272 research outputs found
Three-Wave Modulational Stability and Dark Solitons in a Quadratic Nonlinear Waveguide with Grating
We consider continuous-wave (CW) states and dark solitons (DSs) in a system
of two fundamental-frequency (FF) and one second-harmonic (SH) waves in a
planar waveguide with the quadratic nonlinearity, the FF components being
linearly coupled by resonant reflections on the Bragg grating. We demonstrate
that, in contrast with the usual situation in quadratic spatial-domain models,
CW states with the phase shift between the FF and SH components are
modulationally stable in a broad parameter region in this system, provided that
the CW wavenumber does not belong to the system's spectral gap. Stationary
fundamental DSs are found numerically, and are also constructed by means of a
specially devised analytical approximation. Bound states of two and three DSs
are found too. The fundamental DSs and two-solitons bound states are stable in
all the cases when the CW background is stable, which is shown by dint of
calculation of the corresponding eigenvalues, and verified in direct
simulations. Tilted DSs are found too. They attain a maximum contrast at a
finite value of the tilt, that does not depend on the phase mismatch. At a
maximum value of the tilt, which grows with the mismatch, the DS merges into
the CW background. Interactions between the tilted solitons are shown to be
completely elastic.Comment: 10 pages, 12 figures; Journal of Optics A, in pres
Gasperini syndrome as clinical manifestation of pontine demyelination
The Gasperini syndrome is a very rare brainstem disease characterized by the typical combination of ipsilateral lesions of the cranial nerves V-VII and dissociated contralateral hemihypesthesia, whereas both contralateral and ipsilateral hypacusis was described. Since the first description in 1912, only a few cases of this crossed brainstem syndrome were published so far. Pontine infarction and bleedings were the reported causes of the syndrome. Here we report a 44-year-old man with the classical Gasperini syndrome due to pontine demyelination in multiple sclerosis. The clinical findings were correlated with changes on MRI. The present case shows that classical crossed brainstem syndromes are topological terms not invariably associated with brainstem ischemia in particular vascular areas and may contribute to the differential diagnosis of peripheral facial nerve palsy
Approximate solutions and scaling transformations for quadratic solitons
We study quadratic solitons supported by two- and three-wave parametric
interactions in chi-2 nonlinear media. Both planar and two-dimensional cases
are considered. We obtain very accurate, 'almost exact', explicit analytical
solutions, matching the actual bright soliton profiles, with the help of a
specially-developed approach, based on analysis of the scaling properties.
Additionally, we use these approximations to describe the linear tails of
solitary waves which are related to the properties of the soliton bound states.Comment: 11 pages, 9 figures; submitted for publicatio
Spatiotemporally Localized Multidimensional Solitons in Self-Induced Transparency Media
"Light bullets" are multi-dimensional solitons which are localized in both
space and time. We show that such solitons exist in two- and three-dimensional
self-induced-transparency media and that they are fully stable. Our approximate
analytical calculation, backed and verified by direct numerical simulations,
yields the multi-dimensional generalization of the one-dimensional Sine-Gordon
soliton.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Let
Helmholtz bright and boundary solitons
We report, for the first time, exact analytical boundary solitons of a generalized cubic-quintic Non-Linear Helmholtz (NLH) equation. These solutions have a linked-plateau topology that is distinct from conventional dark soliton solutions; their amplitude and intensity distributions are spatially delocalized and connect regions of finite and zero wave-field disturbances (suggesting also the classification as 'edge solitons'). Extensive numerical simulations compare the stability properties of recently-reported Helmholtz bright solitons, for this type of polynomial non-linearity, to those of the new boundary solitons. The latter are found to possess a remarkable stability characteristic, exhibiting robustness against perturbations that would otherwise lead to the destabilizing of their bright-soliton counterpart
Observation of domain wall bimerons in chiral magnets
Topological defects embedded in or combined with domain walls have been
proposed in various systems, some of which are referred to as domain wall
skyrmions or domain wall bimerons. However, the experimental observation of
such topological defects remains an ongoing challenge. Here, using Lorentz
transmission electron microscopy, we report the experimental discovery of
domain wall bimerons in chiral magnet Co-Zn-Mn(110) thin films. By applying a
magnetic field, multidomain structures develop, and simultaneously, chained and
isolated bimerons arise as the localized state between the domains with the
opposite in-plane components of net magnetization. The multidomain formation is
attributed to magnetic anisotropy and dipolar interaction, and domain wall
bimerons are stabilized by the Dzyaloshinskii-Moriya interaction. In addition,
micromagnetic simulations show that domain wall bimerons appear for a wide
range of conditions in chiral magnets with cubic magnetic anisotropy. Our
results promote further study in various fields of physics.Comment: 30 pages, 10 figures (including Supplementary Materials
Spatiotemporally localized solitons in resonantly absorbing Bragg reflectors
We predict the existence of spatiotemporal solitons (``light bullets'') in
two-dimensional self-induced transparency media embedded in a Bragg grating.
The "bullets" are found in an approximate analytical form, their stability
being confirmed by direct simulations. These findings suggest new possibilities
for signal transmission control and self-trapping of light.Comment: RevTex, 3 pages, 2 figures, to be published in PR
Angular Dependences of Third Harmonic Generation from Microdroplets
We present experimental and theoretical results for the angular dependence of
third harmonic generation (THG) of water droplets in the micrometer range (size
parameter ). The THG signal in - and -polarization obtained
with ultrashort laser pulses is compared with a recently developed nonlinear
extension of classical Mie theory including multipoles of order .
Both theory and experiment yield over a wide range of size parameters
remarkably stable intensity maxima close to the forward and backward direction
at ``magic angles''. In contrast to linear Mie scattering, both are of
comparable intensity.Comment: 4 pages, RevTeX, 3 figures available on request from
[email protected], submitted to PR
Higher-order nonlinear modes and bifurcation phenomena due to degenerate parametric four-wave mixing
We demonstrate that weak parametric interaction of a fundamental beam with
its third harmonic field in Kerr media gives rise to a rich variety of families
of non-fundamental (multi-humped) solitary waves. Making a comprehensive
comparison between bifurcation phenomena for these families in bulk media and
planar waveguides, we discover two novel types of soliton bifurcations and
other interesting findings. The later includes (i) multi-humped solitary waves
without even or odd symmetry and (ii) multi-humped solitary waves with large
separation between their humps which, however, may not be viewed as bound
states of several distinct one-humped solitons.Comment: 9 pages, 17 figures, submitted to Phys. Rev.
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