Biomedical subjects

Claudio Conti

Publications and source records attributed to Claudio Conti.

16 recordsLinked to original sources

PubMed2004

Controlled transmission in the forbidden photonic bandgap via transient nonlinear states.

Using three-dimensional time-domain numerical simulations of the nonlinear dispersive Maxwell equations for a defect microcavity in a photonic crystal wire, we show that the transmission through the bandgap can be all-optically modulated via the generation of transient states associated with the nonlinear splitting of the defect mode. Analytical results based on time-domain coupled-mode theory are derived as well.

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PubMed2004

Routing of anisotropic spatial solitons and modulational instability in liquid crystals.

In certain materials, the spontaneous spreading of a laser beam (owing to diffraction) can be compensated for by the interplay of optical intensity and material nonlinearity. The resulting non-diffracting beams are called 'spatial solitons' (refs 1-3), and they have been observed in various bulk media. In nematic liquid crystals, solitons can be produced at milliwatt power levels and have been investigated for both practical applications and as a means of exploring fundamental aspects of light interactions with soft matter. Spatial solitons effectively operate as waveguides, and so can be considered as a means of channelling optical information along the self-sustaining filament. But actual steering of these solitons within the medium has proved more problematic, being limited to tilts of just a fraction of a degree. Here we report the results of an experimental and theoretical investigation of voltage-controlled 'walk-off' and steering of self-localized light in nematic liquid crystals. We find not only that the propagation direction of individual spatial solitons can be tuned by several degrees, but also that an array of direction-tunable solitons can be generated by modulation instability. Such control capabilities might find application in reconfigurable optical interconnects, optical tweezers and optical surgical techniques.

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PubMed2004

Generation and nonlinear dynamics of X waves of the Schrödinger equation.

The generation of finite-energy packets of X waves is analyzed in normally dispersive cubic media by using an X-wave expansion. The three-dimensional nonlinear Schrödinger model is reduced to a one-dimensional equation with anomalous dispersion. Pulse splitting and beam replenishment as observed in experiments with water and Kerr media are explained in terms of a higher-order breathing soliton. The results presented also hold in periodic media and Bose-condensed gases.

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PubMed2004

Vector electromagnetic X waves.

A vector propagation scheme for describing electromagnetic nondiffracting beams (X waves) is introduced. In particular we show that, from the knowledge of the transverse field components on a given transverse plane and at a fixed instant, it is possible to predict the whole electric field everywhere which in particular allows us to investigate the imaging properties of nondiffracting beam. Furthermore, we show that the longitudinal field component crucially depends on the pulse velocity and that it can be neglected only if the velocity is slightly greater than c. The proposed formalism is tested by means of two examples, the vector fundamental and Gaussian X waves which admit analytical treatment. As an application of the propagation scheme, we derive in closed form the expressions for the field propagator showing that its transverse component formally coincides with one of the scalar fundamental X wave.

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PubMed2004

Nonspreading wave packets in three dimensions formed by an ultracold bose gas in an optical lattice.

We predict that an ultracold Bose gas in an optical lattice can give rise to a new form of condensation, namely, nonspreading 3D wave packets that reflect the symmetry of the Laplacian with a negative effective mass along the lattice direction and are allowed to exist in the absence of any trapping potential even in the limit of noninteracting atoms. This result also has strong implications for optical propagation in periodic structures.

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PubMed2004

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 nonlocal 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.

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PubMed2004

Cross-phase modulation in polarization shift-keying lightwave systems.

We investigate the effect of cross-phase modulation in wavelength-division-multiplexed polarization-modulation lightwave systems. Analytical expression for the Q factor penalty in terms of signal power, the number of channels, and other parameters are derived. The theory is compared with numerical experiments.

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PubMed2004

Universal space-time properties of X waves.

Exact results concerning spatiotemporal universal features of three-dimensional propagation-invariant solutions of the wave equation (X waves) are derived. In particular, relations connecting the pulse transverse extension to the longitudinal coordinate and the propagation velocity to the spatial field distribution are obtained for the whole class of X waves.

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PubMed2003

Optical multisoliton generation in nematic liquid crystals.

