Yury N. Kulchin

Tailored hybrid hyperbranched polyglycidol-silica nanocomposites with high third-order nonlinearity

One of the most convenient techniques for optical material fabrication is the sol–gel processing. It can be performed at low temperature that enables one to entrap even relatively unstable organic substances into silica matrix at the nanometer scale, thus developing homogeneous hybrid organic–inorganic nanocomposite materials of various functionalities. Here, novel hybrid organic–inorganic nanocomposites with good optical transparency and high third-order nonlinearity were prepared biomimetically through the mineralization of dendritic macromolecules (hyperbranched polyglycidols) using a compatible ethylene glycol-containing silica precursor. The synthesis was performed at neutral pH media in aqueous solutions without addition of organic solvents at ambient conditions owing to the catalysis of processing. Polyglycidols provided also the formation of gold nanoparticles localized in their core. They served as reducing and stabilizing agents. It is shown that trace amounts of nanoparticles could regulate nonlinear properties of a nanocomposite. High nonlinearity manifests itself in a supercontinuum generation at remarkably short lengths ca. 1 mm. The phenomenon consists of filamentous intense white lighting due to the spectral broadening of initial ultrashort (femtosecond) laser pulses propagating through the material. The developed hybrid nanocomposites possessing large nonlinearity, high-speed optical response, stability under intense lighting, low-cost, and easy preparation are promising for a diverse range of applications as active components for all-optical signal processing from chemical sensing to biological cell imaging and lighting control in telecommunication.

Pulse-width-dependent surface ablation of copper and silver by ultrashort laser pulses

The single-shot spallation thresholds for copper and silver surfaces demonstrate a considerable IR-laser (1030 nm) pulse-width dependent increase over a range of 0.2–12 ps for the former material and a very weak increase for the latter one, while the corresponding thresholds for visible (515 nm) laser pulses remain almost constant. The IR-laser increase of the ablation thresholds is related to two-photon interband (d–s) absorption in copper, contrasting with the linear absorption of visible laser pulses in this material. In silver, common weakly sublinear dependences on the laser pulsewidth were observed, ruling out possible multi-photon—either three(four)-photon in IR, or two-photon in the visible range—interband transitions in this material. Moreover, electron-lattice thermalization times of 1–2 ps were evaluated for these materials in the spallative ablation regime, contrasting strongly with the previously theoretically predicted multi-picosecond thermalization times.

Green synthesis of silver nanoparticles using transgenic Nicotiana tabacum callus culture expressing silicatein gene from marine sponge Latrunculia oparinae

Abstract In the present investigation, transgenic tobacco callus cultures and plants overexpressing the silicatein gene LoSilA1 from marine sponge Latrunculia oparinae were obtained and their bioreduction behaviour for the synthesis of silver nanoparticles (AgNPs) was studied. Synthesized nanoparticles were characterized using UV–visible spectroscopy, Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic flame electron microscopy (AFM) and nanoparticle tracking analysis (NTA). Our measurements showed that the reduction of silver nitrate produced spherical AgNPs with diameters in the range of 12–80 nm. The results of XRD analysis proved the crystal nature of the obtained AgNPs. FTIR analysis indicated that particles are reduced and stabilized in solution by the capping agent, which is likely to be proteins present in the callus extract. Interestingly, the reduction potential of LoSiLA1-transgenic callus line was increased three-fold compared with the empty vector-transformed calli. The synthesized AgNPs were found to exhibit strong antibacterial activity against Escherichia coli and Agrobacterium rhizogenes. The present study reports the first evidence for using genetic engineering for activation of the reduction potential of plant cells for synthesis of biocidal AgNPs.

Fiber-optic Fabry-Perot microresonator for near-field optical microscopy systems

The possibility of developing a new type of interferometric near-field aperture probe for near-field optical microscopy using a fiber-optic Fabry-Perot microresonator with a nanosized orifice formed in one of its output mirrors has been studied theoretically and experimentally. It is shown, both theoretically and experimentally, that this method provides a spatial resolution of no worse than λ/30.

On-demand concentration of analyte on laser-printed polytetrafluoroethylene

Controllable targeted deposition of an analyte dissolved in a liquid drop evaporating on a superhydrophobic surface has recently emerged as a promising concentrator approach with various applications ranging from ultrasensitive bioidentification to DNA molecule sorting. Here, we demonstrate that surface textures with non-uniform wettability fabricated using direct easy-to-implement femtosecond-pulse filament-assisted ablation of polytetrafluoroethylene substrates can be used to concentrate and deposit an analyte at a designated location out of a water droplet. The proposed surface textures contain a central superhydrophilic trap surrounded by superhydrophobic periodically arranged pillars with a hierarchical roughness. By optimizing the arrangement and geometry of the central trap and the surrounding superhydrophobic textures, the analyte dissolved in a 5 μL water drop was fixed onto a 90 × 90 μm2 target. The proposed textures provide a concentration factor of 103, an order of magnitude higher than those for the previously reported surface textures. This promising ultrasensitive versatile platform allows the detection of fingerprints of the deposited analyte via surface-enhanced spectroscopy techniques (Raman scattering or photoluminescence) at an estimated detection threshold better than 10-15 mol L-1.

The spectrum of a bent fiber Fabry-Perot interferometer under small variations of the refractive index of the environment

The phase of light propagating through a bent optical fibre is shown to depend on the refractive index of the medium surrounding the fibre cladding when there is resonance coupling between the guided core mode and cladding modes. This shifts the spectral maxima in the bent fibre-optic Fabry-Perot interferometer. The highest phase and spectral sensitivities achieved with this interferometer configuration are 0,71 and 0,077, respectively, and enable changes in the refractive index of the ambient medium down to 5·10-6 to be detected. This makes the proposed approach potentially attractive for producing highly stable, precision refractive index sensors capable of solving a wide range of liquid refractometry problems.

Distinctive Features of Air Flow Through Large-Scale Floating Wind Turbine

This paper presents new results in the research and development of recently proposed design of the offshore wind power plant with large-scale floating turbine (WEMU design). The main objective of this study is to investigate the vertical vortex inside the turbine, flow interaction with the turbine due to the pitch caused by waves, and to estimate the additional pitching moment. Numerical experiments for new geometrical model design of rotor are carried out using simulation tools based on a finite volume method. Two stable vortexes are found between the upper and low rings, which connect the blades along vertical direction. Additionally, nonlinear equations for the floating rotor equilibrium are solved by an iterative Newton method. The floating rotor is proved to have sufficient stability.

Tomographic distributed fiber measuring networks for reconstructing the distributions of scalar and vector physical fields

The approaches to the development of distributed networks, consisting of fiber optic measuring lines with integral sensitivity is considered. A problem of tomography reconstruction of scalar and vector physical fields parameters by this network signals is discussed.