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

Abstract

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 μs) to 1.5×10¹⁶ cm^-3 (4 μs) and 9400 K (3 μs) to 7200 K (5 μs), depending on the delay time. Emission spectra of C2 and CN molecules were used to eva­luate the rotational and vibrational temperature.