357 research outputs found
Three-dimensional spatiotemporal optical solitons in nonlocal nonlinear media
We demonstrate the existence of stable three-dimensional spatiotemporal
solitons (STSs) in media with a nonlocal cubic nonlinearity. Fundamental
(nonspinning) STSs forming one-parameter families are stable if their
propagation constant exceeds a certain critical value, that is inversely
proportional to the range of nonlocality of nonlinear response. All spinning
three-dimensional STSs are found to be unstable.Comment: 14 pages, 6 figures, accepted to PRE, Rapid Communication
Spatiotemporal discrete multicolor solitons
We have found various families of two-dimensional spatiotemporal solitons in
quadratically nonlinear waveguide arrays. The families of unstaggered odd, even
and twisted stationary solutions are thoroughly characterized and their
stability against perturbations is investigated. We show that the twisted and
even solutions display instability, while most of the odd solitons show
remarkable stability upon evolution.Comment: 18 pages,7 figures. To appear in Physical Review
Soliton excitation in waveguide arrays with an effective intermediate dimensionality
We reveal and observe experimentally significant modifications undertaken by
discrete solitons in waveguide lattices upon the continuous transformation of
the lattice structure from one-dimensional to two-dimensional. Light evolution
and soliton excitation in arrays with a gradually increasing number of rows are
investigated, yielding solitons with an effective reduced dimensionality
residing at the edge and in the bulk of the lattice.Comment: 14 pages, 5 figures, to appear in Physical Review Letter
Stable three-dimensional spinning optical solitons supported by competing quadratic and cubic nonlinearities
We show that the quadratic interaction of fundamental and second harmonics in
a bulk dispersive medium, combined with self-defocusing cubic nonlinearity,
give rise to completely localized spatiotemporal solitons (vortex tori) with
vorticity s=1. There is no threshold necessary for the existence of these
solitons. They are found to be stable against small perturbations if their
energy exceeds a certain critical value, so that the stability domain occupies
about 10% of the existence region of the solitons. We also demonstrate that the
s=1 solitons are stable against very strong perturbations initially added to
them. However, on the contrary to spatial vortex solitons in the same model,
the spatiotemporal solitons with s=2 are never stable.Comment: latex text, 10 ps and 2 jpg figures; Physical Review E, in pres
Light bullets in Bessel optical lattices with spatially modulated nonlinearity
We address the stability of light bullets supported by Bessel optical lattices with out-of-phase modulation of the linear and nonlinear refractive indices. We show that spatial modulation of the nonlinearity significantly modifies the shapes and stability domains of the light bullets. The addressed bullets can be stable, provided that the peak intensity does not exceed a critical value. We show that the width of the stability domain in terms of the propagation constant may be controlled by varying the nonlinearity modulation depth. In particular, we show that the maximum energy of the stable bullets grows with increasing nonlinearity modulation depth.Peer ReviewedPostprint (published version
Identification and quantification of pathogenic helminth eggs using a digital image system
AbstractA system was developed to identify and quantify up to seven species of helminth eggs (Ascaris lumbricoides -fertile and unfertile eggs-, Trichuris trichiura, Toxocara canis, Taenia saginata, Hymenolepis nana, Hymenolepis diminuta, and Schistosoma mansoni) in wastewater using different image processing tools and pattern recognition algorithms. The system was developed in three stages. Version one was used to explore the viability of the concept of identifying helminth eggs through an image processing system, while versions 2 and 3 were used to improve its efficiency. The system development was based on the analysis of different properties of helminth eggs in order to discriminate them from other objects in samples processed using the conventional United States Environmental Protection Agency (US EPA) technique to quantify helminth eggs. The system was tested, in its three stages, considering two parameters: specificity (capacity to discriminate between species of helminth eggs and other objects) and sensitivity (capacity to correctly classify and identify the different species of helminth eggs). The final version showed a specificity of 99% while the sensitivity varied between 80 and 90%, depending on the total suspended solids content of the wastewater samples. To achieve such values in samples with total suspended solids (TSS) above 150Â mg/L, it is recommended to dilute the concentrated sediment just before taking the images under the microscope. The system allows the helminth eggs most commonly found in wastewater to be reliably and uniformly detected and quantified. In addition, it provides the total number of eggs as well as the individual number by species, and for Ascaris lumbricoides it differentiates whether or not the egg is fertile. The system only requires basically trained technicians to prepare the samples, as for visual identification there is no need for highly trained personnel. The time required to analyze each image is less than a minute. This system could be used in central analytical laboratories providing a remote analysis service
Polarization conversion spectroscopy of hybrid modes
Enhanced polarization conversion in reflection for the Otto and Kretschmann
configurations is introduced as a new method for hybrid-mode spectroscopy.
Polarization conversion in reflection appears when hybrid-modes are excited in
a guiding structure composed of at least one anisotropic media. In contrast to
a dark dip, in this case modes are associated to a peak in the converted
reflectance spectrum, increasing the detection sensitivity and avoiding
confusion with reflection dips associated with other processes as can be
transmission.Comment: 4 pages, 4 figure
Two-dimensional solitons at interfaces between binary superlattices and homogeneous lattices
We report on the experimental observation of two-dimensional surface solitons
residing at the interface between a homogeneous square lattice and a
superlattice that consists of alternating "deep" and "shallow" waveguides. By
exciting single waveguides in the first row of the superlattice, we show that
solitons centered on deep sites require much lower powers than their respective
counterparts centered on shallow sites. Despite the fact that the average
refractive index of the superlattice waveguides is equal to the refractive
index of the homogeneous lattice, the interface results in clearly asymmetric
output patterns.Comment: 16 pages, 5 figures, to appear in Physical Review
Observation of two-dimensional lattice interface solitons
We report on the experimental observation of two-dimensional solitons at the
interface between square and hexagonal waveguide arrays. In addition to the
different symmetry of the lattices, the influence of a varying refractive index
modulation depth is investigated. Such variation strongly affects the
properties of surface solitons residing at different sides of the interface.Comment: 14 pages, 5 figures, to appear in Optics Letter
Stable spatiotemporal solitons in Bessel optical lattices
We investigate the existence and stability of three-dimensional (3D) solitons
supported by cylindrical Bessel lattices (BLs) in self-focusing media. If the
lattice strength exceeds a threshold value, we show numerically, and using the
variational approximation, that the solitons are stable within one or two
intervals of values of their norm. In the latter case, the Hamiltonian-vs.-norm
diagram has a "swallowtail" shape, with three cuspidal points. The model
applies to Bose-Einstein condensates (BECs) and to optical media with saturable
nonlinearity, suggesting new ways of making stable 3D BEC solitons and "light
bullets" of an arbitrary size.Comment: 9 pages, 4 figures, Phys. Rev. Lett., in pres
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