Physics of pulsed laser ablation at 248 nm: Plasma energetics and Lorentz interactions

Abstract

Pulsed KrF (248 nm) excimer laser ablation of targets can generate quasi-neutral ground state atomic particle plasmas with energies in the range of 200 -1100 eV. Onset of plasma formation occurs when optical intensities exceed 108 W/cm². The expanding ensemble has a pronounced angular energy dependence, the highest energies peaked in the direction normal to the target. Correlation of the temporal nature of the laser pulse and the ensuing ion mass pulses suggest that transfer of energy is, indeed, a very rapid process -probably less than 5 ns. A wide range of elemental and several compound targets were studied to determine how ion energy distributions were influenced by atomic mass. The energetic plasma beams interact with magnetic fields as predicted from the Lorentz force. Results are consistent with an inverse bremsstrahlung and Lorentz force mechanism for particle acceleration.