共查询到20条相似文献,搜索用时 15 毫秒
1.
A theory of the propagation instability of plane, monochromatic, circularly polarized electromagnetic waves of relativistic
intensity in matter is developed for a spatially three-dimensional geometry including arbitrary polarization of the scattered
radiation. Harmonic generation owing to striction and relativistic nonlinearity is examined, as well as scattering owing to
electron recoil, the decay instability of the harmonics with formation of scattered electromagnetic waves (Stokes components
of the stimulated Raman scattering and plasmons), the interaction of electromagnetic waves in the plasma (antistokes stimulated
Raman scattering), and the generation of a radiative continuum. The transition of the three-dimensional theory to a one-dimensional
problem in the nonrelativistic limit is discussed.
Zh. éksp. Teor. Fiz. 113, 2034–2046 (June 1998) 相似文献
2.
The polarization of the high harmonics generated in plasmas by the bremsstrahlung of electrons oscillating under the influence
of high-power plasma-heating electromagnetic radiation is described on the basis of a simple model of a cold plasma. It is
shown that when the polarization of the heating radiation differs from plane polarization by a small but finite amount, the
high harmonics are generated with almost perpendicular polarization, and the degree of circular polarization of the harmonics
increases with the number of the harmonic.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 313–316 (10 March 1998) 相似文献
3.
The excitation of electromagnetic pulses is examined in various generation schemes. The physical mechanism for excitation
of the radiation is studied and the field from transition radiation by high current relativistic electron beams is analyzed.
An analysis of the efficiency of the various generation schemes shows that the electron efficiency of beam radiators based
on transition radiation may be quite substantial for beam parameters that are easily realized experimentally.
Zh. Tekh. Fiz. 69, 90–95 (October 1999) 相似文献
4.
The theory of spatiotemporal dynamics of gamma radiation in a resonant medium upon excitation of two-frequency gamma magnetic resonance in magnetic materials is considered. The radiation absorption at the fundamental frequency and the harmonic generation are investigated under conditions when the frequency of gamma radiation is shifted by the half-sum or half-difference of the frequencies of radio-frequency magnetic fields. It is shown that the propagation of gamma radiation through an absorber is characterized by a steady-state gamma intensity (resonant transparency). A consistent radio-frequency spectral analysis demonstrates that the intensities of harmonics drastically change at the transparency region boundaries due to nonlinear interference. The theory of quantum and dynamical beats of synchrotron radiation under conditions of induced resonant transparency is proposed. 相似文献
5.
Radiative processes in a nonequilibrium e-h plasma are theoretically studied using a self-consistent solution of the kinetic equation and Maxwell’s equations. The terahertz emission from a finite-thickness semiconductor sample is due to the retardation and nonstationarity of the electromagnetic interaction of the photocurrent in the e-h plasma and the radiation field. The duplex waveform of the terahertz electromagnetic pulse for an arbitrary ratio of the radiation formation length and the plate thickness originates due to coherent radiative processes accompanying the generation of the e-h plasma at the input boundary and its extinction at the output boundary of a semiconductor plate through which a weakly absorbed ultrashort laser pulse propagates. The theoretical conclusions show analogies with the radiative phenomena accompanying the start-stop motion of external currents (Tamm problem) and the nonlinear interaction of optical waves in a finite-thickness medium. 相似文献
6.
A self-consistent theory is developed for current drive by intense radiation in the presence of the ion-acoustic instability.
The spectrum of ion-acoustic turbulent noise generated by the driven current and concentrated in a limited cone of angles
along the propagation direction of the wave is found. Excitation of the instability is accompanied by the establishment of
an electron drift that is excited by the electromagnetic wave and has a velocity on the order of the ion acoustic speed. This
current drive regime is realized over a wide range of intensities, as long as the region of turbulence in the angles of the
acoustic wave vector is expanding. At yet higher intensities, the driven current increases in proportion to the intensity
of the fundamental wave. Similar behavior is found for driven heat fluxes.
