Ajay K. Upadhyay

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.

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.

Propagation of chirped laser pulses in a plasma channel

Propagation of an initially chirped, Gaussian laser pulse in a preformed parabolic plasma channel is analyzed. A variational technique is used to obtain equations describing the evolution of the phase shift and laser spot size. The effect of initial chirp on the laser pulse length and intensity of a matched laser beam propagating in a plasma channel has been analyzed. The effective pulse length and chirp parameter of the laser pulse due to its interaction with plasma have been obtained and graphically depicted. The resultant variation in laser frequency across the laser pulse is discussed.

Simultaneous evolution of spot size and length of short laser pulses in a plasma channel

Nonlinear, nonparaxial propagation of an intense, short, Gaussian laser pulse in a preformed plasma channel having a parabolic radial density profile is analyzed. The variational technique is used to obtain equations describing the evolution of laser spot size and pulse length in the channel. Relativistic nonlinearity and group velocity dispersion effects have been taken into account and numerical methods are used to study the simultaneous evolution of the laser spot and pulse length.

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.

Tailoring the laser pulse shape to improve the quality of the self-injected electron beam in laser wakefield acceleration

In laser wakefield acceleration, tailoring the shape of the laser pulse is one way of influencing the laser-plasma interaction and, therefore, of improving the quality of the self-injected electron beam in the bubble regime. Using three-dimensional particle-in-cell simulations, the evolution dynamics of the laser pulse and the quality of the self-injected beam, for a Gaussian pulse, a positive skew pulse (i.e., one with sharp rise and slow fall), and a negative skew pulse (i.e., one with a slow rise and sharp fall) are studied. It is observed that with a negative skew laser pulse there is a substantial improvement in the emittance (by around a factor of two), and a modest improvement in the energy-spread, compared to Gaussian as well as positive skew pulses. However, the injected charge is less in the negative skew pulse compared to the other two. It is also found that there is an optimal propagation distance that gives the best beam quality; beyond this distance, though the energy increases, the beam qua...

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.

Pulse distortion and modulation instability in laser plasma interaction

The present paper deals with the propagation of a short, intense, Gaussian laser pulse in plasma. Using a one dimensional model, a wave equation including finite pulse length and group velocity dispersion is set up and solved to obtain the intensity distribution across the laser pulse. It is shown that the pulse profile becomes asymmetric as it propagates through plasma. Further, the growth rate of modulation instability and range of unstable frequencies across the laser pulse have been derived and graphically analyzed.

Wakefield effects on the evolution of symmetric laser pulses in a plasma channel

The present study deals with the propagation of short laser pulses in a parabolic plasma channel. A variational technique is used to obtain simultaneous evolution equations describing the laser pulse length and spot size in the presence of relativistic and ponderomotive nonlinearities. The effect of wakefields (inside the pulse) on the propagation characteristics of the laser beam is studied. Numerical methods are used to graphically analyze the evolution of the laser pulse length and intensity.

Effect of wakefields on the propagation of a short laser pulse in a plasma channel

The effect of electric wakefields (generated inside the pulse) on the propagation of a short, asymmetric laser pulse in a plasma channel is analyzed. A nonlinear wave equation governing the propagation dynamics of a moderately intense laser pulse in a plasma channel along with equations describing the generation of wakefields is set up. The simultaneous evolution describing the pulse length and spot size in the presence of wakefields is derived using a variational technique. Using numerical methods the evolution of spot size, pulse length and intensity is graphically analyzed. The frequency chirp induced due to the combined effects of group velocity dispersion and self-phase modulation is also obtained. A comparative study of the propagation characteristics of two pulses, one having a fast rise and slow fall time while the other with a slow rise and fast fall time, has been presented.