Temporal and spatial analysis of plasmas during graphite laser ablation in low-pressure N2

Ablation of graphite in low-pressure nitrogen (1-50 Pa) has been carried out by excimer laser radiation (308 nm) at the fluence of 12 J/cm(2). The time- and space-resolved emission spectra of the laser-induced plasma are mainly dominated by the atomic carbon lines and by the bands of C-2 molecule (Deslandres-D'Azambuja and Swan systems) and CN radical (Violet system). Continuum and atomic emissions are predominant in the plasma core region at early times, whereas molecular bands are very intense in the outer regions. However, a significant contribution of C2, with its Deslandres-D'Azambuja system, close to the target and of atomic carbon at longer distances from the target is observed. Emissions from different chemical species in different plasma regions are attributed both to different mechanisms of excitation of the emitting species, related to their own excitation energies, and to molecule formation due to gas-phase reactions during plasma expansion. (C) 2002 Elsevier Science B.V All rights reserved.