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We present experimental and numerical evidence of control and synchronization of burst events in modulated CO2 lasers. Bursts appear randomly in each laser as trains of large amplitude spikes intercalated by a small amplitude chaotic regime. Experimental data and model display the frequency locking of bursts in a suitable interval of coupling strengths. The analogy with neuronal bursting will also be discussed in view of the role of bursting synchronization in cognitive functions.

By tuning a control parameter, a chaotic system can either display two or more attractors (generalized multistability) or exhibit an interior crisis, whereby a chaotic attractor suddenly expands to include the region of an unstable orbit (bursting regime). Recently, control of multistability and bursting have been experimentally proved in a modulated class B laser by means of a feedback method. In a bistable regime, the method relies on the knowledge of the frequency components of the two attractors. Near an interior crisis, the method requires retrieval of the unstable orbit colliding with the chaotic attractor. We also show that a suitable parameter modulation is able to control bistability in the Lorenz system. We observe that, for every given modulation frequency, the chaotic attractor is destroyed under a boundary crisis. The threshold control amplitude depends on the control frequency and the location of the operating point in the bistable regime. Beyond the boundary crisis, the system remains in the steady state even if the control is switched off, demonstrating control of bistability.

We have proposed an adaptive procedure in order to estimate unknown parameters of a numerical model of a chaotic CO2 laser, which is observed through a time series that represents the output intensity of a laser. To do that, we consider a coupled system with the same functional form and adjustable parameters. The salient feature of the proposed technique is that accurate parameter estimation and identical synchronization can be jointly achieved by adaptively adjusting the desired parameters of the coupled system.

We present experimental and numerical evidence of synchronization of burst events in two different modulated CO2 lasers. Bursts appear randomly in each laser as trains of large amplitude spikes intercalated by a small amplitude chaotic regime. Experimental data and model show the frequency locking of bursts in a suitable interval of coupling strength. We explain the mechanism of this phenomenon and demonstrate the inhibitory properties of the implemented coupling

We present experimental and numerical evidence of polarization selection in an isotropic CO2 laser achieved by means of an unpolarized optical feedback. This mechanism can be applied in situations where the direction of polarization plays a crucial role, including polarization coding.

The scientific literature dealing with estuarine chemical pollution is characterized by the extreme diversity of the concerned organizations and by the multiplicity of available documents (internal reports, regional publications, etc.), often hard to access. It seemed important to gather the scattered information, to synthesize the current knowledge and to bring to light their main deficiencies. Because of the lack of information on the effects of other pollutants, we limited ourselves to a few groups of chemical compounds likely to alter the quality of the estuarine environment: metallic trace elements and radionuclides, pesticides and chlorinated diphenyls (PCB), and organic matter and nitrogenized and phosphorated nutritive compounds. However, provided in appendix are the few references we found on pollution by some synthesis organic compounds, by fluorides and by various industrial wastes. We chose to leave apart the problem of prevention and the fight against pollution as well as their socio-economic aspects., La littérature scientifique traitant de la pollution chimique des estuaires est caractérisée par l'extrême diversité des organismes concernés et par la multiplicité de documents difficilement accessibles (rapports internes, publications régionales, etc...). Il nous a semblé utile de rassembler des éléments d'information épars, de synthétiser les connaissances déjà acquises et de mettre en évidence les principales lacunes. Faute d'une information suffisamment étendue sur les effets d'autres polluants, nous nous sommes limités à quelques grands groupes de composés chimiques susceptibles d'altérer la qualité du milieu estuarien : les oligoéléments métalliques et les radionuclides, les pesticides et les diphényles chlorés (PCB), enfin la matière organique et les composés nutritifs azotés et phosphorés. On trouvera néanmoins en annexe les quelques références que nous avons trouvées sur la pollution par certains composés organiques de synthèse, par les fluorures, par les rejets d'industries diverses, etc... Nous avons volontairement laissé de côté le problème de la prévention et de la lutte contre la pollution ainsi que leurs aspects socio-économiques. [OCR NON CONTRÔLE]