Time-dependent channel formation in a laser-produced plasma

The formation of density channels in an underdense plasma is studied as a function of the laser pulse length. For pulse lengths of less than 300 ps, the channels have a finite axial length and end short of the peak density. As the pulse length is increased beyond 300 ps, the channel lengthens to the opposite side of the density profile and a situation can be obtained in which most of the beam propagates through the plasma within the vacuum propagation cone. The process of channel formation is successfully modeled by two-dimensional hydrodynamic simulations.