The ion and velocity structure in a laser produced plasma

The early expansion of the plasma produced by the laser irradiation of a polyethylene foil in vacuum has been studied by making time resolved observations at right angles to the target normal. Spectral line emission has been scanned to give the spatial distribution of the ion species carbon I-VI. The lines observed are Doppler broadened by the ion streaming motion, and this broadening has been interpreted to give velocity as a function of time and of distance from the target normal. For one ion species (carbon V) a reconstruction has been made of the ion trajectories. Velocities of 2-3*10 7 cm s -1 have been deduced from Doppler shifts observed parallel to the target normal and are in agreement with previous time of flight measurements.