Biomedical subjects
Publications and source records attributed to S Residori.
We show that the Talbot effect can be used to increase the gain of two-wave mixing in a stack of thin nonlinear media. We demonstrate that a large gain enhancement is achieved for a few nonlinear elements, provided that they are placed at distances that satisfy Talbot recurrences.
We present a unifying description close to a spatial bifurcation of localized states, appearing as large amplitude peaks nucleating over a pattern of lower amplitude. Localized states are pinned over a lattice spontaneously generated by the system itself. We show that the phenomenon is generic and requires only the coexistence of two spatially periodic states. At the onset of the spatial bifurcation, a forced amplitude equation is derived for the critical modes, which accounts for the appearance of localized peaks.
Experimental evidence of bouncing localized structures in a nonlinear optical system is reported. Oscillations in the position of the localized states are described by a consistent amplitude equation, which we call the Lifshitz normal form equation, in analogy with phase transitions. Localized structures are shown to arise close to the Lifshtiz point, where nonvariational terms drive the dynamics into complex and oscillatory behaviors.
We report a new mechanism for the secondary instabilities of traveling wave patterns in dissipative systems. In close analogy to nonlinear optics and plasma physics, it is a process of three-wave interaction that leads to sum-frequency generation. The primary traveling wave gives rise to two additional wave components, an upper and a lower frequency. We outline the mechanism and we show that this process does occur for wave patterns obtained in an optical experiment.
We report an experimental study on the effect of an external multiplicative noise on a subcritical bifurcation leading to the parametric amplification of surface waves. We show that the probability density function of the wave amplitude in the presence of noise has two maxima that do not correspond to any of the deterministic states. When the deterministic forcing is varied in the presence of noise, these most probable values give two new branches in the bifurcation diagram that involve a much larger difference in oscillation amplitude. The bistable region is also strongly enlarged. This noise induced bistability can be understood in the general framework of noise induced transitions.
We show that feedback, which introduces a dependence of the electric field on the liquid-crystal director, renders the Fréedericksz transition first order. Experimentally, the feedback is introduced as a light loop in a liquid-crystal light valve. Theoretically, we include the feedback term into the Frank free energy and we derive an amplitude equation that is valid close to the transition. The theoretical description is in qualitative agreement with the experimental observations. Depending on the values of the feedback parameters, both theory and experiment exhibit bistability, propagation of fronts, and a Maxwell point.
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