Time- and space-resolved emission spectroscopy measurements were performed to investigate plasma dynamics during laser evaporation of a graphite target. The evolution of the velocity and the emission intensity of the excited species versus the distance and the pressure of the foreign gas are studied. The time-resolved emission intensity of C II* transition at 426.7 nm shows a double-peak structure, resulting from the stratification of the plasma into fast and slow components. Intense molecular emission is found to occur behind a front separating the plasma from the foreign gas. Two stages of expansion are found in the generated plume, the first one starting just after the laser irradiation, the second beginning some time later depending on the nature and the pressure of the foreign gas. The two stages are well described, using a viscous drag force model for the first one and a delayed ideal blast wave model for the second.

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Emission spectroscopy diagnostics of carbon plasma created by Nd–Yag laser ablation of a graphite target in nitrogen atmosphere is presented. The influence of the laser energy density in the range of 3–60 J cm−2 on the evolution of the maximum emission intensity and the time of flight of the temporal profile of C2 Swan band and CN violet system is studied at 3 mm from the target surface and at two nitrogen pressures 0.5 and 1 mbar. It has been observed that for fluences ⩽10 J cm−2, the C2 and CN evolutions have the same behaviour and for higher fluences, their evolutions are quite different. For this purpose, a study of the spatio-temporal evolution of the C2 and CN as well as neutral and ionic atomic species of carbon and nitrogen is performed for two values of laser fluences, 8 and 35 J cm−2. The different processes leading to CN formation are proposed and discussed.

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