A. G. Litvak

Structural features of the self-action dynamics of ultrashort electromagnetic pulses

Self-focusing dynamics of electromagnetic pulses of arbitrary duration is analyzed numerically and analytically. The wave-field evolution is considered by the wave equation in the reflectionless approximation under quite general assumptions about the dispersion of the medium. Methods for qualitative investigation of the self-focusing dynamics of quasimonochromatic radiation are generalized to the case of wave packets with the length of a few oscillation periods. In particular, sufficient conditions for collapse and many other integral relations are obtained by the momentum method. A self-similar-type transformation is used to show that new structural features are primarily associated with the nonlinear dispersion of the medium (with the dependence of the group velocity of a wave packet on its amplitude). Numerical analysis confirms that the self-focusing of radiation is preceded by an increase in the steepness of the longitudinal profile.

Features of plasma glow in low pressure terahertz gas discharge

Investigations of the low pressure (1–100 Torr) gas discharge in the powerful (1 kW) quasi-optical terahertz (0.55 THz) wave beams were made. An intense afterglow was observed after the end of gyrotron terahertz radiation pulse. Afterglow duration significantly exceeded radiation pulse length (8 μs). This phenomenon could be explained by the strong dependence of the collisional-radiative recombination rate (that is supposed to be the most likely mechanism of electron losses from the low pressure terahertz gas discharge) on electron temperature.

Self-focusing of laser radiation in cluster plasma

The self-focusing of laser radiation in plasma with ionized gaseous clusters is studied both analytically and numerically. An electrodynamic model is proposed for cluster plasma in a field of ultrashort laser pulse. The radiation self-action dynamics are studied using the equation for wave-field envelope with allowance for the electronic nonlinearity of the expanded plasma bunches and the group-velocity dispersion in a nanodispersive medium. It is shown that, for a laser power exceeding the self-focusing critical power, the wave-field self-compression occurs in a medium with dispersion of any type (normal, anomalous, or combined). Due to the strong dependence of the characteristic nonlinear field on the size of ionized cluster, the corresponding processes develop faster than in a homogeneous medium and give rise to the ultrashort pulses.

The structural features of wave collapse in medium with normal group velocity dispersion

The dynamic characteristics of self-action in three-dimensional wave packets described by the nonlinear Schrödinger equation with a hyperbolic space operator were studied analytically and numerically. The class of the initial wave field distributions for which self-focusing effects predominated over dispersion spreading and caused the arising of wave collapses was considered. The collapse of tubular wave packets was shown to be accompanied by packet shape changes during its contraction to the axis of the system. The nonlinear stabilization of collapses resulted in wave field fragmentation in the longitudinal direction followed by the expansion of the bunches thus formed along the axis. The dynamics of collapses was numerically studied taking into account medium nonlinearity saturation and nonlinear dissipation.

The nonlinear dynamics of wave systems with spatio-temporal collapses

Wave energy concentration processes in nonlinear media are analysed. A classification of nonlinear systems with wave collapses according to the character of the field energy localization into singularity domains is presented, and examples of the evolution are considered. A detailed analysis is given for the case of the bievolutional (spatio-temporal) behavior of strong electro-magnetic waves in media with nonlinearity inertia where an arbitary energy flux can be trapped into contracting filaments, or moving focus distributions.

Near-sonic Langmuir solitons

Abstract A new class of near-somic Langmuir solitons with a discrete spectrum of eigenvalues is obtained taking into account charge separation in ion-sound oscillations of a plasma.

On the collapse of wave packets in a medium with normal group velocity dispersion

A solution to the problem of realizing the collapse of three-dimensional wave packets in nonlinear media with normal group velocity dispersion is proposed. Wave packets with pronounced hyperbolic topology are shown to collapse; i.e., the field increases infinitely near the system axis. In particular, wave collapse of the tubular axisymmetric packets occurs through the concentration of the compressed ring field distribution at the axis. The collapse is shown to stabilize due to the saturation of nonlinearity or nonlinear dissipation, which restrict the field increase and lead to the packet splitting in the transverse direction.

Self-focusing of wave packets and envelope shock formation in nonlinear dispersive media

The self-action of three-dimensional wave packets is analyzed analytically and numerically under the conditions of competing diffraction, cubic nonlinearity, and nonlinear dispersion (dependence of group velocity on wave amplitude). A qualitative analysis of pulse evolution is performed by the moment method to find a sufficient condition for self-focusing. Self-action effects in an electromagnetically induced transparency medium (without cubic nonlinearity) are analyzed numerically. It is shown that the self-focusing of a wave packet is accompanied by self-steepening of the longitudinal profile and envelope shock formation. The possibility of envelope shock formation is also demonstrated for self-focusing wave packets propagating in a normally dispersive medium.

Single-qubit gates for ensemble qubits via off-resonant Raman interaction

In this paper we analyze the fidelity of single-qubit gates based on off-resonant Raman interaction when they are applied to qubits implemented as ensembles of active centers. In particular, we investigate the additional errors induced by the inhomogeneous broadening of the qubit ensemble. We propose a new scheme which can be used to significantly decrease these errors and to realize high-fidelity logic gates for ensemble qubits.

Low pressure gas discharge in the quasioptical beams of the powerful terahertz radiation

Summary form only given. Results of the experimental investigation of the gas discharge in the beams of the powerful terahertz radiation are presented. Study of the self-sustained and initiated discharges by using the radiation of one of the two pulsed gyrotrons (developed in IAP RAS) with frequency values of 0.55 THz@1kW (8 μβ pulse length) and 0.67 THz@100kW (20 μβ) was made in the wide range of pressures (0.01-1500 Torr) in different gases (helium, argon). Self-sustained discharge could be maintained in the pressure range from 20 Torr to two atmospheres. By using the several methods of discharge initiation it was possible to expand the range of discharge existence to the pressure value of about 0.01 Torr. It was shown that the low pressure (dozens of Torr and less) discharge has a number of features compared with the discharge of high pressure: the presence of the powerful afterglow with length of about 20-50 microseconds after gyrotron pulse, the lack of a strongly inhomogeneous spatial structure of the discharge glow (at pressures less than 10 Torr), the lack of screening of the discharge appearance location from the gyrotron radiation. The size of the discharge plasma at pressure value of 0.01 Torr was about of 1 mm. Such a discharge can be used as the pointed source of UV radiation, including the projection lithography.