INTERNAL STATE POPULATIONS AND THE TIME-OF-FLIGHT OF GROUND-STATE SPECIES EJECTED AFTER THE 193 NM EXCIMER-LASER ABLATION OF CUO, BAO2, ANDY2O3

Laser-induced fluorescence is used to measure time-of-flight (TOF) and internal state distributions of atoms, ions, and diatomics ejected af ter the 193 nm ablation of Y2O3, BaO2, and CuO. These measurements ind icate that the bulk of material is ejected with speeds in the range of 10(4)-10(5) cm/s while particle speeds in the emitting component of t he plume exceed 10(6) cm/s. The TOF profiles of all the species were n on-Maxwellian containing extended low-velocity ''tails.'' It is postul ated that these tails arise from the evaporation and/or sputtering of target material that occurs after the laser ablation pulse. This parti cle emission is caused either by residual energy deposited in the targ et after the explosive vaporization/ablation pulse or from radiation e xchange and/or ion bombardment from the expanding plasma plume. The ex tent of these ''tails'' increases with increasing fluence, generating oscillations in the TOF distributions of Cu atoms from CuO at high flu ence. Rotational and vibrational temperatures were estimated for YO an d BaO molecules in the plume, and no CuO was detected.