595 research outputs found
Incoherent interaction of nematicons in bias-free liquid-crystal cells
We study experimentally the propagation dynamics and interaction of a pair of
mutually incoherent nematicons: spatial optical solitons in nematic liquid
crystals. In contrast to earlier studies, we consider a bias-free
liquid-crystal cell and compare the soliton interaction in copropagating and
counterpropagating geometries. We analyze the dependence of nematicon
interaction on input power and observe a direct manifestation of a long-range
nonlocal nonlinearity. Attraction of counterpropagating solitons requires
higher powers and longer relaxation times than that of copropagating nematicons
due to losses-induced power asymmetry of counterpropagating nematicons.Comment: 5 pages, z figure
Enhanced soliton interactions by inhomogeneous nonlocality and nonlinearity
We address the interactions between optical solitons in the system with
longitudinally varying nonlocality degree and nonlinearity strength. We
consider a physical model describing light propagation in nematic liquid
crystals featuring a strongly nonlocal nonlinear response. We reveal that the
variation of the nonlocality and nonlinearity along the propagation direction
can substantially enhance or weaken the interaction between out-of-phase
solitons. This phenomenon manifests itself as a slowdown or acceleration of the
soliton collision dynamics in one-dimensional geometries or of the soliton
spiraling rate in bulk media. Therefore, one finds that by engineering the
nonlocality and nonlinearity variation rate one can control the output soliton
location.Comment: 22 pages, 5 figures, to appear in Physical Review
Complex dynamics and configurational entropy of spatial optical solitons in nonlocal media
Intense light propagating in a nonlinear medium can generate an ensemble of
interacting filaments of light, or spatial solitons. Using nematic liquid
crystals, we demonstrate that they undergo a collective behavior typical of
complex systems, including the formation of clusters and sound-like vibrations,
as well as the reduction of the configurational entropy, controlled by the
degree of nonlocality of the medium.Comment: 14 pages, 4 figures. Optics Letters, to be publishe
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
Light self-trapping in a large cloud of cold atoms
We show that, for a near-resonant propagating beam, a large cloud of cold
87Rb atoms acts as a saturable Kerr medium and produces self-trapping of light.
By side fluorescence imaging we monitor the transverse size of the beam and,
depending on the sign of the laser detuning with respect to the atomic
transition, we observe self-focusing or -defocusing, with the waist remaining
stationary for an appropriate choice of parameters. We analyze our observations
by using numerical simulations based on a simple 2-level atom model.Comment: 3 pages, 4 figures, submitted to Optics Letter
Spatially incoherent modulational instability in a non local medium
We investigate one-dimensional transverse modulational instability in a non
local medium excited with a spatially incoherent source. Employing undoped
nematic liquid crystals in a planar pre-tilted configuration, we investigate
the role of the spectral broadening induced by incoherence in conjunction with
the spatially non local molecular reorientation. The phenomenon is modeled
using the Wigner transform.Comment: 13 pages with 4 figures included. To be published in Laser Physics
Letter
High-energy terahertz surface optical rectification
The interest in surface terahertz emitters lies in their extremely thin active region, typically hundreds of atomic layers, and the agile surface scalability. The ultimate limit in the achievable emission is determined by the saturation of the several different mechanisms concurring to the THz frequency conversion. Although there is a very prolific debate about the contribution of each process, surface optical rectification has been highlighted as the dominant process at high excitation, but the effective limits in the conversion are largely unknown.
The current state of the art suggests that in field-induced optical rectification a maximum limit of the emission may exist and it is ruled by the photocarrier induced neutralisation of the medium's surface field. This would represent the most important impediment to the application of surface optical rectification in high-energy THz emitters.
We experimentally unveil novel physical insights in the THz conversion at high excitation energies mediated by the ultrafast surface optical rectification process. The main finding is that the expected total saturation of the Terahertz emission vs pump energy does not actually occur. At high energy, the surface field region contracts towards the surface. We argue that this mechanism weakens the main saturation process, re-establishing a clearly observable quadratic dependence between the emitted THz energy and the excitation. This is relevant in enabling access to intense generation at high fluences
Signal processing by opto-optical interactions between self-localized and free propagating beams in liquid crystals
The reorientational nonlinearity of nematic liquid crystals enables a
self-localized spatial soliton and its waveguide to be deflected or destroyed
by a control beam propagating across the cell. We demonstrate a simple
all-optical readdressing scheme by exploiting the lens-like perturbation
induced by an external beam on both a nematicon and a co-polarized guided
signal of different wavelength. Angular steering as large as 2.2 degrees was
obtained for control powers as low as 32mW in the near infrared
The boundary force exerted on spatial solitons in cylindrical strongly nonlocal media
We investigate the propagation of the spatial soliton in cylindrical strongly
nonlocal media by a novel method of image beam of light. The effect of the
boundary on the soliton acting as the dynamic force for the soliton steering is
equivalent to the force between the soliton beam and the image beam. The
trajectory of the soliton is analytically studied which is in good agreement
with the experimental results.Comment: 3 Pages, 3 figure
- …