arXiv subjects

Larry Velasco

Publications and source records attributed to Larry Velasco.

7 recordsLinked to original sources

arXiv2006

Dissipative magneto-optic solitons

Magneto-optic behaviour is a specific, non-reciprocal example of gyrotropic behaviour. When coupled to photo-induced Faraday rotation it is possible to discriminate this effect from the background of other nonlinear effects Non-reciprocal behaviour is characteristic of artificial gyrotropy and can be used in optical isolators and a range of coherence and quantum problems. This is all in sharp contrast to natural gyrotropy, like optical activity. it is also important to go beyond third-order, Kerr, optical nonlinearity and move towards a saturable model of terms in the polarisation. In this spirit, this chapter seeks to determinate the influence of a magneto-optic presence upon an optically nonlinear material that is modelled by a cubic-quintic form of polarisation. In addition, the coefficients of the envelope equation will be made complex, to take into account both linear and nonlinear damping and cubic gain processes. The emphasis is upon the simulation outcomes, however, rather the applications.

cond-mat.soft↗

arXiv2006

Gyrotropic impact upon negatively refracting surfaces

Surface wave propagation at the interface between different types of gyrotropic materials and an isotropic negatively refracting medium, in which the relative permittivity and relative permeability are, simultaneously, negative is investigated. A general approach is taken that embraces both gyroelectric and gyromagnetic materials, permitting the possibility of operating in either the low GHz, THz or the optical frequency regimes. The classical transverse Voigt configuration is adopted and a complete analysis of non-reciprocal surface wave dispersion is presented. The impact of the surface polariton modes upon the reflection of both plane waves and beams is discussed in terms of resonances and an example of the influence upon the Goos-Hanchen shift is given.

cond-mat.mtrl-sci↗

arXiv2006

Ultra-narrow Bright Spatial Solitons Interacting with Left-handed Surfaces

A vectorial FDTD method is used to present a numerical study of very narrow spatial solitons interacting with the surface of what has become known as a left-handed medium. After a comprehensive discussion of the background and the family of surface modes to be expected on a left-handed material, bounded by dispersion-free right-handed material, it is demonstrated that robust outcomes of the FDTD approach yield dramatic confirmation of these waves. The FDTD results show how the linear and nonlinear surface modes are created and can be tracked in time as they develop. It is shown how they can move backwards, or forwards, depending either upon a critical value of the local nonlinear conditions at the interface, or the ambient linear conditions. Several examples are given to demonstrate the power and versatility of the method, and the sensitivity to the launching conditions.

cond-mat.mtrl-sci↗

arXiv2006

Control of planar nonlinear guided waves and spatial solitons with a left-handed medium

The evidence that double negative media, with an effective negative permittivity, and an effective negative permeability, can be manufactured to operate at frequencies ranging from microwave to optical is ushering in a new era of metamaterials. They are referred to here as 'left-handed', even though a variety of names is evident from the literature. In anticipation of a demand for highly structured integrated practical waveguides, this paper addresses the impact of this type of medium upon waveguides that can be also nonlinear. After an interesting historical overview and an exposure of some straightforward concepts, a planar guide is investigated, in which the waveguide is a slab consisting of a left-handed medium sandwiched between a substrate and cladding that are simple dielectrics. The substrate and cladding display a Kerr-type nonlinear response. Because of the nonlinear properties of the Kerr media, the power flow direction can be controlled by the intensity of the electric field. A comprehensive finite-difference-time-domain (FDTD) analysis is presented that concentrates upon spatial soliton behaviour. An interesting soliton-lens arrangement is investigated that lends itself to a novel cancellation effect.

cond-mat.mtrl-sci↗

arXiv2006

Excitation of vortices using linear and nonlinear magnetostatic waves

It is shown that stationary vortex structures can be excited in a ferrite film. This is the first proposal for creating vortex structures in the important cm and mm wavelength ranges. It is shown that both linear and nonlinear structures can be excited using a three-beam interaction created with circular antennae. These give rise to a special phase distribution created by linear and nonlinear mixing. An interesting set of three clockwise rotating vortices joined by one counter-rotating one presents itself in the linear regime: a scenario that is only qualitatively changed by the onset of nonlinearity. It is pointed out that control of the vortex structure, through parametric coupling, based upon a microwave resonator, is possible and that there are many interesting possibilities for applications.

cond-mat.mtrl-sci↗

arXiv2006

Gyroelectric cubic-quintic dissipative solitons

The influence of an externally applied magnetic field upon classic cubic quintic dissipative solitons is investigated using both exact simulations and a Lagrangian technique. The basic approach is to use a spatially inhomogeneous magnetic field and to consider two important geometries, namely the Voigt and the Faraday effects. A layered structure is selected for the Voigt case with the principal aim being to demonstrate non-reciprocal behaviour for various classes of spatial solitons that are known to exist as solutions of the complex Ginzburg-Landau cubic-quintic envelope equation under dissipative conditions. The system is viewed as dynamical and an opportunity is taken to display the behaviour patterns of the spatial solitons in terms of two-dimensional dynamical plots involving the total energy and the peak amplitude of the spatial solitons. This action this leads to limit cycle plots that beautifully reveal the behaviour of the solitons solutions at all points along the propagation axis. The closed contour that exists in the absence of a magnetic field is opened up and a limit point is exposed. The onset of chaos is revealed in a dramatic way and it is clear that detailed control by the external magnetic field can be exercised. The Lagrangian approach is adjusted to deal with dissipative systems and through the choice of particular trial functions, aspects of the dynamic behaviour of the spatial are predicted by this approach. Finally, some vortex dynamics in the Faraday configuration are investigated.

physics.optics↗

arXiv2005

Negative Refraction in Perspective

The concept of negative refraction is attracting a lot of attention. The initial ideas and the misconceptions that have arisen are discussed in sufficient detail to understand the conceptual structure that binds negative refraction to the existence of backward wave and forward wave phenomena. A presentation of the properties of isotropic media supporting backward waves is followed by a discussion of negative phase velocity media, causality, anisotropic crystals and some connections to photonic crystals. The historical background is always coupled to a detailed presentation of all the issues. The paper is driven numerically and is illustrated with the outcomes of original FDTD simulations.

cond-mat.mtrl-sci↗