Comparative analysis of ferroelectric domain statistics via nonlinear diffraction in random nonlinear materials

© 2018 [Optical Society of America]. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved.We present an indirect, non-destructive optical method for domain statistic characterization in disordered nonlinear crystals having homogeneous refractive index and spatially random distribution of ferroelectric domains. This method relies on the analysis of the wave-dependent spatial distribution of the second harmonic, in the plane perpendicular to the optical axis in combination with numerical simulations. We apply this technique to the characterization of two different media, Calcium Barium Niobate and Strontium Barium Niobate, with drastically different statistical distributions of ferroelectric domains.Peer ReviewedPostprint (published version

Decreased CD90 expression in human mesenchymal stem cells by applying mechanical stimulation

BACKGROUND: Mesenchymal stem cells (MSC) are multipotent cells which can differentiate along osteogenic, chondrogenic, and adipogenic lineages. The present study was designed to investigate the influence of mechanical force as a specific physiological stress on the differentiation of (MSC) to osteoblast-like cells. METHODS: Human MSC were cultured in osteoinductive medium with or without cyclic uniaxial mechanical stimulation (2000 μstrain, 200 cycles per day, 1 Hz). Cultured cells were analysed for expression of collagen type I, osteocalcin, osteonectin, and CD90. To evaluate the biomineral formation the content of bound calcium in the cultures was determined. RESULTS: After 14 days in culture immunfluorescence staining revealed enhancement of collagen type I and osteonectin expression in response to mechanical stimulation. In contrast, mechanically stimulated cultures stained negative for CD90. In stimulated and unstimulated cultures an increase in the calcium content over time was observed. After 21 days in culture the calcium content in mechanical stimulated cultures was significantly higher compared to unstimulated control cultures. CONCLUSION: These results demonstrate the influence of mechanical force on the differentiation of human MSC into osteoblast-like cells in vitro. While significant enhancement of the biomineral formation by mechanical stimulation is not detected before 21 days, effects on the extracellular matrix became already obvious after 14 days. The decrease of CD90 expression in mechanically stimulated cultures compared to unstimulated control cultures suggests that CD90 is only transiently expressed expression during the differentiation of MSC to osteoblast-like cells in culture

Toll-8/Tollo Negatively Regulates Antimicrobial Response in the Drosophila Respiratory Epithelium

Barrier epithelia that are persistently exposed to microbes have evolved potent immune tools to eliminate such pathogens. If mechanisms that control Drosophila systemic responses are well-characterized, the epithelial immune responses remain poorly understood. Here, we performed a genetic dissection of the cascades activated during the immune response of the Drosophila airway epithelium i.e. trachea. We present evidence that bacteria induced-antimicrobial peptide (AMP) production in the trachea is controlled by two signalling cascades. AMP gene transcription is activated by the inducible IMD pathway that acts non-cell autonomously in trachea. This IMD-dependent AMP activation is antagonized by a constitutively active signalling module involving the receptor Toll-8/Tollo, the ligand Spätzle2/DNT1 and Ect-4, the Drosophila ortholog of the human Sterile alpha and HEAT/ARMadillo motif (SARM). Our data show that, in addition to Toll-1 whose function is essential during the systemic immune response, Drosophila relies on another Toll family member to control the immune response in the respiratory epithelium

Mechanics rules cell biology

Cells in the musculoskeletal system are subjected to various mechanical forces in vivo. Years of research have shown that these mechanical forces, including tension and compression, greatly influence various cellular functions such as gene expression, cell proliferation and differentiation, and secretion of matrix proteins. Cells also use mechanotransduction mechanisms to convert mechanical signals into a cascade of cellular and molecular events. This mini-review provides an overview of cell mechanobiology to highlight the notion that mechanics, mainly in the form of mechanical forces, dictates cell behaviors in terms of both cellular mechanobiological responses and mechanotransduction

CORRUGATED WAVEGUIDES USED AS BISTABLE COMPONENTS

On développe une théorie électromagnétique des réseaux gravés sur des diélectriques présentant un effet Kerr. Pour des puissances incidentes adéquates, ces réseaux peuvent avoir deux valeurs très différentes de leurs efficacités, dépendant de leur état antérieur. Ceci permet d'envisager leur utilisation comme composants optiques bistables. L'utilisation de résonances électromagnétiques (plasmons, ondes guidées, ...) permet une réduction intéressante des seuils de basculement. Une étude numérique pour les deux polarisations fondamentales (TE et TM) permet d'optimiser le dispositif. Une interprétation phénoménologique du comportement bistable est donnée, dans le cas d'un coupleur à prisme, en recherchant la trajectoire, dans le plan complexe, de pôles et de zéros du facteur de réflexion quand la puissance incidente varie.An electromagnetic theory of gratings ruled on a Kerr dielectric medium is presented in this paper. For convenient incident powers, gratings may exhibit two distinct values of their efficiencies, depending on their previous state. It is thus possible to use them as bistable optical components. The use of electromagnetic resonances (plasmons, guided waves, ...) allow reducing the bistability thresholds to interesting values. A numerical study for the TE and TM fondamental polarizations is done to optimize the device. A phenomenological explanation of the bistable behavior is done for a prism coupler by studying the reflectivity poles and zeros loci in the complex plane, when the incident power is varied

Second harmonic scattered light from a zinc-sulfide thin film

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Modal theory of diffraction : a powerful tool for the study of grating couplers in nonlinear optics

It is shown that the simultaneous use of the coupled-mode formalism and of the rigorous theory of diffraction in linear optics leads to a simple modal theory of grating couplers on nonlinear waveguides. Two examples are considered : optical Kerr effect and second harmonic generation. In Kerr-type grating couplers, despite its simplicity, this modal analysis is able to predict $\ll$ exotic $\gg$ behaviors such as, for example, chaos

Analysis of domain statistics of disordered structures via second harmonic diffraction

Summary form only given. When a fundamental beam propagates perpendicular to the optical axis of a nonlinear crystal with randomly distributed ferroelectric domains showing inverted sign of 2 nd order nonlinearity (χ 2 ), the generated second harmonic (SH) signal is spatially distributed in a plane, perpendicular to the optical axis [1]. Because the angular distribution of the SH intensity in this plane depends on the particular domain size and distribution, the characterization of the angular emission pattern could bring information about these parameters, which is difficult to be obtained by imaging methods since the domain size can be very small (few hundreds of nm). The domain statistics of such nonlinear materials was considered in the study of the SH diffraction pattern in a one-dimensional (1D) model by Le Grand et al. [2-4]. However, this model yields some discrepancies between the theoretical fits and experimental results [4]. In this work we compare experimental results of the SH angular distribution with the predictions of a more precise 2D model for extracting domain statistics

Laser induced damage investigation at 1064 nm in KTiOPO4 crystals and its analogy with RbTiOPO4

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Super-Resolution inscription in thin film multilayers

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