A new ("linear-parametric") mechanism of a direct conversion of an ultrashort laser pulse into terahertz radiation is suggested. The conversion is due to the ionization-induced excitation and the subsequent electromagnetic emission of the superluminous polarization wave created by the axicon-focused laser pulse. For a few-cycle pulse with an optimum carrier-envelope phase, the considered mechanism is found to be much more effective than the alternative one based on the excitation of plasma oscillations in the laser wakefield by the ponderomotive force and able to provide THz radiation of the gigawatt power level with the use of moderate optical intensity (approximately 10(14)-10(15) W/cm2).

Articles you may be interested inSimulation of resonance hyper-Rayleigh scattering of molecules and metal clusters using a time-dependent density functional theory approach J. Chem. Phys. 141, 124305 (2014); 10.1063/1.4895971Inter-channel effects in monosolvated atomic iodide cluster anion detachment: Correlation of the anisotropy parameter with solvent dipole moment

A plasma-resonance field-ionization instability of uniform gas breakdown produced by intense laser fields via tunneling ionization of atoms is studied theoretically and by computer simulation. The field amplitude and produced plasma are found to be unstable relative to spatial modulation in the direction of electric field with the spatial period shorter than the wavelength. In a dense gas the process, at the nonlinear stage of instability, becomes explosive and leads to the formation of thin resonance layers and sharp peaks of the field amplitude.[S0031-9007 (97)02954-2] PACS numbers: 52.40.Nk, 52.50.JmIt is well known that a powerful electromagnetic wave beam in a medium with positive (focusing) nonlinearity is subject to filamentation instability with a characteristic transverse scale large compared to the wavelength. This instability was predicted about thirty years ago based on the paraxial approximation for the scalar wave field [1]. Its manifestations were repeatedly observed in experiments with powerful laser and microwave pulses (see, for example, [2,3] and references therein).A less known fact is the existence of "vector" smallscale instability of the wave in a transparent medium with a "defocusing" (ionization-type) nonlinearity. This instability was originally described based on the vector wave equation [4], and studied theoretically and experimentally [5-7] as one of a wider class of ionizationfield (or electrodynamic) instabilities of high-frequency and microwave discharges in gases. Further, we will use the term "plasma-resonance ionization (PRI) instability," revealing the underlying physical mechanism of its generation. The PRI instability results in the filamentation of the wave and produced plasma with density gradients parallel to the wave electric field and with the spatial period shorter than the wavelength. So, it may be considered as an ionization analog of the known modulation instability of the field in a collisionless plasma with positive (ponderomotive-force-induced) nonlinearity. However, unlike the latter, it evolves not only in a narrow plasma resonance region (near the critical-density surface) but covers the entire transmission medium and affects significantly its electrodynamic characteristics.The PRI instability, probably, has not yet been observed in experiments with powerful ionizing laser pulses, since the majority of the experiments realized the electronimpact (avalanche-type) mechanism of gas ionization; the characteristic time of instability for this mechanism turns out to be longer than the time of the avalanche itself or the time of gas heating. However, advances in the generation of powerful laser pulses with field amplitudes comparable to atomic fields have stimulated interest in studies on the dynamics of the laser breakdown determined by opticalfield-induced (tunneling) ionization of gas atoms [8][9][10][11][12][13][14].The growth rate of the PRI instability with this ionization mechanism, as we find below, can be high enough so that, at the final stage of the breakdo...

This paper is an overview of the activity and state-of-the-art in the field of plasma aerospace applications. Both experimental results and theoretical ideas are analysed. Principal attention is focused on understanding the physical mechanisms of the plasma effect on hypersonic aerodynamics. In particular, it is shown that drag reduction can be achieved using a proper distribution of heat sources around a flying body. Estimates of the energetic efficiency of the thermal mechanism of aerodynamic drag reduction are presented. The nonthermal effect caused by the interaction of a plasma flow with a magnetic field is also analysed. Specifically, it is shown that appropriate spatial distribution of volumetric forces around a hypersonic body allows for complete elimination of shock wave generation. It should be noted that in an ideal case, shock waves could be eliminated without energy consumption.

The propagation of an electromagnetic wave along a planar waveguiding structure that contains gaseous/solid-state plasma slabs with time-varying free carrier density is considered in the case when the time scale of the density variation is much greater than the wave period (adiabatic approximation). Both ionization and deionization (recombination, attachment) processes are included. General relations describing frequency shifting and energy losses of a guided wave are derived for an arbitrary open/closed waveguiding structure. Relations between the energy of the wave and its frequency conserved during the process of plasma density variation (adiabatic invariants) are found. Detailed analyses are given for surface waves guided by the boundary of a time-varying plasma half-space and a plasma slab. Slow variations of plasma density are shown to be energetically more efficient than fast variations. A new effect of reflection of the wave envelope that occurs without reflection of the fast oscillating carrier is pointed out.