Biomedical subjects

Michel Zamboni-Rached

Publications and source records attributed to Michel Zamboni-Rached.

7 recordsLinked to original sources

PubMed2006

Analytical expressions for the longitudinal evolution of nondiffracting pulses truncated by finite apertures.

Starting from some general and plausible assumptions based on geometrical optics and on a common feature of the truncated Bessel beams, a heuristic derivation is presented of very simple analytical expressions capable of describing the longitudinal (on-axis) evolution of axially symmetric nondiffracting pulses truncated by finite apertures. The analytical formulation is applied to several situations involving subluminal, luminal, or superluminal localized pulses, and the results are compared with those obtained by numerical simulations of the Rayleigh-Sommerfeld diffraction integrals. The results are in excellent agreement. The present approach can be rather useful, because it yields, in general, closed-form expressions, avoiding the need for time-consuming numerical simulations, and also because such expressions provide a powerful tool for exploring several important properties of the truncated localized pulses, such as their depth of fields, the longitudinal pulse behavior, and the decaying rates.

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PubMed2005

Theory of "frozen waves": modeling the shape of stationary wave fields.

In this work, starting by suitable superpositions of equal-frequency Bessel beams, we develop a theoretical and experimental methodology to obtain localized stationary wave fields (with high transverse localization) whose longitudinal intensity pattern can approximately assume any desired shape within a chosen interval 0 < or = z < or = L of the propagation axis z. Their intensity envelope remains static, i.e., with velocity v = 0, so we have named "frozen waves" (FWs) these new solutions to the wave equations (and, in particular, to the Maxwell equation). Inside the envelope of a FW, only the carrier wave propagates. The longitudinal shape, within the interval 0 < or = z < or = L, can be chosen in such a way that no nonnegligible field exists outside the predetermined region (consisting, e.g., in one or more high-intensity peaks). Our solutions are notable also for the different and interesting applications they can have--especially in electromagnetism and acoustics--such as optical tweezers, atom guides, optical or acoustic bistouries, and various important medical apparatuses.

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PubMed2004

Localized X-shaped field generated by a superluminal electric charge.

It is now well known that Maxwell equations admit of wavelet-type solutions endowed with arbitrary group velocities (0< v(g)< infinity). Some of them, which are rigidly moving and have been called localized solutions, attracted large attention. In particular, much work has been done with regard to the superluminal localized solutions (SLSs), the most interesting of which are the "X-shaped" ones. The SLSs have been actually produced in a number of experiments, always by suitable interference of ordinary-speed waves. In this paper we show, by contrast, that even a superluminal charge creates an electromagnetic X-shaped wave: namely, on the basis of Maxwell equations, we are able to evaluate the field associated with a superluminal charge (under the approximation of pointlikeness): it results in constituting a very simple example of a true X wave.

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PubMed2004

Focused X-shaped pulses.

The space-time focusing of a (continuous) succession of localized X-shaped pulses is obtained by suitably integrating over their speed, i.e., over their axicon angle, thus generalizing a previous (discrete) approach. New superluminal wave pulses are first constructed and then tailored so that they become temporally focused at a chosen spatial point, where the wave field can reach very high intensities for a short time. Results of this kind may find applications in many fields, besides electromagnetism and optics, including acoustics, gravitation, and elementary particle physics.

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PubMed2004

Chirped optical X-shaped pulses in material media.

We analyze the properties of chirped optical X-shaped pulses propagating in material media without boundaries. We show that such ("superluminal") pulses may recover their transverse and longitudinal shapes after some propagation distance, whereas the ordinary chirped Gaussian pulses can recover their longitudinal width only (since Gaussian pulses suffer a progressive transverse spreading during their propagation). We therefore propose the use of chirped optical X-type pulses to overcome the problems of both dispersion and diffraction during pulse propagation.

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PubMed2003

Superluminal localized solutions to Maxwell equations propagating along a waveguide: the finite-energy case.

In a previous paper we have shown localized (nonevanescent) solutions to Maxwell equations to exist, which propagate without distortion with superluminal speed along normal-sized waveguides, and consist in trains of "X-shaped" beams. Those solutions possessed infinite energy. In this paper we show how to obtain, by contrast, finite-energy solutions, with the same localization and superluminality properties.

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PubMed2002

Superluminal X-shaped beams propagating without distortion along a coaxial guide.

In a previous paper we showed that localized superluminal solutions to the Maxwell equations exist, which propagate down (nonevanescence) regions of a metallic cylindrical waveguide. In this paper we construct analogous nondispersive waves propagating along coaxial cables. Such new solutions, in general, consist in trains of (undistorted) superluminal "X-shaped" pulses. Particular attention is paid to the construction of finite total energy solutions. Any results of this kind may find application in the other fields in which an essential role is played by a wave equation (like acoustics, geophysics, etc.).

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