Discrimination of composite graphite samples using remote filament-induced breakdown spectroscopy.

Remote filament-induced breakdown spectroscopy (R-FIBS) using ultrashort laser pulses was used to measure the carbon/clay ratios between three graphite composites of different hardness at a standoff distance of approximately 6 m. Measurements using R-FIBS and femtosecond laser-induced breakdown (fs-LIBS) reveal similar selectivity and ability to excite emission. Comparison of the two stand-off techniques with optical microscopy and electron microprobe point detection confirmed the qualitative analysis capability of both femtosecond remote probing techniques. The R-FIBS technique produced more accurate results compared to fs-LIBS due to the intensity clamping nature of the filament ablation source. Measurement of the plasma temperatures for the metallic emission lines (approximately 8500 K) and the C(2) Swan lines (approximately 4500 K) suggest that the plasmas from different microdomains (clay and graphite) are not in equilibrium.