arXiv subjects

Jam Yazdanpanah

Publications and source records attributed to Jam Yazdanpanah.

3 recordsLinked to original sources

arXiv2018

On Nonlinear Evolutions of the Intense, Short Laser Pulse in the Under-Dense Plasma

Nonlinear evolutions of an ultra-intense, short laser pulse due to the wake excitation inside the plasma are studied by means of detailed Particle-In-Cell (PIC) simulations and comprehensive analyses. Pulse lengths both longer and shorter than the plasma wavelength are considered. It is turned out that the system shows adiabatic behavior as long as the plasma evolves very slowly in the Pulse Co-Moving (PCM) frame due to the ignorable radiation back-reactions. A sophisticated treatment of the adiabatic regime is presented, based on the proper application of the local conservation laws in the PCM frame in conjunction with the Lorentz transformations. In this context, equations for the overall pulse evolutions are reduced into a single equation in terms of the global pulse group-velocity. Due to the proven equality between the local phase velocities of the plasma wave and the radiation, anomalies are observed in this regime, in the global group velocity and the plasma dispersion. The group velocity shows non-explicit density dependency and of remaining above the linear value over a long period of the propagation. These results are successfully examined against PIC simulations and their consistency with the other system evolutions and the physical intuition is fully discussed. Afterward, the interaction locality is examined in terms of the plasma dispersion and the resultant spectral evolutions. And it is found that for pulse lengths larger than the plasma wavelength, the plasma-wave evolutions inside the pulse region result in the strong light phase-modulation along with the amplitude-modulation and whereby violation of the adiabatic description. The development of these phenomena is by production of the effective radiation back-reactions.

physics.plasm-ph↗

arXiv2015

Theory of the ultra-intense short-pulse laser interaction with under-dense plasma

A comprehensive theory is proposed to describe the propagation and absorption of ultra-intense, short laser pulse through the under-dense plasma. The kinetic aspects of plasma are fully incorporated using extensive particle-in-cell (PIC) simulations. It is turned out that the plasma behavior is characterized by both its density and the ratio of the pulse length to the plasma wavelength. According to exact analyses and direct simulation evidences, at ultra-low densities the laser pulse is adiabatically depleted (absorbed) by the wake excitation. And the depletion is accompanied by the overall radiation red-shift. At these densities, for pulse lengths larger than the plasma wavelength the Raman type scatterings also occur without causing instability. When the plasma density grows toward the critical density, a completely new regime appears with the main character of highly unsteady light propagation. Here, based on analyses and simulations, the radiation pressure induced wave breaking (RPIWB) heavily destroys the oscillatory structure of the electron wave behind the first plasma period. On the other hand, the electron density profile induced by the ponderomotive force ahead of the pulse begins to steepen and eventually acts as a flying mirror. As a result, the pulse becomes bake scattered and its penetration becomes limited. The radiation pressure of reflecting pulse sustains a longitudinal electric field which accelerates electrons produced via RPIWB causing the plasma to undergo volumetric heating. Mostly important, based on a newly proposed model it is shown that the interaction becomes saturated at a definite time and that the overall absorption and plasma heating are directly related to this time. Also it is found that the saturation time decreases by a factor of ( , and are initial electron density, critical density and initial laser gamma factor)...

physics.plasm-ph↗

arXiv2015

Electron residual energy due to stochastic heating in field-ionized plasma

The electron residual energy originated from the stochastic heating in under-dense field-ionized plasma is here investigated. The optical response of plasma is initially modeled by using the concept of two counter-propagating electromagnetic waves. The solution of motion equation of a single electron indicates that by including the ionization, the electron with higher residual energy compared to the case without ionization could be obtained. In agreement with chaotic nature of the motion, it is found that the electron residual energy will significantly be changed by applying a minor change to the initial conditions. Extensive kinetic 1D-3V particle-in-cell (PIC) simulations have been performed in order to resolve full plasma reactions. In this way, two different regimes of plasma behavior are observed by varying the pulse length. The results indicate that the amplitude of scattered fields in sufficient long pulse length is high enough to act as a second counter-propagating wave for triggering the stochastic electron motion. On the other hand, the analyses of intensity spectrum reveal this fact that the dominant scattering mechanism tends to Thomson rather Raman scattering by increasing the pulse length. A covariant formalism is used to describe the plasma heating so that it enables us to measure electron temperature inside the pulse region.

physics.plasm-ph↗