1,077 research outputs found
Modulation Instability and Pattern Formation in Spatially Incoherent Light Beams
We present the first experimental observation of modulation instability of
partially spatially incoherent light beams in non-instantaneous nonlinear
media. We show that even in such a nonlinear partially coherent system (of
weakly-correlated particles) patterns can form spontaneously. Incoherent MI
occurs above a specific threshold that depends on the beams' coherence
properties (correlation distance), and leads to a periodic train of
one-dimensional (1D) filaments. At a higher value of nonlinearity, incoherent
MI displays a two-dimensional (2D) instability and leads to self-ordered arrays
of light spots.Comment: 16 pages, 4 figure
Incoherent matter-wave solitons
The dynamics of matter-wave solitons in Bose-Einstein condensates (BEC) is
considerably affected by the presence of a surrounding thermal cloud and by
condensate depletion during its evolution. We analyze these aspects of BEC
soliton dynamics, using time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory.
The condensate is initially prepared within a harmonic trap at finite
temperature, and solitonic behavior is studied by subsequently propagating the
TDHFB equations without confinement. Numerical results demonstrate the collapse
of the BEC via collisional emission of atom pairs into the thermal cloud,
resulting in splitting of the initial density into two solitonic structures
with opposite momentum. Each one of these solitary matter waves is a mixture of
condensed and noncondensed particles, constituting an analog of optical
random-phase solitons.Comment: 4 pages, 2 figures, new TDHFB result
Phase Retrieval with Application to Optical Imaging
This review article provides a contemporary overview of phase retrieval in
optical imaging, linking the relevant optical physics to the information
processing methods and algorithms. Its purpose is to describe the current state
of the art in this area, identify challenges, and suggest vision and areas
where signal processing methods can have a large impact on optical imaging and
on the world of imaging at large, with applications in a variety of fields
ranging from biology and chemistry to physics and engineering
Vector solitons in (2+1) dimensions
We address the problem of existence and stability of vector spatial solitons
formed by two incoherently interacting optical beams in bulk Kerr and saturable
media. We identify families of (2+1)-dimensional two-mode self-trapped beams,
with and without a topological charge, and describe their properties
analytically and numerically.Comment: 3 pages, 5 figures, submitted to Opt. Let
On the nature of Coulomb corrections to the e^+e^- pair production in ultrarelativistic heavy-ion collisions
We manifest the origin of the wrong conclusion made by several groups of
authors on the absence of Coulomb corrections to the cross section of the
e^+e^- pair production in ultrarelativistic heavy-ion collisions. The source of
the mistake is connected with an incorrect passage to the limit in the
expression for the cross section. When this error is eliminated, the Coulomb
corrections do not vanish and agree with the results obtained within the
Weizs\"acker-Williams approximation.Comment: 7 pages, LaTe
Induced Coherence and Stable Soliton Spiraling
We develop a theory of soliton spiraling in a bulk nonlinear medium and
reveal a new physical mechanism: periodic power exchange via induced coherence,
which can lead to stable spiraling and the formation of dynamical two-soliton
states. Our theory not only explains earlier observations, but provides a
number of predictions which are also verified experimentally. Finally, we show
theoretically and experimentally that soliton spiraling can be controled by the
degree of mutual initial coherence.Comment: 4 pages, 5 figure
Causality effects on accelerating light pulses
We study accelerating and decelerating shape-preserving temporal Airy wave-packets propagating in dispersive media. We explore the effects of causality, and find that, whereas decelerating pulses can asymptotically reach zero group velocity, pulses that accelerate towards infinite group velocity inevitably break up, after a specific critical point. The trajectories and the features of causal pulses are analyzed, along with the requirements for the existence of the critical point and experimental schemes for its observation. Finally, we show that causality imposes similar effects on accelerating pulses in the presence of local Kerr-like nonlinearities
Coulomb corrections and multiple e+e- pair production in ultra-relativistic nuclear collisions
We consider the problem of Coulomb corrections to the inclusive cross
section. We show that these corrections in the limiting case of small charge
number of one of the nuclei coincide with those to the exclusive cross section.
Within our approach we also obtain the Coulomb corrections for the case of
large charge numbers of both nuclei.Comment: 7 pages, REVTeX
Super-diffusion in optical realizations of Anderson localization
We discuss the dynamics of particles in one dimension in potentials that are
random both in space and in time. The results are applied to recent optics
experiments on Anderson localization, in which the transverse spreading of a
beam is suppressed by random fluctuations in the refractive index. If the
refractive index fluctuates along the direction of the paraxial propagation of
the beam, the localization is destroyed. We analyze this broken localization,
in terms of the spectral decomposition of the potential. When the potential has
a discrete spectrum, the spread is controlled by the overlap of Chirikov
resonances in phase space. As the number of Fourier components is increased,
the resonances merge into a continuum, which is described by a Fokker-Planck
equation. We express the diffusion coefficient in terms of the spectral
intensity of the potential. For a general class of potentials that are commonly
used in optics, the solutions of the Fokker-Planck equation exhibit anomalous
diffusion in phase space, implying that when Anderson localization is broken by
temporal fluctuations of the potential, the result is transport at a rate
similar to a ballistic one or even faster. For a class of potentials which
arise in some existing realizations of Anderson localization atypical behavior
is found.Comment: 11 pages, 2 figure
Soliton dynamics and self-induced transparency in nonlinear nanosuspensions
We study spatial soliton dynamics in nano-particle suspensions. Starting from the Nernst-Planck and Smoluchowski equations, we demonstrate that in these systems the underlying nonlinearities as well as the nonlinear Rayleigh losses depend exponentially on optical intensity. Two different nonlinear regimes are identified depending on the refractive index contrast of the nanoparticles involved and the interesting prospect of self-induced transparency is demonstrated. Soliton stability is systematically analyzed for both 1D and 2D configurations and their propagation dynamics in the presence of Rayleigh losses is examined. The possibility of synthesizing artificial nonlinearities using mixtures of nanosuspensions is also considered
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