Electronically controlled surface plasmon dispersion and optical transmission through metallic hole arrays using liquid crystal.

The enhanced optical properties of metal films periodically perforated with an array of sub-wavelength size holes have recently been widely studied in the field of surface plasmon optics. The ability to design the optical transmission of such nanostructures, which act as plasmonic crystals, by varying their geometrical parameters gives them great flexibility for numerous applications in photonics, opto-electronics, and sensing. Transforming these passive optical elements into devices that may be actively controlled has presented a new challenge. Here, we report on the realization of an electrically controlled nanostructured optical system based on the unique properties of surface plasmon polaritonic crystals in contact with a liquid crystal (LC) layer. We discuss the effect of LC layer modulation on the surface plasmon dispersion, the related optical transmission and the underlying mechanism. The reported effect may be used to achieve active spectral tuneability and switching in a wide range of applications.

Quantum ground state of self-organized atomic crystals in optical resonators

Cold atoms, driven by a laser and simultaneously coupled to the quantum field of an optical resonator, may self-organize in periodic structures. These structures are supported by the optical lattice, which emerges from the laser light they scatter into the cavity mode and form when the laser intensity exceeds a threshold value. We study theoretically the quantum ground state of these structures above the pump threshold of self-organization by mapping the atomic dynamics of the self-organized crystal to a Bose-Hubbard model. We find that the quantum ground state of the self-organized structure can be the one of a Mott insulator, depending on the pump strength of the driving laser. For very large pump strengths, where the intracavity-field intensity is maximum and one would expect a Mott-insulator state, we find intervals of parameters where the phase is compressible. These states could be realized in existing experimental setups.

Fabrication of cerium oxide nanoparticles: Characterization and optical properties

Ceria (CeO2) is a technologically important rare earth material because of its unique properties and various engineering and biological applications. A facile and rapid method has been developed to prepare ceria nanoparticles using microwave with the average size 7 nm in the presence of a set of ionic liquids based on the bis (trifluoromethylsulfonyl) imide anion and different cations of 1-alkyl-3-methyl-imidazolium. The structural features and optical properties of the nanoparticles were determined in depth with X-ray powder diffraction, transmission electron microscope, N-2 adsorption-desorption technique, dynamic light scattering (DLS) analysis, FTIR spectroscopy, Raman spectroscopy, UV-vis absorption spectroscopy, and Diffuse reflectance spectroscopy. The energy band gap measurements of nanoparticles of ceria have been carried out by UV-visible absorption spectroscopy and diffuse reflectance spectroscopy. The surface charge properties of colloidal ceria dispersions in ethylene glycol have been also studied. To the best of our knowledge, this is the first report on using this type of ionic liquids in ceria nanoparticle synthesis. (C) 2011 Elsevier Inc. All rights reserved.

CO and optical observations of the Magellanic Bridge

We present (CO)-C-12(1-0) molecular line and BV CCD observations towards 0311-7651: a region in the Magellanic Bridge where cold atomic Hydrogen has previously been detected by Kobulnicky & Dickey: Additionally, BV images of a comparison held 1 degrees to the South were taken. No CO was detected to a limit of similar to 0.06 Kelvin, and the colour-magnitude diagrams show no evidence for a stellar association in either field.

HI and optical spectroscopy towards the M15 intermediate- velocity cloud

We present single-dish Arecibo 21-cm H i observations, covering a 0 degrees 675x0 degrees 625 RA-Dec. grid, of the intermediate-velocity cloud (IVC) centred upon the M15 globular cluster. The velocity and positional structure of the IVC gas at V-LSR=70 km s(-1) are investigated; it is found to be clumpy and has a peak surface density N(H i)similar to 8x10(19) cm(- 2). Additionally, we have performed a long H i integration towards HD 203664, a Galactic halo star some 3 degrees1 from M15, in which optical IVC absorption has previously been detected. No H i with a velocity exceeding 60 km s(-1) was found to a brightness temperature limit of 0.05 K. However, additional pointings did detect IVC gas approximately mid-way between HD 203664 and M15. Finally, we present both Arecibo H i pointings and low-resolution spectra in the Ca ii H and K lines towards 15 field stars in the general field towards M15, in an attempt to obtain the distance to the IVC. Intermediate- velocity H i is detected towards seven sightlines. Stellar spectral types are derived for 12 of the sample. Assuming that these stars lie on the main sequence, their distances are estimated to lie in the range 150 less than or equal tod less than or equal to 1350 pc. No Ca ii absorption is observed, either because the IVC is further away than similar to 1350 pc or more likely because the gas along these sightlines is of too low a density to be detected by the current observations.

