Multiple structure formation and molecule dynamics in transient plasmas generated by laser ablation of graphite

Transient plasmas generated by ns - laser ablation of graphite in air have been investigated by complementary optical diagnosis techniques to study complex multiple structures generated in carbon laser produced plasmas (C-LPP) during the expansion phase. The overall emission was investigated by ICCD fast camera imaging and revealed the structuring of C-LPP into four distinct structures with different evolutions. The dynamic of the C-LPP was analyzed on various expansion directions in order to understand the formation of the main CN dominant structure and of lateral "flaps" with dominant C-2 emission. The kinetic and thermal energies of the resulted atoms, ions and molecules were investigated by means of space-and time-resolved optical emission spectroscopy and using the Boltzmann plot and Stark broadening approaches. The effect of the background gas pressure on the formation of molecular carbon structures is discussed and an optimum range of working pressure which maximizes the generation of C-2 is found. Based on the acquired data a scenario for the complex carbon structures generation in C-PLL as function of the background gas is proposed.