15 research outputs found
Simple and efficient generation of gap solitons in Bose-Einstein condensates
We suggest an efficient method for generating matter-wave gap solitons in a
repulsive Bose-Einstein condensate, when the gap soliton is formed from a
condensate cloud in a harmonic trap after turning on a one-dimensional optical
lattice. We demonstrate numerically that this approach does not require
preparing the initial atomic wave packet in a specific state corresponding to
the edge of the Brillouin zone of the spectrum, and losses that occur during
the soliton generation process can be suppressed by an appropriate adiabatic
switching of the optical lattice.Comment: 7 pages, 10 figure
Azimuthons in weakly nonlinear waveguides of different symmetries
We show that weakly guiding nonlinear waveguides support stable propagation
of rotating spatial solitons (azimuthons). We investigate the role of waveguide
symmetry on the soliton rotation. We find that azimuthons in circular
waveguides always rotate rigidly during propagation and the analytically
predicted rotation frequency is in excellent agreement with numerical
simulations. On the other hand, azimuthons in square waveguides may experience
spatial deformation during propagation. Moreover, we show that there is a
critical value for the modulation depth of azimuthons above which solitons just
wobble back and forth, and below which they rotate continuously. We explain
these dynamics using the concept of energy difference between different
orientations of the azimuthon.Comment: 12 pages, 8 figure
Spatial phase dislocations in femtosecond laser pulses
We show that spatial phase dislocations associated with optical vortices can be embedded in femtosecond laser beams by computer-generated holograms, provided that they are built in a setup compensating for the introduced spatial dispersion of the broad spectrum. We present analytical results describing two possible arrangements: a dispersionless 4 setup and a double-pass grating compressor. Experimental results on the generation of optical vortices in the output beam of a 20 fs Ti:sapphire laser and the proof-of-principle measurements with a broadband-tunable cw Ti:sapphire laser confirm our theoretical predictions.This research was partially supported by the National
Science Fund (Bulgaria), under contract F-1303/2003, and
the Australian Research Council
Theory of nonlocal soliton interaction in nematic liquid crystals
We investigate interactions between spatial nonlocal bright solitons in nematic liquid crystals using an analytical (“effective particle”) approach as well as direct numerical simulations. The model predicts attraction of out-of-phase solitons and the existence of their stable bound state. This nontrivial property is solely due to the nonlocal nature of the nonlinear response of the liquid crystals. We further predict and verify numerically the critical outwards angle and degree of nonlocality which determine the transition between attraction and repulsion of out-of-phase solitons
Stable higher-charge discrete vortices in hexagonal optical lattices
We show that double-charge discrete optical vortices may be completely stable
in hexagonal photonic lattices where single-charge vortices always exhibit
dynamical instabilities. Even when unstable the double-charge vortices
typically have a much weaker instability than the single-charge vortices, and
thus their breakup occurs at longer propagation distances
Scattering of dipole-mode vector solitons: Theory and experiment
We study, both theoretically and experimentally, the scattering properties of
optical dipole-mode vector solitons - radially asymmetric composite
self-trapped optical beams. First, we analyze the soliton collisions in an
isotropic two-component model with a saturable nonlinearity and demonstrate
that in many cases the scattering dynamics of the dipole-mode solitons allows
us to classify them as ``molecules of light'' - extremely robust spatially
localized objects which survive a wide range of interactions and display many
properties of composite states with a rotational degree of freedom. Next, we
study the composite solitons in an anisotropic nonlinear model that describes
photorefractive nonlinearities, and also present a number of experimental
verifications of our analysis.Comment: 8 pages + 4 pages of figure
Two dimensional modulational instability in photorefractive media
We study theoretically and experimentally the modulational instability of
broad optical beams in photorefractive nonlinear media. We demonstrate the
impact of the anisotropy of the nonlinearity on the growth rate of periodic
perturbations. Our findings are confirmed by experimental measurements in a
strontium barium niobate photorefractive crystal.Comment: 8 figure
Collapse arrest and soliton stabilization in nonlocal nonlinear media
We investigate the properties of localized waves in systems governed by
nonlocal nonlinear Schrodinger type equations. We prove rigorously by bounding
the Hamiltonian that nonlocality of the nonlinearity prevents collapse in,
e.g., Bose-Einstein condensates and optical Kerr media in all physical
dimensions. The nonlocal nonlinear response must be symmetric, but can be of
completely arbitrary shape. We use variational techniques to find the soliton
solutions and illustrate the stabilizing effect of nonlocality.Comment: 4 pages with 3 figure
Collapse of Incoherent Light Beams in Inertial Bulk Kerr Media
We use the coherent density function theory to show that partially coherent beams are unstable and
may collapse in inertial bulk Kerr media. The threshold power for collapse, and its dependence on
the degree of coherence, is found analytically and checked numerically. The internal dynamics of the
walk-off modes is illustrated for collapsing and diffracting partially coherent beams
Dynamic control of the spatial modes in the external resonator of a semilinear phase-conjugate mirror
We describe a technique that causes the radiation within the external resonator of a self-starting, semilinear phase-conjugate mirror to collapse into a single spatial mode. We have developed a model based on competition between gratings in one interaction volume to explain the observed dynamic behavior. The model shows that, once the system reaches the steady state, two gratings, whose amplitudes vary throughout space in proportion to each other, form. As a result, we can obtain analytic solutions for the steady state by using an interpretation of four-wave mixing in terms of two-wave mixing. This interpretation can be used in both the transmission and the reflection geometries for real or complex coupling with no absorption.</p