1,341 research outputs found
Time-reversal focusing of an expanding soliton gas in disordered replicas
We investigate the properties of time reversibility of a soliton gas,
originating from a dispersive regularization of a shock wave, as it propagates
in a strongly disordered environment. An original approach combining
information measures and spin glass theory shows that time reversal focusing
occurs for different replicas of the disorder in forward and backward
propagation, provided the disorder varies on a length scale much shorter than
the width of the soliton constituents. The analysis is performed by starting
from a new class of reflectionless potentials, which describe the most general
form of an expanding soliton gas of the defocusing nonlinear Schroedinger
equation.Comment: 7 Pages, 6 Figure
Bistability and instability of dark-antidark solitons in the cubic-quintic nonlinear Schroedinger equation
We characterize the full family of soliton solutions sitting over a
background plane wave and ruled by the cubic-quintic nonlinear Schroedinger
equation in the regime where a quintic focusing term represents a saturation of
the cubic defocusing nonlinearity. We discuss existence and properties of
solitons in terms of catastrophe theory and fully characterize bistability and
instabilities of the dark-antidark pairs, revealing new mechanisms of decay of
antidark solitons.Comment: 8 pages, 10 figures, accepted in PR
Spontaneously generated X-shaped light bullets
We observe the formation of an intense optical wavepacket fully localized in
all dimensions, i.e. both longitudinally (in time) and in the transverse plane,
with an extension of a few tens of fsec and microns, respectively. Our
measurements show that the self-trapped wave is a X-shaped light bullet
spontaneously generated from a standard laser wavepacket via the nonlinear
material response (i.e., second-harmonic generation), which extend the soliton
concept to a new realm, where the main hump coexists with conical tails which
reflect the symmetry of linear dispersion relationship.Comment: 5 pages, 4 figures, submitted for publicatio
Optimal frequency conversion in the nonlinear stage of modulation instability
We investigate multi-wave mixing associated with the strongly pump depleted
regime of induced modulation instability (MI) in optical fibers. For a complete
transfer of pump power into the sideband modes, we theoretically and
experimentally demonstrate that it is necessary to use a much lower seeding
modulation frequency than the peak MI gain value. Our analysis shows that a
record 95 % of the input pump power is frequency converted into the comb of
sidebands, in good quantitative agreement with analytical predictions based on
the simplest exact breather solution of the nonlinear Schr\"odinger equation
Modulational instability in dispersion-kicked optical fibers
We study, both theoretically and experimentally, modulational instability in
optical fibers that have a longitudinal evolution of their dispersion in the
form of a Dirac delta comb. By means of Floquet theory, we obtain an exact
expression for the position of the gain bands, and we provide simple analytical
estimates of the gain and of the bandwidths of those sidebands. An experimental
validation of those results has been realized in several microstructured fibers
specifically manufactured for that purpose. The dispersion landscape of those
fibers is a comb of Gaussian pulses having widths much shorter than the period,
which therefore approximate the ideal Dirac comb. Experimental spontaneous MI
spectra recorded under quasi continuous wave excitation are in good agreement
with the theory and with numerical simulations based on the generalized
nonlinear Schr\"odinger equation
Heteroclinic structure of parametric resonance in the nonlinear Schr\"odinger equation
We show that the nonlinear stage of modulational instability induced by
parametric driving in the {\em defocusing} nonlinear Schr\"odinger equation can
be accurately described by combining mode truncation and averaging methods,
valid in the strong driving regime. The resulting integrable oscillator reveals
a complex hidden heteroclinic structure of the instability. A remarkable
consequence, validated by the numerical integration of the original model, is
the existence of breather solutions separating different Fermi-Pasta-Ulam
recurrent regimes. Our theory also shows that optimal parametric amplification
unexpectedly occurs outside the bandwidth of the resonance (or Arnold tongues)
arising from the linearised Floquet analysis
Active subnanometer spectral control of a random laser
We demonstrate an experimental technique that allows to achieve a robust
control on the emission spectrum of a micro random laser and to select
individual modes with sub-nanometer resolution. The presented approach relies
on an optimization protocol of the spatial profile of the pump beam. Here we
demonstrate not only the possibility to increase the emission at a wavelength,
but also that we can isolate an individual peak suppressing unwanted
contributions form other modes
Crossover dynamics of dispersive shocks in Bose-Einstein condensates characterized by two and three-body interactions
We show that the perturbative nonlinearity associated with three-atom
interactions, competing with standard two-body repulsive interactions, can
change dramatically the evolution of 1D dispersive shock waves in a
Bose-Einstein condensate. In particular, we prove the existence of a rich
crossover dynamics, ranging from the formation of multiple shocks regularized
by coexisting trains of dark and antidark matter waves, to 1D soliton collapse.
For a given scattering length, all these different regimes can be accessed by
varying the number of atoms in the condensate.Comment: 4 pages, 5 figure
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