共查询到20条相似文献,搜索用时 31 毫秒
1.
T. M. Zaboronkova 《Radiophysics and Quantum Electronics》1997,40(7):579-583
We study the linear stage of the parametric instability of high-frequency surface waves guided by a homogeneous plasma layer
on a metallic substrate when a TM-polarized plane electromagnetic wave is incident on the layer. The instability growth rate
and the threshold value of the pumping wave amplitude are determined. It is shown that the instability can be thresholdless
in a certain range of permittivities and thicknesses of the layer.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 40, No. 7, pp. 870–876, July, 1997. 相似文献
2.
3.
The inviscid supersonic flows in corners between intersecting compression wedges were studied numerically. Under usual conditions,
the flows in such corner configurations are conically self-similar. Besides, shock waves formed by wedges are plane and they
interact with one another in these flows and the downstream development of the shock interaction structure at that occurs
in a region which is bounded in cross-sectional directions by the walls and contracts towards the corner rib, and in this
sense the above interaction of shocks may be subjected to influence of the rib. The corner flows of another type with an interaction
of shocks not subjected to the “rib effect”, in other words free, were considered. This was ensured by that the corner configurations
were designed with a gradually expanding gap along the rib in a way that the reflected shocks arising as a result of interaction
passed through the gap without falling onto the walls. This eliminated the influence of a local flow near the corner rib on
the interaction of plane shock waves formed by the wedges.
The inviscid flows symmetric with respect to the bisector plane of the corner dihedral angle were considered. The computations
showed that, in the gapped corner configurations with the free interaction of shocks, if these interactions were irregular,
the cross-flow patterns were practically the same as in the original corner configurations without a gap.
The conditions for the flows over corner configurations were also considered under which the interaction of shocks corresponded
to the Neumann criterion of mechanical equilibrium. These conditions are equivalent to those, which take place in two-dimensional
steady flows, when a hysteresis phenomenon is possible, which manifests itself in changing the moment of transition from a
regime of regular reflection of shocks to an irregular one and conversely at a direct and inverse courses of varying the flow
parameters—the Mach number and the inclination angle of the wedges. The conducted computations showed that a hysteresis is
possible for considered corner flows in gapped configurations, but it must be followed by a detachment of shocks from the
corner apex and a breakdown of the conical flow structure. 相似文献
4.
I. R. Smirnovskii 《Radiophysics and Quantum Electronics》1998,41(8):661-664
We study the dissipation phenomena in the front of the plasma “precursor” of a shock wave in a weakly ionized plasma without
allowance for the influence of the magnetic field. Possible energy dissipation mechanisms are discussed for the ions reflected
from the potential barrier. The potential “jump” at the precursor, front is due to ion sound dispersion and has a spatial
scale of the order of the Debye radius D. The relaxation path of the momentum of reflected ions is estimated in the case of
their scattering from electrons, which turned out to be much greater than D and much smaller than the electron free path.
It is assumed that gas ionization and fluorescence results from the essentially nonequilibrium formation of epithermal electrons
and their fast relaxation. A similar process in the decaying plasma gives rise to enhanced induced radiation.
Radiophysical Research Institute, St. Petersburg State University, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii,
Radiofizika, Vol. 41, No. 8, pp. 978–984, August, 1998. 相似文献
5.
I. R. Smirnovskii 《Technical Physics》1999,44(12):1444-1448
It is shown that multiple ion reflection, arising as a result of collisional dissipation, from a shock front can produce an
ion-sound shock wave with an arbitrarily large Mach number. For an exponentially small number of reflected ions, the ion-sound
shock wave “degenerates” into a collisionless quasishock wave. The comparative role of viscosity and sound dispersion with
different initial nonisothermality of the plasma is discussed.
Zh. Tekh. Fiz. 69, 52–56 (December 1999) 相似文献
6.
The scattering of a plane electromagnetic wave by a solitary scatterer randomly positioned near a perfectly reflecting surface
is investigated in the dipole approximation taking into account infinite multiplicity of scattering. It is shown that the
presence of multiply reflected waves increases the “effective” polarizability of the particle and adds another component of
the dipole moment along the normal to the surface. As a result, the backscattering enhancement effect becomes stronger, and
the angle of incidence at which amplification of the p-polarized wave vanishes becomes smaller. The influence of multiply scattered waves increases as the particle approaches the
boundary in this case.
