230 research outputs found
Multi-electron-recombination rates estimated within dense plasmas
We investigate the rates for multielectron recombination within a dense
plasma environment in local thermodynamic equilibrium (LTE). We find that these
multielectron recombination rates can be high within dense plasmas, and they
should be treated in the simulations of the plasmas created by intense
radiation, in particular for plasmas created by intense VUV radiation from
free-electron-laser (FEL) or for modelling the inertial confinement fusion
(ICF) plasmas
Impact of ultrafast electronic damage in single particle x-ray imaging experiments
In single particle coherent x-ray diffraction imaging experiments, performed
at x-ray free-electron lasers (XFELs), samples are exposed to intense x-ray
pulses to obtain single-shot diffraction patterns. The high intensity induces
electronic dynamics on the femtosecond time scale in the system, which can
reduce the contrast of the obtained diffraction patterns and adds an isotropic
background. We quantify the degradation of the diffraction pattern from
ultrafast electronic damage by performing simulations on a biological sample
exposed to x-ray pulses with different parameters. We find that the contrast is
substantially reduced and the background is considerably strong only if almost
all electrons are removed from their parent atoms. This happens at fluences of
at least one order of magnitude larger than provided at currently available
XFEL sources.Comment: 15 pages, 3 figures submitted to PR
Direct determination of triplet phases and enantiomorphs of non-centrosymmetric structures. II. Experimental results
Direct measurements of triplet phase relationships for non-centrosymmetric light-atom organic structures with medium-size unit cells are reported. The phase information can be extracted from the three- beam profiles of a Renninger [psi]-scan experiment. The measurements were carried out with a special [psi]-circle diffractometer installed on a rotating Cu-anode generator. The incident-beam divergence is reduced to 0.02°. The experimental results confirm the theoretical considerations of paper I of this work [Hümmer & Billy (1986). Acta Cryst. A42, 127-133]. As triplet phases of +90° can be distinguished, the absolute structure can be determined unambiguously. The measurements show that the triplet-phase-dependent interference effects may be superposed on phase-independent Umweganregung or Aufhellung effects. By a comparison of the [psi]-scan profiles of two centrosymmetrically related three-beam cases, the triplet phases of which have opposite signs, it is possible to evaluate the phase-independent effects and to determine the value of the triplet phase with an accuracy of at least 90°
Hanbury Brown and Twiss interferometry at a free-electron laser
We present measurements of second- and higher-order intensity correlation
functions (so-called Hanbury Brown and Twiss experiment) performed at the
free-electron laser (FEL) FLASH in the non-linear regime of its operation. We
demonstrate the high transverse coherence properties of the FEL beam with a
degree of transverse coherence of about 80% and degeneracy parameter of the
order 10^9 that makes it similar to laser sources. Intensity correlation
measurements in spatial and frequency domain gave an estimate of the FEL
average pulse duration of 50 fs. Our measurements of the higher-order
correlation functions indicate that FEL radiation obeys Gaussian statistics,
which is characteristic to chaotic sources.Comment: 19 pages, 6 figures, 1 table, 40 reference
Cooperative effects in nuclear excitation with coherent x-ray light
The interaction between super-intense coherent x-ray light and nuclei is
studied theoretically. One of the main difficulties with driving nuclear
transitions arises from the very narrow nuclear excited state widths which
limit the coupling between laser and nuclei. In the context of direct
laser-nucleus interaction, we consider the nuclear width broadening that occurs
when in solid targets, the excitation caused by a single photon is shared by a
large number of nuclei, forming a collective excited state. Our results show
that for certain isotopes, cooperative effects may lead to an enhancement of
the nuclear excited state population by almost two orders of magnitude.
Additionally, an update of previous estimates for nuclear excited state
population and signal photons taking into account the experimental advances of
the x-ray coherent light sources is given. The presented values are an
improvement by orders of magnitude and are encouraging for the future prospects
of nuclear quantum optics.Comment: 22 pages, 4 figures, 5 tables; updated to the published version, one
additional results tabl
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