Recent developments in the theory of plasma-based collisionally excited x-ray lasers
(XRL) have shown an optimization potential based on the dependence of the absorption
region of the pumping laser on its angle of incidence on the plasma. For the experimental
proof of this idea, a number of diagnostic schemes were developed, tested, qualified
and applied. A high-resolution imaging system, yielding the keV emission profile perpendicular
to the target surface, provided positions of the hottest plasma regions, interesting
for the benchmarking of plasma simulation codes. The implementation of a highly efficient
spectrometer for the plasma emission made it possible to gain information about the
abundance of the ionization states necessary for the laser action in the plasma. The
intensity distribution and deflection angle of the pump laser beam could be imaged
for single XRL shots, giving access to its refraction process within the plasma. During
a European collaboration campaign at the Lund Laser Center, Sweden, the optimization
of the pumping laser incidence angle resulted in a reduction of the required pumping
energy for a Ni-like Mo XRL, which enabled the operation at a repetition rate of 10
Hz. Using the experiences gained there, the XRL performance at the PHELIX facility,
GSI Darmstadt with respect to achievable repetition rate and at wavelengths below
20 nm was significantly improved, and also important information for the development
towards multi-100 eV plasma XRLs was acquired. Due to the setup improvements achieved
during the work for this thesis, the PHELIX XRL system now has reached a degree of
reproducibility and versatility which is sufficient for demanding applications like
the XRL spectroscopy of heavy ions. In addition, a European research campaign, aiming
towards plasma XRLs approaching the water-window (wavelengths below 5 nm) was initiated.
(orig.)$$$$
Nowadays the electron beams with a high intensity are particularly interesting in
research and the applied physics. Producing such beams for which high intensity and
low emittance are synonyms with efficiency, means developing new high luminosity electron
sources, i.e. the photocathodes. This thesis, essentially experimental, is oriented
in this way. After an introduction of Clermont-Ferrand and the LAL of Orsay experimental
apparatus where the experiments took place, the chapter one presents the field emission
and the photo-field emission. Then, we prove that the quantum efficiency of the photocathodes
with silicon tips is higher for wavelengths near 800 nm. This fact is essential because
it allows the use of lasers in the fundamental wavelength - Titan-Saphir for instance.
In the chapter 2, we remind how the silicon tips are realized and how to improve surface
conditions. Procedures and the surface analysis with the SEM and XPS are described.
With a Nd-Yag laser, pumped with laser diode setting up with the participation of
IRCOM Opticians of Limoges, the photocathode supplied 1 Ampere per pulse at a quantum
efficiency of 0.25%. The description of this experiment and the results are the object
of the chapter 3. The space charge outside the photocathode space prevents the electrons
to go through. The Child-Langmuir formula limits the current with the DC gun at about
30 Ampere. To improve this result we have to use a photo-injector. In chapter 4 we
prove that the silicon tip photocathode are compatible with RF gun requirements by
PRIAM modeling and low level measure in a cold model of CANDELA RF gun. Technical
department of CERN helped us to prepare this very sensitive experiment. (author)$$$$
The aim of the presented experiment was to investigate the feasibility of satellite-based
global quantum key distribution. In this context, a free-space quantum key distribution
experiment over a real distance of 144 km was performed. The transmitter and the receiver
were situated in 2500 m altitude on the Canary Islands of La Palma and Tenerife, respectively.
The small and compact transmitter unit generated attenuated laser pulses, that were
sent to the receiver via a 15-cm optical telescope. The receiver unit for polarisation
analysis and detection of the sent pulses was integrated into an existing mirror telescope
designed for classical optical satellite communications. To ensure the required stability
and efficiency of the optical link in the presence of atmospheric turbulence, the
two telescopes were equipped with a bi-directional automatic tracking system. Still,
due to stray light and high optical attenuation, secure key exchange would not be
possible using attenuated pulses in connection with the standard BB84 protocol. The
photon number statistics of attenuated pulses follows a Poissonian distribution. Hence,
by removing a photon from all pulses containing two or more photons, an eavesdropper
could measure its polarisation without disturbing the polarisation state of the remaining
pulse. In this way, he can gain information about the key without introducing detectable
errors. To protect against such attacks, the presented experiment employed the recently
developed method of using additional ''decoy'' states, i.e., the the intensity of
the pulses created by the transmitter were varied in a random manner. By analysing
the detection probabilities of the different pulses individually, a photon-number-splitting
attack can be detected. Thanks to the decoy-state analysis, the secrecy of the resulting
quantum key could be ensured despite the Poissonian nature of the emitted pulses.
For a channel attenuation as high as 35 dB, a secret key rate of up to 250 bit/s was
achieved. Our outdoor experiment was carried out under real atmospheric conditions
and with a channel attenuation comparable to an optical link from ground to a satellite
in low earth orbit. Hence, it definitely shows the feasibility of satellite-based
quantum key distribution using a technologically comparatively simple system. (orig.)$$$$
Full text: An overview of the state of the art in modern astrophysics and cosmology
is given, emphasizing the 'Dark Energy Problem', one of the fundamental problems of
theoretical physics at present. In particular is analyzed the possibility that the
universe could be a three-dimensional membrane embedded in a higher dimensional space.
