Recent LIBS Research
Areas of emphasis:
- Sensitive detection of energetic materials/explosives
- Sensitive detection of chemical warfare agents
- Sensitive detection of biological warfare agents
- Detection of lead contamination in paints and soils
Sensitive Detection of Energetic Materials/Explosives
Laser Induced Breakdown Spectroscopy (LIBS) spectra of a large variety of energetic materials have been acquired at ARL using laboratory, field-portable, and standoff systems. The identification of energetic materials depends on the relative intensities of the atomic and molecular emission lines present in the spectra. The entrainment of air into the LIBS plasma contributes to the oxygen and nitrogen emission lines. By using either an argon buffer gas (close-contact) or double pulse LIBS (ideal for standoff), the oxygen and nitrogen ratios are indicative of the sample composition, improving the ability to discriminate explosive and non-explosive materials.
Single-shot spectra of RDX residue on aluminum and the interferent samples oil, dust and fingerprint residue were acquired at 20 m using the ST-LIBS system . Using principal components analysis (PCA), the RDX can be separated nearly completely from the interferent samples. More advanced chemometric models have recently been developed by our group that enable us to identify explosive-containing mixtures as well.
References: [F. C. De Lucia Jr., R. S. Harmon, K. L. McNesby, R. J. Winkel Jr., A. W. Miziolek; Laser-induced breakdown spectroscopy analysis of energetic materials; APPLIED OPTICS; Vol. 42, No. 30 (2003), pp. 6148-6152.][J. L. Gottfried, F. C. De Lucia, Jr., C. A. Munson, Andrzej W. Miziolek; Strategies for Trace/Residue Explosives Detection Using LIBS, LIBS2006, Montreal, Qc, Canada, poster presented September 6-7, 2006.]
Sensitive Detection of Chemical Warefare Agents
Single-shot spectra of nerve agent simulants (dimethyl methyl phosphonate DMMP, C3H9O3P and diisopropyl methyl phosphonate DIMP, C7H17O3P) and interferents (plant food fertilizer and liquid detergent) were acquired at 20 m using the ST-LIBS system. Even though both simulants contain the same elements, the ratios of the atomic/molecular emission lines can be used to discriminate between them.
A partial least squares discriminant analysis (PLSDA) model was built using the aluminum substrate (samples 1-20), nerve agent simulants DEEP (21-40), DEMP (41-60), DMMP (61-80), DIMP (81-100) and fertilizer (101-120). The test TEP samples (121-140) are correctly identified as a nerve agent simulant while the test interferents (detergent and fertilizer) do not result in false positives (they fall below the red threshold).
Reference: [ J. L. Gottfried, F. C. DeLucia, Jr., C. A. Munson, A. W. Miziolek; Standoff Detection Biomaterials Using Laser-Induced Breakdown Spectroscopy (ST-LIBS), Pittcon 2007, Chicago, Illinois, February 25-March 2, 2007.]
Sensitive Detection of Biological Warfare Agents
Single-shot spectra of the anthrax surrogate Bacillus subtilis (top) and the ricin surrogate ovalbumin (bottom) were acquired with the field-portable MP-LIBS system. Linear correlation was used to identify unknown powders on indoor surfaces based on a spectral library.
Single-shot spectra of the anthrax surrogate Bacillus subtilis (aka Bacillus globigii or BG), the ricin surrogate ovalbumin, and 24 potential interferents such as dust, sugar, fertilizer, etc. were acquired at 20 m using a ST-LIBS system. A PLS-DA model was constructed based on 750 samples. A second source of BG (samples 751-800), BG on a glass substrate (801-850), and BG on an aluminum substrate (851-900) were tested against the model and correctly identified as BG (they fall above the blue threshold).
References: [Jennifer Gottfried, Andrzej Miziolek, Chase Munson, Frank DeLucia, Jr., Roy Walters; Evaluation of the MP-LIBS Backpack Sensor for the Detection and Identification of Indoor Powders, Pittcon 2006, Orlando, Florida, March 12-17, 2006.][ J. L. Gottfried, F. C. DeLucia, Jr., C. A. Munson, A. W. Miziolek; Standoff Detection Biomaterials Using Laser-Induced Breakdown Spectroscopy (ST-LIBS), Pittcon 2007, Chicago, Illinois, February 25-March 2, 2007.]
Detection of Lead Contaimination in Paints and Soil
LIBS emission spectra from paint samples doped with Pb powder for the laboratory and portable systems. A baseline contribution to the 405.8 nm emission line is evident in the undoped sample. Spectra are 25 shot averages. The entire LIBS event is captured by the portable system, while the laboratory system employs a 100 ns delay (from the laser onset) and a 20 µs gate.
LIBS spectra obtained from 10 soil samples from the SIAD (Sierra Army Depot, CA) site showing the emission lines due to Zn (213.8 nm), Pb (220.4 nm), and Al (228.2 nm).
Reference: [R. T. Wainner, R. S. Harmon, A. W. Miziolek, K. L. McNesby, P. D. French; Analysis of environmental lead contamination: comparison of LIBS field and laboratory instruments; SPECTROCHIMICA ACTA Part B; Vol. 56, No. 6 (2001), pp. 777-793.]