Dynamics and density distribution of laser-produced plasma using optical interferometry

Abstract

Dynamic evolution and spatio-temporally resolved density profiles of laser-produced plasma in air were investigated using optical interferometry. A series of interferograms were obtained with a pulse energy of 50 mJ and delay times from 50 ns to 2650 ns. With increasing delay time, the expansion profiles of the shock wave change from a flat ellipsoid to a spheroid. The phase shift has been extracted using a two-dimensional (2D) fast Fourier transformation algorithm and the radial distribution of the refractive index is calculated using the inverse Abel transformation assuming that the plasma is axisymmetric along the direction of the incident laser beam. Interferograms of the 2D expansion and evolution of the plasma plume and the shock wave were obtained by exploiting the spatial dependence of the refractive index. The electron densities in the plasma region and the air densities in the compressed air region were calculated from the refractive-index distributions obtained. Our results provided further understanding of the expansion and the dynamic evolution of the laser-produced plasma and the shock wave and of the spatio-temporal evolution of the density of plasma in air.