Laser beam propagation and channel formation in underdense plasmas

Abstract

Experimental results are presented which show the formation of density channels in a preformed plasma by a 100 ps laser beam focused with different f/number lenses. The density channels are diagnosed by an interferometer. The experiments are made with both line foci and circular foci up to intensities of 5×1016 W/cm2. The experimental channel size and density perturbation compare favorably with the predictions of two-dimensional theoretical models. The limited axial extent of the channels is shown to be due to the onset of the filamentation instability.