Biomedical subjects

Juan P Torres

Publications and source records attributed to Juan P Torres.

13 recordsLinked to original sources

PubMed2006

Broadband light generation by noncollinear parametric downconversion.

Broadband light generation is demonstrated by noncollinear spontaneous parametric downconversion with a cw pump laser. By use of a suitable noncollinear phase-matching geometry and a tightly focused pump beam, downconverted signals that feature a bell-shaped spectral distribution with a bandwidth approaching 200 nm are obtained. As an application of the generated broadband light, submicrometer axial resolution in an optical coherence tomography scheme is demonstrated; a free-space resolution down to 0.8 microm was achieved.

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PubMed2005

Engineering the frequency correlations of entangled two-photon states by achromatic phase matching.

We put forward a new method to control the spectra of photon pairs generated in parametric downconversion that allows their spectral properties to be tuned from correlation to anticorrelation, including uncorrelation. The method employs tilted pulses and can be implemented in materials and frequency bands for which conventional methods do not hold.

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PubMed2004

Enhancing the axial resolution of quantum optical coherence tomography by chirped quasi-phase matching.

We show theoretically that a chirped quasi-phase-matching nonlinear crystal structure can significantly enhance the axial resolution in quantum optical coherence tomography by increasing the spectral width of the generated entangled photon pairs. For pulsed pumps we show how the pump-pulse duration affects the maximum resolution attainable.

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PubMed2004

Orbital angular momentum of entangled counterpropagating photons.

We elucidate the paraxial orbital angular momentum of entangled photon pairs generated by spontaneous parametric downconversion in different noncollinear geometries in which the entangled photons counterpropagate. We find, in particular, the orbital angular momentum of entangled pairs generated in transverse-emitting configurations, in which none of the known rules for selecting orbital angular momentum holds.

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PubMed2004

Four-wave mixing of light beams with engineered orbital angular momentum in cold cesium atoms.

We report an experimental demonstration that shows that the spatial structure carried by engineered coherent superpositions of light beams with orbital angular momentum can be mapped into the nonlinear polarization induced in a cloud of cold cesium atoms. The structure of such polarization was revealed by nearly degenerate four-wave-mixing processes.

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PubMed2004

Eigenvalue control and switching by fission of multisoliton bound states in planar waveguides.

We report the results of numerical studies of the fission of N-soliton bound states at the interface formed by a Kerr nonlinear medium and a linear dielectric in a planar waveguide. A variety of effects are shown to occur, with applications to all-optical eigenvalue soliton control.

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PubMed2004

Quasi-phase-matching engineering for spatial control of entangled two-photon states.

We show that transverse engineering of quasi-phase-matched geometries can be used to tailor the spatial mode function that describes the quantum state of photon pairs generated in spontaneous parametric down-conversion. We study several geometries and reveal how properly engineered gratings affect, in particular, the spatial correlations embedded in two-photon entangled states.

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PubMed2004

Observation of self-trapping of light in walk-off-compensating tandems.

We report the first experimental observation, to our knowledge, of the self-trapping of light in walk-off-compensating optical tandems. The experiment was conducted with picosecond light pulses in a ten-plate optically contacted tandem made of potassium titanyl phosphate prepared for phase matching along a special geometry featuring a huge local walk-off. The observation should open the door to the exploration of multicomponent soliton formation in new classes of materials and settings.

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PubMed2003

Arresting wave collapse by wave self-rectification.

We put forward a mechanism for tailoring, and even arresting, the collapse of wave packets in nonlinear media, whose dynamics is governed by nonlocal two-dimensional nonlinear Schrödinger-like equations. The key ingredient of the scheme is the self-generation of nonlocal nonlinearities mediated by wave rectification.

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PubMed2003

Observation of multiple soliton generation mediated by amplification of asymmetries.

We report the experimental observation of the formation of multiple optical quadratic solitons in a process mediated by the amplification of minute asymmetries in the diffraction properties of the input light. Experiments were conducted in phase-matched second-harmonic generation in a bulk crystal of periodically poled potassium titanyl phosphate pumped at 1064 nm. The different mechanisms that influence the process were investigated numerically, and the pulsed nature of the pump light was found to play a key role in the observed light distributions.

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PubMed2002

Globally linked vortex clusters in trapped wave fields.

We put forward the existence of a rich variety of fully stationary vortex structures, termed H clusters, made of an increasing number of vortices nested in paraxial wave fields confined by trapping potentials. However, we show that the constituent vortices are globally linked, rather than products of independent vortices. Also, they always feature a monopolar global wave front and exist in nonlinear systems, such as the Bose-Einstein condensates. Clusters with multipolar global wave fronts are nonstationary or, at best, flipping.

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PubMed2001

Management of the angular momentum of light: preparation of photons in multidimensional vector states of angular momentum.

We put forward schemes to prepare photons in multidimensional vector states of orbital angular momentum. We show realizable light distributions that yield prescribed states with finite or infinite normal modes. In particular, we show that suitable light vortex pancakes allow the add-drop of specific vector projections. We suggest that such photons might allow the generation of engineered quNits in multidimensional quantum information systems.

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PubMed2001

Transverse instability of incoherent solitons in Kerr media.

We calculate the growth rate of the small-amplitude perturbations superimposed on a one-dimensional soliton that is fully coherent in the self-trapping dimension, yet uniform and partially incoherent in the other transverse dimension. Such solitons become transversely stable only if the correlation distance is below a specific threshold value. We show that this threshold for transverse instability fully coincides with the threshold value for modulational instability.

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