Algebraic bright and vortex solitons in defocusing media

We demonstrate that spatially inhomogeneous defocusing nonlinear landscapes with the nonlinearity coefficient growing toward the periphery as (1+|r|(α)) support one- and two-dimensional fundamental and higher-order bright solitons, as well as vortex solitons, with algebraically decaying tails. The energy flow of the solitons converges as long as nonlinearity growth rate exceeds the dimensionality, i.e., α>D. Fundamental solitons are always stable, while multipoles and vortices are stable if the nonlinearity growth rate is large enough.     

On the influence of the electron-velocity spread in a beam on the mechanism of Cherenkov beam–plasma interaction

The instability of an electron beam in cold plasma is considered in the linear potential approximation with different velocity-distribution functions of beam electrons. It is demonstrated that the mechanism of beam instability in plasma changes as the electron-velocity spread is increased: the hydrodynamic single-particle instability mode evolves into the hydrodynamic collective mode or the single-particle kinetic one. Instability growth rates in different modes are determined analytically and numerically.     

Soliton control in fading optical lattices

We predict new phenomena, such as soliton steering and soliton fission, in optical lattices that fade away exponentially along the propagation direction. Such lattices, featuring tunable decay rates, arise in photorefractive crystals in the wavelength range 360-400 nm. We show that the predicted phenomena offer different opportunities for soliton control.     

Multipole-mode surface solitons

We discover multipole-mode solitons supported by the surface between two distinct periodic lattices imprinted in Kerr-type nonlinear media. Such solitons are possible because the refractive index modulation at both sides of the interface glues together their out-of-phase individual constituents. Remarkably, we find that the new type of solitons may feature highly asymmetric shapes, and yet they are stable over wide domains of their existence, a rare property to be attributed to their surface nature.     

Two-dimensional multipole solitons in nonlocal nonlinear media

We present the experimental observation of scalar multipole solitons in highly nonlocal nonlinear media, including dipole, tripole, quadrupole, and necklace-type solitons, organized as arrays of out-of-phase bright spots. These complex solitons are metastable, but with a large parameters range where the instability is weak, permitting their experimental observation.     

Surface gap solitons

We put forward the existence of surface gap solitons at the interface between uniform media and an optical lattice with defocusing nonlinearity. Such new type of solitons forms when the incident and reflected waves at the interface of the lattice experience Bragg scattering, and feature a combination of the unique properties of both surface waves and gap solitons. We discover that gap surface solitons exist only when the lattice depth exceeds a threshold value, that they can be made completely stable, and that they can form stable bound states.     

Tunable ultrafast nonlinear optofluidic coupler

We present an optofluidic nonlinear coupler fabricated by selective filling of two strands of a photonic crystal fiber with the liquid CCl4 which exhibits a large ultrafast Kerr nonlinearity. We demonstrate power dependent switching in this novel optofluidic device. The large thermo-optical effect of liquids enables us to tune the behavior of the nonlinear coupler by changing the coupling strength with temperature. This opens the road towards flexible designs and realization of a new class of tunable ultrafast nonlinear couplers with switching times below 1 ps.     

Beam instabilities in the collective Cherenkov effect and anomalous Doppler effect in a spatially bounded system near the nontransparency band

Beam instabilities of the type of the collective induced Cherenkov effect and the anomalous Doppler effect, which develop in a longitudinally bounded electrodynamic system near its nontransparency band (i.e., when the electromagnetic wave excited by the beam has zero group velocity), are considered. The dispersion equation is derived, which defines the instability increments taking into account the emission of radiation from the electrodynamic system. The solutions to the dispersion equation are analyzed for various parameters of the electron beam and of the electrodynamic system.