Emission characteristics of a low-pressure laser-induced plasma: Selective excitation of ionic emission lines of copper

Under reduced pressures, the plasmas produced by irradiation of a Q-switched Nd:YAG laser have favorable features as an excitation source for solid samples in atomic emission spectrometry, such as relatively low fluctuation of the emission intensity and a high signal-to-background ratio. For the analytical application of low-pressure laser-induced plasma spectroscopy (LP-LIPS), the spectra should be examined regarding the type of emission lines and their relative intensities. Further, information on the excitation mechanism in the plasma could be useful in determining optimum operation conditions of the experimental parameters. Spectrum patterns of LP-LIP are principally determined by the type of the filled gas. Especially, particular ionic lines of Cu are selectively excited when Ar or Ne are employed as the filled gas. This feature seems to be due to the (quasi-) resonance charge transfer collisions between a ground state ion of the Ar or Ne gas and a ground state atom of Cu. The plasma plume expanding after the laser irradiation also becomes an excitation source for sample atoms introduced by laser ablation.