Biomedical subjects

P Di Trapani

Publications and source records attributed to P Di Trapani.

14 recordsLinked to original sources

PubMed2006

Near-field dynamics of ultrashort pulsed Bessel beams in media with Kerr nonlinearity.

The near-field dynamics of a femtosecond Bessel beam propagating in a Kerr nonlinear medium (fused silica) is investigated both numerically and experimentally. We demonstrate that the input Bessel beam experiences strong nonlinear reshaping. Due to the combined action of self-focusing and nonlinear losses the reshaped beam exhibits a radial compression and reduced visibility of the Bessel oscillations. Moreover, we show that the reshaping process starts from the intense central core and gradually replaces the Bessel beam profile during propagation, highlighting the conical geometry of the energy flow.

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PubMed2006

Nonlinear X-wave formation by femtosecond filamentation in Kerr media.

We investigate the formation of X waves during filamentation in Kerr media. From the standard model developed for femtosecond filamentation in liquids, solids, and gases, the influence of several physical effects and parameters is numerically studied in the strongly nonlinear regime where group velocity dispersion alone is insufficient to arrest collapse. The collapse is shown to be arrested by multiphoton absorption and plasma defocusing, but not by dispersion. The postcollapse dynamics takes the form of a pulse splitting, which induces large gradients in the near field and seeds the formation of X waves, appearing both in the near and far fields. We discuss the universal features of the X-wave patterns, among which the long arms in the far field that follow the linear dispersive properties of the medium [Conti, Phys. Rev. Lett. 90, 170406 (2003); Kolesik, Phys. Rev. Lett. 92, 253901 (2004)] and are accompanied by a strong modulated axial emission.

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PubMed2005

Quantum-noise-initiated symmetry breaking of spatial solitons.

The spectra of chi(2) spatial solitons are measured close to the soliton-formation threshold and show the presence of sidebands, shifted by 39 THz from the laser line. By comparing with the predictions of a quantum optical field model, solved numerically in the full (3 + 1)-dimensional space, it is claimed that the observed temporal instability of the spatial soliton is seeded by vacuum state fluctuations of the electromagnetic field.

Journal Article↗

PubMed2005

Near- and far-field evolution of laser pulse filaments in Kerr media.

Measurements of the spatio-temporal and far-field profiles of ultrashort laser pulses experiencing conical emission, continuum generation, and beam filamentation in a Kerr medium outline the spontaneous formation of wave packets with X -like features, thus supporting recent numerical results [M. Kołesik, E. Wright, and J. Moloney, Phys. Rev. Lett. 92, 253901 (2004)]. Numerical simulations show good agreement with experimental data.

Computer Simulation↗

PubMed2004

Noise-seeded spatiotemporal modulation instability in normal dispersion.

In optical second-harmonic generation with normal dispersion, the virtually infinite bandwidth of the unbounded, hyperbolic, modulational instability leads to quenching of spatial multisoliton formation and to the occurrence of a catastrophic spatiotemporal breakup when an extended beam is left to interact with an extremely weak external noise with a coherence time much shorter than that of the pump.

Journal Article↗

PubMed2004

Self-reconstruction of light filaments.

By observing how a light filament generated in water reconstructs itself after hitting a beam stopper in the presence and in the absence of a nonlinear medium, we describe the occurrence of an important linear contribution to reconstruction that is associated with the conical nature of the wave. A possible scenario by which conical wave components are generated inside the medium by the distributed stopper or reflector created by nonlinear losses or plasma is presented.

Journal Article↗

PubMed2004

Detection of sub-shot-noise spatial correlation in high-gain parametric down conversion.

Using a 1 GW, 1 ps pump laser pulse in high-gain parametric down conversion allows us to detect sub-shot-noise spatial quantum correlation with up to 100 photoelectrons per mode by means of a high efficiency charge coupled device. The statistics is performed in single shot over independent spatial replica of the system. Evident quantum correlations were observed between symmetrical signal and idler spatial areas in the far field. In accordance with the predictions of numerical calculations, the observed transition from the quantum to the classical regime is interpreted as a consequence of the narrowing of the down-converted beams in the very high-gain regime.

