483 research outputs found
Nonlocal incoherent solitons
We investigate the propagation of partially coherent beams in spatially
nonlocal nonlinear media with a logarithmic type of nonlinearity. We derive
analytical formulas for the evolution of the beam parameters and conditions for
the formation of nonlocal incoherent solitons.Comment: 5 pages, 3 figure
Generic features of modulational instability in nonlocal Kerr media
The modulational instability (MI) of plane waves in nonlocal Kerr media is
studied for a general, localized, response function. It is shown that there
always exists a finite number of well-separated MI gain bands, with each of
them characterised by a unique maximal growth rate. This is a general property
and is demonstrated here for the Gaussian, exponential, and rectangular
response functions. In case of a focusing nonlinearity it is shown that
although the nonlocality tends to suppress MI, it can never remove it
completely, irrespectively of the particular shape of the response function.
For a defocusing nonlinearity the stability properties depend sensitively on
the profile of the response function. It is shown that plane waves are always
stable for response functions with a positive-definite spectrum, such as
Gaussians and exponentials. On the other hand, response functions whose spectra
change sign (e.g., rectangular) will lead to MI in the high wavenumber regime,
provided the typical length scale of the response function exceeds a certain
threshold. Finally, we address the case of generalized multi-component response
functions consisting of a weighted sum of N response functions with known
properties.Comment: 9 pages, 5 figure
Asymmetric partially coherent solitons in saturable nonlinear media
We investigate theoretically properties of partially coherent solitons in optical nonlinear media with slow
saturable nonlinearity. We have found numerically that such a medium can support spatial solitons which are
asymmetric in shape and are composed of only a finite number of modes associated with the self-induced
waveguide. It is shown that these asymmetric spatial solitons can propagate many diffraction lengths without
changes, but that collisions change their shape and may split them apart. [S1063-651X(99)12808-3
Spatial solitons and light-induced instabilities in colloidal media
We study nonlinear light propagation in colloidal nanosuspensions. We introduce a novel model for the nonlinear response of colloids
which describes consistently the system in the regimes of low and high light
intensities and low/large concentrations of colloidal particles. We employ
this model to study the light-induced instabilities and demonstrate the
formation of stable spatial solitons as well as the existence of a bistability regime
Bright optical beams in weakly nonlocal media: variational analysis
We employ a variational technique to describe the propagation of a Gaussian beam in a nonlinear, weakly
nonlocal medium and derive the conditions for breathing soliton formation in both one and two transverse
dimensions. The reduced one-dimensional results agree quantitatively with known exact nonlocal soliton
solutions. We subsequently formulate a simple procedure for estimating the strength of a weak nonlocality and
verify its applicability by direct numerical simulations
Soliton interactions and transformations in colloidal media
We study nonlinear light propagation in colloidal suspensions of spherical dielectric nanoparticles. We analyze the existence and properties of one-dimensional self-trapped beams (spatial optical solitons) in such media and demonstrate the existence of
Spatial Solitons in Optically-Induced Gratings
We study experimentally nonlinear localization effects in optically-induced
gratings created by interfering plane waves in a photorefractive crystal. We
demonstrate the generation of spatial bright solitons similar to those observed
in arrays of coupled optical waveguides. We also create pairs of out-of-phase
solitons which resemble ``twisted'' localized states in nonlinear lattices.Comment: 3 pages, 4 figures. accepted in O
Nonlinear Optical Effects at Ferroelectric Domain Walls
Ferroelectric materials tend to form macroscopic domains of electric polarization. These domains have different orientations and coexist in the medium being separated by domain walls. In general, symmetry and structure of ferroelectric domain walls differ from their parent materials and consequently lead to abundant physical properties. In this book chapter, we review the nonlinear optical effects which are bundled with ferroelectric domain walls or whose properties can be significantly enhanced by the presence of domain walls. In particular, we have reviewed Google Scholar articles from 2008 to 2018 using the keywords “nonlinear Čerenkov radiation from ferroelectrics”. We show that the spatially steep modulation of the second-order nonlinear optical coefficient across the domain wall leads to strong emission of the Čerenkov second harmonic in bulk materials. This feature also enables an effective nondestructive method for three-dimensional visualization and diagnostics of ferroelectric domain structures with very high resolution and high contrast
Photophoretic manipulation of absorbing aerosol particles with vortex beams: theory versus experiment
We develop a theoretical approach for describing the optical trapping and manipulation of carbon nanoclusters in air with a dual-vortex optical trap, as realized recently in experiment [V. Shvedov et al., Opt. Express 17, 5743 (2009)]. We calculate both longitudinal and transverse
photophoretic forces acting on a spherical absorbing particle, and then compare our theoretical predictions with the experimental data
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