Self-focusing and filamentation of optical vortex beams: Spatiotemporal analysis

We report numerical simulations supported by experimental observations of self-focusing, fillamentation, and supercontinuum generation by an optical vortex beam in a Kerr nonlinear medium in the regime of dominating nonlinearity. Despite the strong self-focusing resulting in multiple filaments ordered along the vortex ring the optical vortex remains well preserved at the exit of the nonlinear medium and in the far-field. The presented quasi-(3+1)- dimensional numerical simulations under azimuthal initial vortex ring perturbations confirm qualitatively the experimentally observed survival of the optical vortex in the course of the white light generation

Performance modelling of the Cambridge Fast Ring protocol

The Cambridge Fast Ring is high-speed slotted ring. The features that make it suitable for use at very large transmission rates are the synchronous transmission, the simplicity of the medium-access-control protocol, and the possibility of immediate retransmission of erroneous packets. A novel analytical model of the Cambridge Fast Ring with normal slots is presented. The model is shown to be accurate and usable over wide range of parameters. A performance analysis based on this model is presented

Laser system with an antiresonant optical ring

Various applications of an antiresonant ring, consisting of a beam splitter and a number of optical reflectors, are described. With a beam splitter having a transmission coefficient and a reflection coefficient, an optical beam incident on the beam splitter along a first axis is split into two components which circulate around the ring in opposite directions. They are recombined to reflect back the beam along the first axis, with none of the beam power being directed along a second axis. The ring can be part of the cavity of two otherwise independent lasers, with two separate laser mediums external to the ring, or with a multi-wavelength laser medium in the ring. The ring together with a second-harmonic generation crystal and a dispersive phase shifter in the ring can generate the second harmonic of an optical beam

Dynamics of ring dark solitons in Bose-Einstein condensates and nonlinear optics

Quasiparticle approach to dynamics of dark solitons is applied to the case of ring solitons. It is shown that the energy conservation law provides the effective equations of motion of ring dark solitons for general form of the nonlinear term in the generalized nonlinear Schroedinger or Gross-Pitaevskii equation. Analytical theory is illustrated by examples of dynamics of ring solitons in light beams propagating through a photorefractive medium and in non-uniform condensates confined in axially symmetric traps. Analytical results agree very well with the results of our numerical simulations.Comment: 10 pages, 4 figure

A thin ring model for the OH megamaser in IIIZw35

We present a model for the OH megamaser emission in the starburst galaxy IIIZw35. The observed diffuse and compact OH maser components in this source are explained by a single phase of unsaturated clumpy gas distributed in a thin ring structure and amplifying background continuum. We emphasize the importance of clumpiness in the OH masing medium, an effect that has not been fully appreciated previously. The model explains why multiple bright spots are seen only at the ring tangents while smoother emission is found elsewhere. Both the observed velocity gradients and the line to continuum ratios around the ring enquire a geometry where most of the seed photons come from a continuum emission which lies outside the OH ring. To explain both the OH and continuum brightness, free-free absorbing gas is required along the ring axis to partially absorb the far side of the ring. It is proposed that the required geometry arises from an inwardly propagating ring of starburst activity

Neutron star, β\beta-stable ring-diagram equation of state and Brown-Rho scaling

Neutron star properties, such as its mass, radius, and moment of inertia, are calculated by solving the Tolman-Oppenheimer-Volkov (TOV) equations using the ring-diagram equation of state (EOS) obtained from realistic low-momentum NN interactions $V_{low-k}$. Several NN potentials (CDBonn, Nijmegen, Argonne V18 and BonnA) have been employed to calculate the ring-diagram EOS where the particle-particle hole-hole ring diagrams are summed to all orders. The proton fractions for different radial regions of a $\beta$-stable neutron star are determined from the chemical potential conditions $\mu_n-\mu_p = \mu_e = \mu_\mu$. The neutron star masses, radii and moments of inertia given by the above potentials all tend to be too small compared with the accepted values. Our results are largely improved with the inclusion of medium corrections based on Brown-Rho scaling where the in-medium meson masses, particularly those of $\omega$, $\rho$ and $\sigma$, are slightly decreased compared with their in-vacuum values. Representative results using such medium corrected interactions are neutron star mass $M\sim 1.8 M_{\odot}$, radius $R\sim 9$ km and moment of inertia $\sim 60 M_{\odot}km^2$. The mass-radius trajectories given by the above four realistic NN potentials are by and large overlapping.Comment: 12.7 pages, 13 figures, 3 table

Magnonic crystal based forced dominant wavenumber selection in a spin-wave active ring

Spontaneous excitation of the dominant mode in a spin-wave active ring -- a self-exciting positive-feedback system incorporating a spin-wave transmission structure -- occurs at a certain threshold value of external gain. In general, the wavenumber of the dominant mode is extremely sensitive to the properties and environment of the spin-wave transmission medium, and is almost impossible to predict. In this letter, we report on a backward volume magnetostatic spin-wave active ring system incorporating a magnonic crystal. When mode enhancement conditions -- readily predicted by a theoretical model -- are satisfied, the ring geometry permits highly robust and consistent forced dominant wavenumber selection.Comment: 4 pages, 3 figure

Spatial Confinement Causes Lifetime Enhancement and Expansion of Vortex Rings with Positive Filament Tension

We study the impact of spatial confinement on the dynamics of three-dimensional excitation vortices with circular filaments. In a chemically active medium we observe a decreased contraction of such scroll rings and even expanding ones, despite of their positive filament tension. We propose a kinematical model which takes into account the interaction of the scroll ring with a confining Neumann boundary. The model reproduces all experimentally observed regimes of ring evolution, and correctly predicts the results obtained by numerical simulations of the underlying reaction-diffusion equations

A Novel Structure for Double Negative NIMs towards UV Spectrum with High FOM

A novel ring structure is proposed for double negative NIMs at visible light spectrum with high FOM (e.g. about 11 at a wavelength of 583 nm) and low loss. Besides the effective medium theory, an equivalent circuit model is also given to explain physically why our novel structure can give double negative behavior with low loss. Adapted from the original ring structure, two other types of structures, namely, disk and nanowire structures, are also given to further push double negative NIMs toward ultraviolet (UV) spectrum

Coherent oscillation by self‐induced gratings in the photorefractive crystal BaTiO_3

We report here the demonstration of several new optical oscillator configurations including a unidirectional ring oscillator and a self‐pumped phase conjugate mirror. The gain medium is BaTiO_3, pumped by a 632.8‐nm He‐Ne laser at power levels down to 50 μW