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PubMed2004

Nonlinear space-time dynamics of ultrashort wave packets in water.

We have monitored the space-time transformation of a 150-fs pulse undergoing self-focusing and filamentation in water, by means of the nonlinear gating technique. We have observed that pulse splitting and subsequent recombination apply to axial temporal intensity only, whereas the space-integrated pulse profile preserves its original shape.

Journal Article↗

PubMed2004

Spatiotemporal three-dimensional mapping of nonlinear X waves.

The spatiotemporal intensity profile of a 100-fs wave packet at the output of a X2 crystal, tuned for mismatched second-harmonic generation, is probed via sum-frequency generation with a compressed, 20-fs pulse, revealing the appearance of an X-type wave shape.

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PubMed2003

Spatial versus temporal deterministic wave breakup of nonlinearly coupled light waves.

We investigate experimentally the competition between spatial and temporal breakup due to modulational instability in chi((2)) nonlinear mixing. The modulation of the wave packets caused by the energy exchange between fundamental and second-harmonic components is found to be the prevailing trigger mechanism which, according to the relative weight of diffraction and dispersion, leads to the appearance of a multisoliton pattern in the low-dimensional spatial or temporal domain.

Journal Article↗

PubMed2003

Spontaneously generated X-shaped light bullets.

We observe the formation of an intense optical wave packet fully localized in all dimensions, i.e., both longitudinally (in time) and in the transverse plane, with an extension of a few tens of fsec and microns, respectively. Our measurements show that the self-trapped wave is an X-shaped light bullet spontaneously generated from a standard laser wave packet via the nonlinear material response (i.e., second-harmonic generation), which extend the soliton concept to a new realm, where the main hump coexists with conical tails which reflect the symmetry of linear dispersion relationship.

Journal Article↗

PubMed2003

Nonlinear X waves in second-harmonic generation: experimental results.

X waves, spatiotemporal generalization of the monochromatic Bessel- (or Durnin-) type beams, are known in linear acoustic, microwave and optics for their unique property of defeating both spatial and temporal spreadings. Recently, we brought to the attention that X-type waves are also the key to understand the spatiotemporal dynamics observed in the nonlinear (high intensity) regime. Indeed, X waves represent the normal-propagation mode for a wide class of parametric interactions described by hyperbolic nonlinear models featuring spatial self-focusing and temporal self-broadening. Here, we provide a complete and detailed description of the experiment in which the spontaneous appearance of X waves has been observed. The experiment concerns frequency doubling of a 170-fs, 50-microm standard laser wave packet in a 22-mm lithium triborate crystal, tuned for second-harmonic generation with positive phase mismatch, positive group-velocity dispersion, and large group-velocity mismatch. Conventional beam-profile and autocorrelation measurements at the crystal output face show evidence of spatiotemporal self-trapping. The characterization of the free-space propagation reveals sub-Gaussian diffraction and pulse broadening, consistent with the presence of angular dispersion. Space-resolved autocorrelations indicate the generation of an X-type profile.

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PubMed2003

Nonlinear electromagnetic X waves.

Nonlinear optical media that are normally dispersive support a new type of localized (nondiffractive and nondispersive) wave packets that are X shaped in space and time and have slower than exponential decay. High-intensity X waves, unlike linear ones, can be formed spontaneously through a trigger mechanism of conical emission, thus playing an important role in experiments.

Journal Article↗

PubMedDate not supplied

[Effect of glycerol formal on the embryonic development of the rat].

In order to evaluate the effect on embryonic development of a solvent commonly used in pharmacological investigations, glycerol formal was administered to pregnant rats from days 6 through 15 of gestation at the daily doses of 0.25, 0.50 and 1.0 ml/Kg i.m. Glycerol formal did not induce systemic toxicity in the mothers, but showed an embryotoxic and teratogenic activity on the products of conception.

Animals↗