Time-resolved parametric studies of laser ablation using inductively coupled plasma atomic emission spectroscopy

The quantity of ablated mass and its composition strongly depend on the number of laser pulses and laser fluence at the sample target surface. For chemical analysis, thin-film deposition,cutting, and other laser-ablation applications, the quantity of mass removed vs. number of laser pulses is important. In addition, the composition of the vapor can be critical, for example, in providing accurate chemical analysis or well-defined thin film structures. In this work, mass ablation rate and ablated mass composition were studied by monitoring the time dependence of emission intensity using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP) during repetitive laser ablation at a single location on the sample target. Spectral emission intensity in the ICP is directly related to the quantity of mass ablated by the laser. The ratio of spectral emission lines in the ICP gives an indication of the relative composition of ablated constituents. In this work, a brass sample was ablated using several lasers with various properties. Emission intensities of Cu and Zn ionic lines, after the occurrence of an initial signal spike, increase with increasing number of laser pulses at high fluence, whereas at low fluence no significant changes were observed in the mass ablation rate. The zinc-to-copper ratio was used to monitor fractionation processes during repetitive laser ablation. The ratio increased with increasing ablation time at low fluence. In contrast, the ratio was almost constant, and close to the accurate level at high laser fluences. The effect of various laser parameters on the mass ablation rate and mass composition are discussed in this paper.

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