Pulsed ablation of carbon/graphite surfaces and development of plume-kinetics model

Abstract

Plumes were generated by ablation of graphite using a 248 nm excimer laser in the presence of low-pressure argon at 50-1000 mTorr. The pulsed laser deposition of energy on carbon/graphite targets at fluences of 1-5 J/cm 2 in low pressure argon backgrounds yields emissive plumes with large kinetic energies (estimated between 10-200 eV ), driving the formation of a shock front with large Mach numbers (M). The plumes were investigated using element specific imaging (filtered and gated ICCD camera), time-of-flight experiments, and UV - VIS - IR spectroscopy. We expect to see contributions from atomic carbon as well as the C2 diatomic. Studies showed the importance of plume/substrate interaction in causing secondary excitation/interaction phenomena. The propagation of the shock front is independent of ionization species and adequately characterized by the Sedov-Taylor shock model during the early life-time of the plume if the dimensionality is allowed to deviate from ideal spherical expansion. The ideal efficiency of energy conversion from laser pulse to shock expansion is investigated. The low background pressures between 50 and 1000 mTorr are sufficient for the generation of a strong shock front with significant thickness, but may be too low to develop three-dimensional flow. It can be shown that shock strength is proportional to the Mach number.