Emission imaging spectroscopic and shadowgraphic studies on the growth dynamics of graphitic carbon particles synthesized by CO2 laser vaporization

Emission imaging spectroscopy and shadowgraphy were applied to study the growth of carbon particles synthesized by 20-ms CO2 laser-pulse irradiation at 0.5-1.5 x 10(5) W/cm(2) onto a graphite target in an Ar gas atmosphere (300-760 Torr). Emission images of growing carbon clusters and/or particles in a vaporization plume, measured with a temporal resolution of 1.67 ms, showed a constricted structure near the target that expanded widely into the Ar gas environment. On the other hand, the emission images of Ct, not showing the constricted structure, indicated its presence close to the target and expansion in a narrow region. When directly ejected and/or formed carbon species (C, C-2, and C-3 , respectively) with velocities of 0.3-2.6 x 10(3) cm/s depart from the graphite surface, the formation of hot carbon clusters and/or particles begins and continues in the expanding plume. In shadowgraph images, the formation of a mushroom cloud containing darkened areas and black spots (size < 1 mm), probably corresponding to similar to 80-nm-diameter graphitic carbon particles, was observed after 5 ms from the start of the laser irradiation. The number of particles increased rapidly from 5 to 25 ms. We propose a model of particle growth in a viscous carbon flow, where the temporal and spatial evolution bf carbon species (the cluster formation and decrease in kinetic energies) and the condensation of clusters play essential roles with temperature reduction through the interaction with Ar atoms.