In this paper,an experimental study of collinear geometry double-pulse femtosecond LIBS was performed on a Ni sample in ambient air in an effort to clarify the contributing processes responsible for the signal enhancement observed in comparison with the single-pulse case.Doublepulse LIBS spectra show a very clear enhancement when an optimum inter-pulse delay was used.The influences of the inter-pulse delay between two pulses on the LIBS signal intensity,electron temperature and density were investigated.It is most remarkable that the evolutions of signal enhancement and electron temperature versus the inter-pulse delay showed the same behavior and revealed two main regimes of interaction.These results provide additional insight into the possible emission enhancement mechanisms in the double pulse configuration.
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