Standoff Femtosecond Filament-Induced Breakdown Spectroscopy for Classification of Geological Materials
The femtosecond (fs) filaments delivering substantial peak intensities at the remote locations are being exploited in several practical applications together with in-situ remote/standoff (ST) investigations. The optical emissions produced during the filament interaction are analyzed to study the composition of distant targets. In this article, we present comparative results obtained from qualitative studies of territorial rocks (collected in central Dharwar craton, South India) in the near-field with fs laser induced breaksown specroscopy (fs LIBS) as well as in the standoff mode using fs filament induced breakdown spectroscopy (fs FIBS) techniques. The granitoids possessing distinct mineralogical and chemical characteristics were analyzed in their original form in ambient air from a distance of (i) ̴15 cm with tightly focused fs pulses and (ii) ̴6.5 m using fs filaments. Various atomic emission lines belonging to significant elements such as Ca, K, Na, Al, Fe, and Mg, were identified and labeled from both fs LIBS and fs FIBS spectra of each sample. Few spectral lines corresponding to trace elements such as Ba, Ti, and V were also identified. A good correlation of constituent elements spectral line intensities, especially in the standoff mode, was observed with the weight percentage of their oxides obtained from X-ray fluorescence (XRF) data. Furthermore, results from principal component analysis (PCA) employed in tandem with normalized/unnormalized fs ST-FIBS data of these geological rocks demonstrated a high degree of qualitative classification in comparison with the normalized/unnormalized fs LIBS data. Therefore, we firmly believe that the results from the present work extend the application of fs filaments to standoff analysis of geological beds and mineral ores in the ambient atmospheric conditions intended at unpleasant environment detection.