EM Beam Research Articles

Resonant excitation of the upper hybrid wave by two em beams

Resonant excitation of an upper hybrid wave by the mixing of two coaxial Gaussian em beams in a collisionless hot magnetoplasma has been investigated; the electric vectors of beams are polarized along a uniform static magnetic field and the beams propagate perpendicular to the magnetic field. The resonant excitation of the upper hybrid wave occurs when the difference frequency of the two em waves and difference of their propagation vectors satisfy the dispersion relation corresponding to the upper hybrid wave. Furthermore, because of the Gaussian intensity distribution of the two beams the electrons are redistributed by the ponderomotive force, cross focusing of the two em beams occurs, and the power of the excited upper hybrid beam (which depends on the background electron concentration, the intensities of the two em beams, and the magnetic field) are correspondingly modified. The present analysis is also applicable to an inhomogeneous magnetoplasma in the WKB approximation.

Excitation of a plasma wave by a right-handed Gaussian EM beam

This paper presents an investigation of the excitation of an electron plasma wave in a hot collisionless magnetoplasma by a right-handed Gaussian EM beam (pump wave) when the plasma wave and the pump wave are propagating along the static magnetic field. On account of the Gaussian intensity distribution of the pump wave, pondermotive force becomes finite and the electrons are redistributed. This redistribution is highly dependent on whether ωc≳2ω0 or ωc<2ω0, where ωc is the electron cyclotron frequency and ω0 is the pump-wave frequency. The modified background electron density leads to coupling between the plasma wave and the pump wave. When the initial power of the pump wave is greater than the critical power for self-focusing, oscillatory self-focusing of the pump wave occurs and the coupling of the two waves are modified. Moreover, the effect of changing the intensity of the magnetic field affects the self-focusing of the pump wave, and the plasma-wave excitation is accordingly affected.

Cross-focusing of two co-axial Gaussian electromagnetic beams in a magnetoplasma and plasma wave generation

Presents an investigation of the cross-focusing of two Gaussian electromagnetic beams (two-dimensional) and consequent plasma wave generation at difference frequency Delta omega (= omega 1 approximately omega 2; omega 1 and omega 2 being angular frequencies of the two pump waves) in a hot collisionless magnetoplasma. The two Gaussian EM beams are assumed to be propagating along the static magnetic field in the extraordinary mode. Because of Gaussian intensity distribution of the two EM beams ponderomotive force becomes finite and redistribution of the electrons occurs. If the initial powers of the two EM beams are more than the critical powers for self-focusing, the beams get self-focused. The fact that the ponderomotive force is dependent on the intensities of both the beams, leads to 'cross-focusing' i.e. focusing of one beam is affected by the other. Plasma wave generation at difference frequency which depends on the background electron density and effective intensity of the two beams gets accordingly modified. It is seen that the magnitude of the magnetic field considerably affects the plasma wave excitation.

Excitation of a plasma wave by two coaxial Gaussian EM beams

In the present paper we have investigated the excitation of a plasma wave of frequency Δω=ω1∼ω2 in a collisionless hot plasma by two coaxial Gaussian EM beams of frequencies ω1 and ω2 and propagating in the same direction. The mechanism of nonlinearity is assumed to be ponderomotive force arising because of Gaussian intensity distribution of the beams. In the presence of two beams, the nonlinearities introduced by two beams are additive if the difference frequency Δω is comparable to ω1 or ω2 and, hence, cross focusing occurs. For a given power of one beam, the nature of self-focusing becomes considerably modified by changing the power of the second beam. The power associated with the excited plasma wave, which depends on the background electron concentration and the intensity of the two beams, becomes drastically modified with the distance of propagation. The theory presented here is also applicable to a slightly inhomogeneous collisionless hot plasma within the WKB approximation.

Generation of a plasma wave and second harmonic in a magnetoplasma

This paper presents an investigation of the generation of a plasma wave and a second-harmonic electromagnetic wave in a collilsionless hot magnetoplasma by a Gaussian EM beam (pump wave) propagating perpendicular to a static magnetic field in the ordinary mode. Because of the Gaussian intensity distribution of the EM wave, the ponderomotive force becomes finite and the electrons become redistributed; the electron density gradient (so created) and the intensity gradient of the EM wave lead to the generation of a plasma wave at the pump-wave frequency. The intensity of the magnetic field significantly affects the plasma-wave generation. When the pump-wave frequency is equal to the upper-hybrid frequency, resonant excitation of the plasma wave occurs. The plasma wave interacting with the pump wave leads to the generation of a second-harmonic electromagnetic wave. Moreover, as the pump wave propagates in the plasma, its self-focusing occurs; consequently, the plasma-wave and the second-harmonic generation become drastically affected.

Thin Substrate Structure and Electron Scattering after EM Beam Exposure

Electron diffraction studies of organic substrates after electron beam exposure suggest that all have a common structure. As estimated by electron scattering, substrates produced from Parlodion appear to be thinner than those described by Williams et al. as being 7 AU thick.The changes in organic materials produced by electron irradiation have been investigated by a number of researchers. Bahr et al. showed that, in general, irradiation will cause mass loss and that a considerably larger proportion of carbon than of other elements is retained in the final product. For example, an exposure of 3 × 10−2 coulombs/cm2 at 75 kV caused a 54% mass loss and 25% carbon loss in a Formvar film. Earlier investigations showed a 75% mass loss in Parlodion (nitrocellulose) films at the same dose of 70 keV electrons. We have investigated the structural changes in common substrate materials using electron diffraction studies.