RELATIVISTIC SELF-FOCUSING OF ULTRAINTENSE LASER-PULSES IN INHOMOGENEOUS UNDERDENSE PLASMAS

We investigate the propagation of high-intensity short laser pulses in a plasma. A two-parameter perturbation expansion is used to consisten tly treat the nonlinear mass variation and ponderomotive contribution to self-focusing, including plasma inhomogeneity. An analytical expres sion for the critical power is given and it is found that it greatly d epends on the plasma inhomogeneity. A tailoring of the preformed plasm a is suggested in order to obtain a strong reduction of the critical p ower. The temporal evolution of the pulse and plasma dynamics are also considered.