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Diagnostics of laser-induced plasma from a thin film of oil on a silica wafer

In this study, plasma induced by a nanosecond Nd:YAG laser on thin oil films
 deposited on a silica wafer was characterized by evaluating the main plasma
 parameters. Spatially and temporally integrated spectral measurements were
 performed under experimental conditions optimized for elemental analysis of
 trace metals in oil. Time-resolved values of the spectral line intensities,
 electron number density, and plasma temperature were obtained from
 time-integrated measurements by subtracting averaged spectra recorded at
 different time delays. The electron number density was estimated using the
 Stark broadened profile of the hydrogen Balmer alpha line. Ionization
 temperatures were derived from Mg ionic to atomic line intensity ratios. The
 obtained apparent values of time-resolved plasma parameters were in the
 range of 1.1?1017 cm-3 (1.5 ?s) to 1.5?1016 cm-3 (4 ?s) and 9400 K (3 ?s) to
 7200 K (5 ?s), depending on the delay time. Emission spectra of C2 and CN
 molecules were used to evaluate the rotational and vibrational temperature.