In the last 10 years various chemometric methods have been developed and used for the analysis of spectra generated by Laser Induced Breakdown Spectroscopy (LIBS). One of the more successful and proven methods is Partial Least Squares Discriminant Analysis (PLS-DA). Recently PLS-DA was utilized for purposes of provenance of spent brass cartridges and achieved correct classification at around 93% with a false alarm rate of around 5%. The LIBS spectra from the cartridge samples are rich in emission lines from numerous mostly metallic elements comprising the brass and the cited results were based on the analysis of the full broadband high resolution spectra. It was observed that some of the lines were clearly saturated in all spectra, while others were sometimes saturated due to pulse-to-pulse variation. The pulse-to-pulse variation was also evident in the intensity variations of the spectra within cartridges and between cartridges. In order to improve on the accuracy of the classification we have developed some preprocessing strategies including the removal of spectral wavelength ranges susceptible to saturation and normalization techniques to diminish the effects of intensity variations in the spectra. The results indicate incremental improvements when applying additional preprocessing steps to the limit of 100% True Positives and 0% False Positives when utilizing selected wavelengths that are normalized and averaged.
There exists an unmet need in the discovery and identification of certain improvised explosive (IE) materials. IE
contain a wide range of materials, many of which are not well classified by available hand-held tools, especially
metal powders and food products. Available measurement approaches are based in the identification of specific subgroups
such as nitro/nitrate and chlorate/perchlorate, normally with Raman spectroscopy. The presence of metal
powders is not detected by these approaches, and further the powders themselves scatter the laser radiation used in
the excitation of the spectra, making other components more difficult to discern. Preliminary work with laserinduced
breakdown spectroscopy (LIBS) shows that metal powders are easily detected and identified, and that fuel
compounds in flash powder mixtures are easily classified with principal component analysis into those containing
oxygen and chlorine or those containing oxygen and nitrogen. Alkali and alkali metal signals are readily used to
determine the cation of any salt submitted to analysis.
In this paper we discuss several science education modules that we developed and pilot tested in grades 3-7. The
modules are optically-based and consist of physical kits and associated curriculum materials. The modules emphasize
real-world applications such as color displays, environmental monitoring, telecommunications via a light beam,
CD-players, and bar code readers. Small groups of 4-5 students have used the kits and provided valuable feedback. We
have pilot tested these modules with over 500 students and will highlight several of the modules including pre- and postclass
questionnaires completed by the students. The kits use modern photonic materials including light emitting diodes
and simple solid state optical detectors. We also discuss how these modules are consistent with National Science Content
Standards and cover both science and technology applications.
We discuss experimental results from spectroscopic and kinetic investigations of the reaction sequence starting with
NCI3 + H. Through a series of abstraction reactions, NCI (a1Δ) is produced. We have used sensitive optical emission
diagnostics and have observed both [NCI(a1Δ)]and [NCI(b1Σ)] produced by this reaction. Upon addition of HI to
the flow, the reaction of H + HI produced iodine atoms that were pumped to the excited I(2P1/2) state, and we
observed strong emission from the I atom 2P 1/2 -> 2P3/2 transition at 1.315 μm. With a tunable diode laser we probed
the I atom transition and observed significant transfer of population from ground state (2P3/2) to the excited state
(2P1/2) and have observed optical transparency within the iodine atom energy level manifold.
In this paper we discuss several sensitive diagnostics that have specifically developed for application to COIL and other iodine laser concepts such as AGIL and DOIL. We briefly cover the history of some important diagnostics including recently-developed diode laser sensors for a variety of parameters including: water vapor concentration, singlet oxygen yield, small signal gain, and translational temperature. We also discuss new developments and extensions of prior capabilities including: an ultra-sensitive diagnostic for I2 dissociation, a new monitor for singlet oxygen yield, and a novel diode laser-based imaging system for simultaneous, multipoint spatial distributions of species concentration and temperature. Finally, we mention how these diagnostics have bee successfully applied to the emerging DOIL technology.
In this paper we present results from a spectroscopic and kinetic study of the reaction sequence of NCl3 + H that produces NCl(a1Δ). Using sensitive optical emission diagnostics, we have observed both NCl(a) and (b) produced by this reaction. Upon addition of HI to the flow, the reaction of H + HI produced iodine atoms that were pumped to the excited I(2P1/2) state, and we observed strong emission from the I atom 2P1/2 → 2P3/2 transition at 1.315 μm. We also used a sensitive diode laser spectrometer to probe the I atom transition and observed transfer of population from ground state (2P3/2) to the excited state (2P1/2) with a concomitant reduction in the measured absorption. We interpret this observation as an approach to optical transparency.
Cost-effective and environmentally-sound means of paint and coatings removal is a problem spanning many government, commercial, industrial and municipal applications. For example, the Department of Energy is currently engaged in removing paint and other coatings from concrete and structural steel as part of decommissioning former nuclear processing facilities. Laser-based coatings removal is an attractive new technology for these applications as it promises to reduce the waste volume by up to 75 percent. To function more efficiently, however, the laser-based systems require some form of process control.
Potential human exposure to airborne metals occurs in a broad number of government and civilian operations and processes. Included among these are hard chromium plating, firing ranges, metallurgy and metals processing, lead paint abatement, and decontamination and decommissioning activities at hazardous waste sites. Effective control of these fugitive emissions requires sensitive real time monitoring. Physical Sciences Inc. (PSI) has developed a real time monitor for lead and chromium based on spark-induced breakdown spectroscopy (SIBS). The basis of SIBS is a high energy breakdown creating atomic emission which is sensitively viewed with a radiometer. This technology has been successfully demonstrated to detect low ppbw ((mu) g/m3) concentrations of lead and chromium in incinerator stack gases (joint DoE/EPA test a Research Triangle Park in September 1997), airborne lead at a local firing range (in the airspace of the shooters and in the ventilation system), and chromium at a hard chromium electroplating facility. The PSI SIBS technology is being developed as an inexpensive real time monitor for toxic metals in a variety of applications including: process control, emission compliance and industrial hygiene. Our progress towards developing a commercially viable prototype will be reviewed.