical techniques used here enable us to trace
the evolution of both, an electronic state and atomic dynamics of the
materials. It includes damage mechanisms such as thermal damage (induced by an
increase of the atomic temperature due to energy transfer from x-ray-excited
electrons) and nonthermal phase transitions (induced by changes in the
interatomic potential due to excitation of electrons). We demonstrate that in
the pre-heated materials, typically, the thermal damage threshold stays the
same or lowers with the increase of the in-situ temperature, whereas nonthermal
damage thresholds may be lowered or raised, depending on the particular
material and specifics of the damage kinetics
A convenient synthetic method for 4-nitro-1,3,4,5-tetra-hydrobenz[cd]indoles and its application for an alternative synthesis of (Ā±)-6,7-secoagroclavine
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Electron refluxing and K-shell line emission from Ti foils irradiated with sub-picosecond laser pulses at 527nm
Single shot time-resolved magnetic x-ray absorption at a Free Electron Laser
Ultrafast dynamics are generally investigated using stroboscopic pump-probe
measurements, which characterize the sample properties for a single, specific
time delay. These measurements are then repeated for a series of discrete time
delays to reconstruct the overall time trace of the process. As a consequence,
this approach is limited to the investigation of fully reversible phenomena. We
recently introduced an off-axis zone plate based X-ray streaking technique,
which overcomes this limitation by sampling the relaxation dynamics with a
single femtosecond X-ray pulse streaked over a picosecond long time window. In
this article we show that the X-ray absorption cross section can be employed as
the contrast mechanism in this novel technique. We show that changes of the
absorption cross section on the percent level can be resolved with this method.
To this end we measure the ultrafast magnetization dynamics in CoDy alloy
films. Investigating different chemical compositions and infrared pump
fluences, we demonstrate the routine applicability of this technique. Probing
in transmission the average magnetization dynamics of the entire film, our
experimental findings indicate that the demagnetization time is independent of
the specific infrared laser pump fluence. These results pave the way for the
investigation of irreversible phenomena in a wide variety of scientific areas.Comment: 9 pages, 5 figure
X-ray spectroscopic studies of intense laser interaction with matter
The generation and interaction dynamics of hot electrons from sub-ps and 10 17 - 10 20W/cm lasers with various thickness of Ti foils, were studied through X-ray spectroscopy in three experiments. The two experiments were carried out with the TARANIS laser at Queen's University Belfast with a second harmonic beam (527mm) and with the fundamental beam (1053mm) in the intensity regime 10 17 - 10 18W/cm. We have observed the Ti K-shell radiation yield correlation with the laser intensity and energy absorption efficiency, and thus confirmed the population and temperature of hot electrons generated as a result of the absorbed energy and laser intensity.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
A convenient synthetic method for 4-nitro-1,3,4,5-tetra-hydrobenz[cd]indoles and its application for an alternative synthesis of (Ā±)-6,7-secoagroclavine
Characterizing transmissive diamond gratings as beam splitters for the hard X-ray single-shot spectrometer of the European XFEL
The European X-ray Free Electron Laser (EuXFEL) offers intense, coherent femtosecond pulses, resulting in characteristic peak brilliance values a billion times higher than that of conventional synchrotron facilities. Such pulses result in extreme peak radiation levels of the order of terawattsā
cmā2 for any optical component in the beam and can exceed the ablation threshold of many materials. Diamond is considered the optimal material for such applications due to its high thermal conductivity (2052ā
Wā
mKā1 at 300ā
K) and low absorption for hard X-rays. Grating structures were fabricated on free-standing CVD diamond of 10ā
Āµm thickness with 500ā
Āµm silicon substrate support. The grating structures were produced by electron-beam lithography at the Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, Switzerland. The grating lines were etched to a depth of 1.2ā
Āµm, resulting in an aspect ratio of 16. The characterization measurements with X-rays were performed on transmissive diamond gratings of 150ā
nm pitch at the P10 beamline of PETRAā
III, DESY. In this paper, the gratings are briefly described, and a measured diffraction efficiency of 0.75% at 6ā
keV in the first-order diffraction is shown; the variation of the diffraction efficiency across the grating surface is presented
Limitations of Structural Insight into Ultrafast Melting of Solid Materials with X-ray Diffraction Imaging
In this work, we analyze the application of X-ray diffraction imaging techniques to follow ultrafast structural transitions in solid materials using the example of an X-ray pumpāX-ray probe experiment with a single-crystal silicon performed at a Linac Coherent Light Source. Due to the spatially non-uniform profile of the X-ray beam, the diffractive signal recorded in this experiment included contributions from crystal parts experiencing different fluences from the peak fluence down to zero. With our theoretical model, we could identify specific processes contributing to the silicon melting in those crystal regions, i.e., the non-thermal and thermal melting whose occurrences depended on the locally absorbed X-ray doses. We then constructed the total volume-integrated signal by summing up the coherent signal contributions (amplitudes) from the various crystal regions and found that this significantly differed from the signals obtained for a few selected uniform fluence values, including the peak fluence. This shows that the diffraction imaging signal obtained for a structurally damaged material after an impact of a non-uniform X-ray pump pulse cannot be always interpreted as the materialās response to a pulse of a specific (e.g., peak) fluence as it is sometimes believed. This observation has to be taken into account in planning and interpreting future experiments investigating structural changes in materials with X-ray diffraction imaging
Limitations of Structural Insight into Ultrafast Melting of Solid Materials with X-ray Diffraction Imaging
In this work, we analyze the application of X-ray diffraction imaging techniques to follow ultrafast structural transitions in solid materials using the example of an X-ray pumpāX-ray probe experiment with a single-crystal silicon performed at a Linac Coherent Light Source. Due to the spatially non-uniform profile of the X-ray beam, the diffractive signal recorded in this experiment included contributions from crystal parts experiencing different fluences from the peak fluence down to zero. With our theoretical model, we could identify specific processes contributing to the silicon melting in those crystal regions, i.e., the non-thermal and thermal melting whose occurrences depended on the locally absorbed X-ray doses. We then constructed the total volume-integrated signal by summing up the coherent signal contributions (amplitudes) from the various crystal regions and found that this significantly differed from the signals obtained for a few selected uniform fluence values, including the peak fluence. This shows that the diffraction imaging signal obtained for a structurally damaged material after an impact of a non-uniform X-ray pump pulse cannot be always interpreted as the materialās response to a pulse of a specific (e.g., peak) fluence as it is sometimes believed. This observation has to be taken into account in planning and interpreting future experiments investigating structural changes in materials with X-ray diffraction imaging