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 C2 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 C2
Deslandres-D'Azambuja bands are predominant in the plasma core
region (d⩽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.
Mass- and time-integrated optical emission spectra were recorded during direct XeCl laser ablation (308 nm, 30 ns) of graphite targets in and in atmospheres at various pressures and at different laser fluences . Spectra in vacuo were also acquired. The optical emission spectra of the laser-induced plasma are characterized by strong molecular emission bands of and CN and by lines of atomic ions . At the highest pressures the spectra are dominated by a Swan system (vibrational sequences ) and a CN violet system . Their intensities increase with an increase of gas pressure. Mass spectrometry was also performed on the ablated materials and various chemical species were found; the most common ones were C, CN and .
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