Investigations of laser induced plasma in air by Thomson and Rayleigh scattering
Abstract 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 ms to 21 ms after plasma generation, the electron number density around the centre of the plasma decreased from 4.96 x 1023m 3 to approximately 1.1 x 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 ms 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.
Spectrochimica Acta Part B: Atomic Spectroscopy