Zh. éksp. Teor. Fiz. 111, 107–119 (January 1997) 相似文献
8.
High-order optical-harmonic generation in nonmetallic films interacting with pulses of laser light is examined. The wave functions
of the current carriers in a crystal in an external electromagnetic field are chosen in the form of Volkov-Keldysh solutions.
An explicit expression for the intensity of the sth harmonic, which depends on the crystal parameters, is derived. A plateau and a cutoff effect, similar to those in the case
of harmonic generation on an isolated atom, have been detected. Finally, numerical estimates are made for GaAs films excited
by pulses of radiation from a carbon dioxide laser.
Zh. éksp. Teor. Fiz. 112, 89–96 (July 1997) 相似文献
9.
The mechanisms of self-consistent interaction of tubular relativistic electronic beams with the fields of super-dimensional
periodic structure of a relativistic diffractive generator have been studied in the area of 2 π-type oscillations of fundamental mode. Numerical analysis was carried out with the use of the matrix multimode method in
its nonstationary variation. The electromagnetic field profiles, their mode structure, and their radiation spectrum have been
studied. The conditions for generating frequency stabilization concerned with the longitudinal resonance of the surface spatial
harmonics and volume resonance at the cutoff frequency of the E
0n
mode of cylindrical waveguide have been revealed. 相似文献
10.
The nonlinear optical response of armchair single-walled carbon nanotubes under high-intensity laser irradiation is investigated theoretically and numerically because the generation of high harmonics requires a strong laser field and come from the nonlinear motion of π electrons in carbon nanotubes. A nonperturbative approach is performed to investigate the effect of group velocity on the high harmonics spectrum by nanotubes. A set of the quantum kinetic equations is derived, which includes coupled equations for the density matrix. By solving the density matrix and the current density equations numerically, we have studied the high-order harmonic generation from metallic carbon nanotubes driven by an electromagnetic external field. 相似文献
11.
We analyze the interference between two processes of higher harmonic generation (HHG) in plasma containing mixtures of different
materials (silver and gold nanoparticles, as well as graphite and boron). We find that, for mixtures and individual ingredients,
the limiting orders of generated harmonics of laser radiation approximately coincide with one another. At the same time, for
plasma torches formed by the ablation of mixtures of materials, the HHG efficiency is considerably reduced compared to the
case of the frequency transformation of laser radiation in individual ingredients of these mixtures as a result of destructive
interference in the former case. We demonstrate a considerable spectral broadening of harmonics generated in laser plasma
with pulses passed through filaments formed in air. In this case, the HHG efficiency increases fourfold (from 3 × 10 −6 to 1.2 × 10 −5) compared to the case of radiation free of phase and frequency modulation. The generation of harmonics is also observed upon
the passage of 120-fs laser pulses through plasma containing fullerenes. In this case, the limiting value of generated harmonics
achieves the 33rd order. The efficiency of harmonics in fullerene plasma considerably exceeds a similar process in silver
plasma. 相似文献
13.
Instability of the propagation of nonlinear nonmonochromatic relativistic-intensity electromagnetic waves in a cold subcritical-density
plasma is analyzed in three-dimensional geometry. Angular diagrams of their scattering are presented. The calculations show
that forward and backward scattering may occur. The radiation in a specific direction is a set of harmonics, propagating against
a continuum background, whose frequencies depend on the angle. Radiation at a specific frequency propagates in a set of scattering
cones. The azimuthal cone angles depend on frequency.
Zh. éksp. Teor. Fiz. 116, 1947–1962 (December 1999) 相似文献
14.
Experiments on the generation of high optical harmonics demonstrating that relativistic regimes of interaction of radiation with matter can be implemented in the field of mid-infrared laser pulses with a peak power of 0.3 TW have been reported. The observation of relativistic phenomena at such extraordinary low peak powers of the laser field becomes possible because of the formation of a high-quality space-time mode of the laser field with an exactly specified polarization state. Such a field structure ensures a high intensity of radiation in the focus of the beam and the effective acceleration of electrons by a low-frequency electromagnetic field of a high-contrast laser pulse with an exactly specified polarization at the extremely sharp vacuum-solid interface. 相似文献
15.