These models known as 'brane worlds' can explain the present accelerated expansion
of the Universe as dissipation due to gravity at cosmological scales extra or limit
space infrared (IR). However there are many other problems to solve, including the
problem of 'ghost' modes that are inevitable in any IR modification of gravity. (author)$$$$
Torus destruction in a nonsmooth noninvertible map http://dx.doi.org/10.1016/j.physleta.2011.11.017 by De, Soma (Department of Mathematics and Centre for Theoretical Studies, Indian Institute
of Technology, Kharagpur 721302 (India)); Dutta, Partha Sharathi (Theoretical Physics/Complex
Systems, ICBM, Carl von Ossietzky Universität, PF 2503, 26111 Oldenburg (Germany));
Banerjee, Soumitro (Department of Physics, Indian Institute of Science Education and
Research, Mohanpur 741252, Nadia, West Bengal (India)), E-mail: partha.sharathi.dutta@uni-oldenburg.de Read MoreCollapse
[en]
We consider here a nonsmooth noninvertible map and report new route to chaos from
a resonance loop torus which is not homeomorphic to circle but only endomorphic to
it. We have found that cusp torus cannot develop before the onset of chaos, though
the loop torus appears. The destruction of the loop torus occurs through homoclinic
bifurcation in the presence of an infinite number of nonsmooth loops. We show that
owing to the nonsmooth noninvertible nature of the map, the stable sets can bifurcate
to form nonsmooth closed loops. However, that cannot be interpreted directly as basin
bifurcation. -- Highlights: ► We consider a nonsmooth map which is noninvertible.
► We report a new route to chaos from a resonance loop torus which is not homeomorphic
to a circle but only endomorphic to it. ► The destruction of the torus occurs through
homoclinic bifurcation in the presence of an infinite number of nonsmooth loops. ►
The stable sets can bifurcate to form nonsmooth closed loops. ► The bifurcation of
the stable sets cannot be interpreted directly as bifurcation of the basin of attraction.$$$$
Molecular dynamics for fermions by Feldmeier, H. (Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany)); Schnack,
J. (Osnabrueck Univ. (Germany). Fachbereich Physik); Gesellschaft fuer Schwerionenforschung mbH, Darmstadt (Germany) Read MoreCollapse
[en]
The time-dependent variational principle for many-body trial states is used to discuss
the relation between the approaches of different molecular dynamics models to describe
indistinguishable fermions. Early attempts to include effects of the Pauli principle
by means of nonlocal potentials as well as more recent models which work with antisymmetrized
many-body states are reviewed under these premises. (orig.)$$$$
The equations of fluid mechanics, coupled with those that describe matter transportation
at the molecular level must be handled effectively. Putting the fluid into equations,
we model the Bloch NMR flow equations into the harmonic wave equation for the analysis
of general fluid flow. We derived the solution of the modelled harmonic equation in
non relativistic quantum mechanics and discuss its semi classical application to illustrate
its potential wide-ranging usefulness in the search for the best possible data obtainable
for general fluid flow analysis. Representing the solution of the derived harmonic
wave equation by a normalized state function is quite useful in generating the properly
normalized wave functions and in the efficient evaluation of expectation values of
many operators that can be fundamental to the analysis of fluid flow especially at
the microscopic level. (author)$$$$
Optimal system size for complex dynamics in random neural networks near criticality http://dx.doi.org/10.1063/1.4841396 by Wainrib, Gilles (Laboratoire Analyse Géométrie et Applications, Université Paris XIII,
Villetaneuse (France)); García del Molino, Luis Carlos (Institute Jacques Monod, Université
Paris VII, Paris (France)), E-mail: wainrib@math.univ-paris13.fr, E-mail: garciadelmolino@ijm.univ-paris-diderot.fr Read MoreCollapse
[en]
In this article, we consider a model of dynamical agents coupled through a random
connectivity matrix, as introduced by Sompolinsky et al. [Phys. Rev. Lett. 61(3),
259–262 (1988)] in the context of random neural networks. When system size is infinite,
it is known that increasing the disorder parameter induces a phase transition leading
to chaotic dynamics. We observe and investigate here a novel phenomenon in the sub-critical
regime for finite size systems: the probability of observing complex dynamics is maximal
for an intermediate system size when the disorder is close enough to criticality.
We give a more general explanation of this type of system size resonance in the framework
of extreme values theory for eigenvalues of random matrices$$$$
Resonant electromagnetic scattering in anisotropic layered media http://dx.doi.org/10.1063/1.4824686 by Shipman, Stephen P. (Department of Mathematics, Louisiana State University, Baton
Rouge, Louisiana 70803 (United States)); Welters, Aaron T. (Department of Mathematics,
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)) Read MoreCollapse
[en]
The resonant excitation of an electromagnetic guided mode of a slab structure by exterior
radiation results in anomalous scattering behavior, including sharp energy-transmission
anomalies and field amplification around the frequency of the slab mode. In the case
of a periodically layered ambient medium, anisotropy serves to couple the slab mode
to radiation. Exact expressions for scattering phenomena are proved by analyzing a
pole of the full scattering matrix as it moves off the real frequency axis into the
lower half complex plane under a detuning of the wavevector parallel to the slab.
The real pole is the frequency of a perfect (infinite Q) guided mode, which becomes
lossy as the frequency gains an imaginary part. This work extends results of Shipman
and Venakides to evanescent source fields and two-dimensional parallel wavevector
and demonstrates by example how the latter allows one to control independently the
width and central frequency of a resonance by varying the angle of incidence of the
source field. The analysis relies on two nondegeneracy conditions of the complex dispersion
relation for slab modes (relating poles of the scattering matrix to wavevector), which
were assumed in previous works and are proved in this work for layered media. One
of them asserts that the dispersion relation near the wavevector κ and frequency ω
of a perfect guided mode is the zero set of a simple eigenvalue ℓ(κ, ω), and the other
relates ∂ℓ/∂ω to the total energy of the mode, thereby implying that this derivative
is nonzero$$$$