Influence of surface waves on plasma high-order harmonic generation

The influence of surface plasma waves on high-order harmonic generation from the interaction of intense lasers with overdense plasma is analyzed. It is shown that the surface waves lead to the emission of harmonics away from the optical axis, whereas the high-order on-axis harmonics are lowered in intensity. Our simulation results indicate that surface plasma wave generation plays a crucial role in surface high-order harmonic generation experiments. Furthermore, a novel surface plasma wave generation process different from the well-known two-surface wave decay is observed in the highly relativistic regime.     

Mode-coupling assisted electron accelerations by a plasma wave

The acceleration of electrons by a plasma wave in the presence of density ripple in plasma has been investigated. Plasma density ripple can excite higher harmonics of different phase velocities of the fundamental plasma wave. The combined role of the different harmonics of the plasma wave contributes significantly in electrons energy gain during acceleration by the fundamental plasma wave. Our calculation shows that the plasma electrons gain considerable energy during the acceleration by the plasma waves in the presence of a density ripple in plasma. The initial electron energy and the ripple density play an important role for the acceleration of an electron.     

Reduction of stimulated brillouin scattering by the generation of ion acoustic harmonics

Ion wave harmonics generated by the primary ion acoustic wave excited in stimulated Brillouin scattering are shown to introduce heavy nonlinear damping of the process and to considerably reduce the anomalous reflectivity in an underdense plasma (n/n_c<0.5). The generation of ion wave harmonics acts similarly to strong linear damping and provides an alternative explanation to the heavy damping indicated by experiments.     

Fine Structure of the Local Alfven Resonances in Cold Plasma Placed in Bumpy Magnetic Field

Unlike in the case of an axial magnetic field, in which each mode of electromagnetic wave excited by an external source propagates independently, ripples in a bumpy magnetic field cause the wave to propagate as a wave envelope that contains also satellite harmonics in addition to the main harmonic. The influence of this multimodity on the distribution of electromagnetic waves within the local Alfven resonance regions is studied and compared for the following three cases. In the first case, Alfven resonance takes place for a main harmonic of the wave. In the second case, Alfven resonance occurs in the same region for two main harmonics which are coupled due to the plasma periodic axial inhomogeneity. Alfven resonance for a satellite harmonic is considered in the third case.     

A Note on Second Harmonics Generated by a Surface Wave on a Warm Plasma Half-Space

A part of the second harmonics generated through the self-interaction of a surface wave on a warm plasma half-space is shown not to have a surface wave character but represents a wave propagating obliquely away from the plasma-vacuum interface into the bulk of the plasma.     

Polar light and symmetry of electro-optical effects

General regularities of the interaction of a polar light wave synthesized from the Fourier harmonics of a fundamental frequency with a transparent centrosymmetric optically nonlinear medium are considered. The notion of light polarity is introduced and transverse electro-optical effects specific for the problem of interaction between polar light and isotropic nonlinear media (optical rectification and the linear electro-optical effect) are analyzed. Estimates of values of the effects in combination with published experimental data on optically encoded second harmonic generation in glasses indicate promising opportunities for practical application of the effects of the interaction of polar light and matter in optical systems of information recording and processing.     

The effect of the nonparabolicity of the free carriers dispersion law on the propagation of surface polaritons in a semiconductor-metal structure

The results of a study on the influence of the nonparabolicity of the free carriers dispersion law on the propagation of surface polaritons (SPs) located near the interface between an n-type semiconductor and a metal arc reported. The semiconductor plasma is assumed to be warm and nonisothermal. The nonparabolicity of the electron dispersion law has two effects. The first one is associated with nonlinear self-interaction of the SPs. The nonlinear dispersion equation and the nonlinear Schrodinger equation for the amplitude of the SP envelope are obtained. The nonlinear evolution of the SP is studied on the base of the above mentioned equations. The second effect results in third harmonics generation. Analysis shows that these third harmonics may appear as a pure surface polariton, a pseudosurface polariton, or a superposition of a volume wave and a SP depending on the wave frequency, electron density and lattice dielectric constant.     

