Propagation of finite length laser pulses in plasma channels

Finite pulse length effects are shown to play a major role in the propagati on. stability, and guiding of intense laser beams in plasmas. We present th e quasiparaxial approximation (QPA) to the wave equation that takes finite pulse length effects into account. The QPA is an extension of the usual par axial approximation. The laser field is shown to be significantly modified for pulses less than a few tens of wavelengths long. A pair of coupled enve lope-power equations having finite pulse length effects, as well as relativ istic and atomic electron nonlinearities, is derived and analyzed. Short la ser pulses propagating in plasma channels are found to undergo an envelope oscillation in which the front of the pulse is always damped while the back initially grows. The modulation eventually damps due to frequency spread p hase mixing. In addition, finite pulse length effects are shown to modify n onlinear focusing processes significantly. [S1063-651X(99)13003-4].