144 research outputs found
Pattern formation by kicked solitons in the two-dimensionnal Ginzburg-Landau medium with a transverse grating
We consider the kick-induced mobility of two-dimensional (2D) fundamental
dissipative solitons in models of lasing media based on the 2D complex
Ginzburg-Landau (CGL) equation including a spatially periodic potential
(transverse grating). The depinning threshold is identified by means of
systematic simulations, and described by means of an analytical approximation,
depending on the orientation of the kick. Various pattern-formation scenarios
are found above the threshold. Most typically, the soliton, hopping between
potential cells, leaves arrayed patterns of different sizes in its wake. In the
laser cavity, this effect may be used as a mechanism for selective pattern
formation controlled by the tilt of the seed beam. Freely moving solitons
feature two distinct values of the established velocity. Elastic and inelastic
collisions between free solitons and pinned arrayed patterns are studied too.Comment: 15 pages, 20 figures (with 41 sub-figures
The theory of photorefractive resonance for localized beams in two-carrier photorefractive systems
This paper extends the existing theory of two carrier photorefractivity
resonance, which is generally applied to Iron doped Indium Phosphide (InP:Fe),
to the case of low non-harmonic illumination. The space charge field profile is
computed, and the variations of its amplitude, width and position are
determined as functions of the background intensity. The effect of
photorefractive resonance on these quantities is evidenced, contributing to the
understanding of published experimental results in InP:Fe.Comment: Physical Review A: Atomic, Molecular and Optical Physics Accepted
(2009) To be publishe
Stabilization of vortex beams in Kerr media by nonlinear absorption
We elaborate a new solution for the problem of stable propagation of
transversely localized vortex beams in homogeneous optical media with
self-focusing Kerr nonlinearity. Stationary nonlinear Bessel-vortex states are
stabilized against azimuthal breakup and collapse by multiphoton absorption,
while the respective power loss is offset by the radial influx of the power
from an intrinsic reservoir. A linear stability analysis and direct numerical
simulations reveal a region of stability of these vortices. Beams with multiple
vorticities have their stability regions too. These beams can then form robust
tubular filaments in transparent dielectrics as common as air, water and
optical glasses at sufficiently high intensities. We also show that the
tubular, rotating and speckle-like filamentation regimes, previously observed
in experiments with axicon-generated Bessel beams, can be explained as
manifestations of the stability or instability of a specific nonlinear
Bessel-vortex state, which is fully identified.Comment: Physical Review A, in press, 9 pages, 6 figure
Ultrashort light bullets described by the two-dimensional sine-Gordon equation
By using a reductive perturbation technique applied to a two-level model,
this study puts forward a generic two-dimensional sine-Gordon evolution
equation governing the propagation of femtosecond spatiotemporal optical
solitons in Kerr media beyond the slowly varying envelope approximation. Direct
numerical simulations show that, in contrast to the long-wave approximation, no
collapse occurs, and that robust (2+1)-dimensional ultrashort light bullets may
form from adequately chosen few-cycle input spatiotemporal wave forms. In
contrast to the case of quadratic nonlinearity, the light bullets oscillate in
both space and time and are therefore not steady-state lumps
Fast build up of photorefractive spatial solitons in iron doped indium phosphide
Conférence OralInternational audiencePhotorefractive (PR) spatial soliton propagation hints that all optical routing can be achieved through soliton interactions. This requires, however, fast build up and sensitivity to telecommunication wavelengths. We have investigated the build up of infrared (1,06m) photorefractive solitons in iron doped indium phosphide (InP:Fe) and shown that PR self focusing occurs at input powers of hundreds of W and intensities in the range of W/cm2, showing a build up time down to the microsecond
Stable nonlinear vortices in self-focusing Kerr media with nonlinear absorption
We have studied the stability properties of nonlinear Bessel vortices in self-focusing Kerr media with nonlinear absorption. Nonlinear Bessel vortices are propagation-invariant solutions of the nonlinear Schrödinger equation with cubic nonlinearity and nonlinear absorption. We have found that these vortices can be stable against perturbations, including the azimuthal perturbations that usually break the cylindrical symmetry of standard vortex solitons in self-focusing Kerr media. This property is seen to arise from the stabilizing effect of nonlinear absorption. Our model is the nonlinear Schrödinger equatio
Filtre SIW d'ordre 6 en bande C avec un couplage croisé. Analyse expérimentale du comportement thermique.
National audienceCet article présente un filtre SIW (Substrate Integrated Waveguide) d'ordre 6 en bande C réalisé sur un substrat d'alumine de permittivité 9.9. Un couplage croisé entre résonateurs non-adjacents est introduit afin d'améliorer les réjections; une contrainte indispensable pour les applications spatiales. La compatibilité avec les circuits planaires est assurée par l'intermédiaire d'une transition microruban spécifique. Des tests en température ont été réalisés afin d'évaluer le comportement du filtre dans un environnement spatial. Les résultats expérimentaux sont en accord avec les simulations
West Nile Virus in Morocco, 2003
West Nile virus (WNV) reemerged in Morocco in September 2003, causing an equine outbreak. A WNV strain isolated from a brain biopsy was completely sequenced. On the basis of phylogenetic analyses, Moroccan WNV strains isolated during the 1996 and 2003 outbreaks were closely related to other strains responsible for equine outbreaks in the western Mediterranean basin
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