R. A. Vlasov

Auto-waveguide propagation and the collapse of spiral light beams in non-linear media

The equation governing the propagation of spiral beams in a non-linear medium is analysed. It is shown that, taking into account the saturation effect, spiral beams have a tube-like structure with a periodicity along the axis of a non-linear autoguide. A critical power is found which it is necessary to exceed in order to give rise to the indicated autoguided regime of the beam propagation. Furthermore, in this work a strict self-similar solution is obtained of a non-linear Schrodinger-type equation that describes the collapse of spiral beams, and a new class of self-similar solutions is found for the case of spherical symmetry.

Optical solitons in dense resonant media

Exact single-soliton solutions of the modified system of Maxwell-Bloch equations, in which the dipole-dipole interactions of the atoms of a dense resonant medium are taken into account, are obtained. Two propagation regimes are analyzed: “coherent,” where the pulse duration is much shorter than both relaxation times (Tp ≪ T1, T2), and “incoherent,” where the pulse duration falls between the relaxation times (T2 ≪ Tp ≪ T1). It is predicted, for the first time, that soliton propagation of an ultrashort pulse is possible in a dense resonant absorbing medium in an incoherent interaction regime. The differences between the amplitude and phase characteristics of the solitons considered and the corresponding characteristics of the solitons for McCall-Hahn self-induced transparency are noted.

Evolution of femtosecond solitons in a cubic medium with a two-component relaxing nonlinearity

Soliton propagation in a nonlinear cubic medium with two types of relaxing nonlinearities is investigated. Provided that the pulse duration exceeds the fast relaxation time and be shorter than the slow one, partial compensation of the concerted influence of these relaxations on the soliton dynamics is feasible. A condition for such an optimal regime of soliton pulse propagation is analytically obtained. Computer simulations are in good agreement with analytical predictions.

Relaxation-induced stabilisation of optical pulsed vortex beams in media with a composite cubic–quintic nonlinearity

The problem of the generation of stable (quasi-stable) 3+1D light bullets in nonlinear media is addressed. We consider a medium with a two-component relaxing cubic nonlinearity, and non-relaxing quintic one. It is shown that a special adjustment of the pulse duration and the parameters of the two-component relaxing nonlinearity enables one not only to suppress distortions of the temporal pulse envelope and self-induced frequency shift, but to suppress a destructive effect of the azimuthal instability of vortex pulsed beams as well.

The second laser threshold with up-conversion

The influence of an additional relaxation channel of up-conversion type on the second threshold of a laser with a dense homogeneously broadened active medium is investigated in terms of a two-level model. Local-field effects caused by near dipole-dipole interactions are taken into account in this case. It is shown that the bad-cavity condition is not obligatory for chaotic behavior to appear in a laser system and that the second laser threshold can be substantially reduced by the up-conversion process.

Free polarization decay in media with a short-range dipole-dipole interatomic interaction

The effect that may be exerted by an interatomic dipole-dipole interaction upon optical transient processes in dense resonance media, in particular, free polarization decay, is analyzed. The behavior of the macroscopic polarization after a single-pulse excitation of a dense ensemble of two-level atoms is considered. It is shown that the free polarization signal is of oscillatory nature, with the oscillation frequency varying in time and being dependent on the dipole-dipole interaction constant, the intensity and duration of the exciting pulse, and the detuning of its carrier frequency from the resonance. The free polarization signal decay, which depends on the magnitude and sign of the sum of the detuning of the exciting pulse carrier frequency from the resonance and the Lorentz frequency, may obey either a power or an exponential law. The signal decay rate is determined not only by the inhomogeneous broadening, but also by the ratio of the above parameters.

Light propagation in dense resonant media: intrinsic optical bistability, solitons, and transients

The intrinsic optical bistability, soliton formation, and transient phenomena such as the free polarization decay and photon echo in dense resonant media are investigated, taking into account the short-range dipole-dipole interaction of atoms.

Optical transients in dense resonant media

Transient phenomena such as free polarization decay and photon echo in dense resonant media taking into account short-range dipole-dipole interaction of atoms are investigated.

Sit soliton formation influenced by the dynamic stark effect

The soliton formation is considered which is feasible in quasi-resonant media of multilevel atoms modeled by the generalized two-level systems, taking account of the dynamic Stark effect. A soliton solution of the extended Maxwell-Bloch equations system is found, bistability properties thereof being predicted.