Ranju Mahajan

Self-focusing of cosh-Gaussian laser beam in a plasma with weakly relativistic and ponderomotive regime

This paper presents an investigation of the self-focusing of cosh-Gaussian laser beam in a plasma with linear absorption taking into account the combined effects of relativistic and ponderomotive type nonlinearities. Nonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying envelope approximation is solved using variational approach. Self-focusing and self-phase modulation as well as self-trapping of cosh-Gaussian beam are studied at various values of decentered parameter b, with different absorption levels ki′. Numerical analysis shows that these parameters play vital role on propagation characteristics.

Relativistic self-focusing and self-phase modulation of cosh-Gaussian laser beam in magnetoplasma

In this paper, we have investigated the propagation characteristics of cosh-Gaussian laser beam in magnetoplasma using relativistic nonlinearity. The field distribution in the medium is expressed in terms of beam width parameter a n and decentred parameter b . An appropriate nonlinear Schraodinger equation has been solved analytically using variational approach. The behaviour of beam width parameter with dimensionless distance of propagation ξ for various b values is examined. Self-phase modulation and self-trapping is also studied under variety of parameters. Further, the effect of magnetic field on self-focusing of the beam have been explored.

Relativistic and ponderomotive effects on evolution of laser beam in a non-uniform plasma channel

The nonlinear parabolic partial differential equation governing the evolution of the complex envelope in the slowly varying envelope approximation is solved using the variational approach. The basic nonlinear phenomena of relativistic and ponderomotive self-focusing in a plasma channel are taken into account. Self-focusing, self-phase modulation as well as self-trapping of laser beam is studied in a variety of situations. Further, in the absence of dissipation mechanisms, the stability of the beam is also studied.

Relativistic and ponderomotive effects on evolution of dark hollow Gaussian electromagnetic beams in a plasma

Nonlinear parabolic partial differential equation governing the evolution of complex envelope in slowly varying envelope approximation is solved using variational approach. The basic nonlinear phenomena of relativistic and ponderomotive self-focusing in a plasma are taken into account. Self-focusing, self-phase modulation as well as self-trapping of dark hollow Gaussian beam is studied for higher orders of hollow Gaussian beam ( n ).

Propagation of high power electromagnetic beam in relativistic magnetoplasma: Higher order paraxial ray theory

This paper presents an analysis of self-consistent, steady-state, theoretical model, which explains the ring formation in a Gaussian electromagnetic beam propagating in a magnetoplasma, characterized by relativistic nonlinearity. Higher order terms (up to r4) in the expansion of the dielectric function and the eikonal have been taken into account. The condition for the formation of a dark and bright ring derived earlier by Misra and Mishra [J. Plasma Phys. 75, 769 (2009)] has been used to study focusing/defocusing of the beam. It is seen that inclusion of higher order terms does significantly affect the dependence of the beam width on the distance of propagation. Further, the effect of the magnetic field and the nature of nonlinearity on the ring formation and self-focusing of the beam have been explored.

Relativistic self-focusing of super-Gaussian laser beam in plasma with transverse magneticfield

This paper presents an investigation of a self-consistent, theoretical model, which explains the ring formation in a super-Gaussian laser beam propagating in plasma with transverse magnetic field, characterized by relativistic nonlinearity. Higher order terms (up to r 4 ) in the expansion of the dielectric function and the eikonal have been taken into account. The condition for the formation of a dark and bright ring has been used to study focusing/defocusing of the beam. It is seen that inclusion of higher order terms does significantly affect the dependence of beam width parameter on the distance of propagation. Self-focusing of super-Gaussian beam is studied at various values of super-Gaussian coefficient, m and magnetic field. Further, we have studied some distinct features of critical power curves for varying values of magnetic field.

Self-focusing, self modulation and stability properties of laser beam propagating in plasma: A variational approach

Laboratory as well as Particle in cell (PIC) simulation experiments reveal the strong flow of energetic electrons co-moving with laser beam in laser plasma interaction. Equation governing the evolution of complex envelope in slowly varying envelope approximation is nonlinear parabolic equation. A Lagrangian for the problem is set up and assuming a trial Gaussian profile, we solve the reduced Lagrangian problem for beam width and curvature. Besides self-focusing and self-modulation of laser beam, we observe that stability properties of such plasma system are studied about equilibrium values using this variational approach. We obtained an eigen value equation, which is cubic in nature and investigated the criterion for stability using Hurwitz conditions for laser beam plasma system.

Relativistic effects on evolution of a q-Gaussian laser beam in magnetoplasma: Application of higher order corrections

In this research work, the authors have investigated the propagation characteristics of a q-Gaussian laser beam in a magnetoplasma by considering the relativistic nonlinearity. The field distribution in the medium is expressed in terms of beam width parameter f and q parameter. Higher order terms in the expansion of the dielectric function and the eikonal have been taken into account. The behavior of the beam width parameter with a dimensionless distance of propagation ξ for various values of q is examined. The phenomenon of self-trapping is also studied under variety of parameters. Further, the effect of the magnetic field on the self-focusing of the laser beam has also been explored.

Nonlinear dynamics of intense EM pulses in plasma

The evolution of laser beam in underdense/overdense plasma medium which is key to understanding of several nonlinear processes and underlying physics is governed by nonlinear parabolic equation. The nonlinearity considered here is of relativistic as well as of ponderomotive type. We have set Lagrangian for the problem and reduced Lagrangian problem is solved using appropriate trial function. Equation for the beam width and phase are derived. Further, these equations are used to solve eigen value problem for the stability of laser beam evolution and Hurwitz condition is satisfied.

Growth of high power laser ripple in plasma and its effects on upper hybrid wave excitation: Relativistic effects

The growth of a radially symmetric ripple superimposed on a single intense Gaussian laser beam in a collisionless magnetized plasma is investigated. WKB and Paraxial ray approximations are used to calculate wave equation for the main beam and the ripple. Numerical results show that the relativistic power of laser beam, the dynamics of ripple gets affected by its position and phase angle as well as some other parameters. The effect of growth of ripple on excitation of upper hybrid wave is also studied.