RAY TRAJECTORIES IN LINE-FOCUSED LASER PLASMAS

The problem of radiation propagating along the axial direction of an e longated laser plasma is treated analytically and numerically. With th e paraxial-ray equation, simple expressions for ray trajectories in su ch plasmas are derived that allow one to calculate beam trajectories i n an expanding plasma. Linear, quadratic, exponential, and Gaussian el ectron-density distributions are considered for plane and curved targe ts. Several of the trajectories are exact solutions of the paraxial-ra y equation; others are useful approximations that are compared with nu merical solutions. This theory finds its main application in the field of x-ray lasers, in which it may be helpful to design targets for opt imum beam propagation and to understand the effect of beam deflection on the effective gain and the beam divergence. Furthermore, with this theory, the maximum electron density at which there is gain can be est imated from the far-field deflection angle of an x-ray laser beam. (C) 1997 Optical Society of America.