Nonlinear Propagation Characteristics and Ring Structure of a Gaussian Beam in Collisionless Plasmas with High Order Paraxial Ray Theory

Nonlinear propagation characteristics of a Gaussian beam in collisionless plasma are studied by the high order paraxial ray theory. The ponderomotive nonlinearity is considered as the focus mechanism. To solve the problem of energy non-conversation, we improve the propagation formula for Gaussian beam. The propagation characteristics of the dimensionless beam-width parameter, relative beam intensity and spatial electron density are numerically studied and discussed. It is found that the ring structure emerges from Gaussian beam in the case of self focusing regime, and the initial laser parameters play important parts on the intensity and location of ring structure. Moreover, the wave-packet oscillation modes of beam width and intensity are presented.