LASER ABLATION OF GRAPHITE IN DIFFERENT BUFFER GASES

studied by fast imaging of the plasma emission and post-deposition analyses of collected film deposits. In each case, the soot which was redeposited on the irradiated rod following ablation was highly fullerene-deficient compared to the material collected on the sample disk 1.5 cm from the rod, as determined by laser desorption Fourier Transform Mass Spectrometry ( F I X I S) Investigation of the plasma plume propagation using fast ICCD photography reveals three main phases to the expansion: (1) forward motion, deceleration and stopping of the leading edge of the plume, (2) an apparent reflected shock within the plume which propagates backward and reflects from the rod surface, (3) coalescence of these two components, resulting in continued expansion and dissipation of the plasma and the appearance of glowing ultrafine particles. For the laser plume propagating in 300 Torr of Xe the characteristic time intervals for these three phases are C300 ns, 300-1000 ns, and 1-1000 ps for phases (l), (2), and (3) respectively. The possible explanation of the observed difference in fullerene content is discussed on the basis of different plasma phases resulting in soot deposition on the rod and sam le disk