Comprehensive researches on dynamics of nanosecond laser produced plasmas

Summary form only given. Laser produced plasmas (LPP) have various applications including superconducting films fabrication, laser induced breakdown spectroscopy, and nanoparticles formation. Although massive efforts have been made, dynamics of LPP remain incompletely understood due to the complex interactions among the laser, the target, the plasma plume and the ambient gas. Recently, we are conducting comprehensive researches on the dynamics of 1064 nm 20 ns laser ablated plasmas in air under different experimental conditions with an laser energy density in the order of J/mm². Time and spatial-resolved diagnostics including fast ICCD photograph, streak photograph, spatial resolved optical emission spectroscopy, laser shadowgraph, schlieren photograph and interferogram are applied to obtain the evolution images and the plasma parameters. From series of experiments, (i) initial plasma expansions within and after the laser pulse in air are obtained. Plasma dynamics during the nanosecond laser pulse could be divided into three stages: fast expansion, division into the primary plasma and the front plasma, and stagnation 1. (ii) Influence of spot size on the expansion dynamics of atmospheric LPP, and the evolution of the species from both the target and the air are investigated 2. (iii) Plume splitting of laser ablated Al plasmas at 10-1000 are interpreted from the view of ion distributions. In the beginning, the spectral lines are mainly from the Al III ion. Then, the Bragg peak in stopping power of the ambient gas to Al III could be the dominant reason for the enhanced emission from the fast moving part, and the recombination of Al III to Al I-II ions near the target surface become response to the radiations from the slow moving/stationary part ³.