Characteristics of laser produced plasmas obtained by Fast ICCD photography, schlieren photography and optical emission spectroscopy

Pulsed laser produced plasmas (LPP) are important for industrial applications and fundamental researches, and their complex, multi-physical and cross-chemical processes need to be investigated more comprehensively. In this work, images of the luminous plasma, the spatial density distribution, and the plasma parameters are experimentally investigated by using fast ICCD photography, schlieren photography, and optical emission spectroscopy. Plasmas are produced by a 1064 nm, 15 ns Nd:YAG laser. Free expanding and splitting phenomena are observed in vacuum (at the pressure of about 1×10^-3 Pa) and air (at the pressure of 20 Pa) using fast photography, respectively. Meanwhile, shock waves formed in the atmospheric laser produced plasma are visualized by schlieren photography. The formation of shock waves is interpreted with the Sedov-Taylor theory, and an averaged expansion velocity about 375 m/s of the shock waves is estimated during 200~1000 ns. Atmospheric air is found to have significant confinement effects on the plasma expansions compared to that in vacuum or low pressure ambient. Based on the optical emission spectroscopy, after 1000 ns, at 0.6 mm above the target, the plasma temperature is about 7800 K and the electron number density is approximately 0.64×10¹⁶ cm^-3.