Atmosphere Issues in Detection of Explosives and Organic Residues

摘要

This study makes a comparison of LIBS emission from molecular species in plasmas produced from organic residues on a non-metallic substrate by both a 5 ns Nd:YAG laser (1064 nm) and a 40 fs Ti:Sapphire laser (800 nm) in air and argon atmospheres. The organic samples analyzed had varying amounts of carbon, nitrogen, hydrogen, and oxygen in their molecular structure. The characterization was based on the atomic carbon, hydrogen, nitrogen, and oxygen lines as well as the diatomic species CN (B~2Σ~+ - X~2Σ~+) and the C_2 (d~3Π_g - a~3Π_u). Principal Component Analysis (PCA) was used to identify similarities of the organic analyte via the emission spectra. The corresponding Receiver Operating Characteristics (ROC) curves show the limitations of the PCA model for the nanosecond regime in air.