Zh. Tekh. Fiz. 67, 72–75 (September 1997) 相似文献
7.
V. G. Lapin 《Radiophysics and Quantum Electronics》1997,40(7):566-571
We study the nonlinear interaction of a system of incident and reflected electromagnetic waves of arbitrary polarization,
propagating in a quasihomogeneous plane layer of isotropic plasma obliquely to the boundary, with scattered electromagnetic
waves. These waves are coupled in the double stimulated Mandelstam-Brillouin scattering by a common sound wave that is parallel
to the layer boundary. We examine the influence of the wave polarization on the threshold intensity, instability growth rate,
and characteristics of the stationary solution. It is found that the nonlinear interaction scales are different for waves
of different polarization. In particular, this leads to a change of the wave polarization in the course of the interaction.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 40, No. 7, pp. 851–859, July, 1997. 相似文献
8.
?mer Kavaklolu Baruch Schneider 《International Journal of Infrared and Millimeter Waves》2008,29(4):329-352
A rigorous analytical representation for the multiple scattering coefficients of the fields radiated by an infinite grating
of dielectric circular cylinders excited by an obliquely incident plane electromagnetic wave is derived in terms of the “well-known
scattering coefficients of an isolated dielectric cylinder at oblique incidence” and “Schl?milch series”. In addition, a generalized
sum-integral grating equation is acquired for the multiple scattered amplitude of a cylinder at oblique incidence in the grating
in terms of the scattering coefficients of the insulating dielectric circular cylinder at oblique incidence.
相似文献
9.
Stanic B.V. Drljaca P.M. Boskovic B.O. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(5):1514-1519
Electron plasma waves excitation in suddenly created isotropic plasma as a result of weak nonlinear interaction of linearly polarized plane electromagnetic (EM) wave and electrons has been considered. By the use of standard perturbation method the problem is solved in closed form for the case of a simple harmonic source EM wave. The appearance of the second harmonic and time independent modes have been demonstrated. The efficiency of excitation of these modes is possible to control by varying the frequency of the source wave 相似文献
10.
This paper deals with “waveguide holograms” recorded in a layer of storage material covering a planar dielectric waveguide.
Reference and read-out waves are guided modes of the waveguide. Their field in the storage medium is evanescent. A theory
of the diffraction efficiencies of these waveguide holograms is presented fors-polarized wavefields. To calculate the hologram structure the attenuation of the reference wave caused by absorption in the
light-sensitive storage material is taken into account. Analytical expressions for the local and the overall diffraction efficiencies
and for the intensity profiles of the diffracted fields are derived. The dependence of these quantities on experimental parameters
(the waveguide thickness, the mode numbers of the reference and read-out waves, and the angle of incidence of the plane object
wave) is presented graphically, i.e., by computer plots.
Grating couplers for integrated optics can be made by waveguide holography. We consider this application to be interesting
because incoupling efficiencies for Gaussian beams of up to 96% can be achieved theoretically. 相似文献
11.
S N Antani 《Pramana》1975,4(4):184-191
In this work, we present numerical computation of anomalous absorption of a powerful electromagnetic wave incident normally,
on an isothermal plasma with a linear density gradient. We consider first, the “intensity” dependence of anomalous absorption
treating two important cases: one that of a typical high temperature, high density fusion plasma occurring in a laser-pellet
application and the other that of an ionospheric (F-layer) plasma. It is found that for low incident powers, reflection is
almost constant, corresponding essentially, to classical electronion collisions. As we increase the incident power, however,
we find that the reflection starts dropping and the absorption takes over. This result is interpreted in terms of the instability
generated anomalous absorption of the incident wave. Next, we consider the “wavelength” dependence of anomalous absorption,
wherein we observe that the effect of anomalous absorption is increasing for longer wavelengths of the incident laser radiation. 相似文献
12.
I. L. Sheinman 《Technical Physics》2001,46(5):532-539
A study is made of stable and unstable electromagnetic surface waves at the boundaries of the plane and cylindrical relativistic plasma streams in the frequency range corresponding to positive values of the plasma permittivity. It is demonstrated that there are critical parameters for the transition from slow to fast waves, namely, the angle between the velocity and the wave vector in plane geometry and the smallest mode number in cylindrical geometry. It is shown that the critical parameter for the onset of the firehose instability of an electron stream is the transverse size of the stream. Higher firehose modes of the stream are shown to be suppressed by applying a strong longitudinal magnetic field. 相似文献
13.
