258 research outputs found
Compression of ultrashort UV pulses in a self-defocusing gas
Compression of UV femtosecond laser pulses focused into a gas cell filled
with xenon is reported numerically. With a large negative Kerr index and normal
dispersion, xenon promotes temporal modulational instability (MI) which can be
monitored to shorten ~ 100 fs pulses to robust, singly-peaked waveforms
exhibiting a fourfold compression factor. Combining standard MI theory with a
variational approach allows us to predict the beam parameters suitable for
efficient compression. At powers < 30 MW, nonlinear dispersion is shown to
shift the pulse temporal profile to the rear zone.Comment: 4 pages, 4 figure
Generation of terahertz radiation from ionizing two-color laser pulses in Ar filled metallic hollow waveguides
The generation of THz radiation from ionizing two-color femtosecond pulses
propagating in metallic hollow waveguides filled with Ar is numerically
studied. We observe a strong reshaping of the low-frequency part of the
spectrum. Namely, after several millimeters of propagation the spectrum is
extended from hundreds of GHz up to ~150 THz. For longer propagation distances,
nearly single-cycle near-infrared pulses with wavelengths around 4.5 um are
obtained by appropriate spectral filtering, with an efficiency of up to 0.25%.Comment: 6 pages, 3 figure
Rotating three-dimensional solitons in Bose Einstein condensates with gravity-like attractive nonlocal interaction
We study formation of rotating three-dimensional high-order solitons
(azimuthons) in Bose Einstein condensate with attractive nonlocal nonlinear
interaction. In particular, we demonstrate formation of toroidal rotating
solitons and investigate their stability. We show that variational methods
allow a very good approximation of such solutions and predict accurately the
soliton rotation frequency. We also find that these rotating localized
structures are very robust and persist even if the initial condensate
conditions are rather far from the exact soliton solutions. Furthermore, the
presence of repulsive contact interaction does not prevent the existence of
those solutions, but allows to control their rotation. We conjecture that
self-trapped azimuthons are generic for condensates with attractive nonlocal
interaction
Effect of electron heating on self-induced transparency in relativistic intensity laser-plasma interaction
The effective increase of the critical density associated with the
interaction of relativistically intense laser pulses with overcritical plasmas,
known as self-induced transparency, is revisited for the case of circular
polarization. A comparison of particle-in-cell simulations to the predictions
of a relativistic cold-fluid model for the transparency threshold demonstrates
that kinetic effects, such as electron heating, can lead to a substantial
increase of the effective critical density compared to cold-fluid theory. These
results are interpreted by a study of separatrices in the single-electron phase
space corresponding to dynamics in the stationary fields predicted by the
cold-fluid model. It is shown that perturbations due to electron heating
exceeding a certain finite threshold can force electrons to escape into the
vacuum, leading to laser pulse propagation. The modification of the
transparency threshold is linked to the temporal pulse profile, through its
effect on electron heating.Comment: 13 pages, 12 figures; fixed some typos and improved discussion of
review materia
Rotating soliton solutions in nonlocal nonlinear media
We discuss generic properties of rotating nonlinear wave solutions, the so
called azimuthons, in nonlocal media. Variational methods allow us to derive
approximative values for the rotating frequency, which is shown to depend
crucially on the nonlocal response function. Further on, we link families of
azimuthons to internal modes of classical non-rotating stationary solutions,
namely vortex and multipole solitons. This offers an exhaustive method to
identify azimuthons in a given nonlocal medium.Comment: 14 pages, 9 figures, 3 movies (external links
Ultrafast spatio-temporal dynamics of terahertz generation by ionizing two-color femtosecond pulses in gases
We present a combined theoretical and experimental study of spatio-temporal
propagation effects in terahertz (THz) generation in gases using two-color
ionizing laser pulses. The observed strong broadening of the THz spectra with
increasing gas pressure reveals the prominent role of spatio-temporal reshaping
and of a plasma-induced blue-shift of the pump pulses in the generation
process. Results obtained from (3+1)-dimensional simulations are in good
agreement with experimental findings and clarify the mechanisms responsible for
THz emission
Nonlocal stabilization of nonlinear beams in a self-focusing atomic vapor
We show that ballistic transport of optically excited atoms in an atomic
vapor provides a nonlocal nonlinearity which stabilizes the propagation of
vortex beams and higher order modes in the presence of a self-focusing
nonlinearity. Numerical experiments demonstrate stable propagation of lowest
and higher order vortices over a hundred diffraction lengths, before
dissipation leads to decay of these structures.Comment: 3 figure
Pattern formation in the nonlinear Schrödinger equation with competing nonlocal nonlinearities
We study beam propagation in the framework of the nonlinear Schrödinger equation with competing Gaussian nonlocal nonlinearities. We demonstrate that such system can give rise to self-organization of light into stable states of trains or hexagonal arrays of filaments, depending on the transverse dimensionality. This long-range ordering can be achieved by mere unidirectional beam propagation. We discuss the dynamics of long-range ordering and the crucial role which the phase of the wavefunction plays for this phenomenon. Furthermore we discuss how transverse dimensionality affects the order of the phasetransition
Tracking azimuthons in nonlocal nonlinear media
We study the formation of azimuthons, i.e., rotating spatial solitons, in
media with nonlocal focusing nonlinearity. We show that whole families of these
solutions can be found by considering internal modes of classical non-rotating
stationary solutions, namely vortex solitons. This offers an exhaustive method
to identify azimuthons in a given nonlocal medium. We demonstrate formation of
azimuthons of different vorticities and explain their properties by considering
the strongly nonlocal limit of accessible solitons.Comment: 11 pages, 7 figure
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