Rohit K. Mishra

Second harmonic generation in laser magnetized–plasma interaction

When an intense laser pulse interacts with homogeneous plasma embedded in a transverse magnetic field, transverse current density oscillating with frequency twice that of the laser field is set up. This leads to generation of second harmonic radiation with significant conversion efficiency.

Self-focusing of intense laser beam in magnetized plasma

In this paper, evolution of spot size of an intense laser beam in cold, underdense, magnetized plasma has been studied. The plasma is embedded in a uniform magnetic field perpendicular to both, the direction of propagation and electric vector of the radiation field. Nonlinear current density is set up and the source dependent expansion method is used to determine the evolution of the spot size of a laser beam having a Gaussian profile. It is shown that transverse magnetization of plasma enhances the self-focusing property of the laser beam leading to reduction in critical power required to self-focus the beam.

Spot-size evolution of laser beam propagating in plasma embedded in axial magnetic field

In this paper, evolution of the spot size of an intense laser beam propagating in axially magnetized, cold, underdense plasma has been studied. The effect of longitudinal magnetization on the laser spot for a left as well as a right circularly polarized laser beam has been considered. Critical power for nonlinear self-focusing of the beam in magnetized plasma has been obtained.

Generation of wakefields and terahertz radiation in laser-magnetized plasma interaction

Analytical study of terahertz (THz) radiation generation due to wakefields produced by propagation of short laser pulses in magnetized, homogeneous plasma, in the mildly relativistic regime has been presented. The uniform magnetic field is applied along a direction perpendicular to the electric vector as well as the propagation direction of the laser field. A perturbative technique is used to obtain electric and magnetic wakefields generated within and behind the laser pulse. It is seen that the coupling of the slow velocities with the transverse magnetic field leads to on-axis THz radiation generation.

Propagation of an intense laser beam in a tapered plasma channel

Propagation characteristics and modulation instability of an intense laser beam propagating in an axially tapered plasma channel, having a parabolic radial density profile, are studied. Using the source-dependent expansion technique, the evolution equation for the laser spot is set up and conditions for propagation of the laser beam with a constant spot size (matched beam) are obtained. Further, the dispersion relation and growth rate of modulation instability of the laser pulse as it propagates through linearly and quadratically tapered plasma channels, have been obtained.

Wakefield generation and electron acceleration by intense super-Gaussian laser pulses propagating in plasma

Evolution of longitudinal electrostatic wakefields, due to the propagation of a linearly polarized super-Gaussian laser pulse through homogeneous plasma has been presented via two-dimensional particle-in-cell simulations. The wakes generated are compared with those generated by a Gaussian laser pulse in the relativistic regime. Further, one-dimensional numerical model has been used to validate the generated wakefields via simulation studies. Separatrix curves are plotted to study the trapping and energy gain of an externally injected test electron, due to the generated electrostatic wakefields. An enhancement in the peak energy of an externally injected electron accelerated by wakes generated by super-Gaussian pulse as compared to Gaussian pulse case has been observed.

Effect of chirping on the intensity profile and growth rate of modulation instability of a laser pulse propagating in plasma

This paper deals with the analytical study of the effect of chirping of a laser pulse on its intensity profile, as it propagates in plasma. Considering a matched laser beam, graphical analysis of the intensity distribution across the chirped laser pulse and growth of modulation instability has been presented. Further, considering finite pulse effects to be a perturbation, the growth rate of modulation instability of the chirped laser pulse is evaluated and compared with that obtained due to an unchirped pulse.

Propagation of sinusoidal pulse laser beam in a plasma channel

The propagation of an intense sinusoidal pulse laser beam, in a preformed plasma channel having a parabolic density profile, is analyzed. Considering a nonparaxial, nonlinear wave equation and using a variational technique, simultaneous equations describing the evolution of laser spot and pulse length are obtained. Numerical methods are used to study the effect of pulse length variation on betatron oscillations of the laser spot size as it propagates in the plasma channel. Approximate conditions for propagation of the laser pulse with a constant spot size and pulse length (matched beam propagation) are obtained.

Nonlinear propagation of sinusoidal pulse laser beam in homogeneous plasma

The propagation of an intense laser beam, having a sinusoidal pulse profile, in underdense plasma, is analyzed. Applying variational technique and using a standard trial function for the laser pulse amplitude, simultaneous equations describing the evolution of pulse length and spot size are obtained. Relativistic nonlinearity, finite pulse length, and group velocity dispersion effects have been taken into account. Using numerical methods, a graphical analysis of simultaneous evolution of laser spot size and pulse length is presented.

Filamentation instability of an intense laser beam in axially inhomogeneous plasma

The present paper deals with the filamentation instability of a linearly polarized laser beam propagating in an axially inhomogeneous plasma. A nonlinear wave equation for the laser field driven by relativistic nonlinearity is set up. The laser amplitude is considered to be perturbed in a transverse plane. Assuming an appropriate form of the perturbed amplitude, the perturbed wave equation is solved to give the growth rate of filamentation instability for a laser beam propagating in different axially varying plasma density structures.