Nonlinear second harmonic generation by light wave-plasma interaction in oscillating magnetic field

The nonlinear generation of second harmonic electromagnetic waves in a thin inhomogeneous (dense and rarefied) plasma layer (of lengthd) by obliquely and normally incident light waves is analyzed. We consider the effect of an external time-dependent magnetic field on the generation and amplification of waves. Two cases are considered, when the magnetic field oscillates at a frequency (i) equal to and (ii) double that of the incident wave. For normal incidence, waves are not radiated in case (i), while in case (ii) the second harmonics are radiated equally from the plasma boundaries atx=0 andx=d. For a rarefied plasma, the second harmonics are radiated with equal amplitudes in both cases.     

Laboratory study of nonlinear trapping of magnetized Langmuir waves inside a density depletion

The formation of a small-scale plasma density depletion region extended along the ambient magnetic field and caused by the nonlinear interaction of the upper-hybrid plasma waves with a magnetoplasma has been observed under laboratory conditions modeling the ionospheric heating experiments. Plasma waves are trapped inside the depletion due to their specific dispersion properties. The threshold of the nonlinear wave trapping significantly increases in the vicinity of the harmonics of the electron gyrofrequency.     

高功率微波在等离子体填充波导中的谐波产生

采用等离子体流体理论，研究了高功率微波在等离子体填充波导中的谐波产生，导出了非线性波动方程. 对二次谐波产生进行了数值计算与分析. 理论分析和数值计算表明，高功率微波将在等离子体填充波导中激发起谐波，TE_0n模式与TM_0n模式的基波都将激发起TM类型的谐波. 关键词： 高功率微波 谐波产生 等离子体填充波导     

Evolution of an intense elliptically polarized electromagnetic wave in underdense plasmas

An elliptically polarized electromagnetic wave in an underdense plasma acquires a longitudinal component of the electric field which oscillates as even harmonics of the fundamental frequency. The phase shift between transverse field components and the wave amplitudes exhibit nonlinear oscillations.     

Generating magnetic field pulses in the development of an explosive Alfvén wave instability in a flow-plasma system

The excitation of Alfvén radiation is studied when an explosive instability is developed in a heated gyrotropic plasma penetrated by a monovelocity flow of ionized gas. It is shown that magnetic field pulses are generated in the plasma under certain conditions. The amplitudes of the Alfvén wave harmonics are found and the conditions for stabilization of the explosion due to the nonlinear absorption associated with weakly damped Alfvén wave harmonics are specified.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 8, pp. 1001–1006, August, 1996.This work was supported in part by the Russian Foundation for Fundamental Research under Grant No. 95-02-05255.     

Half-Integer Harmonics Generation in Laser-Produced Plasma

Half integer (3/2ω₀, 1/2ω₀) harmonics generation under oblique incidence of the pump-wave on the spatially inhomogeneous plasma is theoretically investigated. Harmonics generation is connected with the two-plasmon convective instability excitation near the quarter-critical density. Harmonics spectra and intensities depend essentially on the pump wave polarization. In particular, significant harmonics spectra broadening arises under the p-polarized pump wave.     

Coulomb broadening of nonlinear resonances in a field of intense standing wave

The problem of probe-field spectrum is considered for a three-level ion placed in a field of an intense standing light wave. The ion interaction with plasma and the velocity-changing Coulomb scattering are taken into account within the weak-collision model. The system of kinetic equations for the density matrix is solved by the expansion in spatial harmonics and eigenfunctions of the collision operator. The profile of nonlinear addition to the probe-wave absorption is determined for various values of the effective ion-ion collision frequencies and various amplitudes and frequencies of standing wave. It is shown that the broadening of the central nonlinear structure in the spectrum is caused by the Coulomb dephasing effect. The computational results are in qualitative agreement with the available experimental data.     

