Relativistic-ponderomotive effect on the self-focusing of a high-intensity cosh-Gaussian laser beam in plasma: higher-order paraxial regime

This paper presents the self-focusing study of a high intensity cosh-Gaussian laser beam in a collisionless plasma under the combined effect of relativistic and ponderomotive nonlinearity. The highly intense laser beam exerts relativistic-ponderomotive force on the plasma electrons, which modifies dielectric constant/refractive index of the plasma. This study is carried out in a higher-order paraxial ray approximation where higher order terms are taken into account in the expansion of the dielectric function and the eikonal. The nonlinear differential equations for the beam width parameter and the laser beam intensity have been obtained and numerically solved for the specific laser and plasma parameters. The self-focusing of the cosh-Gaussian laser beam has been analysed for different values of the decentred parameter (b) of the beam, plasma density (omega(p0)/omega(0)) and laser intensity (a). The results show that these parameters play an important role for the self-focusing of the cosh-Gaussian laser beam in the plasma. It is found that the focusing of laser beam becomes strong at higher values of a, omega(p0)/omega(0), and b, respectively. The results have also been compared with paraxial region as well as only with relativistic nonlinearity. It is observed that the focusing of the laser beam becomes sharp in the higher-order paraxial region with relativistic-ponderomotive nonlinearity. The self-trapping of the beam has also been studied.