Abstract: The vapor plume produced by a focused normal mode pulsed neodymium glass laser beam (1.06μm, 1ms) on an aluminum plate (1mm) in air at average power densities up to 10⁷W/cm² has been studied by a piano-plate shearing interferometer with a high speed photograph. The frame interference photograph of the vapor plume was obtained. At the different sections, the refractive index curves are derived. Based on the vapor plume refractive index, the electron density is deduced to be about 10¹⁸cm^-3, and the temperature about 4,500K and both of them decrease radially and axially.