Antenna Q Monitoring for Pulsed RF Heating Experiments

Low frequency wave heating experiments conducted on pulsed plasmas are often faced with the task of measuring low antenna resistance. This paper describes a method for monitoring the antenna-plasma Q during a plasma discharge. Knowledge of Q measured at low power can be helpful in the design of a high power antenna and its associated matching network. The concept of an effective Q is introduced and its importance in suppressing harmonics is noted. Q scans for a low frequency Alfvén wave heating experiment conducted on the PRETEXT tokamak are shown. Detailed circuitry of this diagnostic is included.     

Observation of magnetically induced transparency in a classical magnetized plasma

We report the first demonstration of magnetically induced transmission in an opaque magnetized plasma. Magnetically induced transmission in a plasma is a classical analog to the electromagnetically induced transparency in atomic systems. The transmission of radiation through an axially magnetized plasma is obtained by applying an additional one dimensional transverse spatial periodic magnetic field. The transverse-periodic magnetic field uncouples the right-hand electromagnetic wave from interacting with plasma electrons, rendering the plasma band-stop transparent. This provides means to control the extent of absorption of electromagnetic radiation in magnetized plasma.     

Excitation of short-wave oscillations in the ionospheric plasma by the field of a high-power radio wave with extraordinary polarization due to induced scattering by ions

We analyze excitation of electron-cyclotron or upper hybrid oscillations of the ionospheric plasma at a frequency that is close to the pump frequency as a result of induced scattering of a high-power radio wave with extraordinary polarization by ions. The excited oscillations have a small wavelength of the order of the Larmor electron radius, which allows them to propagate near and below the reflection level of an extraordinary radio wave. We found the instability increment and threshold field, which results from collisional absorption of plasma waves. It is shown that the threshold field is minimal near the reflection level of an extraordinary radio wave when the radio wave frequency f₀ is between electron harmonics nf_Be with n≥2. In an ionospheric F layer it is of the order of 1 W/m. Such fields are easily obtained in ionospheric heating experiments allowing for radio-wave field swelling in the reflection region. In the vicinity of electron harmonics f_o≅nf_Be, the threshold field is increasing. For f_o<nf_Be with f_o≅nf_Be the instability does not develop because of the absence of plasma oscillations with a frequency that is close to the pump frequency (the latter also refers to the case f_o<2f_Be). The expressions obtained are generalized to the case in which the instability under consideration is excited by the field of an ordinary radio wave in the region of its quasilongitudinal propagation. We discuss the possibility of using the emergence of very short-wave plasma oscillations for explaining the experimentally observed phenomena. Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow Region, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 5, pp. 541–560, May, 1997.     

Observation of Potential Relaxation Instability in a Bounded Discharge Plasma

A potential relaxation instability (PRI), which causes a periodic motion of a potential jump and plasma expansion accompanying a high-density fluctuation level (?60 percent), is observed in a bounded discharge plasma. The instability is found to create a high electron drift velocity and a spatial growth of density and potential fluctuations, and to accelerate a test wave. An additional supplement of a plasma into the boundary suppresses the instability. At the same time, the fluctuation decreases (<5 percent) and the frequency difference of the wave spectrum between nth and (n - 1) th (n is an integer) higher harmonics decreases as the frequency increases. However, when the potential relaxation instability is excited, this frequency difference keeps constant.     

Fast-Wave Resonances near the Ion Cyclotron Frequency

Wave damping has been observed for the fast (compressional) wave at frequencies that are about 10 percent above the second and third harmonics of the ion cyclotron frequency. Preliminary calculations indicate that this shift is the result of collisions. The waves were launched by a 1-turn loop around the cylindrical plasma column and damped in a magnetic beach. The highly ionized hydrogen or deuterium plasma had an average temperature of 2 eV and an average density of about 2.5 × 1020 m-3.