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1.
Opt Express ; 27(25): 36976-36989, 2019 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-31873468

RESUMO

We show, both experimentally and theoretically, that a slave laser injected with an optical frequency comb can undergo two distinct locking mechanisms, both of which decrease the output optical comb's frequency spacing. We report that, for certain detuning and relative injection strengths, slave laser relaxation oscillations can become undamped and lock to rational frequencies of the optical comb spacing, creating extra comb tones by nonlinear dynamics of the injected laser. We also study the frequency locking of the slave laser at detunings in between the injected comb lines, which add the slave laser's frequency to the comb. Our results demonstrate the effect of the α parameter and stability of the locked states and indicate how the frequency of the relaxation oscillations affect both of these locking mechanisms. These optical locking mechanisms can be applied to regenerate or multiply optical combs.

2.
PLoS Negl Trop Dis ; 13(8): e0007661, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-31425507

RESUMO

BACKGROUND: French Guiana, a French overseas department located in South America between Brazil and Surinam, is the only European territory geographically located in the Amazonian forest complex and is considered endemic for yellow fever (YF). In the context of the emergent threat of YF in Latin America, we conducted a large household cross-sectional survey from June to October 2017 to estimate vaccination coverage in the population and to determine associations with sociodemographic and geographical characteristics. METHODOLOGY/PRINCIPAL FINDINGS: In total, 1,415 households and 2,697 individuals were included from the 22 municipalities of French Guiana. YF vaccination coverage was estimated at 95.0% (95% CI: 93.4-96.2) in the entire territory but was spatially heterogeneous, with the lowest levels estimated in the western part of the territory along the Surinamese cross-border region, particularly in children under 16 years who were not enrolled in school, immigrant adults and disadvantaged populations with low socioeconomic indexes. CONCLUSIONS/SIGNIFICANCE: Despite the good vaccination coverage against YF in the general population of French Guiana resulting from the compulsory nature of YF vaccination for residents and travelers, there is an urgent need to improve vaccination coverage in vulnerable populations living in the northwestern part of the territory to limit the risk of transmission in the context of the emerging YF threat in South America. Despite the relative rarity of YF and the significant number of infectious and tropical diseases in French Guiana, clinicians should adopt a high index of suspicion for YF, particularly in vulnerable and at-risk populations.


Assuntos
Transmissão de Doença Infecciosa/prevenção & controle , Cobertura Vacinal/estatística & dados numéricos , Vacina contra Febre Amarela/administração & dosagem , Febre Amarela/epidemiologia , Febre Amarela/prevenção & controle , Adolescente , Adulto , Idoso , Criança , Pré-Escolar , Estudos Transversais , Demografia , Características da Família , Feminino , Guiana Francesa/epidemiologia , Humanos , Masculino , Pessoa de Meia-Idade , Fatores Socioeconômicos , Adulto Jovem
3.
ACS Omega ; 4(1): 2283-2290, 2019 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-31459471

RESUMO

We have developed a bright optical setup, especially optimized for surface-enhanced Raman scattering (SERS) correlation spectroscopy. We show that the brightness of the experiment combined with the correlation approach permits in situ access to the size and shape of the SERS-active aggregates in solution despite a very weak SERS signal of the adsorbed molecules. As a result, we demonstrate that dimers and larger SERS-active aggregates can be identified through the temporal fluctuations of the SERS signal of only a few hundred of adsorbed molecules, that is, at zeptomole adsorbate concentrations. Monomers covered by a monolayer of MBA were also identified. These results open a way for single nanoparticle sensing, for single-molecule SERS-active aggregate characterization, or for quantitative monitoring of functionalization processes on metallic objects.

4.
Appl Opt ; 57(22): E154-E162, 2018 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-30117851

RESUMO

We model the situation of two lasers in a face-to-face arrangement, optically coupled through an attenuating element, where the distance between the lasers is on a scale typical in photonic integration (hundreds of micrometers to millimeters). We account for the existence of a frequency difference between the two single-mode lasers. Modified versions of the Lang-Kobayashi equations were employed to describe the interaction. By solving this delay differential equation system, we characterized different dynamical regimes including one- and two-color states and self-pulsations. We focus on the effect varying coupling strength and detuning between the lasers has on the frequencies of the lasers. Using the results of this frequency study, we identify the bifurcations causing changes between the different frequency regimes.

5.
Chemphyschem ; 17(1): 128-35, 2016 Jan 04.
Artigo em Inglês | MEDLINE | ID: mdl-26538240

RESUMO

The photophysical and nonlinear optical properties of water-soluble chromophore-functionalised tris-dipicolinate complexes [LnL3](3-) (Ln=Yb and Nd) are thoroughly studied, revealing that only the Yb(III) luminescence can be sensitized by a two-photon excitation process. The stability of the complex in water is strongly enhanced by embedding in dispersible organosilicate nanoparticles (NPs). Finally, the spectroscopic properties of [NBu4]3 [YbL3] are studied in solution and in the solid state. The high brightness of the NPs allows imaging them as single objects using a modified two-photon microscopy setup in a NIR-to-NIR configuration.


Assuntos
Complexos de Coordenação/efeitos da radiação , Microscopia Confocal/métodos , Nanopartículas/efeitos da radiação , Ácidos Picolínicos/efeitos da radiação , Itérbio/química , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Luz , Nanopartículas/química , Ácidos Picolínicos/síntese química , Ácidos Picolínicos/química , Espectroscopia de Luz Próxima ao Infravermelho
6.
Langmuir ; 27(8): 4358-61, 2011 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-21417243

RESUMO

A polymerizable amphiphile polymer containing PEG was synthesized and used to encapsulate quantum dots in micelles. The quantum dot micelles were then polymerized using a "clean" electron beam process that did not require any post-irradiation purification. Fluorescence spectroscopy revealed that the polymerized micelles provided an organic coating that preserved the quantum dot fluorescence better than nonpolymerized micelles, even under harsh conditions.


Assuntos
Micelas , Polimerização , Pontos Quânticos , Elétrons , Polímeros/química
7.
Langmuir ; 24(7): 3016-9, 2008 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-18303920

RESUMO

Water soluble fluorescent nanocrystals were obtained by encapsulation of hydrophobic quantum dots (QDs) with amphiphilic phospholipids derived from the ring opening metathesis of norbornene-based monomers. The robustness of the newly coated quantum dots was assessed by comparative studies under various ionic conditions which indicated an overall enhancement of their fluorescence stability.


Assuntos
Fluorescência , Nanopartículas/química , Fosfolipídeos/química , Polietilenoglicóis/química , Íons , Pontos Quânticos , Solubilidade , Água
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