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Instabilities of waves in nonlinear disordered media
1Laboratoire de Physique et Modelisation des Milieux Condenses, Universite Joseph Fourier, Maison des Magisteres-CNRS, BP 166, 38042 Grenoble Cedex 9, France.
Physical Review Letters
|September 16, 2000
Summary
A new theory reveals that speckle patterns in disordered media become unstable above a nonlinearity threshold. This instability causes spontaneous intensity fluctuations, driven by multiple scattering feedback, regardless of nonlinearity sign.
Area of Science:
- Physics
- Wave Scattering
- Nonlinear Optics
Background:
- Speckle patterns arise from coherent wave interference in disordered media.
- Weakly nonlinear disordered media exhibit complex wave propagation phenomena.
- Understanding temporal fluctuations is crucial for characterizing scattering dynamics.
Purpose of the Study:
- To develop a self-consistent theory for temporal fluctuations in nonlinear speckle patterns.
- To investigate the conditions under which speckle patterns become unstable.
- To elucidate the role of multiple scattering and nonlinearity in pattern dynamics.
Main Methods:
- Formulation of a self-consistent theoretical framework.
- Analysis of temporal fluctuations in a weakly nonlinear disordered medium.
- Investigation of feedback mechanisms in multiple scattering.
Main Results:
- A theoretical threshold for speckle pattern instability was identified.
- Nonlinearity exceeding this threshold leads to spontaneous intensity fluctuations.
- The instability mechanism is driven by feedback from multiple scattering.
- The development of instability is independent of the sign of nonlinearity.
Conclusions:
- Speckle pattern stability in nonlinear disordered media is sensitive to nonlinearity levels.
- Multiple scattering plays a key role in the feedback loop driving instability.
- The findings offer insights into wave propagation in complex nonlinear systems.
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