Plasma channel formation by short pulse laser

A short pulse laser propagating through a preformed plasma exerts a radial ponderomotive force on the electrons and creates a low density plasma channel via ambipolar diffusion. If the radial intensity profile of the laser beam is clamped, i.e., assumed Gaussian in r with fixed half-width r0, then closed form analytic solution of the evolution of plasma density in the channel is obtained in the perturbation approximation, Δn≪n0, where Δn is the modification in electron density over its equilibrium value n0, by solving the linearized equation of continuity. The relevance of the channel for low spot size beams self-focusing is examined.