V N Tishchenko

Thermal self-action of high-power continuous and pulse-periodic CO2 laser radiation in air: I. Numerical simulation of propagation along an atmospheric path

A problem of transportation of high-power laser radiation energy at a wavelength of 10.6 μm in the atmosphere is theoretically considered in terms of its thermal and wind nonlinearities. The power characteristics of continuous and pulse-periodic radiation are studied during propagation along a surface kilometer-long atmospheric path with sharp focusing onto a receiver. Key factors most affecting high-power radiation propagation are found. It is ascertained that an undesirable effect of thermal defocusing can be reduced using a train of low-power short pulses with a quite high repetition rate due to the effect of light-induced “blooming” of the gas medium. The questions of scaling optical paths from the viewpoint of their equivalence in manifestation of thermal nonlinearity are discussed.

Torsional Alfvén and slow magnetoacoustic waves generated by a plasma in a magnetic field

A new effect has been experimentally revealed: a sequence of flashes of a two-component laser plasma creates a flow containing torsional Alfvén and slow magnetoacoustic waves in a magnetic flux tube.

Thermal self-action of high-power continuous and pulse-periodic CO2 laser radiation in air: II. Laboratory experiments

Results of laboratory experiments on nonlinear propagation of high-power pulse-periodic and continuous CO2 laser radiation in a gas medium are presented. The experiments were carried out in a cell filled with a mixture of air and carbon dioxide in different partial concentrations (∼1–4%) under strong absorption and thermal blooming of laser radiation. The experimental conditions simulated the atmospheric propagation of high-power laser radiation along a kilometer-long path. Sharply focused laser beams were used; the regions of heat release along the beam channel were recorded by the shadow imaging technique. We found that, despite increased intensity, the focal waist of a laser beam is characterized by reduced heat release as compared to that in the pre- and postfocal beam regions. The saturation effect of the resonance absorption coefficient of CO2 at high pulse peak intensity (blooming effect) is considered as the most probable physical cause of the above feature. For continuous radiation, this effect is much weaker.

Sound spectrum of a pulsating optical discharge

A spectrum of sound of an optical discharge generated by a repetitively pulsed (RP) laser radiation has been investigated. The parameters of laser radiation are determined at which the spectrum of sound may contains either many lines, or the main line at the pulse repetition rate and several weaker overtones, or a single line. The spectrum of sound produced by trains of RP radiation comprises the line (and overtones) at the repetition rate of train sequences and the line at the repetition rate of pulses in trains. A CO2 laser with the pulse repetition rate of f ≈ 3 – 180 kHz and the average power of up to 2 W was used in the experiments.

Laser plasma simulations of the generation processes of Alfven and collisionless shock waves in space plasma

Generation of Alfven waves propagating along external magnetic field B0 and Collisionless Shock Waves propagating across B0 are studied in experiments with laser- produced plasma and magnetized background plasma. The collisionless interaction of interpenetrating plasma flows takes place through a so-called Magnetic Laminar Mechanism (MLM) or Larmor Coupling. At the edge of diamagnetic cavity LP-ions produce induction electric field E which accelerates BP-ions while LP-ions rotate in opposite direction. The ions movement generates sheared azimuthal magnetic field B which could launches torsional Alfven wave. In previous experiments at KI-1 large scale facility a generation of strong perturbations propagating across B0 with magnetosonic speed has been studied at a moderate value of interaction parameter δ~0.3. In the present work we report on experiments at conditions of 5~R2 and large Alfven-Mach number MA~10 in which strong transverse perturbations traveling at a scale of ~1 m in background plasma at a density of ~3*1013 cm-3 is observed. At the same conditions but smaller MA ~ 2 a generation, the structure and dynamic of Alfven wave with wavelength ~0.5 m propagating along fields B0~100÷500 G for a distance of ~2.5 m is studied.

Generation of laser plasma bunches with a high efficiency of energy concentration for laboratory simulation of collisionless shock waves in magnetised cosmic plasma

We present the results of first experiments on the formation of collisionless shock waves (CSWs) in background plasma by injecting laser plasma bunches transverse to the magnetic field (as a piston) with a maximum energy up to 100 J per unit of solid angle and with a high enough degree of ion magnetisation. With this aim in view, on a unique KI-1 facility at the Institute of Laser Physics, Siberian Branch of the Russian Academy of Sciences (ILP), a plastic (polyethylene) target irradiated by a CO2 laser in the most energy-efficient regime (near the plasma formation threshold) and a highly ionised hydrogen plasma with a high concentration in a large volume (not less than 1 m3) have been employed. As a result of model experiments performed on the basis of a model of collisionless interaction of plasma flows, developed at the VNIIEF and being adequate to the problem under consideration, not only an intensive, background-induced, deceleration of a super-Alfven laser plasma flow, but also the formation in that flow of a strong perturbation having the properties of a subcritical CSW and propagating transverse to the magnetic field, have been first registered in the laboratory conditions.