53 research outputs found
Shock waves in thermal lensing
We review experimental investigation on spatial shock waves formed by the
self-defocusing action of a laser beam propagation in a disordered thermal
nonlinear media.Comment: 9 pages, 12 figure
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
Random laser from engineered nanostructures obtained by surface tension driven lithography
The random laser emission from the functionalized thienyl-S,S-dioxide
quinquethiophene (T5OCx) in confined patterns with different shapes is
demonstrated. Functional patterning of the light emitter organic material in
well defined features is obtained by spontaneous molecular self-assembly guided
by surface tension driven (STD) lithography. Such controlled supramolecular
nano-aggregates act as scattering centers allowing the fabrication of
one-component organic lasers with no external resonator and with desired shape
and efficiency. Atomic force microscopy shows that different geometric pattern
with different supramolecular organization obtained by the lithographic process
tailors the coherent emission properties by controlling the distribution and
the size of the random scatterers
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
Shock-waves in disordered media
We investigate experimentally the effect of disorder on the formation of optical shock waves in thermal media
Experimental evidence of replica symmetry breaking in random lasers
Spin-glass theory is one of the leading paradigms of complex physics and
describes condensed matter, neural networks and biological systems, ultracold
atoms, random photonics, and many other research fields. According to this
theory, identical systems under identical conditions may reach different states
and provide different values for observable quantities. This effect is known as
Replica Symmetry Breaking and is revealed by the shape of the probability
distribution function of an order parameter named the Parisi overlap. However,
a direct experimental evidence in any field of research is still missing. Here
we investigate pulse-to-pulse fluctuations in random lasers, we introduce and
measure the analogue of the Parisi overlap in independent experimental
realizations of the same disordered sample, and we find that the distribution
function yields evidence of a transition to a glassy light phase compatible
with a replica symmetry breaking.Comment: 10 pages, 5 figure
Aging of the Nonlinear Optical Susceptibility of colloidal solutions
Using Z-scan and dynamic light scattering measurements we investigate the
nonlinear optics response of a colloidal solution undergoing dynamics slowing
down with age. We study the high optical nonlinearity of an organic dye
(Rhodamine B) dispersed in a water-clay (Laponite) solution, at different clay
concentrations (2.0 wt% - 2.6 wt%), experiencing the gelation process. We
determine the clay platelets self diffusion coefficient and, by its comparison
with the structural relaxation time, we conclude that the gelation process
proceeds through the structuring of interconnecting clay platelets network
rather than through clusters growth and aggregation.Comment: 4 figures, 4 page
Wave instabilities in the presence of non vanishing background in nonlinear Schrodinger systems
We investigate wave collapse ruled by the generalized nonlinear Schroedinger (NLS) equation in 1+1 dimensions, for localized excitations with non-zero background, establishing through virial identities a new criterion for blow-up. When collapse is arrested, a semiclassical approach allows us to show that the system can favor the formation of dispersive shock waves. The general findings are illustrated with a model of interest to both classical and quantum physics (cubic-quintic NLS equation), demonstrating a radically novel scenario of instability, where solitons identify a marginal condition between blow-up and occurrence of shock waves, triggered by arbitrarily small mass perturbations of different sign
On critical behaviour in systems of Hamiltonian partial differential equations
We study the critical behaviour of solutions to weakly dispersive Hamiltonian systems considered as perturbations of elliptic and hyperbolic systems of hydrodynamic type with two components. We argue that near the critical point of gradient catastrophe of the dispersionless system, the solutions to a suitable initial value problem for the perturbed equations are approximately described by particular solutions to the Painlev\ue9-I (PI) equation or its fourth-order analogue P2I. As concrete examples, we discuss nonlinear Schr\uf6dinger equations in the semiclassical limit. A numerical study of these cases provides strong evidence in support of the conjecture
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