Self-focusing Of Electromagnetic Beams Research Articles

Distortion of an amplitude modulated electromagnetic signal with time-dependent dust charging

AbstractA large amplitude modulated Gaussian electromagnetic beam propagating in a dusty plasma with dust charge fluctuations has been studied. The electrons are heated non-uniformly by the electromagnetic beam. For non-steady state, we obtain nonlinear current density in the presence of dust grains. This expression has been used to study the non-stationary self-focusing and resulting self-distortion of the amplitude modulated electromagnetic beam. It has been observed that the dust charge fluctuation increases the self-focusing of electromagnetic beam. It is also found that the effect of dust charge fluctuations is significant on the modulation index.

Self-focusing of electromagnetic beams in the ionosphere considering Earth's magnetic field

AbstractIn this paper the focusing/defocusing of (i) a single Gaussian electromagnetic beam and (ii) a number of coaxial Gaussian electromagnetic beams, propagating in the extraordinary mode along the Earth's magnetic field in the ionosphere has been investigated in the paraxial approximation. The growth of a sinusoidal instability on account of self-focusing has also been studied. The nonlinearity in the dielectric function, responsible for the focusing/defocusing arises from the redistribution of the electron density, caused by the non-uniform distribution of the electron temperature. The electron temperature is determined by the energy balance for electrons/ions taking into account the Ohmic heating, the collisions and the radiation from the sun. The wave frequency has been assumed to be greater than the plasma frequency. The electron cyclotron frequency due to the Earth's magnetic field in the ionosphere is much larger than the electron collision frequency. This is specifically true for a height of 150 km. Numerical results have been presented for a range of parameters and a discussion of the same has been presented.

Ring formation in self-focusing of electromagnetic beams in plasmas

This article presents a paraxial theory of ring formation as an initially Gaussian beam propagates in a nonlinear plasma, characterized by significant collisional or ponderomotive nonlinearity. Regions in the axial irradiance-(beamwidth)−2 space, for which the ring formation occurs and the paraxial theory is valid, have been characterized; for typical points in these regions the dependence of the beam width parameter and the radial distribution of irradiance on the distance has been specifically investigated and discussed.

Self-focusing of electromagnetic beams in collisional plasmas with nonlinear absorption

In this paper the formalism of self-focusing of electromagnetic waves is extended to include nonlinear absorption by the medium. A complex eikonal has been employed, which does not need any approximation about the relative magnitudes of the real and imaginary parts of the dielectric constant or their dependence on the irradiance of the beam. The specific case of collisional plasmas has been considered as an application of the theory. It is seen that the nonlinearity in absorption tends to cancel the effect of divergence on account of diffraction. The dependence of the beam width and attenuation on distance of propagation has been illustrated for specific cases. The relevance of the investigation to radio wave propagation has also been pointed out.

Minimum power requirements for efficient four-wave mixing and self-focusing of electromagnetic beams in glasses and fluids.

We derive general expressions for the efficiency of cw phase conjugation by degenerate four-wave mixing and for the power ${P}_{\mathrm{cr}}$ for cw self-trapping of coherent electromagnetic beams in fluids and glasses in which these effects arise predominantly from driven nuclear motions (molecular vibrations, molecular reorientation, elastic deformations, etc.). Apart from their dependence on beam frequency \ensuremath{\omega}, medium temperature T, and refractive index n, these expressions are functions only of the integrated (polarized and depolarized) light scattering strengths versus scattering angle in the medium and the attenuation coefficient \ensuremath{\alpha}. There is no other dependence on the scattering mechanism. When attenuation is entirely due to scattering, the expressions simplify and suggest that unprecedented low powers (in the microwatt regime for microwaves) can produce self-focusing and strong phase conjugation, as well as other beam mixing effects, when beam geometries are optimized in the scattering medium. In this case we find, for example, ${P}_{\mathrm{cr}}$\ensuremath{\sim}${\mathrm{nk}}_{B}$T${\ensuremath{\omega}}^{2}$/c\ensuremath{\alpha} (${\mathrm{k}}_{\mathrm{B}}$ is Boltzmann's constant and c is the velocity of light) provided that there is significant beam diffraction in length ${\ensuremath{\alpha}}^{\mathrm{\ensuremath{-}}1}$. Our results also apply to some other media such as electron plasma.

Self-focusing of electromagnetic beams in semiconductors

The self-focusing of an electromagnetic beam in parabolic and nonparabolic semiconductors has been investigated in the presence of a longitudinal magnetic field. The wave equation has been solved in paraxial ray and WKB approximations by expanding the dielectric tensor as epsilon = epsilon f(EE* mod r=0)+ gamma r2. No restriction is put on the amount of nonlinearity and the effect of the self-induced inhomogeneity is taken into account. For intense beams and strong magnetic fields, the nature of self-focusing is considerably different from that predicted by earlier analyses. The self-made waveguide propagation is discussed in detail.

Self-focusing of electromagnetic beams in a flowing plasma: kinetic approach

Studies the self-focusing of a Gaussian electromagnetic beam in a collisional plasma, flowing transverse to the direction of propagation. On account of the finite flow velocity of the plasma, the collision term in the Boltzmann transfer equation gets modified. Hence the heating of the carriers and diffusion in the presence of the Gaussian beam becomes flow velocity dependent; the self-focusing of the beam thus gets considerably modified.

950. The self-focusing of electromagnetic beams in a strongly ionized magnetoplasma: M Sodha et al,J Phys D: Appl Phys, 7 (16), 1974, 2188–2197

950. The self-focusing of electromagnetic beams in a strongly ionized magnetoplasma: M Sodha et al,J Phys D: Appl Phys, 7 (16), 1974, 2188–2197

The self-focusing of electromagnetic beams in a strongly ionized magnetoplasma

The paper presents an investigation of the self-focusing of Gaussian electromagnetic beams propagating in a strongly ionized plasma along a static magnetic field. The nonlinearity in the dielectric tensor of the plasma arises because of the heating and consequent redistribution of electrons along the wavefront. At low values of magnetic field the main source of electron energy dissipation is thermal conduction; for large magnetic fields the carrier mean free path becomes comparable to or greater than the Larmor radius of the electrons, and the collisional loss of energy becomes dominant. This investigation reveals that the length of self-focusing of the beam in the extraordinary as well as ordinary mode of propagation is reduced by the application of the magnetic field, for low values of the magnetic field (ωc double less-than sign ω). For higher values of the magnetic field the self-focusing of the extraordinary mode is further enhanced while that of the ordinary mode is reduced.

Self focusing of electromagnetic beams in InSb: Predominance of nonlocal effects

On the basis of a phenomenological treatment, the nonlinear dielectric constant of nondegenerate nonparabolic semiconductors like InSb (having both +e and −e carriers) has been studied for Gaussian electromagnetic beams. The nonlinearity resulting from redistribution of carriers in the sample at low temperatures has been shown to be an order of magnitude higher than that due to the non-parabolicity of energy bands. Self focusing of electromagnetic beams as a result of these nonlinearities has been discussed.