Abstract
In this work role of density profiles for the nonlinear propagation of intense laser beam through plasma channel is analyzed. By employing the expression for the dielectric function of different density profile plasma, a differential equation for beamwidth parameter is derived under WKB and paraxial approximation. The laser induces modifications of the dielectric function through nonlinearities. It is found that density profiles play vital role in laser-plasma interaction studies. To have numerical appreciation of the results the propagation equation for plasma is solved using the fourth order Runge-Kutta method for the initial plane wave front of the beam, using boundary conditions. The spot size of the laser beam decreases as the beam penetrates into the plasma and significantly adds self-focusing in plasma. This causes the laser beam to become more focused by reduction of diffraction effect, which is an important phenomenon in inertial confinement fusion and also for the understanding of self-focusing of laser pulses. Numerical computations are presented and discussed in the form of graphs for typical parameters of laser-plasma interaction.
Highlights
There has been considerable interest in the interaction of laser beam with plasma
The dielectric constant of the plasma depends on amplitude of laser beam, which further changes the propagation characteristics of the laser beam
For ultrafast laser pulses lasting the order of a picoseconds or less, the drift velocity of electrons in a plasma can be comparable to the velocity of light, causing a significant increase in the mass of the electron and in the effective dielectric constant of the plasma
Summary
There has been considerable interest in the interaction of laser beam with plasma. Among the nonlinear optical effects, the self-interaction of intense laser beam occupies a significant place. The ponderomotive expulsion of electrons from the beam path such that the ponderomotive force is balanced by the electrostatic field set up between the displacement electrons and the ions that remains on axis These factors lead to a positive focusing effect that becomes stronger as the laser beam decreases in diameter and becomes more intense. A preformed plasma density profile can prevent the beam diffraction and allows the propagation of an intense laser beam with long distance, and this is beneficial to the abovementioned applications In view of this in the present paper we have made an analytical investigation followed by numerical calculations to study relativistic ponderomotive self-focusing of a laser beam in inhomogeneous plasma with different density profiles. Numerical results and discussions are made supported by figures
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