The integrability conditions of the electromagnetic field equations in a continuum with defects and their wave solutions are found. The following dislocation effects on the electromagnetic wave propagation in a continuous medium are investigated: the change in the direction of the electromagnetic wave propagation in a continuous medium; the rotation of the polarization plane of electromagnetic field wave in a continuous medium; the excitation of longitudinal components of the electromagnetic wave in a continuous medium and the change in the electromagnetic wave intensity related to this phenomenon. The energy balance equation for the electromagnetic field in a continuum with a stationary distribution of dislocation is found and it is shown that an electromagnetic wave excites exciton modes localized at dislocations in the solid. 相似文献
14.
Yu. I. Mankov 《Technical Physics》2011,56(8):1147-1157
Spectrum modification and damping of Josephson plasma waves induced by random inhomogeneities of the critical current through
the superconductor contact and the averaged Green function of such excitations are analyzed. In the self-consistent approximation
that makes it possible to take into account multiple wave scattering on the inhomogeneities, the frequency and damping of
averaged waves, as well as position ν
m
and peak width Δν of the Fourier transform imaginary part of the averaged Green function, are determined as functions of
wavevector k. The evolution of such functions with the variation of the correlation radius and the relative r.m.s. fluctuations of inhomogeneities
is studied. The inhomogeneity-induced wave frequency decrease observed in the long wavelength spectral region qualitatively
agrees with the ν
m
behavior. It is established that in the case of “long-range” inhomogeneities, the linear dependence of damping on k changes to the inversely proportional one, and damping tends to zero as k → 0, while Δν at small k attains its maximal values due to nonuniform broadening. In the presence of “short-range” inhomogeneities, the wave damping
and Δν are found to be similar functions of k. The results are compared to the numerical calculation data. 相似文献
15.
Shaolin Liao Ronald J. Vernon 《International Journal of Infrared and Millimeter Waves》2007,28(6):479-490
The newly developed Taylor-Interpolation-FFT (TI-FFT) algorithm dramatically increases the computational speeds for millimeter
wave propagation from a planar (cylindrical) surface onto a “quasi-planar” (“quasi-cylindrical”) surface. Two different scenarios
are considered in this article: the planar TI-FFT is for the computation of the wave propagation from a plane onto a “quasi-planar” surface and the cylindrical TI-FFT is for the computation of wave propagation from a cylindrical surface onto a “quasi-cylindrical” surface. Due to the
use of the FFT, the TI-FFT algorithm has a computational complexity of O(N
2 log2
N
2) for an N × N computational grid, instead of N
4 for the direct integration method. The TI-FFT algorithm has a low sampling rate according to the Nyquist sampling theorem.
The algorithm has accuracy down to −80 dB and it works particularly well for narrow-band fields and “quasi-planar” (“quasi-cylindrical”)
surfaces. 相似文献
16.
V. L. Frolov V. V. Chugurin G. P. Komrakov N. A. Mityakov E. N. Myasnikov V. O. Rapoport E. N. Sergeev V. P. Uryadov F. I. Vybornov V. A. Ivanov V. V. Shumaev A. M. Nasyrov I. A. Nasyrov K. M. Groves 《Radiophysics and Quantum Electronics》2000,43(6):446-468
Experimental studies of the features of artificial ionospheric turbulence was performed at the “Sura” heating facility in
August 1998 using numerous diagnostic tools, such as scintillation, chirp-sounding, backscattering, and stimulated electromagnetic
emission (SEE) measurements, as well as sounding a HF-disturbed volume (DV) by probing waves. It has been found that generation
of strong artificial large-scale irregularities (ALSIs), which manifest themselves through the F-spread on ionograms, scintillations
of the satellite signal propagated through the DV, and amplitude fluctuations of the probing wave sounding the DV, is observed
not only for an overdense heating, at fo≤foF2, but also at higher frequencies fo>foF2≥f
uh
(here fo is the pump-wave frequency, foF2 is the critical frequency of the F2-layer for O-mode electromagnetic wave, and f
uh
is the plasma frequency at the upper-hybrid resonance height). This means that transfer of the pump-wave energy in the plasma
due to the development of thermal parametric (resonance) instability, rather than thermal self-focussing instability, plays
the key role in the ALSI generation in the case where the O-mode HF wave is used for the overdense heating. This conclusion
is also confirmed by the fact that the ALSI generation is suppressed in the gyroharmonic frequency range, which is similar
to the well-studied quenching of the downshifted maximum (DM) in SEE spectra. In this paper, we discuss new ALSI features
revealed by the measurements, as well as the limits by which one can control the ALSI spectrum using complex pumping schemes.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 6, pp. 497–519, June, 2000. 相似文献
17.
