Sharif Digital Repository

This work is devoted to improving relativistic self-focusing of intense laser beam in underdense unmagnetized plasma. New density profiles are introduced to achieve beam width parameter up to the wavelength of the propagating laser. By investigating variations of the beam width parameter in presence of different density profiles it is found that the beam width parameter is considerably decreased for the introduced density ramp comparing with uniform density and earlier introduced density ramp profiles. By using this new density profile high intensity laser pulses are guided over several Rayleigh lengths with extremely small beam width parameter  

A high intensity laser normal incident (1020 W/cm2) on a vacuum-plasma interface produces high harmonics in reflected components. Efficiency of high harmonics increases with the intensity laser incident. So the non-relativistic velocities of the particles vary to the relativistic velocities. Consequently, electrons in such high fields are predicted to quiver nonlinearly, moving in figure eight patterns, rather than in straight lines, and thus to radiate photons at harmonics of the frequency of the incident laser light. To meet the challenge of high power, short wavelength coherent radiation generation, it is quite to investigate the conditions under which harmonics generation efficiency can... 

A high intensity laser incident on a vacuum-plasma interface, insert an Intensive electromagnetic force on electrons and charged particles. Relativistic charged particle movements lead to the high order harmonics generation of the incident wave. Efficiency of high harmonics increases with the intensity laser incident, So that the non-relativistic velocities of the particles vary to the relativistic velocities. Efficiency of high harmonics increases with the intensity laser incident. In previous works that has done in this field the researcher have reported-odd harmonics generated in direction of propagation of laser incident and even harmonics generated in normal direction of propagation of... 

The propagation of a Gaussian beam in underdense plasma with upward increasing density ramp is analyzed. In this work are shown that the spot size oscillations of laser beam increases and its amplitude shrinks with proper plasma density ramp. This causes the laser beam to become more focused and penetrations deep into the plasma by reduction of diffraction effect. The related focusing parameters are optimized to get the best possible focusing at the relativistic threshold intensity of Nd-glass laser and the effect of the laser intensity in the self-focusing parameters is also investigated. The analytical calculations are presented and showed more reliable results in comparison to the... 

In this work propagation of a high frequency electromagnetic wave in underdense plasma in presence of an external magnetic field is investigated. When a constant magnetic field perpendicular to the motion of electrons is applied, then the electrons rotate around the magnetic field lines and generate electromagnetic part in the wake with a nonzero group velocity. By using of the Maxwell equations and nonlinear differential equation for the electric field a direct one-dimensional (1D) procedure for calculating hydrodynamic equations are developed and the electric and magnetic field profiles in the plasma are investigated. It is shown that by using the external (dc) magnetic field in constant...