We describe our results obtained from stoichiometric ratio studies of three different energetic, inorganic samples (ammonium perchlorate (AP), boron potassium nitrate (BPN), and ammonium nitrate (AN)) using the technique of laser-induced breakdown spectroscopy (LIBS) with nanosecond pulses. Signal collection was independently executed using both gated and nongated spectrometers. The oxygen peak at 777.31？nm (O) and nitrogen peaks at 742.50？nm (N1), 744.34？nm (N2), and 746.91？nm (N3) were used for evaluating the O/N ratios. Temporal analysis of plasma parameters and ratios was carried out for the gated data. O/N1, O/N2, and O/N3 ratios retrieved from the gated AP data were in excellent agreement with the actual stoichiometry. In the case of gated BPN data, O/N2 and O/N3 ratios were in good agreement. The stoichiometry results obtained with nongated spectrometer, although less accurate than that obtained with gated spectrometer, suggest that it can be used in applications where fair accuracy is sufficient. Our results strongly indicate that non-gated LIBS technique is worthwhile in the kind of applications where precision classification is not required. 1. Introduction Nanosecond (ns) laser-induced breakdown spectroscopy (LIBS) has been extensively employed in elemental analysis, impurity detection [1, 2], and identification/classification of materials [3, 4]. In recent years this technique has been applied to study a variety of materials such as alloys, biological samples, pharmaceuticals, and explosives amongst various others [5–8]. The strength of this technique emanates from prerequisites that an ideal analytical tool should possess—minimal sample preparation, simultaneous multielement detection, ability to analyze all three states of matter, the necessity of short-time scales involved for measurement and analysis, and most importantly the capability of remote detection. In most of the cases requirement for sample preparation is negligible. This technique involves the interaction of an intense laser pulse with a sample leading to plasma generation [9–12]. The material absorbs light through multiphoton/inverse Bremsstrahlung process that heats the sample surface further to which electrons acquire energy, and as the energy absorbed grows, it leads to collisions and breakdown. Breakdown is followed by the plasma expansion and consequently the creation of shock waves. The plasma expansion rate is observed to be highest towards the focusing lens [13]. During the cooling stage constituent ions/electrons of expanding plasma recombine to form neutral atoms,
References
[1]
F. Y. Yueh, J. P. Singh, and H. Zhang, Encyclopedia of Analytical Chemistry, John Wiley & Sons, London, UK, 2000.
[2]
K. E. Eseller, F. Y. Yueh, and J. P. Singh, “Non-intrusive, on-line, simultaneous multi-species impurity monitoring in hydrogen using LIBS,” Applied Physics B, vol. 102, no. 4, pp. 963–969, 2011.
[3]
N. C. Dingari, I. Barman, M. A. Kumar, S. P. Tewari, and G. M. Kumar, “Incorporation of support vector machines in the LIBS toolbox for sensitive and robust classification amidst unexpected sample and system variability,” Analytical Chemistry, vol. 84, pp. 2686–2694, 2012.
[4]
J. L. Gottfried, F. C. de Lucia Jr., C. A. Munson, and A. W. Miziolek, “Double-pulse standoff laser-induced breakdown spectroscopy for versatile hazardous materials detection,” Spectrochimica Acta B, vol. 62, no. 12, pp. 1405–1411, 2007.
[5]
I. V. Cravetchi, M. Taschuk, G. W. Rieger, Y. Y. Tsui, and R. Fedosejevs, “Spectrochemical microanalysis of aluminum alloys by laser-induced breakdown spectroscopy: identification of precipitates,” Applied Optics, vol. 42, no. 30, pp. 6138–6147, 2003.
[6]
A. C. Samuels, F. C. de Lucia Jr., K. L. McNesby, and A. W. Miziolek, “Laser-induced breakdown spectroscopy of bacterial spores, molds, pollens, and protein: initial studies of discrimination potential,” Applied Optics, vol. 42, no. 30, pp. 6205–6209, 2003.
