Generation of Plasma Wave at Pump-Wave Frequency and Second Harmonic Generation at Ultrarelativistic Laser Power

In this paper, the influence of ponderomotive and relativistic nonlinearities on the filamentation of an ultraintense laser pulse is investigated in three dimensions within the paraxial ray approximations. Generation of electron plasma wave (EPW) structure at pump-wave frequency and the second harmonic generation in these filamentary structures are reported. The generation of the plasma wave is due to intensity gradient (in the transverse direction of the laser beam in filamentary structure) and density gradient (due to ponderomotive-force effect). For typical laser-plasma parameters: The laser intensity = 2.5 times10²⁰ W/cm²; the particles density = 1.9 times 10¹⁹ cm^-3; and it is found that the maximum intensity of EPW is in the range of 2.0 times 10¹³ W/cm². Interaction of the plasma wave with the incident laser beam leads to second harmonic generation, and the yield comes out to be ap 2.1 times 10^-7.