Polarization dependence of second harmonic generation from plasmonic nanoprism arrays.

The second order nonlinear optical response of gold nanoprisms arrays is investigated by means of second harmonic generation (SHG) experiments and simulations. The polarization dependence of the nonlinear response exhibits a 6-fold symmetry, attributed to the local field enhancement through the excitation of the surface plasmon resonances in bow-tie nanoantennas forming the arrays. Experiments show that for polarization of the input light producing excitation of the plasmonic resonances in the bow-tie nanoantennas, the SHG signal is enhanced; this despite the fact that the linear absorption spectrum is not dependent on polarization. The results are confirmed by electrodynamic simulations which demonstrate that SHG is also determined by the local field distribution in the nanoarrays. Moreover, the maximum of SHG intensity is observed at slightly off-resonance excitation, as implemented in the experiments, showing a close relation between the polarization dependence and the structure of the material, additionally revealing the importance of the presence of non-normal electric field components as under focused beam and oblique illumination.

Circular dichroism enhancement in plasmonic nanorod metamaterials.

Optical activity is a fundamental phenomenon originating from the chiral nature of crystals and molecules. While intrinsic chiroptical responses of ordinary chiral materials to circularly polarized light are relatively weak, they can be enhanced by specially tailored nanostructures. Here, nanorod metamaterials, comprising a dense array of vertically aligned gold nanorods, is shown to provide a significant enhancement of the circular dichroism response of an embedded material. A nanorod composite, acting as an artificial uniaxial crystal, is filled with chiral mercury sulfide nanocrystals embedded in a transparent polymer. The metamaterial, being inherently achiral, enables optical activity enhancement or suppression. Unique properties of inherently achiral structures to tailor optical activities pave a way for flexible characterization of optical activity of molecules and nanocrystal-based compounds.

Nonlocality-driven supercontinuum white light generation in plasmonic nanostructures.

Structured plasmonic metals are widely employed for achieving nonlinear functionalities at the nanoscale due to their ability to confine and enhance electromagnetic fields and strong, inherent nonlinearity. Optical nonlinearities in centrosymmetric metals are dominated by conduction electron dynamics, which at the nanoscale can be significantly affected by the nonlocal effects. Here we show that nonlocal corrections, being usually small in the linear optical response, define nonlinear properties of plasmonic nanostructures. Using a full non-perturbative time-domain hydrodynamic description of electron plasma under femtosecond excitation, we numerically investigate harmonic generation in metallic Archimedean nanospirals, revealing the interplay between geometric and nonlocal effects. The quantum pressure term in the nonlinear hydrodynamic model results in the emergence of fractional nonlinear harmonics leading to broadband coherent white-light generation. The described effects present a novel class of nonlinear phenomena in metallic nanostructures determined by nonlocality of the electron response.

[Morphological features of oesophagogastric junction mucosa in children with gastroesophageal reflux disease].

In present work we studied the morphological features of the esophageal mucosa in 63 children with gastroesophageal reflux disease (GERD). The biopsies were taken at level of 3 cm above a Z-line and at level of 0.5-1 cm above a Z-line. The results of our study showed that the mucosa of the esophago-gastric junction may contain areas covered with columnar epithelium of 44.4% of children in the biopsies from the level of 0.5-1.0 cm above the Z-line. Inflammatory changes in the mucosa of the esophago-gastric junction identified in 71.4% of cases. The inflammation in the majority of cases (82.1%) was observed in the presence of H. pylori infection (p < 0.001). In addition, H. pylori in our study, we noted the relationship detection carditis in overweight child. When compared with the height-weight parameters, the excess body weight was observed in 17 of 28 patients. We couldn't found increasing detection of the cardia in patients with erosive GERD compared with non-erosive variants.

[Digestive insufficiency of the stomach in children from the positions of clinical morphology and its role in the assessment of the indications for nutritional support ].

The structure of gastric mucosa (GM) of the stomach fundus (SF) was studied in children with various gastrointestinal diseases. In children, the main structural parameters of the SF (GM thickness, depth of glands and thickness of the mucosal epithelium area) varied widely (3.5-5.3 times). The following ranges were allocated: hypotrophy ("atrophy"), eutrophy (area of mean values) and hypertrophy of SF GM thickness, depth of the glands and thickness of the mucosal epithelium area. Hypotrophy ("atrophy") of the SF glands was found in approximately one third of the children of different age which could lead to decrease in the digestive function of the stomach and cause specific clinical symptoms of dyspepsia. Atrophic changes of SF GM were observed in children of all age groups. Most often (49%), fundic glands hypotrophy was observed in children of early age. With age, the incidence of atrophic changes of SF GM decreased. Atrophic changes in the GM can be detected during microanatomical or histopathological (using morphometry) examination of the SF.

Photonic signal processing on electronic scales: electro-optical field-effect nanoplasmonic modulator.

We develop a highly efficient approach for the modulation of photonic signals at the nanoscale, combining an ultrasubwavelength plasmonic guiding scheme with a robust electroabsorption effect in degenerate semiconductors. We numerically demonstrate an active electro-optical field-effect nanoplasmonic modulator with a revolutionary size of just 25 × 30 × 100 nm(3), providing signal extinction ratios as high as 2 at switching voltages of only 1 V. The design is compatible with complementary metal-oxide-semiconductor (CMOS) technology and allows low-loss insertion in standard plasmonic and Si-photonic circuitry.

Amplified spontaneous emission of surface plasmon polaritons and limitations on the increase of their propagation length.

Amplified spontaneous emission of surface plasmon polaritons (SPPs) at the interface of a resonant gain medium has been observed. The amplification is accompanied by significant spectral narrowing and limits the gain available for compensation of SPP propagation losses. The effect is similar to the deteriorating influence of amplified spontaneous emission in laser resonators.

Generation of traveling surface plasmon waves by free-electron impact.

The injection of a beam of free 50 keV electrons into an unstructured gold surface creates a highly localized source of traveling surface plasmons with spectra centered below the surface plasmon resonance frequency. The plasmons were detected by a controlled decoupling into light with a grating at a distance from the excitation point. The dominant contribution to the plasmon generation appears to come from the recombination of d-band holes created by the electron beam excitation.