Manzoor Ahmad Wani

Density Transition Based Self-Focusing of cosh-Gaussian Laser Beam in Plasma with Linear Absorption ⁄

Density transition based self-focusing of cosh-Gaussian laser beam in plasma with linear absorption has been studied. The field distribution in the plasma is expressed in terms of beam width parameter, decentered parameter, and linear absorption coefficient. The differential equation for the beam width parameter is solved by following Wentzel–Kramers–Brillouin (WKB) and paraxial approximation through parabolic wave equation approach. The behaviour of beam width parameter with dimensionless distance of propagation is studied at optimum values of plasma density, decentered parameter and with different absorption levels in the medium. The results reveal that these parameters can affect the self-focusing significantly.

Self-Focusing of Hermite-Cosh-Gaussian Laser Beams in Plasma under Density Transition

Self-focusing of Hermite-Cosh-Gaussian (HChG) laser beam in plasma under density transition has been discussed here. The field distribution in the medium is expressed in terms of beam-width parameters and decentered parameter. The differential equations for the beam-width parameters are established by a parabolic wave equation approach under paraxial approximation. To overcome the defocusing, localized upward plasma density ramp is considered, so that the laser beam is focused on a small spot size. Plasma density ramp plays an important role in reducing the defocusing effect and maintaining the focal spot size up to several Rayleigh lengths. To discuss the nature of self-focusing, the behaviour of beam-width parameters with dimensionless distance of propagation for various values of decentered parameters is examined by numerical estimates. The results are presented graphically and the effect of plasma density ramp and decentered parameter on self-focusing of the beams has been discussed.

Self-Focusing/Defocusing of Chirped Gaussian Laser Beam in Collisional Plasma with Linear Absorption*

This paper presents an investigation on the self-focusing/defocusing of chirped Gaussian laser beam in collisional plasma with linear absorption. We have derived the differential equation for the beam width parameter by using WKB and paraxial approximations and solved it numerically. The effect of chirp and other laser plasma parameters is seen on the behavior of beam width parameter with dimensionless distance of propagation. The results are discussed and presented graphically. Our simulation results show that the amplitude of oscillations decreases with the distance of propagation. Due to collisional frequency, the laser beam shows fast divergence which can be minimized by the introduction of chirp parameter. The chirp decreases the effect of defocusing and increases the ability of self-focusing of laser beam in collisional plasma.

Relativistic propagation of Hermite-Gaussian laser beams in plasma with density transition

Propagation of Hermite-Gaussian laser beam in a collision-less plasma with density transition has been investigated by taking in to account the relativistic effect. The differential equation for beam width parameter is obtained by using paraxial approach. The spot size of the laser beam decreases as the beam penetrates deeper in to the plasma due to the role of a plasma density ramp. Since the laser beam shows an oscillatory self-focusing and defocusing behavior with the propagation distance. The density ramp could be important for the self-focusing of a high-power laser by choosing the suitable laser and plasma parameters. To reduce the defocusing, localized upward plasma density ramp is introduced, so that an earlier and stronger self-focusing is obtained.