LASER-ABLATION PROCESSES INVESTIGATED USING INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROSCOPY (ICP-AES)

The symbiotic relationship between laser ablation mechanisms and analy tical performance using inductively coupled plasma-atomic emission spe ctroscopy are addressed in this work. For both cases, it is important to ensure that the ICP conditions (temperature and electron number den sity) are not effected by the ablated mass. By ensuring that the ICP c onditions are constant, changes in spectral emission intensity will be directly related to changes in laser ablation behavior. Mg ionic line to atomic line ratios and excitation temperature were measured to mon itor the ICP conditions during laser-ablation sample introduction. The quantity of ablated mass depends on the laser pulse duration and wave length. The quantity of mass removed per unit energy is larger when ab lating with shorter laser wavelengths and pulses. Preferential ablatio n of constituents from a multicomponent sample was found to depend on the laser beam properties (wavelength and pulse duration). For nanosec ond-pulsed lasers, thermal vaporization dominates the ablation process . For picosecond-pulsed lasers, a non-thermal mechanism appears to dom inate the ablation process. This work will describe the mass ablation behavior during nanosecond and picosecond laser sampling into the ICP. The behavior of the ICP under mass loading conditions is first establ ished, followed by studies of the ablation behavior at various power d ensities. A thermal vaporization model is used to explain nanosecond a blation, and a possible non-thermal mechanism is proposed to explain p referential ablation of Zn and Cu from brass samples during picosecond ablation. (C) 1998 Elsevier Science B.V.