Small oscillations of the charge in a rectangular waveguide are considered. The electromagnetic field generated by these oscillations
and its effect on the charge are investigated. It is found that at a certain frequency there is a self-consistent regime of
oscillations wherein the charge oscillates under the influence of its self-field in the absence of external forces. The combination
of such a charge and the self-consistent alternating field has the property of a quasiparticle, which is named an electromagneton.
Zh. Tekh. Fiz. 67, 120–121 (November 1997) 相似文献
16.
Harmonic generation from relativistically oscillating plasma surfaces formed during the interaction of high contrast lasers
with solid-density
targets has been shown to be an efficient source of extreme ultraviolet (XUV) and X-ray radiation. Recent work has demonstrated
that the exceptional
coherence properties of the driving laser can be mirrored in the emitted radiation, permitting diffraction limited performance
and attosecond phase
locking of the harmonic radiation. These unique properties may allow the coherent harmonic focusing (CHF) of high harmonics
generated from solid
density targets to intensities on the order of the Schwinger limit of 10 29 W cm -2 with laser systems available in the near future [Phys. Rev. Lett. 93, 115002 (2004)] and thus pave the way for unique experiments exploring the nonlinear
properties of vacuum on ultra-fast timescales. In this paper we investigate experimentally as well as numerically the prospect
of focusing high
harmonics under realistic experimental conditions and demonstrate, using particle in cell (PIC) simulations, that precise
control of the wavefronts
and thus the focusability of the generated harmonics is possible with pre-shaped targets. 相似文献
17.
以电子回旋脉塞非线性理论为基础, 结合三维电磁仿真软件, 通过导入高频场数值解替代理论解析的方法, 对波瓣波导谐振腔高次谐波太赫兹回旋管进行了理论和模拟研究. 给出了该类回旋管的起振电流、耦合系数以及注波互作用效率等重要参数, 并在此基础上设计了一只工作频率为0.4 THz, 工作模式TE 33模三次谐波波瓣波导谐振腔回旋管, 其电子注参数为1.0 A, 40.5 kV, 横纵速度比1.5,互作用区引导磁场为5.09 T, 输出功率达到3.3 kW. 相似文献
18.
Specific features of optical and nonradiative transitions in molecular systems in the field of an intense electromagnetic wave are studied with account of squeezed vibrational states. It is shown that a field of laser radiation considerably enhances the tunneling processes in electronic vibrational systems and makes it possible to obtain the generation of higher harmonics. Conditions are found under which squeezed vibrational states can lead to some stabilization of excited electronic states with respect to the processes of luminescence. 相似文献
19.
A new framework is introduced for kinetic simulation of laser–plasma interactions in an inhomogeneous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell’s equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell’s equations are solved using an Ohm’s law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere’s law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies. 相似文献
20.
The self-induced transparency effects that emerge when short (on the relaxation time scale) light pulses propagate in a two-level
noninverted medium are well known in optics. The interaction of microwave pulses with an initially rectilinear electron beam
under cyclotron resonance conditions can serve as a classical analog of the described effects. In this case, at a certain
intensity of the input signal, the cyclotron absorption is replaced by self-induced transparency when the input pulse propagates
almost without any change of its profile, forming a soliton whose amplitude and duration are rigidly related to its velocity.
In a certain domain of parameters, this process is accompanied by significant two- or threefold compression of the initial
pulse, which is of practical interest for the generation of multigigawatt picosecond microwave pulses. Since the soliton velocity
lies between the unperturbed group velocity of the radiation and the translational velocity of the particles, another nontrivial
effect in the case of interaction with a counterpropagating electron beam is the possibility of a significant deceleration
or full stopping of the electromagnetic pulse. 相似文献
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