Spatiotemporal evolution of laser-induced plasmas in air: Influence of pressure

In this paper, we focused on the influence of gas pressure on the dynamic characteristics of laser-induced plasma (LIP) in air. The energy-dependent transmittances of a 1064 nm laser to LIPs generated at the pressure of 0.2–5 atm were measured. Laser Rayleigh scattering and Thomson scattering methods were applied to investigate the evolution of laser-produced shock wave and radial distribution of electron number density (n_e) and electron temperature (T_e) of LIP in air. The fraction of the shock wave energy to the total laser energy absorbed is about 40%–52% and increases upon increasing pressure. The higher the gas pressure, the greater n_e and T_e within the central of LIP and a faster decaying rate of T_e and n_e. The electron number density decays exponentially with time, and the decay index is between −0.891 and −1.177. A torus structure in LIPs is generated during the later stage of plasma decay and significantly affects the distribution of T_e, n_e and the intensity of plasma emission.