Second harmonic generation from metallic arrays of rectangular holes

The generation process of second harmonic (SH) radiation from holes periodically arranged on a metal surface is investigated. Three main modulating factors affecting the optical response are identified: the near-field distribution at the wavelength of the fundamental harmonic, how SH light couples to the diffraction orders of the lattice, and its propagation properties inside the holes. It is shown that light generated at the second harmonic can excite electromagnetic modes otherwise inaccessible in the linear regime under normal incidence illumination. It is demonstrated that the emission of SH radiation is only allowed along off-normal paths precisely due to that symmetry. Two different regimes are studied in the context of extraordinary optical transmission, where enhanced linear transmission either occurs through localized electromagnetic modes or is aided by surface plasmon polaritons (SPPs). While localized resonances in metallic hole arrays have been previously investigated, the role played by SPPs in SH generation has not been addressed so far. In general, good agreement is found between our calculations (based on the finite difference time domain method) and the experimental results on localized resonances, even though no free fitting parameters were used in describing the materials. It is found that SH emission is strongly modulated by enhanced fields at the fundamental wavelength (either localized or surface plasmon modes) on the glass metal interface. This is so in the transmission side but also in reflection, where emission can only be explained by an efficient tunneling of SH photons through the holes from the output to the input side. Finally, the existence of a dark SPP at the fundamental field is identified through a noninvasive method for the first time, by analyzing the efficiency and far-field pattern distribution in transmission at the second harmonic.Comment: This paper was published in JOSA B and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/josab/abstract.cfm?URI=josab-32-1-15. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under la

Estudio preliminar sobre el efecto del ultrasonido en las propiedades fisicoquímicas del vino tinto

Ultrasound is regarded as a potential alternative method for improving the quality of some wines. This study was initiated with the objective of evaluating the effects of ultrasound on some important physicochemical properties of red wine such as chromatic characteristics (CC), electrical conductivity (EC), pH, titratable acidity (TA), total phenolic compounds (TPCs) and DPPH (1,1-diphenyl-2-picryl-hydrazyl) free radical scavenging activity (DFRSA). The operational parameters assessed were ultrasound power, ultrasound frequency, exposure time and bath temperature. Results illustrated that there were significant changes in CC, EC and TPC while pH and TA hardly changed except for samples treated at high temperatures. DFRSA was correlated to TPC during ultrasonic treatment. Application of principal component analysis to the experimental data suggested that exposure time was the factor with the greatest ability to induce changes on wine. Results suggested that ultrasound may be applied to improve some physicochemical properties of red wine.El ultrasonido se considera uno de los métodos alternativos potenciales para mejorar la calidad de algunos vinos. Se comenzó este estudio con el objetivo de evaluar los efectos del ultrasonido en algunas de la propiedades fisicoquímicas importantes del vino tinto como son: las características cromáticas (CC), la conductividad eléctrica (EC), el pH, la acidez (TA), los compuestos fenólicos totales (TPC) y el DPPH (1,1-difenil-2-picrilhidrazil) de actividad de eliminación de radicales libres (DFRSA). Los parámetros operacionales examinados fueron: la potencia de ultrasonido, la frecuencia de ultrasonido, el tiempo de exposición y la temperatura de baño. Los resultados ilustraron la existencia de cambios significativos en CC, EC y TPC, mientras que el pH y TA prácticamente no cambiaron excepto en las muestras tratadas con altas temperaturas. DFRSA tuvo correlación con TPC durante el tratamiento con ultrasonido. La aplicación de análisis de componentes principales a los datos experimentales sugirió que el tiempo de exposición era el factor con mayor habilidad para inducir cambios en el vino. Los resultados sugirieron que el ultrasonido podría aplicarse para mejorar algunas de las propiedades fisicoquímicas del vino tinto.National Natural Science Foundation of China [No. 31101324]Natural Science Foundation of Shaanxi Province, China [No. 2015JM3097]Technology Transfer Promotion Project of Xi’an, Shaanxi Province, China [No.CXY1434(5)]Fundamental Research Funds for the Central Universities of China [Nos. GK201302039, GK201404006

A possible third component in the L dwarf binary system DENIS-P J020529.0-115925 discovered with the Hubble Space Telescope

We present results showing that the multiple system DENIS-P J020529.0-115925 is likely to be a triple system of brown dwarfs. The secondary of this previously known binary system shows a clear elongation on six images obtained at six different epochs. Significant residuals remain after PSF subtraction on these images, characteristic of multiplicity, and indicating that the secondary is probably a double itself. Dual-PSF fitting shows that the shape of the secondary is consistent with that of a binary system. These measurements show that the probability that DENIS-P J020529.0-115925 is a triple system is very high. The photometric and spectroscopic properties of the system are consistent with the presence of three components with spectral types L5, L8 and T0.Comment: 15 pages, 3 tables, 6 figures, accepted for publication in AJ. High resolution version available at ftp://ftp.mpe.mpg.de/people/hbouy/publications/denis0205.ps.g

