Three-dimensional number density mapping in the plume of a low-temperature laser-ablated magnesium plasma

Simultaneous optical absorption and laser-induced fluorescence measurements have been used to map the three-dimensional number densities of ground-state ions and neutrals within a low-temperature KrF laser-produced magnesium plasma expanding into vacuum. Data is reported for the symmetry plane of the plasma, which includes the laser interaction point at a delay of 1 ms after the ;30 ns KrF laser ablation pulse and for a laser fluence of 2 J cmy2 on target. The number density distributions of ion and neutral species within this plane indicate that two distinct regions exist within the plume; one is a fast component containing ions and neutrals at maximum densities of ;3=1013 cmy3 and ;4=1012 cmy3, respectively and the second is a high-density region containing slow neutral species, at densities up to ;1=1015 cmy3. q1998 Elsevier Science B.V.