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Center for Nonlinear Studies |
Laser Induced Breakdown Spectroscopy (LIBS) is a powerful and sensitive spectroscopic technique where light emitted from a laser-generated micro-plasma can be used to determine the composition of a sample on the basis of elemental and molecular emission intensities. LIBS holds particular promise for the stand-off detection and identification of explosives, radioactive specimens, biological assays, and many other organic and nonorganic materials because of the ability to detect a broad range of chemical species and trace amounts of materials (parts per million) with a single laser shot in real time. However, atmospheric conditions, sample matrix, surface density, nature of excitation, laser modality, and multiplicity of pulses influence the signal strength and repeatability of LIBS experiments. In this work, nanosecond (ns) and femtosecond (fs) single pulse (SP) and dual pulse (DP) with carbon dioxide (CO2 ) LIBS has been used to monitor the temporal evolution of carbon(C), hydrogen-alpha (H-α), carbon-carbon (C2) and carbon-nitrogen (CN) spectral emissions from atmospheric recombination in a specific series of linear chain dicarboxylic acids with an increasing number of carbon atoms from two to seven. We also illustrate the effect that these constraints, along with the presence that a chiral carbon in the chain, have on the peak intensities of the individual lines with respect to each other.
Laser-Ablation Molecular Isotopic Spectrometry (LAMIS) was also used to addresses the importance of sample matrix from the boron oxide (BO) B-X transition at 255 nm for samples containing natural Boron-11 (11B) and Boron-10 (10B) isotopes. When breakdown occurs, diatomic isotopologues are formed that reveal a wavelength shift in their optical emission spectra, due to slight variations in the initial equilibrium, vibrational and rotational energies of the isotopologues. This facilitates the determination of the relative abundance of isotopes in the material from LIBS analysis. Also, dual-pulse (DP) LIBS can reduce shot-to-shot variation and has been shown to lower detection limits of an element by an order of magnitude or more. Therefore a study of the effects of dual pulse interactions with a CO2 laser has been conducted demonstrating a linear correlation between known concentration and calculated concentration for varying isotopic ratios of Boron-10 and Boron -11 enriched boric acid using a least square model.
Host: Scott Jackson and Dana Dattelbaum