Computational challenges in atomic, molecular and optical physics

Six challenges are discussed. These are the laser-driven helium atom; the laser-driven hydrogen molecule and hydrogen molecular ion: electron scattering (with ionization) from one-electron atoms; the vibrational and rotational structure of molecules such as H-3(+) and water at their dissociation limits; laser- heated clusters; and quantum degeneracy and Bose-Einstein condensation. The first four concern fundamental few-body systems where use of high-performance computing (HPC) is currently making possible accurate modelling from first principles. This leads to reliable predictions and support for laboratory experiment as well as true understanding of the dynamics. Important aspects of these challenges addressable only via a terascale facility are set out. Such a facility makes the last two challenges in the above list meaningfully accessible for the first time, and the scientific interest together with the prospective role for HPC in these is emphasized.

Determination of absolute configuration of conformationally flexible cis-dihydrodiol metabolites: Effect of diene substitution pattern on the circular dichroism spectra and optical rotations

Absolute configurations of a number of cis-dihydrodiols (cis-1,2-dihydroxy-3,5-cyclohexadienes), synthetically useful products of TDO-catalyzed dihydroxylations of 1,2- and 1,3-disubstituted benzene derivatives, have been determined by a comparison of calculated and experimental CD spectra and optical rotations and by methods involving X-ray crystallography, H-1 NMR spectra of diastereoisomeric derivatives, and by stereochemical correlations. The computations disclosed a significant effect of the substituents on conformational equilibria of cis-dihydrodiols and chiroptical properties of individual conformers. The assigned absolute configurations of cis-dihydrodiols have allowed the validity of a simple predictive model for TDO-catalyzed arene dihydroxylations to be extended.

Absolute configuration of conformationally flexible cis-dihydrodiol metabolites by the method of confrontation of experimental and calculated electronic CD spectra and optical rotations

We have determined the absolute configurations of conformationally flexible cis-dihydrodiol metabolites (cis-1,2-dihydroxy-3,5-cyclohexadienes), bearing different substituents (e.g., Br, F, CF3, CN, Me) in 3- and 5-positions, by the method of confrontation of experimental and calculated electronic CD spectra and optical rotations. Convergent results were obtained by both methods in eight out of ten cases. For the difficult cases, where either conformer population and/or chiroptical properties (calculated rotational strengths of the long-wavelength Cotton effect or optical rotations) of contributing conformers remain inconclusive, the absolute configuration could still be correctly assigned based on one of the biased properties (either ECD or optical rotation). This approach appears well-suited for a broad spectrum of conformationally flexible chiral molecules.

Electrical, Thermal and Optical Diagnostics of an Atmospheric Plasma Jet System

Plasma diagnostics of atmospheric plasmas is a key tool in helping to understand processing performance issues. This paper presents an electrical, optical and thermographic imaging study of the PlasmaStream atmospheric plasma jet system. The system was found to exhibit three operating modes; one constricted/localized plasma and two extended volume plasmas. At low power and helium flows the plasma is localized at the electrodes and has the electrical properties of a corona/filamentary discharge with electrical chaotic temporal structure. With increasing discharge power and helium flow the plasma expands into the volume of the tube, becoming regular and homogeneous in appearance. Emission spectra show evidence of atomic oxygen, nitric oxide and the hydroxyl radical production. Plasma activated gas temperature deduced from the rotational temperature of nitrogen molecules was found to be of order of 400 K: whereas thermographic imaging of the quartz tube yielded surface temperatures between 319 and 347 K.

Correlation Between the Electrical and Optical Properties of an Atmospheric Pressure Plasma During Siloxane Coating Deposition

The effect of varying process parameters on atmospheric plasma characteristics and properties of nanometre thick siloxane coatings is investigated in a reel-to-reel deposition process. Varying plasma operation modes were observed with increasing applied power for helium and helium/oxygen plasmas. The electrical and optical behaviour of the dielectric barrier discharge were determined from current/voltage, emission spectroscopy and time resolved light emission measurements. As applied power increased, multiple discharge events occurred, producing a uniform multi-peak pseudoglow discharge, resulting in an increase in the discharge gas temperature. The effects of different operating modes on coating oxidation and growth rates were examined by injecting hexamethyldisiloxane liquid precursor into the chamber under varying operating conditions. A quenching effect on the plasma was observed, causing a decrease in plasma input power and emission intensity. Siloxane coatings deposited in helium plasmas had a higher organic component and higher growth rates than those deposited in helium/oxygen plasmas.