148 research outputs found
Resonant charging of Xe clusters in Helium nanodroplets under intense laser fields
We theoretically investigate the impact of multiple plasmon resonances on the
charging of Xe clusters embedded in He nanodroplets under intense pump-probe
laser excitation. Our molecular dynamics simulations on Xe309He10000 give clear evidence for selective
resonance heating in the He shell and the Xe cluster, but no corresponding
double hump feature in the final Xe charge spectra is found. Though the
presence of the He shell substantially increases the maximum charge states, the
pump-probe dynamics of the Xe spectra from embedded system is similar to that
of the free species. In strong contrast to that, the predicted electron spectra
do show well-separated and pronounced features from highly efficient plasmon
assisted electron acceleration for both resonances in the embedded clusters. A
detailed analysis of the underlying ionization and recombination dynamics is
presented and explains the apparent disaccord between the resonance features in
the ion and electron spectra.Comment: revised manuscrip
Ionization heating in rare-gas clusters under intense XUV laser pulses
The interaction of intense extreme ultraviolet (XUV) laser pulses
(, \,W/cm) with small rare-gas clusters
(Ar) is studied by quasi-classical molecular dynamics simulations. Our
analysis supports a very general picture of the charging and heating dynamics
in finite samples under short-wavelength radiation that is of relevance for
several applications of free-electron lasers. First, up to a certain photon
flux, ionization proceeds as a series of direct photoemission events producing
a jellium-like cluster potential and a characteristic plateau in the
photoelectron spectrum as observed in [Bostedt {\it et al.}, Phys. Rev. Lett.
{\bf 100}, 013401 (2008)]. Second, beyond the onset of photoelectron trapping,
nanoplasma formation leads to evaporative electron emission with a
characteristic thermal tail in the electron spectrum. A detailed analysis of
this transition is presented. Third, in contrast to the behavior in the
infrared or low vacuum ultraviolet range, the nanoplasma energy capture
proceeds via {\it ionization heating}, i.e., inner photoionization of localized
electrons, whereas collisional heating of conduction electrons is negligible up
to high laser intensities. A direct consequence of the latter is a surprising
evolution of the mean energy of emitted electrons as function of laser
intensity.Comment: figure problems resolve
Ionization avalanching in clusters ignited by extreme-ultraviolet driven seed electrons
We study the ionization dynamics of Ar clusters exposed to ultrashort
near-infrared (NIR) laser pulses for intensities well below the threshold at
which tunnel ionization ignites nanoplasma formation. We find that the emission
of highly charged ions up to Ar can be switched on with unit contrast by
generating only a few seed electrons with an ultrashort extreme ultraviolet
(XUV) pulse prior to the NIR field. Molecular dynamics simulations can explain
the experimental observations and predict a generic scenario where efficient
heating via inverse bremsstrahlung and NIR avalanching are followed by resonant
collective nanoplasma heating. The temporally and spatially well-controlled
injection of the XUV seed electrons opens new routes for controlling
avalanching and heating phenomena in nanostructures and solids, with
implications for both fundamental and applied laser-matter science.Comment: 5 pages, 4 figure
Radiographic features of liver allograft rejection
The radiographic features of 19 transplanted patients with failure of the liver allograft were evaluated. These features were: poor filling, stretching, attenuation of intrahepatic biliary ducts documented by T-tube cholangiogram, attenuation of branches of the hepatic artery seen on angiogram as well as a decrease of blood flow through the liver seen on angiogram and nuclear medicine dynamic scintigram. These findings were secondary to swelling of the transplanted liver and were not specific for rejection; they may also be present in hepatic infarction or infection
- …