104 research outputs found
Beam Instabilities in the Scale Free Regime
The instabilities arising in a one-dimensional beam sustained by the
diffusive photorefractive nonlinearity in out-of-equilibrium ferroelectrics are
theoretically and numerically investigated. In the "scale-free model", in
striking contrast with the well-known spatial modulational instability, two
different beam instabilities dominate: a defocusing and a fragmenting process.
Both are independent of the beam power and are not associated to any specific
periodic pattern.Comment: 4 pages, 3 figure
Built-in reduction of statistical fluctuations of partitioning objects
Our theoretical and numerical investigation of the movement of an object that partitions a microtubule filled with small particles indicates that vibrations warranted by thermal equilibrium are reached only after a time that increases exponentially with the number of particles involved. This points to a basic mechanical process capable of breaching, on accessible time scales, the ultimate ergodic constraints that force randomness on bound microscale and nanoscale systems
Shock waves in disordered media
We experimentally investigate the interplay between spatial shock waves and
the degree of disorder during nonlinear optical propagation in a thermal
defocusing medium. We characterize the way the shock point is affected by the
amount of disorder and scales with wave amplitude. Evidence for the existence
of a phase diagram in terms of nonlinearity and amount of randomness is
reported. The results are in quantitative agreement with a theoretical approach
based on the hydrodynamic approximation.Comment: 4 pages, 5 figure
Optical supercavitation in soft-matter
We investigate theoretically, numerically and experimentally nonlinear
optical waves in an absorbing out-of-equilibrium colloidal material at the
gelification transition. At sufficiently high optical intensity, absorption is
frustrated and light propagates into the medium. The process is mediated by the
formation of a matter-shock wave due to optically induced thermodiffusion, and
largely resembles the mechanism of hydrodynamical supercavitation, as it is
accompanied by a dynamic phase-transition region between the beam and the
absorbing material.Comment: 4 pages, 5 figures, revised version: corrected typos and reference
Soliton stripes in two-dimensional nonlinear photonic lattices
We study experimentally the interaction of a soliton with a nonlinear
lattice. We observe the formation of a novel type of composite soliton created
by strong coupling of mutually incoherent periodic and localized beam
components. By imposing an initial transverse momentum on the soliton stripe,
we observe the effect of lattice compression and deformation.Comment: three pages, four figure
Nonlinear Gamow vectors in nonlocal optical propagation
Shock waves dominate in a wide variety of fields in physics dealing with nonlinear phenomena, nevertheless the description of their evolution is not resolved for the entire dynamics. Here we propose an analytical method based on Gamow vectors, which belong to irreversible quantum mechanics. We theoretically and experimentally show the appearance of these decaying states during shock evolution
allowing to describe the whole wave propagation. These results open new ways to the control of extreme nonlinear regimes such as supercontinuum generation or in the analogies of fundamental physical theories
Measurement of scaling laws for shock waves in thermal nonlocal media
We are able to detect the details of spatial optical collisionless
wave-breaking through the high aperture imaging of a beam suffering shock in a
fluorescent nonlinear nonlocal thermal medium. This allows us to directly
measure how nonlocality and nonlinearity affect the point of shock formation
and compare results with numerical simulations.Comment: 4 pages, 4 figure
One-Two Dimensional Nonlinear Pulse Interaction
The peculiar intergrability of the Davey-Stewartson equation allows us to
find analytically solutions describing the simultaneous formation and
interaction of one-dimensional and two-dimensional localized coherent
structures. The predicted phenomenology allows us to address the issue of
interaction of solitons of different dimensionality that may serve as a
starting point for the understanding of hybrido-dimensional collisions recently
observed in nonlinear optical media.Comment: 11 pages + 4 figure
Route to nonlocality and observation of accessible solitons
We develop a general theory of spatial solitons in a liquid crystalline
medium exhibiting a nonlinearity with an arbitrary degree of effective
nonlocality. The model accounts the observability of "accessible solitons" and
establishes an important link with parametric solitons.Comment: 4 pages, 2 figure
Subwavelength anti-diffracting beams propagating over more than 1,000 Rayleigh lengths
Propagating light beams with widths down to and below the optical wavelength require bulky large-aperture lenses and remain focused only for micrometric distances. Here, we report the observation of light beams that violate this localization/depth- of-focus law by shrinking as they propagate, allowing resolution to be maintained and increased over macroscopic propagation lengths. In nanodisordered ferroelectrics we observe a non-paraxial propagation of a sub-micrometre-sized beam for over 1,000 diffraction lengths, the narrowest visible beam reported to date. This unprecedented effect is caused by the nonlinear response of a dipolar glass, which transforms the leading opticalwave equation into a Klein-Gordon-type equation that describes a massive particle field. Our findings open the way to high-resolution optics over large depths of focus, and a route to merging bulk optics into nanodevices
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