Ionization spectrum transformation and compression of powerful femtosecond laser pulses in experiments on the propagation in gas-filled dielectric capillaries

The propagation of an intense (I≤10⁶ W/cm²) femtosecond laser radiation with a duration of ～100 fs through gas-filled dielectric capillaries was studied. The radiation with a power up to 0.2 TW propagates along the paths up to 20 cm with a transmission efficiency of ～45%. The beam transverse structure at the output is close to the capillary fundamental mode under gas-ionization conditions. The transformation of pulse spectrum was studied as a function of input intensity. It is demonstrated experimentally that the pulse is compressed to a duration of ～30 fs due to the compensation of ionization-induced self-phase modulation in a linear dispersive element at the capillary output.     

Decrease in durability of brittle solids in cyclic tests

In this work a phenomenological model Is proposed for fatigue fracture, based on analysis of basic experimental results on cyclic testing taking into account the basic physical assumptions on which the mechanism for the growth of a fracture crack is based. A number of theoretical relations are obtained that reveal qualitatively and quantitatively the basic concepts concerning the mechanism of fatigue fracture: the magnitude of the local heating at the vertex of the fracture crack, equations for its rate of growth, decrease in the potential barrier, safe stress amplitude, and the kinetic equation for cyclic durability.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 3–8, June 1981.     

Tunable soliton self-bending in optical lattices with nonlocal nonlinearity

We address the phenomenon of soliton self-bending in Kerr-type nonlocal nonlinear media with an imprinted transverse periodic modulation of the linear refractive index. We show that the imprinted optical lattice makes possible to control the mobility of soliton by varying the depth and the frequency of the linear refractive index modulation.     

Stable soliton complexes in two-dimensional photonic lattices

We show that two-dimensional photonic Kerr nonlinear lattices can support stable soliton complexes composed of several solitons packed together with appropriately engineered phases. This may open up new prospects for encoding pixellike images made of robust discrete or lattice solitons.     

Solitons in geometric potentials

We show that the geometrically induced potential existing in undulated slab waveguides dramatically affects the properties of solitons. In particular, whereas solitons residing in the potential maxima do not feature power thresholds and are stable, their counterparts residing in the potential minima are unstable and may exhibit a power threshold for their existence. Additionally, the geometric potential is shown to support stable multipole solitons that cannot be supported by straight waveguides. Finally, the geometric potential results in the appearance of the effective barriers that prevent transverse soliton motion.     

Solitons in a medium with linear dissipation and localized gain

We present a variety of dissipative solitons and breathing modes in a medium with localized gain and homogeneous linear dissipation. The system possesses a number of unusual properties, like exponentially localized modes in both focusing and defocusing media, existence of modes in focusing media at negative propagation constant values, simultaneous existence of stable symmetric and antisymmetric localized modes when the gain landscape possesses two local maxima, as well as the existence of stable breathing solutions.     

Vortex twins and anti-twins supported by multiring gain landscapes

We address the properties of multivortex soliton complexes supported by multiring gain landscapes in focusing Kerr nonlinear media with strong two-photon absorption. Stable complexes incorporating two, three, or four vortices featuring opposite or identical topological charges are shown to exist. In the simplest geometries with two amplifying rings vortex twins with equal topological charges exhibit asymmetric intensity distributions, while vortex anti-twins may be symmetric or asymmetric, depending on the gain level and separation between rings.     

Rotating vortex solitons supported by localized gain

We show that ringlike localized gain landscapes imprinted in focusing cubic (Kerr) nonlinear media with strong two-photon absorption support new types of stable higher-order vortex solitons containing multiple phase singularities nested inside a single core. The phase singularities are found to rotate around the center of the gain landscape, with the rotation period being determined by the strength of the gain and the nonlinear absorption.     

Stable radially symmetric and azimuthally modulated vortex solitons supported by localized gain

We discover that a spatially localized gain supports stable vortex solitons in media with cubic nonlinearity and two-photon absorption. The interplay between nonlinear losses and gain in amplifying rings results in the suppression of otherwise ubiquitous azimuthal modulation instabilities of radially symmetric vortex solitons. We find that the topology of the gain profile imposes restrictions on the maximal possible charge of vortex solitons. Symmetry breaking occurs at high gain levels, resulting in the formation of necklace vortex solitons composed of asymmetric bright spots.