Spectral lines of Yb lasing in 1.03–1.05 μm region structured by 50–200 μm spots were found at focusing a pulsed LiF:F2+ color center laser of 0.5–5.0 GW/cm2 intensity on highly doped Yb:YAG or Yb:glass plates in a resonator. Small spots at the spectrograph located ≈ 1 m apart from
the resonator indicated a “sub-diffraction” directivity of Yb generation, 1–2 orders better than the diffraction limit 10−3–10−2 rad determined by the pumped volume dimensions. Observed features of Yb emission are explained assuming off-axis oscillations
in Yb laser on phase-synchronized photons due to a strong spatial-angular selection of radiation in the resonator. Propagation
of near diffraction free beams at angles to the axis built at the spectrograph slit for every 10–15 ns pulse of Yb generation
a magnified “image” of a structure of generating channels in the active medium. This image projection brought a corresponding
structure of spots in Yb spectra. It was found that channels may be formed due to a high-frequency spatial modulation (micrometers
scale) of the refractive index profile in samples caused by the oscillating amplitude of thermoelastic stresses in the pumped
medium. Obtained data demonstrate a possibility to study (with high spatial and temporal resolution) non-equilibrium stales
of materials in small volumes using laser radiation emerging from these objects. This study results evidence for the novel
concept of the spatial distribution of electromagnetic field of a photon: not in the form of a “travelling” wave but in the
form of a wave with maxima and nodes located at fixed positions along the photon propagation direction. 相似文献
18.
The absorption-induced acoustic-axis splitting in a viscoelastic crystal with an arbitrary anisotropy is considered. It is
shown that after “switching on” absorption, the linear vector polarization field in the vicinity of the initial degeneracy
point having an orientation singularity with the Poincaré index n = ±1/2, transforms to a planar distribution of ellipses with two singularities n = ±1/4 corresponding to new axes. The local geometry of the slowness surface of elastic waves is studied in the vicinity
of new degeneracy points and a self-intersection line connecting them. The absorption-induced transformation of the classical
picture of conical refraction is studied. The ellipticity of waves at the edge of the self-intersection wedge in a narrow
interval of propagation directions drastically changes from circular at the wedge ends to linear in the middle of the wedge.
For the wave normal directed to an arbitrary point of this wedge, during movement of the displacement vector over the corresponding
polarization ellipse, the wave ray velocity s runs over the same cone describing refraction in a crystal without absorption. In this case, the end of the vector moves
along a universal ellipse whose plane is orthogonal to the acoustic axis for zero absorption. The areal velocity of this movement
differs from the angular velocity of the displacement vector on the polarization ellipse only by a constant factor, being
delayed by π/2 in phase. When the wave normal is localized at the edge of the wedge in its central region, the movement of
vector s along the universal ellipse becomes drastically nonuniform and the refraction transforms from conical to wedge-like. 相似文献
19.
20.
Chun-Yi Wang 《International Journal of Infrared and Millimeter Waves》1986,7(3):365-378
The cyclotron maser instability is conventionally treated as a pure electromagnetic instability(5). Waveguide modes can'be equivalent to plane waves reflected slantingly upon the two sides of the waveguide. According to the principles of plasma physics(6) the electromagnetic and the electrostatic modes can't be decoupled when the wave vector isn't strictly perpendicular or parallel to the d-c magnetic field. Therefore the conventional treatment is incomplete and invalid in the case of intense beams.Vlasov kinetic theory of the cyclotron maser instability taking into account the space-charge wave is presented. It is found that the respective couplings between the negative-energy cyclotron mode and the RHCP waveguide mode as well as the fast space-charge mode are responsible for the wave-guide maser instability. 相似文献