Comparison of plume dynamics for laser ablated metals: Al and Ti

Emissive plumes from pulsed laser ablation of bulk Ti and Al from KrF laser irradiation at laser fluence up to 3.5 J/cm(2) and argon background pressures of 0-1 Torr have been observed using gated intensified charged-coupled device imagery. Mass loss for Ti increases from 0.1 to 0.8 mu g/pulse as pulse energy increase from 174 to 282 mJ/pulse (35-170 photons/atom) and decreases by similar to 30% as pressure increases from vacuum to 1 Torr. Early plume energies are described by the free expansion velocities of 1.57 +/- 0.02 and of 1.81 +/- 0.07 cm/mu s for Ti and Al, respectively, and up to 90% of the incoming laser energy can be attributed to the Al shock front in the mid-field. The ablation thresholds of 90 +/- 27 mJ (1.12 +/- 0.34 J/cm(2)) for Ti and 126 +/- 13 mJ (1.58 +/- 0.16 J/cm(2)) for Al also represent 30%-70% of the incident laser energy. The decrease in mass loss at higher pressures is attributed to plasma shielding of the target surface.