[7]
M. Hoehse, D. Mory, S. Florek, F. Weritz, I. Gornushkin, and U. Panne, “A combined laser-induced breakdown and Raman spectroscopy Echelle system for elemental and molecular microanalysis,” Spectrochimica Acta B, vol. 64, no. 11-12, pp. 1219–1227, 2009.
[8]
Y. Dikmelik, C. McEnnis, and J. B. Spicer, “Femtosecond and nanosecond laser-induced breakdown spectroscopy of trinitrotoluene,” Optics Express, vol. 16, no. 8, pp. 5332–5337, 2008.
[9]
A. W. Miziolek, V. Palleschi, and I. Schechter, Laser-Induced Breakdown Spectroscopy (LIBS) Fundamentals and Applications, Cambridge University Press, New York, NY, USA, 2006.
[10]
D. A. Cremers and L. J. Radziemski, Handbook of Laser-Induced Breakdown Spectroscopy, John Wiley & Sons, London, UK, 2006.
[11]
J. P. Singh and S. N. Thakur, Laser-Induced Breakdown Spectroscopy, Elsevier Science, Amsterdam, The Netherlands, 2007.
[12]
F. J. Fortes and J. J. Laserna, “The development of fieldable laser-induced breakdown spectrometer: no limits on the horizon,” Spectrochimica Acta B, vol. 65, no. 12, pp. 975–990, 2010.
[13]
N. Kawahara, J. L. Beduneau, T. Nakayama, E. Tomita, and Y. Ikeda, “Spatially, temporally, and spectrally resolved measurement of laser-induced plasma in air,” Applied Physics B, vol. 86, no. 4, pp. 605–614, 2007.
[14]
S. Sreedhar, S. V. Rao, P. P. Kiran, S. P. Tewari, and G. M. Kumar, “Stoichiometric analysis of ammonium nitrate and ammonium perchlorate with nanosecond laser induced breakdown spectroscopy,” in Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XI, A. Fountain III and P. J. Gardner, Eds., vol. 7665 of Proceedings of SPIE, Orlando, Fla, USA, 2010.
[15]
S. Sreedhar, M. A. Kumar, G. M. Kumar, P. P. Kiran, S. P. Tewari, and S. V. Rao, “Laser-induced breakdown spectroscopy of RDX and HMX with nanosecond, picosecond, and femtosecond pulses,” in Chemical, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XI, A. W. Fountain III and P. J. Gardner, Eds., vol. 7665 of Proceedings of SPIE, Orlando, Fla, USA, 2010.
[16]
K. E. Eseller, F. Y. Yueh, and J. P. Singh, “Laser-induced breakdown spectroscopy measurement in methane and biodiesel flames using an ungated detector,” Applied Optics, vol. 47, no. 31, pp. G144–G148, 2008.
[17]
S. Rai, A. K. Rai, and S. N. Thakur, “Identification of nitro-compounds with LIBS,” Applied Physics B, vol. 91, no. 3-4, pp. 645–650, 2008.
[18]
S. Rai, A. K. Rai, I. M. L. Das, and K. C. Tripathi, “Implementation of statistical methods on LIBS data for classification of residues of energetic materials (nitro compounds),” Advanced Materials Letters, vol. 2, pp. 32–37, 2011.
[19]
M. A. Kumar, S. Sreedhar, I. Barman, et al., “Laser-induced breakdown spectroscopy-based investigation and classification of pharmaceutical tablets using multivariate chemometric analysis,” Talanta, vol. 87, pp. 53–59, 2011.
[20]
J. Anzano, R. J. Lasheras, B. Bonilla, and J. Casas, “Classification of polymers by determining of C1:C2:CN:H:N:O ratios by laser-induced plasma spectroscopy (LIPS),” Polymer Testing, vol. 27, no. 6, pp. 705–710, 2008.
