LASER ABLATION OF ALUMINUM AT 193, 248, AND 351 NM

Pulsed laser ablation of an aluminum target at 193, 248, and 351 nm has been investigated by laser-induced fluorescence (LIF) spectroscopy. Velocity distributions of the ablated Al atoms have been measured directly by monitoring their flight times from the target to the probe laser beam, and by Doppler laser spectroscopy. The velocity distributions resulting from the three wavelengths can all be characterized as hyperthermal, with average velocities of between 4.5 X 10(5) and 6.5 X 10(5) cm/s over a fluence range of 0. 3-6.5 J/cm2. Average values of the Al atom distribution can also be derived by measuring the AlO internal energy distribution of the "hot" Al atom reaction with low pressures of O2. For excimer laser ablation of aluminum at 248 nm, we have found an average Al atom velocity of > 2 X 10(5) cm/s. Possible mechanisms for the production of these hyperthermal velocity distributions are discussed.