Terahertz Generation by Cross-Focused Cosh-Gaussian Laser Beams in Plasma

Generation of Terahertz (THz) radiations by interaction of two Cosh-Gaussian (ChG) laser beam with collisionless plasmas has been investigated theoretically. Due to the non-uniform distribution of intensity over the wave fronts of the laser beams ponderomtive force starts acting on plasma electrons which leads to the depletion of electrons from high intensity regions of illuminated portion of plasma. This modification in electrons distribution results in change in the optical properties of the plasma resulting in the cross focusing of the two laser beams. Fourier analysis indicates that the plasma electrons experience nonlinear force at difference of the frequencies of pump beams. The resulting current density due to this frequency component acts as a source for the generation of THz radiations. Dynamics of the laser beams has been investigated by solving the set of coupled nonlinear Schrodinger wave equations (NLSE) for the two laser beams with the help of variational theory. It has been observed that the decentered parameters of pump laser beams play a vital role in enhancing the efficiency of the THz generation. Key Words:cosh-Gaussian laser beam, Ponderomotive force, Nonlinear Schrodinger wave equation, Variation technique.