[21]
F. C. de Lucia Jr. and J. L. Gottfried, “Characterization of a series of nitrogen-rich molecules using laser induced breakdown spectroscopy,” Propellants, Explosives, Pyrotechnics, vol. 35, no. 3, pp. 268–277, 2010.
[22]
C. L. Moreno, S. Palanco, J. J. Laserna et al., “Test of a stand-off laser-induced breakdown spectroscopy sensor for the detection of explosive residues on solid surfaces,” Journal of Analytical Atomic Spectrometry, vol. 21, no. 1, pp. 55–60, 2006.
[23]
V. Sturm and R. Noll, “Laser-induced breakdown spectroscopy of gas mixtures of air, CO2, N2, and C3H8 for simultaneous C, H, O, and N measurement,” Applied Optics, vol. 42, no. 30, pp. 6221–6225, 2003.
[24]
J. L. Gottfried, F. C. de Lucia Jr., C. A. Munson, and A. W. Miziolek, “Strategies for residue explosives detection using laser-induced breakdown spectroscopy,” Journal of Analytical Atomic Spectrometry, vol. 23, no. 2, pp. 205–216, 2008.
[25]
E. J. Judge, G. Heck, E. B. Cerkez, and R. J. Levis, “Discrimination of composite graphite samples using remote filament-induced breakdown spectroscopy,” Analytical Chemistry, vol. 81, no. 7, pp. 2658–2663, 2009.
[26]
H. Estupinan, D. Y. Pena, Y. O. Garcia, R. Cabanzo, and Mejia-Ospino, “Stoichiometry analysis of titanium oxide coating by LIBS,” The European Physical Journal D, vol. 53, pp. 69–73, 2009.
[27]
D. Mirell, O. Chalus, K. Peterson, and J. C. Diels, “Remote sensing of explosives using infrared and ultraviolet filaments,” Journal of the Optical Society of America B, vol. 25, no. 7, pp. B108–B111, 2008.
[28]
P. Lucena, A. Do？a, L. M. Tobaria, and J. J. Laserna, “New challenges and insights in the detection and spectral identification of organic explosives by laser induced breakdown spectroscopy,” Spectrochimica Acta B, vol. 66, no. 1, pp. 12–20, 2011.
[29]
H. Zhang, F. Y. Yueh, and J. P. Singh, “Laser-induced breakdown spectrometry as a multimetal continuous-emission monitor,” Applied Optics, vol. 38, pp. 1459–1466, 1999.
[30]
J. L. Gottfried, F. C. de Lucia Jr., C. A. Munson, and A. W. Miziolek, “Discrimination of explosive residues on organic and inorganic substrates using laser-induced breakdown spectroscopy,” Journal of Analytical Atomic Spectrometry, vol. 24, no. 3, pp. 288–296, 2009.
[31]
J. L. Gottfried, F. C. de Lucia Jr., C. A. Munson, and A. W. Miziolek, “Laser-induced breakdown spectroscopy for detection of explosives residues: a review of recent advances, challenges, and future prospects,” Analytical and Bioanalytical Chemistry, vol. 395, no. 2, pp. 283–300, 2009.
[32]
F. C. de Lucia Jr., J. L. Gottfried, C. A. Munson, and A. W. Miziolek, “Multlvariate analysis of standoff laser-induced breakdown spectroscopy spectra for classification of explosive-containing residues,” Applied Optics, vol. 47, no. 31, pp. G112–G121, 2008.
[33]
F. C. de Lucia Jr., A. C. Samuels, R. S. Harmon et al., “Laser-induced breakdown spectroscopy (LIBS): a promising versatile chemical sensor technology for hazardous material detection,” IEEE Sensors Journal, vol. 5, no. 4, pp. 681–689, 2005.
[34]
NIST database of atomic spectral data, http://physics.nist.gov/PhysRefData/ASD.
[35]
H. R. Griem, Plasma Spectroscopy, McGraw-Hill, New York, NY, USA, 1964.
