An investigation of neutral and ion number densities within laser-producedtitanium plasmas in vacuum and ambient environments

Optical absorption spectroscopy in combination with laser-induced fluoresce nce imaging is applied to determine spatially and temporally resolved numbe r densities within laser-produced titanium plasmas, expanding into vacuum a nd low-pressure nitrogen. Contour mapping of species number density and sub sequent volumetric integration to yield the total number of absorbing speci es in the plume are demonstrated for Ti I expanding into vacuum. The result s obtained indicate that for an incident KrF energy density of similar to 4 J cm(-2) the total plume content is > 10(17) Ti neutrals and ions. The grou nd-state neutral and ground-state ion yields are both observed to increase linearly with laser fluence above thresholds of similar to 2.2Jcm(-2) and s imilar to 3.7Jcm(-2), respectively. Reduction in absorption linewidths and spatial widening of the corresponding LIF images, observed for plume expans ion in the presence of low-pressure ambient gases, reflects the reduction i n species velocities and randomisation of the velocity distributions of plu me species with increasing ambient pressure.