127 research outputs found
Non linearly induced self waveguiding structure in dye doped nematic liquid crystals confined in capillaries
We report on experiments dealing with the propagation of a collimated laser beam in a dye doped nematic confined in a capillary of optical fiber size. The nematic is aligned in a such a way that the source beam is self focused. The behavior of the beam - focusing, multifocus regime, filamentation and undulation - already observed in larger cylindrical geometry and pure nematic is shown here to be reproduced in the dye doped medium, at much lower powers. Another feature is reported here: a stable regime looking like a waveguide appears in certain conditions, in which the beam to propagate in a narrow tube. This regime is simply modeled in terms of saturated reorientation of the nematic
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
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
Soliton mobility in nonlocal optical lattices
We address the impact of nonlocality in the physical features exhibited by
solitons supported by Kerr-type nonlinear media with an imprinted optical
lattice. We discover that nonlocality of nonlinear response can profoundly
affect the soliton mobility, hence all the related phenomena. Such behavior
manifests itself in significant reductions of the Peierls-Nabarro potential
with increase of the degree of nonlocality, a result that opens the rare
possibility in nature of almost radiationless propagation of highly localized
solitons across the lattice.Comment: 16 pages, 4 figure
Design of a photo-written cavity neodymium doped fibre laser, tunable around a particular absorption molecular line
Observation of optical spatial solitons in a highly nonlocal medium
We report on the observation and quantitative assessment of self-trapped
pulsating beams in a highly non-local nonlinear regime. The experiments were
conducted in nematic liquid crystals and allow a meaningful comparison with the
prediction of a scalar theory in the perturbative limit, while addressing the
need for beyond-paraxial analytical treatments.Comment: 16 pages, 3 figure
Self-confined light waves in nematic liquid crystals
The study of light beams propagating in the nonlinear, dispersive, birefringent and nonlocal medium of nematic liquid crystals has attracted widespread interest in the last twenty years or so. We review hereby the underlying physics, theoretical modelling and numerical approximations for nonlinear beam propagation in planar cells filled with nematic liquid crystals, including bright and dark solitary waves, as well as optical vortices. The pertinent governing equations consist of a nonlinear Schrödinger-type equation for the light beam and an elliptic equation for the medium response. Since the nonlinear and coupled nature of this system presents difficulties in terms of finding exact solutions, we outline the various approaches used to resolve them, pinpointing the good agreement obtained with numerical solutions and experimental results. Measurement and material details complement the theoretical narration to underline the power of the modelling
Curved optical solitons subject to transverse acceleration in reorientational soft matter
We demonstrate that optical spatial solitons with non-rectilinear trajectories can be made to propagate in a uniaxial dielectric with a transversely modulated orientation of the optic axis. Exploiting the reorientational nonlinearity of nematic liquid crystals and imposing a linear variation of the background alignment of the molecular director, we observe solitons whose trajectories have either a monotonic or a non-monotonic curvature in the observation plane of propagation, depending on either the synergistic or counteracting roles of wavefront distortion and birefringent walk-off, respectively. The observed effect is well modelled in the weakly nonlinear regime using momentum conservation of the self-collimated beams in the presence of the spatial nonlocality of the medium response. Since reorientational solitons can act as passive waveguides for other weak optical signals, these results introduce a wealth of possibilities for all-optical signal routing and light-induced photonic interconnects
Spectroscopie infrarouge dans un jet supersonique. Etude de la bande v17 du trioxane (H2 CO)_3
SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 81046 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc
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