On the cooling of the plasma fireball produced by a laser spark in front of liquids and solids

The results of experimental and theoretical investigation of the late, conductive–advective cooling of the fireball, produced by a laser spark in gas near a surface of condensed matter, are presented. The laser spark was initiated by the focusing of a 0.5 J 8 ns Nd:YAG laser. The fireball cooling rate was studied by using a fast frame camera and monochromatic imaging. A theoretical model is developed to describe the conductive–advective cooling stage. The model is reduced to a single nonlinear temperature diffusion equation. In the spherically symmetric case, a similarity solution found earlier is verified and employed for interpreting the experimental results.