Resonant holographic interferometry of laser-ablation plumes

Two-dimensional species-resolved, holographic interferometry has been used to measure absolute-line-density profiles of KrF laser ablation plumes in vacuum and gas. Laser ablation plumes are generated by focusing a KrF excimer laser (40 ns, 248 nm, ≤0.8 J) on a solid aluminum target at a fluence of 2–5 J/cm2. Aluminum neutral absolute-line-density profiles are measured to characterize the interaction of ablated material with background gases versus vacuum. The interferograms are made using a 20 ns pulsed dye laser tuned near (≤±0.020 nm) the 394.401 nm aluminum neutral transition from the ground state. Calculations have been performed to obtain absolute-line-density profiles from the resonant fringe shift data. Peak aluminum neutral line densities of up to 1×1015 cm−2 have been measured for plumes in backgrounds of 14 mTorr and 1 Torr argon and in vacuum.