Munish Aggarwal

Combined effect of relativistic and ponderomotive nonlinearity on self-focusing of Gaussian laser beam in a cold quantum plasma

In the present paper, we have investigated self-focusing of Gaussian laser beam in relativistic ponderomotive (RP) cold quantum plasma. When de Broglie wavelength of charged particles is greater than or equal to the inter particle distance or equivalently the temperature is less than or equal to the Fermi temperature, quantum nature of the plasma constituents cannot be ignored. In this context, we have reported self-focusing on account of nonlinear dielectric contribution of RP plasma by taking into consideration the impact of quantum effects. We have setup the nonlinear differential equation for the beam-width parameter by paraxial ray and Wentzel Kramers Brillouin approximation and solved it numerically by the Runge Kutta Fourth order method. Our results show that additional self-focusing is achieved in case of RP cold quantum plasma than relativistic cold quantum plasma and classical relativistic case. The pinching effect offered by quantum plasma and the combined effect of relativistic and ponderomotive nonlinearity greatly enhances laser propagation up to 20 Rayleigh lengths.

Self-Focusing of Quadruple Gaussian Laser Beam in an Inhomogenous Magnetized Plasma with Ponderomotive Non-Linearity: Effect of Linear Absorption

The propagation of quadruple Gaussian laser beam in a plasma characterized by axial inhomogeneity and nonlinearity due to ponderomotive force in the paraxial ray approximation is investigated. An appropriate expression for the nonlinear dielectric constant has been developed in the presence of external magnetic field, with linear absorption and due to saturation effects for arbitrary large intensity. The effects of different types of plasma axial inhomogeneities on self-focusing of laser beam have been studied with the typical laser and plasma parameters. Self-focusing of quadruple Gaussian laser beam in the presence of externally applied magnetic field and saturating parameter is found significantly improved in the case of extraordinary mode. Our results reveal that initially converging beam shows oscillatory convergence whereas initially diverging beam shows oscillatory divergence. The beam is more focussed at lower intensity in both cases viz. extraordinary and ordinary mode.

Self-focusing of Gaussian laser beam in weakly relativistic and ponderomotive cold quantum plasma

The paper presents investigation on self-focusing and self-phase modulation of Gaussian laser beam in a weakly relativistic and ponderomotive regime by taking into account the quantum effects. We have reported additional self-focusing for reduced value of beam width parameter on account of nonlinear dielectric contribution of relativistic ponderomotive plasma. Moreover, the significant contribution of the quantum effects to enhance the self-focusing and minimize the longitudinal phase shift has been noticed. A comparison has also been attempted with relativistic and ponderomotive, relativistic cold quantum and classical relativistic regimes. In the present investigation, we have observed that for the case of relativistic ponderomotive cold quantum plasma, the focusing is found to be earlier and strongest. Also, the minimum amount of phase shift is obtained. We have setup the nonlinear differential equations for the beam-width parameter and self-phase modulation by using variational approach and solved the...

Resonant third harmonic generation in clusters with density ripple: Effect of pulse slippage

A model is presented for the resonant third harmonic generation of short pulse lasers in cluster plasma in the presence of density ripple. Because of ripple in cluster density and plasma electron density outside the cluster, the phase-matching condition for the third harmonic process is satisfied, leading to resonant enhancement of harmonic generation. We explore the impact of laser intensity, cluster size, and collisional frequency of electrons on the efficiency of third harmonic generation. Moreover, since the group velocity of the third harmonic wave is greater than that of the fundamental wave, it causes the slippage of the generated harmonic pulse out of the fundamental laser pulse and its amplitude increases with time.

Dynamics of filament formation in magnetized laser produced plasma

This paper presents an investigation of growth dynamics of spikes in a collisionless magnetoplasma. In most cases, magnetic field (self-generated or externally applied) permeates plasma. Therefore, it is very important to study the role of the magnetic field and growth of the spikes dynamics. In the current investigation, we have set up and solved the nonlinear differential equations for the growth and the width of the spikes in the presence of externally applied magnetic field. We have considered collisionless, magnetized plasma with ponderomotive nonlinearity. The effect of focusing/defocusing of main beam and magnetic field on growth dynamics of the spikes is studied.

Effect of the transverse magnetic field on spatiotemporal dynamics of quadruple Gaussian laser beam in plasma in weakly relativistic and ponderomotive regime

The spatiotemporal dynamics of a quadruple Gaussian laser beam in plasma is studied in the presence of an external magnetic field by taking into account the relativistic and ponderomotive nonlinearities. Using the paraxial approximation approach, two coupled equations for longitudinal (in time) and transverse (in space) beam width parameters are derived. Their evolution determines the pulse dynamics in time and space. The effects of the initial laser parameters, such as the lateral separation and laser intensity on self-focusing and self-compression mechanisms, are discussed. The results illustrate that the laser beam is focussed and compressed in an enhanced manner in the presence of an external magnetic field. The three dimensional spatiotemporal profile of the normalized intensity of the pulse is studied at different positions where the beam is either focussed or compressed. A three dimensional portrait of the normalized intensity as a function of distance and time is also shown.

Self-focusing of q-Gaussian laser beam in relativistic plasma using exponential density based transition

We have investigated self-focusing of a q-Gaussian laser beam in a relativistic plasma channel using exponential density based transition. The present paper is devoted to the importance of using a ramp density profile in decreasing the beam width parameter considerably. The preference of ramp type plays a better role in guiding the high intensity laser pulses to several Rayleigh lengths. Our results obtained from numerical analysis show that laser self-focusing can be controlled by varying laser intensity parameter, q-values and suitable density ramp parameter. We have derived the nonlinear differential equation for the beam width parameter using WKB and Paraxial ray approximation and solved it numerically using the Runge Kutta method to study the nature of self-focusing and defocusing. It is observed that self-focusing of q-Gaussian laser beam can be increased with increasing laser intensity parameter. Moreover, in case of q-Gaussian laser beam, it is easier to focus lower q-values using suitable type of...

Growth of Gaussian Spikes on Gaussian Laser Beam in a Plasma with Relativistic Nonlinearity

Summary form given only. In the present paper we have investigated the growth of a Gaussian perturbation superimposed on a Gaussian laser beam. Nonlinearity we have taken is of relativistic type. We have set up and solved ordinary differential equations for growth parameter and beam width of spike. Effects of relativistic nonlinearity have been seen and presented here.