The nonlocal nonlinearity stemming from molecular reorientation in nematic liquid crystals supports the formation of multiple solitary waves, following the onset of spatial modulational instability from both wide and focused input beams. We report experimental observations of such phenomena at power levels of hundreds of milliwatts in planar cells with a voltage bias.

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PubMed2003

Optical modulational instability in a nonlocal medium.

We report the first observation of modulational instability in nematic liquid crystals encompassing a nonlocal behavior. The experimental results are quantitatively compared with the theory revealing the fundamental features associated to a nonlocal nonlinearity.

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PubMed2003

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.

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PubMed2003

X waves generated at the second harmonic.

The process of optical frequency doubling in the undepleted regime can lead to the generation of an X-wave envelope with group velocity locked to the pump beam. Its parameters and its angular spectrum are directly related to the zeroth- and first-order dispersive features of the nonlinear process. This constitutes a novel mechanism for spatiotemporal localization of light.

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PubMed2003

X-wave-mediated instability of plane waves in Kerr media.

Plane waves in Kerr media spontaneously generate paraxial X-waves (i.e., nondispersive and nondiffractive pulsed beams) that get amplified along propagation. This effect can be considered to be a form of conical emission (i.e., spatiotemporal modulational instability), and can be used as a key for the interpretation of the out-of-axis energy emission in the splitting process of focused pulses in normally dispersive materials. A new class of spatiotemporal localized wave patterns is identified. X-wave instability and nonlinear X waves are predicted for both focusing and defocusing media and are expected in periodical Bose condensed gases.

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PubMed2003

Paraxial envelope X waves.

Localized, stationary, X-type solutions of the paraxial wave equation are described. Unlike conventional X waves, these are luminal, envelope X waves sustained by a material medium because of the interplay of dispersion and diffraction.

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PubMed2003

Novel vitamin E analogue decreases syngeneic mouse mammary tumor burden and reduces lung metastasis.

A nonhydrolyzable ether analogue of RRR-alpha-tocopherol, 2,5,7,8-tetramethyl-2R-(4R, 8R, 12-trimethyltridecyl)chroman-6-yloxyacetic acid, called RRR-alpha-tocopheryloxyacetic acid or RRR-alpha-tocopherol ether-linked acetic acid analogue (alpha-TEA), exhibits antitumor activity in vitro and in vivo using a syngeneic BALB/c mouse mammary tumor model (line 66 clone 4 stably transfected with green fluorescent protein). Treatment of cells with 5, 10, and 20 micro g/ml alpha-TEA for 3 days produced 6, 34, and 50% apoptosis, respectively, and treatment of cells with 10 micro g/ml for 2, 3, 4, and 5 days produced 20, 35, 47, and 58% apoptosis, respectively. A liposomal formulation of alpha-TEA administered by aerosol reduced s.c. tumor growth and lung metastasis. Alpha-TEA-treated animals showed a significant decrease in tumor volumes over 17 days of aerosol treatment (P < 0.001). Forty percent of aerosol as well as untreated control mice had visible, macroscopic lung metastases versus none (0%) of the alpha-TEA-treated mice. On the basis of fluorescence microscopic examination of the surface (top and bottom) of flattened whole left lung lobes, an average of 60 +/- 15 and 102 +/- 17 versus 11 +/- 4 fluorescent microscopic metastases was observed in aerosol control and untreated control versus alpha-TEA-treated animals, respectively. Alpha-TEA formulated in ethanol + peanut oil (5 mg/mouse/day) delivered by gavage did not reduce s.c. primary tumor burden; however, fluorescent microscopic lung metastases were significantly reduced (P < 0.0021). In summary, alpha-TEA formulated in liposomes and delivered by aerosol is a potent antitumor agent and reduces lung metastasis.

Administration, Oral↗

PubMed2000

From parametric gap solitons to chaos by means of second-harmonic generation in Bragg gratings.

We review the theory of light localization due to the combined action of single or double Bragg coupling between dichromatic counterpropagating envelopes and parametric mixing nonlinearities. We discuss existence, stability, and excitation of such localized envelopes. We also investigate the link between stationary gap solitons and input-output response of nonlinear quadratic Bragg gratings. Frustrated transmission and multistable switching is expected to occur under suitable integrable (cascading) limits. Substantial deviations from these conditions lead to the onset of spatial chaos. (c) 2000 American Institute of Physics.

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