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Propagation et émission du rayonnement en milieu diffusant. Application à l'imagerie des milieux complexes.

Abstract : In this manuscript, we raise different aspects of the propagation and emission of electromagnetic waves in a scettering medium.

In the first part, we show that the Radiative Transfer Equation (RTE) is a very good tool to study light propagation in a complex medium. Thanks to this formalism, we study the evolution of the spatial coherence of the beam inside the medium. Next, we derive rigorously the diffusion approximation by using a modal approach of the RTE and clarify the role of the absorption. Finally, we study the temporal fluctuations of the scattered intensity and show that the use of the RTE allows to go beyond the diffusive regime described by the diffusing-waves spectroscopy theory (DWS).

The second part is dedicated to the study of light emission in complex media. First, we study the amplification of scattered light in a gain system called random laser and show that it exists a laser threshold in the incoherent feedback regime. This threshold is quantified by using a modal approach of the RTE. Next, we study the modification of the fluorescent decay rate of a single molecule embedded in a complex medium. We derive a model allowing the replacement of the scattering medium by an homogeneous equivalent medium taking into account the multiple scattering and the interactions between scatterers. Finally, we compute the expression of the time-reversed field in a complex medium. To do that, we extend the well-known expression derived in acoustic to the case of electromagnetic waves.
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https://tel.archives-ouvertes.fr/tel-00202291
Contributor : Romain Pierrat <>
Submitted on : Friday, January 4, 2008 - 6:00:43 PM
Last modification on : Friday, July 3, 2020 - 9:28:02 AM
Long-term archiving on: : Tuesday, April 13, 2010 - 4:16:41 PM

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  • HAL Id : tel-00202291, version 1

Citation

Romain Pierrat. Propagation et émission du rayonnement en milieu diffusant. Application à l'imagerie des milieux complexes.. Physique Atomique [physics.atom-ph]. Ecole Centrale Paris, 2007. Français. ⟨tel-00202291⟩

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