Focusing of dark hollow Gaussian electromagnetic beams in a plasma

This paper presents an investigation of the focusing of dark hollow Gaussian electromagnetic beams (HGB) in plasma, considering collisional, ponderomotive, and relativistic nonlinearities. A paraxial like approach, in which the parameters are expanded, in terms of radial distance from the maximum of irradiance rather than that from the axis, has been adopted. To highlight the nature of focusing, both critical curves and the divider curves have been obtained as a plot of dimensionless radius vs. power of the beam. The effect of the order of HGB (n), and nature of nonlinearity on self focusing of the beam has also been explored.