Dynamics of laser beams in inhomogeneous electron positron ion plasmas

Nonlinear interaction of laser and electron–positron–ion plasmas is investigated by invoking the variational principle and numerical simulation, in terms of a nonlinear Schr o¨dinger equation with inhomogeneities effect. It is shown that the plasma inhomogeneity has great influence on the laser beam dynamics. The laser beam can be self-trapped, focused, or defocused depending on the inhomogeneity character. The linearly decreasing axial plasma density makes the laser beam defocus, while the linearly increasing axial plasma density results in self-trapping of the beam. The self-focusing of the trapped beam is found in a high-density region. For the Gaussian types of density distribution, the beam field submits nonlinearly oscillating regime. The results provide an efficient way to manipulate the dynamics of laser beam propagating in plasma.