Laser photofragmentation (PF) and subsequent nitric oxide (NO) laser-induced fluorescence (LIF) have been developed to measure the concentration of energetic materials (EM’s), such as 2, 4, 6-trinitrotoluene (TNT), in soil and other media. Gas-phase EM’s photodissociate, releasing NO<sub>2</sub>, when exposed to laser radiation near 226 nm. Laser-excited NO<sub>2</sub> predissociates to form NO that gives an intense fluorescence when excited near 226 nm. The EM concentration is inferred from the intensity of the NO fluorescence. A PF-LIF laser-based sensor is being developed to be used with the U.S. Army Corps of Engineers’ Waterways Experiment Station’s cone penetrometer to measure <i>in situ</i> the concentration of subsurface TNT. Several factors that affect the PF-LIF signal waveforms, such as sample temperature, laser power, and heating time, were investigated. Also, effects on the PF-LIF signal of adding water and fertilizer to the TNT mixtures were studied. Decay times were determined by least-squares fitting of the exponential PF-LIF signal waveforms. The use of PF-LIF waveforms promises to enable diagnostics of the sample’s characteristics that would otherwise not be possible <i>in situ</i>.
© 1999 Optical Society of America
(020.4180) Atomic and molecular physics : Multiphoton processes
(120.1880) Instrumentation, measurement, and metrology : Detection
(280.3420) Remote sensing and sensors : Laser sensors
(300.2530) Spectroscopy : Fluorescence, laser-induced
(300.6500) Spectroscopy : Spectroscopy, time-resolved
Gary M. Boudreaux, Tracy S. Miller, Amanda J. Kunefke, Jagdish P. Singh, Fang-Yu Yueh, and David L. Monts, "Development of a Photofragmentation Laser-Induced-Fluorescence Laser Sensor for Detection of 2, 4, 6-Trinitrotoluene in Soil and Groundwater," Appl. Opt. 38, 1411-1417 (1999)