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Novosibirsk, Russia

The essence of the positive-column plasma constriction for static (the diffusion mode) and dynamic ionization equilibrium (the stratificated and constricted modes) is analyzed. Two physical parameters, namely, the effective ionization rate of gas atoms and the ambipolar diffusion coefficient of electrons and ions, determine the transverse distribution of discharge species and affect the current states of plasma. Transverse constriction of the positive column takes place as the gas ionization level (discharge current) and pressure increase. The stratified mode (including the constricted one) is observed between the two adjacent types of self-sustained discharge phases when they coexist together at the same time or in the same place as a coherent binary mixture. In the case, a occurrence of the discharge phase with more high electron density presently involve a great decrease in the cross-section of the current channel for d.c. discharges. Additional physical factors, such as cataphoresis and electrophoresis phenomena and spatial gas density inhomogeneity correlated with a circulatory flow in d.c. discharges, are mainly responsible for the current hysteresis and partially constricted discharge. © 2014 AIP Publishing LLC. Source

Medvedev A.E.,RAS Institute of Laser Physics
Russian Physics Journal | Year: 2012

A transport equation has been derived for a plasma treated as a continuous medium. In contrast to the well-known magnetohydrodynamic approach, in deriving the equation, the spatial charge density was taken into account which has made it possible to determine the self electric field of the plasma and the consistent motion of charged particles of different charge sign. Analysis of the equation terms that describe the contributions of various types of energy to the plasma transport has been performed. In the limit of dominant thermal energy, the criteria for plasma quasineutrality and ideality transforms into the well-known criterion defined by the squared ratio of the Debye radius to the characteristic size, and plasma transport is reduced to ambipolar diffusion. Based on the equation obtained, models of moderate-pressure and atmospheric-pressure glow discharges can be considered to interpret experiments with fields too low to provide ionization, so that a bulk plasma is sustained by charge carriers coming from near-electrode regions, and the cross-section of the current filament is determined by the balance of forces that represent the action of the thermal energy and of the energy of electrical interaction between the plasma particles. © 2012 Springer Science+Business Media, Inc. Source

Boichenko S.,RAS Institute of Laser Physics | Konig K.,Irkutsk State University
Journal of the Optical Society of America B: Optical Physics | Year: 2015

We theoretically demonstrate a technique allowing a highly efficient observation of all single-molecule emitters in one fluorescent image, regardless of the orientations of their transition dipole moments. To perform this technique, we combine near-unity collection efficiency for an arbitrarily oriented emitter and the elimination of the excitation efficiency dependence on the emitter's orientation. The former task is solved by placing the emitter in a special metallo-dielectric antenna [Opt. Lett. 36, 3545 (2011)]; the latter, by means of laser-scanning confocal fluorescence microscopy using elliptically polarized cylindrical vector beams [J. Exp. Theor. Phys. Lett. 97, 52 (2013)]. We present conditions under which the collection efficiency for arbitrarily oriented emitters is <98% and the excitation efficiency of an emitter of minimally excitable orientation amounts to >92% of the excitation efficiency of an emitter of maximally excitable orientation. These conditions are satisfied in the broad spectral range between 0.4 and 1.0 μm: the emitters can be excited with any wavelength and emit any fluorescence spectra in this range. The presented results are based on simulation data. © 2015 Optical Society of America. Source

In this paper it is shown, by analyzing the results of experimental studies, that the outer boundary of the atmospheric pressure discharge pinch is determined by the condition of equality of plasma flows based on the thermal and electric field energy. In most cases, the number of charged particles coming from near-electrode zones is sufficient to compensate for losses in the discharge bulk. At large currents and enhanced heating, plasma is in the diffusion mode of losses, with recombination of charged particles at the pinch boundary. © 2016 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg. Source

Bryukvina L.,RAS Institute of Laser Physics
Journal of Luminescence | Year: 2015

Abstract The periodic filamentation patterns across and along laser channel tracks, induced by high-intensity femtosecond laser pulses in magnesium and sodium fluoride crystals, have been disclosed. The patterns are rationalized by deterministic vectorial effect, difference in propagations of linearly- and circularly-polarized laser pulses, and appearances of the orbital angular momentum of the light beams due to optical astigmatism. © 2015 Elsevier B.V. All rights reserved. Source

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