Interferometric investigation of the shock wave interaction with laser-produced spark

A shock wave propagating in a relaxing plasma is highly dissipated when passing through the central heated region of a laser-produced spark, the fire-ball. To explain the details of this phenomenon an interferometric investigation was made. A shock wave produced by the breakdown at a plate surface was directed to the focal region of the laser spark. Electron and neutral densities were measured by holographic and Mach-Zender interferometry, respectively. The presented results indicate that the damping of the shock wave occurs in the boundary layer of 2 mm of the fire-ball characterized by an approximately 5-fold decrease of the neutral gas density. (D.Gy.)