Biomedical subjects

Roberta Zambrini

Publications and source records attributed to Roberta Zambrini.

4 recordsLinked to original sources

PubMed2006

Quasi-intrinsic angular momentum and the measurement of its spectrum.

We introduce the concept of quasi-intrinsic angular momentum to denote fields for which the mean value of the angular momentum is unaltered by a lateral shift of the rotation axis but the spectrum changes. This property is exemplified by the orbital angular momentum of a beam of light about its propagation direction. We propose an interferometric experiment to measure efficiently the exact angular momentum spectrum and variance for light beams with any arbitrary spatial distribution.

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PubMed2006

Convective instability induced by two-points nonlocality.

We consider diffusive nonlinear systems with nonlocal two-points coupling, generally induced by misalignment in optical feedback. We expand the stability analysis in F. Papoff and R. Zambrini [Phys. Rev. Lett. 94, 243903 (2005)] to determine convective and absolute thresholds. Nonlocality leads to different effects in comparison to well-known problems with drift, as the existence of opposite phase and group velocities for some modes and an instability region. The theoretical predictions are in agreement with numerical results in a nonlocal system with saturable nonlinearity over wide parameter regions. The knowledge of the stability diagram for any uniform state allows us to interpret the rich dynamics due to the interplay between finite size, noise, and multiple states.

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PubMed2005

Convection-induced nonlinear symmetry breaking in wave mixing.

We show that the combined action of diffraction and convection (walk-off) in wave mixing processes leads to a nonlinear symmetry breaking in the generated traveling waves. The dynamics near to threshold is reduced to a Ginzburg-Landau model, showing an original dependence of the nonlinear self-coupling term on the convection. Analytical expressions of the intensity and velocity of traveling waves emphasize the utmost importance of convection in this phenomenon. These predictions are in excellent agreement with the numerical solutions of the full dynamical model.

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PubMed2004

Photonic band-gap inhibition of modulational instabilities.

Spatial structures as a result of a modulational instability are studied in a nonlinear cavity with a photonic crystal. The interaction of the modulated refractive index with the nonlinearity inhibits the instability via the creation of a photonic band gap. A novel mechanism of light localization due to defects and pattern inhibition is also described.

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