Ultrafast Population Dynamics of Surface-Active Dyes during Electrochemically Controlled Ion Transfer across a Liquid|Liquid Interface

We present for the first time experimental measurements on the ultrafast population dynamics of the model surface-active dye methyl orange (MO) during its ion transfer across the water|1,2-dichloroethane interface by using time-resolved surface second harmonic generation (TR-SSHG). The interfacial dynamics reveals that the population of MO relaxes to the ground state within 160 fs without any significant contribution of the molecular reorientation. It is concluded that the MO transfer across the interface considerably affects the population of MO at the interface but has no effect on the dynamics of the molecule itself

Universal scaling of plasmon coupling in metal nanostructures: Checking the validity for higher plasmonic modes using second harmonic generation

The universal scaling of plasmon coupling in metallic nanostructures is now a well-established feature. However, if the interaction between dipolar plasmon modes has been intensively studied, this is not the case of the coupling between higher order ones. Using Mie theory extended to second harmonic generation, we investigate the coupling between quadrupolar plasmon modes in metallic nanoshells. Like in the case of dipolar plasmon modes, a universal scaling behavior is observed in agreement with the plasmon hybridization model

Observation and analysis of creation, decay, and regeneration of annular soliton clusters in a lossy cubic-quintic optical medium

We observe and analyze formation, decay, and subsequent regeneration of ring-shaped clusters of (2+1)-dimensional spatial solitons (filaments) in a medium with the cubic-quintic (focusing-defocusing) self-interaction and strong dissipative nonlinearity. The cluster of filaments, that remains stable over ~17.5 Rayleigh lengths, is produced by the azimuthal modulational instability from a parent ring-shaped beam with embedded vorticity l = 1. In the course of still longer propagation, the stability of the soliton cluster is lost under the action of nonlinear losses. The annular cluster is then spontaneously regenerated due to power transfer from the reservoir provided by the unsplit part of the parent vortex ring. A (secondary) interval of the robust propagation of the regenerated cluster is identified. The experiments use a laser beam (at wavelength 800 nm), built of pulses with temporal duration 150 fs, at the repetition rate of 1 kHz, propagating in a cell filled by liquid carbon disulfide. Numerical calculations, based on a modified nonlinear Schr\"odinger equation which includes the cubic-quintic refractive terms and nonlinear losses, provide results in close agreement with the experimental findings.Comment: To be published in Phys. Rev.

Second harmonic scattering from silver nanocubes

The second harmonic light scattered from silver nanocubes dispersed in an aqueous suspension is investigated. The first hyperpolarizability is determined and corrected for resonance enhancement. It is shown to be similar to that of silver nanospheres with a comparable volume. The polarization-resolved analysis of the scattered harmonic intensity exhibits a surface response strongly modulated by the different multipolar field contributions. As a result, the shape does not play a leading role anymore for nanoparticles with a centrosymmetric shape when retardation must be considered. Comparing the right angle and forward-scattered polarized intensity responses, the unequal balance of the eight nanocube corners' contribution to the total response is revealed despite the high degree of centrosymmetry of the cubic shape. It is then demonstrated with a simple model that the nanocubes' first hyperpolarizability exhibits an octupolar tensorial symmetry. The surface integral equation method calculations are finally provided to investigate further the role of the corners’ and edges’ rounding

Self-Assembled Molecular Rafts at Liquid|Liquid Interfaces for Four-Electron Oxygen Reduction

The self-assembly of the oppositely charged watersoluble porphyrins, cobalt tetramethylpyridinium porphyrin (CoTMPyP4+) and cobalt tetrasulphonatophenyl porphyrin (CoTPPS4−), at the interface with an organic solvent to form molecular “rafts”, provides an excellent catalyst to perform the interfacial four-electron reduction of oxygen by lipophilic electron donors such as tetrathiafulvalene (TTF). The catalytic activity and selectivity of the self-assembled catalyst toward the four-electron pathway was found to be as good as that of the Pacman type cofacial cobalt porphyrins. The assembly has been characterized by UV−visible spectroscopy, Surface Second Harmonic Generation, and Scanning Electron Microscopy. Density functional theory calculations confirm the possibility of formation of the catalytic CoTMPyP4+/ CoTPPS4− complex and its capability to bind oxygen

Effects of eight neuropsychiatric copy number variants on human brain structure

Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen’s d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions

Diffusion hyper Rayleigh de nanoparticules métalliques

L'origine de la réponse de diffusion hyper Rayleigh des particules métalliques d'or et d'argent d'un diamètre variant de quelques nanomètres à 150 nm a été déterminée par une analyse de l'intensité harmonique en fonction de la taille des particules et de la polarisation de la lumière. Les expériences démontrent que les particules n'ont pas une forme parfaitement sphérique et que la réponse de diffusion hyper Rayleigh est d'origine dipolaire électrique. Ces résultats sont renforcés par les mesures de dépendance en taille et en longueur d'onde d'hyperpolarisabilité. N'étant pas supportées par les mode les existants, les expériences sont décrites dans le cadre d'un nouveau modèle théorique dans lequel la polarisation non linéaire des particules à la fréquence harmonique est localisée à la surface. Les effets retardés sont introduits pour correctement décrire le cas des plus grosses particulesLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Diffusion hyper Rayleigh des assemblages moléculaires

Le caractère cohérent du processus de doublage de fréquence, processus de conversion de deux photons à la fréquence fondamentale en un photon à la fréquence harmonique, permet de sonder la matière à des échelles sub-longueur d'onde. Pour mettre en évidence cette propriété, la technique de diffusion hyper Rayleigh a été employée pour sonder l'organisation dans des assemblages moléculaires dispersés en solution liquide. Après une étude initiale de quelques solvants usuels purs, l'influence de l'environnement sur la réponse du cristal violet, une sonde moléculaire octupolaire de référence, a été étudiée. Ces études ont été poursuivies pour des sondes moléculaires amphiphiles afin d'étudier des solutions mixtes comprenant à la fois des sondes libres et des sondes engagées dans des assemblages moléculaires appelés micelles. En raison de la centrosymétrie de ces assemblages, la composante dipolaire de la réponse harmonique diffusée s'affaiblit, laissant la réponse harmonique totale dominée par une forte contribution quadripolaire clairement mise en évidence par ces mesures de diffusion hyper Rayleigh résolue en polarisation. Un modèle complet décrivant les différentes composantes de la réponse harmonique totate est introduit pour interpréter globalement les observations sur ces solutions mixtes. Enfin, les études préliminaires d'un système biomimétique reconstitué à l'interface air-eau par doublage de fréquence sont présentéesThe coherent character of the frequency doubling process, process of conversion of two photons at the fundamental frequency into one photon at the harmonic frequency, makes it possible to probe matter on sub-wavelength scales. To highlight this property, the technique of hyper Rayleigh scattering was employed to probe the organization in molecular assemblies dispersed in liquid solutions. After an initial study on a selection of solvents, the influence of the environment on the response of the crystal violet, an octupolar probe molecule was studied. These studies were carried on for amphiphilic molecular probes in order to study mixed suspensions of free probes and probes incorporated in molecular assemblies, for instance micelles. Because of the centrosymmetry of these assemblies, the dipolar component of the scattered harmonic intensity vanishes, leaving a harmonic intensity dominated by the quadripolar contribution. These measurements are performed with the technique of polarized resolved hyper Rayleigh scattering. A complete model describing the various components of the total harmonic intensity is introduced to describe the observations. In a final chapter, preliminary studies on reconstituted biomimetic systems at the air-water interface by frequency doubling are presentedLYON1-BU.Sciences (692662101) / SudocSudocFranceF