Investigations of laser-induced plasma in air by Thomson and Rayleigh scattering

Laser Thomson scattering and Rayleigh scattering methods were applied to investigate the dynamics of laser-induced plasmas in atmospheric air. Laser-induced plasma was generated by a 1064 nm, 200 mJ Nd: YAG laser. Another nanosecond Nd: YAG laser (532 nm, 50 mJ) was used as the probe laser. The temporally and spatially resolved electron number density and temperature distributions of the laser-induced plasma were determined from the Thomson scattering spectra. From 1 μs to 21 μs after plasma generation, the electron number density around the centre of the plasma decreased from 4.96 × 1023m‐3 to approximately 1.1 × 1021m‐3, while the electron temperature dropped from approximately 51,500 K to 6900 K. The plasma images and the measured distribution of the electron number density and temperature indicated the formation of a toroidal structure approximately 18 μs after plasma generation. The Rayleigh scattering results show that the Taylor-Sedov model cannot well describe the early evolution of the shockwave in radial directions.