125 research outputs found
Robust self-trapping of vortex beams in a saturable optical medium
We report the first observation of robust self-trapping of vortex beams
propagating in a uniform condensed medium featuring local saturable
self-focusing nonlinearity. Optical vortices with topological charge m=1, that
remain self-trapped over ~ 5 Rayleigh lengths, are excited in carbon disulfide
using a helical light beam at 532 nm and intensities from 8 to 10 GW/cm^2. At
larger intensities, the vortex beams lose their stability, spontaneously
breaking into two fragments. Numerical simulations based on the nonlinear
Schr\"odinger equation including the three-photon absorption and nonpolynomial
saturation of the refractive nonlinearity demonstrate close agreement with the
experimental findings.Comment: 27 pages, 7 figures,to be published in Phys. Rev. A (2016
Generation of multiple ultrashort solitons in a third-order nonlinear composite medium with self-focusing and self-defocusing nonlinearities
Theoretical consideration of the propagation of femtosecond-Gaussian pulses
in a 1D composite medium, consisting of alternating self-focusing (SF) and
self-defocusing (SDF) waveguide segments with normal group-velocity dispersion
predicts the generation of trains of bright solitons when an optical pulse
first propagates in the SF segment, followed by the SDF one. The multiple
temporal compression (MTC) process, based on this setting, offers a method for
controllable generation of multiple ultrashort temporal solitons. Numerical
solutions of the generalized nonlinear Schr\"{o}dinger equation modeling this
system demonstrate that the intrapulse Raman scattering plays a major role in
the temporal and spectral dynamics. Collisions between ultrashort solitons with
different central wavelengths are addressed too. The paper provides, for the
first time, a procedure for producing controllable trains of ultrashort
temporal solitons by incident optical pulses propagating in a composite medium.Comment: To be published in Phys. Rev.
Observation of Replica Symmetry Breaking in the 1D Anderson Localization Regime in an Erbium-Doped Random Fiber Laser
The analogue of the paramagnetic to spin-glass phase transition in disordered
magnetic systems, leading to the phenomenon of replica symmetry breaking, has
been recently demonstrated in a two-dimensional random laser consisting of an
organic-based amorphous solid-state thin film. We report here the first
demonstration of replica symmetry breaking in a one-dimensional photonic system
consisting of an erbium-doped random fiber laser operating in the
continuous-wave regime based on a unique random fiber grating system, which
plays the role of the random scatterers and operates in the Anderson
localization regime. The clear transition from a photonic paramagnetic to a
photonic spin glass phase, characterized by the probability distribution
function of the Parisi overlap, was verified and characterized. In this unique
system, the radiation field interacts only with the gain medium, and the fiber
grating, which provides the disordered feedback mechanism, does not interfere
with the pump
Optical limiting behavior of bismuth oxide-based glass in the visible range
The authors report experimental results on the optical limiting behavior of a bismuth oxide-based glass by exciting the samples with nanosecond laser pulses at 532 and 598 nm. The results show that two-photon and free-carrier absorption processes contribute for the nonlinear absorption. Values for β, the two-photon absorption coefficient, and σe, the absorption cross section due to free carriers, were determined. The values for β and σe are dependent on the amount of bismuth oxide in the glass composition
Generation of robust temporal soliton trains by the multiple-temporal-compression (MTC) method
We report results of systematic numerical analysis for multiple soliton
generation by means of the recently reported multiple temporal compression
(MTC) method, and compare its efficiency with conventional methods based on the
use of photonic crystal fibers (PCFs) and fused silica waveguides (FSWs). The
results show that the MTC method is more efficient to control the soliton
fission, giving rise to a larger number of fundamental solitons with high
powers, that remain nearly constant over long propagation distances. The high
efficiency of the MTC method is demonstrated, in particular, in terms of
multiple soliton collisions and the Newton's-cradle phenomenology.Comment: To be published in Optics Communications (Special Issue - Solitons
and coherent structures in optics: 50th anniversary of the prediction of
optical solitons in fiber
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