Partially incoherent optical vortices in self-focusing nonlinear media

We observe stable propagation of spatially localized single- and double-charge optical vortices in a self-focusing nonlinear medium. The vortices are created by self-trapping of partially incoherent light carrying a phase dislocation, and they are stabilized when the spatial incoherence of light exceeds a certain threshold. We confirm the vortex stabilization effect by numerical simulations and also show that the similar mechanism of stabilization applies to higher-order vortices.     

级联介质的空间排布对光场特性的影响

基于菲涅尔衍射原理，应用傅里叶变换方法，从理论上推导了高斯光束经级联非线性介质传输后任意位置处光场分布的解析表达式,研究了光场峰值强度、峰值出现的位置以及光束的束宽和调制因子等参量在级联介质中的变化规律。结果表明：随着非线性效应的增强，光场峰值强度逐渐增大，峰值距离逐渐缩短，光束束宽不断减小而调制因子逐渐增大。在介质排布中要尽量错开光束峰值位置，采用均匀排布方案虽然可以降低元件受损的风险，但还需对介质均匀配置的间距进行有效优化。     

The stratification of a wave packet in a nonlinear medium

The possibility of controlled large-scale stratification of the wave impulse in the nonlinear medium is discussed. The wide class of exact analytical solutions, describing, in the bounds of the nonlinear geometrical optics, the formation of the new intensity maxima, are found. The characteristics dimensions of the oscillations of the packet are much greater than the wave length.     

Dynamics of optical pulses in a dispersive chiral medium

The dynamics of frequency-modulated pulses in an isotropic nonreciprocal chiral medium is studied. It is shown that the discrepancy between the group velocities and carrier frequencies of the circular components of the pulse causes it to split up both along the fiber and in the spectral domain. The strong dependence of the material parameters on the pulse frequency may lead to the asymmetric dynamics of the electric and magnetic fields of the pulse in different frequency intervals. For both components of the wave field, envelopes moving with a supraluminal speed may arise.     

Composite spatial solitons in a saturable nonlinear bulk medium

We review the generation of the recently predicted multi-component spatial optical solitons in a saturable nonlinear bulk medium. We present numerical simulations for an effectively isotropic model and experimental results for a set of different combinations of a Gaussian beam co-propagating incoherently with a beam of a more complex internal structure, such as a higher order transverse laser mode. We discuss the different formation processes and the general properties of a variety of different dipole-mode composite solitons and expand our investigations to the generation of a quadrupole-mode composite soliton. Received: 1 December 2000 / Revised version: 12 January 2001 / Published online: 21 March 2001     

Transformation of the wave spectrum in a medium having smooth space-time fluctuations

Conclusions In conclusion let us sum up concerning the question of the applicability limits of the quasistatic approximation. For u₀TL the equations for the phase and frequency dispersions, which determine the width of the time spectrum of the waves (specifically, (2.9)), and likewise the equations for the arrival angle (2.6) and the amplitudes of the waves (3.5) are in agreement with the results of the quasistatic calculation with a sufficient degree of accuracy. For u₀TL there is naturally no such correspondence any more, and here the dispersion of the medium plays an essential role. Let us emphasize the fact that in the presence of dispersion the delay effect (including the Eqs. (2.13) and (2.14) for the phase fluctuations) is determined by the group velocity of the waves. However in considering such questions as the variation of the average energy flux in the wave and the shape of the power spectrum the quasistatic approach is inapplicable in principle even for fulfillment of the condition u₀TL.Gor'kii State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 16, No. 1, pp. 69–81, January, 1973.     

Moving near-gap solitons in the nonlinear optical medium

For a one-dimensional nonlinear optical medium with a periodic refraction index, new two-parameter soliton solutions of electrodynamics equations have been found. These solutions represent two interacting waves that propagate in two opposite directions. The oscillation frequency of each wave may fall either into the forbidden gap in the linear spectrum or outside it, and the group velocity may vary from zero to a maximal value that is determined by the parameters of the medium. Algebraic soliton solutions have been found as the limit of the nonlinear solutions, when the nonlinear wave frequency tends to the frequency of one of the linear-spectrum branches.     

On the possibility of suppression of self-focusing of a femtosecond laser pulse during its propagation in a cubic nonlinear medium

Based on a computer simulation, the self-focusing of an axially symmetric beam in a cubic nonlinear medium under the anomalous dispersion conditions is studied with the account for the time dispersion of nonlinear response, which manifests for femtosecond pulses. It is shown that, at a certain value of the parameter of linear modulation of the pulse (or of its chirp), the dispersion of nonlinear response can lead either to the suppression of formation of a nonlinear focus and to the possibility of formation of optical shock waves in time or even to a change in the regime of the beam self-action owing to the action of the local response, i.e., to the change from the self-focusing of the beam to the regime of its defocusing.     

Observation of optical spatial solitons in a highly nonlocal medium

We report on the observation and quantitative assessment of self-trapped pulsating beams in a highly nonlocal nonlinear regime. The experiments were conducted in nematic liquid crystals and allow a meaningful comparison with the prediction of a scalar theory in the perturbative limit, while addressing the need for beyond-paraxial analytical treatments.     

Dynamics of the nonlinear excitation of a wave packet in order-disorder ferroelectrics

Microscopic pseudospin formalism is used to examine the main laws governing the nonlinear excitation of a packet of pseudospin waves in ferroelectrics of isomorphous KDP. The nonlinear frequency shift of the packet is determined along with its temperature dependence. A qualitative analysis is made, of the dynamics of the “center of gravity” of the packet. Volgograd University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 98–102, August, 1997.