Analysis and Discrimination of Volcanic Rocks by Benchtop and Standoff LIBS

Laser Induced Breakdown Spectroscopy (LIBS)is a simple atomic emission spectroscopy technique capable of real-time, essentially non-destructive determination of the elemental composition of any substance (solid, liquid, or gas). As a technology for geochemical analysis, LIBS is presently undergoing rapid research and development, that has attractive potential for rapid man-portable and/or stand-off analysis in the field. In LIBS, a pulsed laser beam is focused on a sample such that energy absorption produces a high-temperature microplasma. Small amounts of material (picograms-nanograms) are dissociated and ionized, with both continuum and atomic/ionic emission generated by the plasma during cooling. A broadband spectrometer-detector is used to spectrally and temporally resolve the light from the plasma and record the intensity of elemental emission lines. Since the technique is simultaneously sensitive to all elements, a single laser shot can be used to track the spectral intensity of specific elements or record the broadband LIBS emission spectra, which are unique 'geochemical fingerprints' of a material.

In this study, a broad spectrum of volcanic materials was analyzed using both a commercial 'benchtop' LIBS system with broadband detection from ~200-965nm and a developmental 25m 'standoff' LIBS system with broadband detection from ~200-840nm. In each case, broadband LIBS spectra were acquired with a single laser shot. Subsequent classification and discrimination of different volcanic materials (e.g. lavas, tuffs, and tephra) has been achieved with a high degree of success using two different chemometric techniques, ‘soft independent method of class analogy' (SIMCA) and ‘partial least squares discriminant analysis' (PLS-DA).