High-resolution investigations of C2 and CN optical emissions in laser-induced plasmas during graphite ablation

Graphite ablation in low-pressure nitrogen atmosphere has been carried out by XeCl excimer laser radiation at the fluence of 12 J cm(-2). The induced-plasma plume has been investigated by time- and space-resolved emission spectroscopy. The recorded spectra are dominated by diatomic molecule bands: the C-2 Deslandres-D'Azambuja and Swan systems and the CN violet system. From experimental measurements, it turns out that the continuum, the atomic emissions and the C-2 Deslandres-D'Azambuja bands are predominant in the plasma core region (d less than or equal to 1 mm) at short times, whereas the molecular bands of the Swan and violet systems are very intense in the outer plasma regions. The different temporal and spatial histories of emissions of the different chemical species in the plasma plume could be attributed to the peculiar processes occurring during plasma expansion.