Laser ablation processes investigated using inductively coupled plasma atomic emission spectroscopy (ICP-AES)

The symbiotic relationship between laser ablation mechanisms and analytical performance using inductively coupled plasma-atomic emission spectroscopy are addressed in this work. For both cases, it is important to ensure that the ICP conditions (temperature and electron number density) are not effected by the ablated mass. By ensuring that the ICP conditions 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 monitor the ICP conditions during laser-ablation sample introduction. The quantity of ablated mass depends on the laser pulse duration and wavelength. The quantity of mass removed per unit energy is larger when ablating with shorter laser wavelengths and pulses. Preferential ablation of constituents from a multicomponent sample was found to depend on the laser beam properties (wavelength and pulse duration). For nanosecond-pulsed lasers, thermal vaporization dominates the ablation process. For picosecond-pulsed lasers, a non-thermal mechanism appears to dominate 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 established, followed by studies of the ablation behavior at various power densities. A thermal vaporization model is used to explain nanosecond ablation, and a possible non-thermal mechanism is proposed to explain preferential ablation of Zn and Cu from brass samples during picosecond ablation. (C) 1998 Elsevier Science B.V