Nonlinear propagation of intense short pulses through underdense plasmas

Currently there is much interest in the interaction of high-intensity ultra-short laser pulses with plasmas. Applications include the recently proposed Fast Ignitor Concept for Inertial Confinement Fusion. In the present work we make an analytical investigation of nonlinear propagation of intense short pulses through underdense plasmas. When a laser beam is focused into a plasma, self-focusing and self-channeling can occur as a result of relativistic modification of electron mass in the laser field and the reduction of electron density on the focal region due to the expulsion of electrons by laser ponderomotive force. The paper presents a paraxial theory of self-focusing of intense laser pulses due to expulsion of plasma electrons produced by the extreme ponderomotive force of a focused laser pulse. The nonlinear dielectric constant, self-focusing equation relating the variation of beamwidth parameter with distance of propagation, self-trapping condition and critical power are evaluated. The results suggest a self-focusing of the laser pulse in the plasma.