Biomedical subjects

M I Bakunov

Publications and source records attributed to M I Bakunov.

5 recordsLinked to original sources

PubMed2004

Two-dimensional theory of Cherenkov radiation from short laser pulses in a magnetized plasma.

The Cherenkov wakes excited by intense laser drivers in a perpendicularly magnetized plasma are a potential source of high-power terahertz radiation. We present a two-dimensional (2D) theory of the emission of magnetized wakes excited by a short laser pulse. The 2D model reveals the important role of the transverse size of the laser pulse missed in previous simple one-dimensional estimations of the radiation. We derived expressions for the radiated fields and for the angular/frequency distribution of the radiated energy. Beats in the radiation pattern behind the moving pulse are predicted and explained. For the interpretation of existing experimental results, the time dependence of the energy flux parallel and perpendicular to the laser path is examined.

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PubMed2002

Interaction of an electromagnetic wave with a suddenly stopped ionization front.

The theory of the interaction of an electromagnetic wave with a uniformly moving ionization front in a gas is extended to include the case when the front suddenly stops. This nonstationary character of the wave/front interaction, which is typical for experiments carried out in a finite-size gas tube, gives rise to fresh physical effects. First, currents induced near the plasma boundary after the front stops produce a static magnetic field not only in the plasma behind the front but also in the vacuum ahead of the front. Second, in the regime where the transmitted wave falls off behind the front, the skinning field leaks through the stopped front and produces a burst of highly frequency up-shifted radiation.

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PubMed2002

Energetics of electromagnetic wave transformation in a time-varying magnetoplasma medium.

The transformation of a circularly polarized electromagnetic wave in a magnetoplasma medium with increasing plasma density is considered. The wave propagates along the static magnetic field. Complete analysis, including ion motion, is given both for slow (compared to the wave frequency) and rapid ionization rate. In the case of slow temporal variation of the plasma density, a relation between the energy of the wave and its frequency, which is conserved during the plasma creation process (adiabatic invariant), is found. The existence of significant energy losses follows from the invariant. The dissipative mechanism is explained via consideration of the case of a sudden growth of plasma density in time from one value to another. It is shown that energy transforms into the kinetic energy of carriers, and preionization of the medium plays a principal role in the dissipation process. In the special case of a whistler wave, up to 50% of the energy may be transformed into an ion-cyclotron wave when dense plasma is rapidly created.

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PubMed2001

Bulk-to-surface-wave self-conversion in optically induced ionization processes.

Nonlinear time evolution of a p-polarized wave mode with inhomogeneous transverse structure producing tunnel ionization of a gas is investigated by numerical simulation and theoretical analysis. A phenomenon of trapping of electromagnetic radiation via its adiabatic conversion into surface waves guided by the field-created plasma structure is found out numerically. This process is accompanied by significant frequency downshifting of the electromagnetic radiation. The underlying physical mechanism is explained using a simple theoretical model. The described phenomena may play significant role in the self-channeling and frequency tuning of intense (approximately 10(14)-10(18) W/cm(2)) laser pulses in dense gases.

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PubMed2001

Interaction of an electromagnetic wave packet with an ionization front: copropagating configuration.

The interaction of a TM polarized wave packet with a moving ionization front is theoretically investigated. We extend our previous study [IEEE Trans. Plasma Sci. 27, 655 (1999)], where we considered the case when the wave packet is incident on the front, by including the case often used in experiments when the front overtakes the wave packet. We focus on the energy transformation into the generated waves-the point that is rarely addressed in literature due to complications arising from the presence of Langmuir waves. Our quantitative results show the importance of losses via Langmuir wave excitation compared to other possible losses due to the excitation of stationary transverse electron currents in the plasma. Applicability to the generation of frequency upshifted radiation is discussed.

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