Stable multiple-charged localized optical vortices in cubic-quintic nonlinear media

The stability of two-dimensional bright vortex solitons in a media with focusing cubic and defocusing quintic nonlinearities is investigated analytically and numerically. It is proved that above some critical beam powers not only one- and two-charged but also multiple-charged stable vortex solitons do exist. A vortex soliton occurs robust with respect to symmetry-breaking modulational instability in the self-defocusing regime provided that its radial profile becomes flattened, so that a self-trapped wave beam gets a pronounced surface. It is demonstrated that the dynamics of a slightly perturbed stable vortex soliton resembles an oscillation of a liquid stream having a surface tension. Using the idea of sustaining effective surface tension for spatial vortex soliton in a media with competing nonlinearities the explanation of a suppression of the modulational instability is proposed.Comment: 4 pages, 3 figures. Submitted to Journal of Optics A. The proceedings of the workshop NATO ARW, Kiev 2003 Singular Optics 200

New types of stable nonlinear whistler waveguides

International audienceThe stationary self-focusing of whistler waves with frequencies near half of the electron-cyclotron frequency in the ionospheric plasma is considered in the framework of a two-dimensional generalized nonlinear Schrödinger equation including fourth-order dispersion effects and nonlinearity saturation. New types of soliton-like (with zero topological charge) and vortex-like nonlinear waveguides are found, and their stability confirmed both analytically and numerically

High Field Anomalies of Equilibrium and Ultrafast Magnetism in Rare-Earth-Transition Metal Ferrimagnets

Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in the equilibrium and ultrafast magnetic properties of the ferrimagnetic rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the magnetization compensation temperature, each of the magnetizations of the antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis loops. Contrary to state-of-the-art theory, which explains such loops by sample inhomogeneities, here we show that they are an intrinsic property of the rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and have a non-zero orbital momentum in the ground state and, therefore, a large magnetic anisotropy, we are able to reproduce the experimentally observed behavior in equilibrium. The same theory is also able to describe the experimentally observed critical slowdown of the spin dynamics in the vicinity of the magnetization compensation temperature, emphasizing the role played by the orbital momentum in static and ultrafast magnetism of ferrimagnets

H-T Phase Diagram of Rare-Earth -- Transition Metal Alloy in the Vicinity of the Compensation Point

Anomalous hysteresis loops of ferrimagnetic amorphous alloys in high magnetic field and in the vicinity of the compensation temperature have so far been explained by sample inhomogeneities. We obtain H-T magnetic phase diagram for ferrimagnetic GdFeCo alloy using a two-sublattice model in the paramagnetic rare-earth ion approximation and taking into account rare-earth (Gd) magnetic anisotropy. It is shown that if the magnetic anisotropy of the $f$-sublattice is larger than that of the $d$-sublattice, the tricritical point can be at higher temperature than the compensation point. The obtained phase diagram explains the observed anomalous hysteresis loops as a result of high-field magnetic phase transition, the order of which changes with temperature. It also implies that in the vicinity of the magnetic compensation point the shape of magnetic hysteresis loop is strongly temperature dependent.Comment: 8 pages, 3 figure

Selection Rules for All-Optical Magnetic Recording in Iron Garnet

Finding an electronic transition a subtle excitation of which can launch dramatic changes of electric, optical or magnetic properties of media is one of the long-standing dreams in the field of photo-induced phase transitions [1-5]. Therefore the discovery of the magnetization switching only by a femtosecond laser pulse [6-10] triggered intense discussions about mechanisms responsible for these laser-induced changes. Here we report the experimentally revealed selection rules on polarization and wavelengths of ultrafast photo-magnetic recording in Co-doped garnet film and identify the workspace of the parameters (magnetic damping, wavelength and polarization of light) allowing this effect. The all-optical magnetic switching under both single pulse and multiple-pulse sequences can be achieved at room temperature, in narrow spectral ranges with light polarized either along or crystallographic axes of the garnet. The revealed selection rules indicate that the excitations responsible for the coupling of light to spins are d-electron transitions in octahedral and tetrahedral Co-sublattices, respectively

Educational research networks principles of organization

Relevance. Modern society has global transformations; as a result, the level characteristics of its system development are changing, new opportunities and new situations to implement a self-organizing system to solve problems of self-government appear. Thus, there is the need to organize the multiplicity of interactions in the new environment, including education. The success of the development mechanisms, organizing innovative activities in the educational systems of different levels is largely determined by the active development of interaction network forms and interaction effective management. The article is devoted to development of theoretical ideas about the processes of network interaction in education to justify and describe the principles of modern scientific-educational network on the basis of system-synergetic approach. A leading approach to study this problem can be considered as system-synergetic which allows studying network interaction within the scientific and educational network as a holistic entity consisting of interrelated elements, structured and complex. The results of the study showed that described principles of effective networking and the conditions of scientific and educational networks development allow you to combine and re-combine the accumulated actors of this knowledge and practical experience interaction, turning them into the means of its innovative activities. The article can be useful to heads of educational institutions of different levels, as well as researchers of innovative processes development problems in education. © 2018 Authors