Preliminary studies on stand-off laser induced breakdown spectroscopy detection of aerosols

Abstract

Laser induced breakdown spectroscopy (LIBS) was demonstrated in stand-off mode as a detection technique for polydisperse liquid aerosols. The goal of this work was to assess the possibility of producing optical breakdown in an aerosol at 10 meters of distance, and to detect the analytical signal resulting from the optical discharge. The doublet characteristic of Na in the spectral region 588.6 nm – 589.5 nm was examined. For data analysis a method is proposed based on the study of the standard deviation of the acquired signal resulting from successive laser shots on the aerosol. This method rests on the high variability of the LIBS signal characteristic in aerosols systems (the percentage of spectra collected with analytical signal was around 30%). The standard deviation method was compared with the more traditional methods of ensemble-average and single-shot data analysis. The limit of detection (L.O.D.) was estimated for each method using a linear approximation, resulting in a value of 55 ppm for standard deviation method while in the case of the ensemble-average method calculation was unsuccessful due to the large uncertainty of the data. The principal advantage of the standard deviation method is that it allows the real-time elemental analysis from highly variable LIBS signals without the need of a priori knowledge of the sample which it is particularly suited for aerosol analysis in stand-off mode of detection.