Phase diagram of a polydisperse soft-spheres model for liquids and colloids

The phase diagram of soft spheres with size dispersion has been studied by means of an optimized Monte Carlo algorithm which allows to equilibrate below the kinetic glass transition for all sizes distribution. The system ubiquitously undergoes a first order freezing transition. While for small size dispersion the frozen phase has a crystalline structure, large density inhomogeneities appear in the highly disperse systems. Studying the interplay between the equilibrium phase diagram and the kinetic glass transition, we argue that the experimentally found terminal polydispersity of colloids is a purely kinetic phenomenon.Comment: Version to be published in Physical Review Letter

Nonlinear emission dynamics of a GaAs microcavity with embedded quantum wells

The emission dynamics of a GaAs microcavity at different angles of observation with respect to the sample normal under conditions of nonresonant picosecond-pulse excitation is measured. At sufficiently high excitation densities, the decay time of the lower-polariton emission increases with the polariton wavevector; at low excitation densities the decay time is independent of the wavevector. The effect of additional nonresonant continuous illumination on the emission originating from the bottom of the lower polariton branch is investigated. The additional illumination leads to a substantial increase in the emission intensity (considerably larger than the intensity of the photoluminescence excited by this illumination alone). This fact is explained in terms of acceleration of the polariton relaxation to the radiative states due to scattering by charge carriers created by the additional illumination. The results obtained show, that at large negative detunings between the photon and exciton modes, polariton-polariton and polariton-free carrier scattering are the main processes responsible for the filling of states near the bottom of the lower polariton branch.Comment: 10 pages, 6 figures. This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics: Condesed Matter. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Order in driven vortex lattices in superconducting Nb films with nanostructured pinning potentials

Driven vortex lattices have been studied in a material with strong pinning, such as Nb films. Samples in which natural random pinning coexists with artificial ordered arrays of defects (submicrometric Ni dots) have been fabricated with different geometries (square, triangular and rectangular). Three different dynamic regimes are found: for low vortex velocities, there is a plastic regime in which random defects frustrate the effect of the ordered array; then, for vortex velocities in the range 1-100 m/s, there is a sudden increase in the interaction between the vortex lattice and the ordered dot array, independent on the geometry. This effect is associated to the onset of quasi long range order in the vortex lattice leading to an increase in the overlap between the vortex lattice and the magnetic dots array. Finally, at larger velocities the ordered array-vortex lattice interaction is suppresed again, in agreement with the behavior found in numerical simulations.Comment: 8 text pages + 4 figure

Universal features of electron-phonon interactions in atomic wires

The effect of electron-phonon interactions in the conductance through metallic atomic wires is theoretically analyzed. The proposed model allows to consider an atomic size region electrically and mechanically coupled to bulk electrodes. We show that under rather general conditions the features due to electron-phonon coupling are described by universal functions of the system transmission coefficients. It is predicted that the reduction of the conductance due to electron-phonon coupling which is observed close to perfect transmission should evolve into an enhancement at low transmission. This crossover can be understood in a transparent way as arising from the competition between elastic and inelastic processes.Comment: 5 pages, 5 figure

Separation and fractionation of order and disorder in highly polydisperse systems

Microcanonical Monte Carlo simulations of a polydisperse soft-spheres model for liquids and colloids have been performed for very large polydispersity, in the region where a phase-separation is known to occur when the system (or part of it) solidifies. By studying samples of different sizes, from N=256 to N=864, we focus on the nature of the two distinct coexisting phases. Measurements of crystalline order in particles of different size reveal that the solid phase segregates between a crystalline solid with cubic symmetry and a disordered phase. This phenomenon is termed fractionation.Comment: 8 pages, 5 figure

Perturbation expansion for 2-D Hubbard model

We develop an efficient method to calculate the third-order corrections to the self-energy of the hole-doped two-dimensional Hubbard model in space-time representation. Using the Dyson equation we evaluate the renormalized spectral function in various parts of the Brillouin zone and find significant modifications with respect to the second-order theory even for rather small values of the coupling constant U. The spectral function becomes unphysical for $U \simeq W$, where W is the half-width of the conduction band. Close to the Fermi surface and for U<W, the single-particle spectral weight is reduced in a finite energy interval around the Fermi energy. The increase of U opens a gap between the occupied and unoccupied parts of the spectral function.Comment: 17 pages, 11 Postscript figures, Phys. Rev. B, accepte

Equilibrium fluid-solid coexistence of hard spheres

We present a tethered Monte Carlo simulation of the crystallization of hard spheres. Our method boosts the traditional umbrella sampling to the point of making practical the study of constrained Gibb's free energies depending on several crystalline order-parameters. We obtain high-accuracy estimates of the fluid-crystal coexistence pressure for up to 2916 particles (enough to accommodate fluid-solid interfaces). We are able to extrapolate to infinite volume the coexistence pressure (p_{co}=11.5727(10) k_B T/\sigma^3) and the interfacial free energy (\gamma_{100}=0.636(11) k_B T/\sigma^2).Comment: 6 pages, 4 pdf figures. Version to be published in PRL. Appendices contain Supplemental Materia