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Nonparaxial, nonlinear propagation of a relativistic laser pulse in a preformed plasma channel having a parabolic density profile is analyzed. Nonlinearity arises due to relativistic motion of plasma electrons and their coupling with plasma channel. The effect of nonlinearities on betatron oscillations is analyzed and the nonlinear critical channel depth required for propagation of a matched laser pulse is evaluated. Mismatch due to nonlinear effects and additional condition for matched pulse propagation are obtained. Amplitude of the matched, as well as mismatched, beam is derived and finite pulse effects are studied.

The combined effect of relativistic and ponderomotive nonlinearities on the propagation characteristics and modulation instability of a laser beam propagating through partially stripped plasma is studied. Under the present approach it is seen that the ponderomotive nonlinearity tends to defocus the laser beam as against the nonlinear relativistic self-focusing phenomenon. Also density perturbation arising due to the ponderomotive nonlinearity when combined with relativistic nonlinearity tends to increase the modulation instability of the laser beam. The peak growth rate is enhanced in comparison to the case where ponderomotive nonlinearity is neglected.

Raman backscattering in plasma is subject to—collisional and collisionless—absorption of the interacting waves. A model for studying its role over a wide parameter range is developed by coupling the envelope equations for pump, probe, and plasma waves with those describing heating of the plasma. The latter is treated as a warm fluid, making the model useful for moderate temperatures and field amplitudes. The main effect is the time-dependent Bohm–Gross shift of the Langmuir resonance frequency, which can either enhance or suppress amplification; this can be further controlled by varying the frequency of the pump. Anisotropy in the collisional processes for longitudinal and transverse waves leads to temperature anisotropy at high field amplitudes. Direct Landau damping of the plasma wave, as well as its contribution to the frequency shift, can be neglected due to rapid saturation.

Photon acceleration of a laser pulse occurs in a medium with a space and time-varying permittivity. Using Hamiltonian formulation, a theoretical study of the frequency upshift of a probe laser pulse, which is considered as a "quasiphoton" or "test particle," propagating through an amplified plasma density wake of two copropagating laser pulses, is presented. The linear superposition of wakefields studied using an analytical model shows that the presence of a controlling pulse amplifies the wake of a driver pulse. The amplified wake amplitude can be controlled by varying the delay between the two pulses. Two-dimensional particle-in-cell simulations demonstrate wake superposition due to the two copropagating laser pulses. A phase space analysis shows that the probe photon can experience a significant frequency upshift in the amplified density wake. Furthermore, the range of photon frequencies trapped and accelerated is determined by the amplitude of the density wake.

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.

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.

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.

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.

Modulation instability of a laser pulse propagating through transversely magnetized underdense plasma is studied. It is observed that interaction of laser radiation with plasma in the presence of uniform magnetic field results in an additional perturbed transverse plasma current density along with the relativistic and ponderomotive nonlinear current densities, thus affecting the modulational interaction. In the plane wave limit it is observed that modulational interaction is more stable for magnetized plasma as compared to the unmagnetized case. The analysis shows that there is a significant reduction in the growth rate of modulation instability over a given range of unstable wave numbers due to magnetization of plasma.