The injection of CO2 into deep aquifers can potentially affect the quality of groundwater supplies were leakage to occur
from the injection formation or fluids. Therefore, the detection of CO2 and/or entrained contaminants that migrate into
shallow groundwater aquifers is important both to assess storage permanence and to evaluate impacts on water
resources. Naturally occurring elements (i.e., Li, Sr) in conjunction with isotope ratios can be used to detect such
leakage. We propose the use of laser induced breakdown spectroscopy (LIBS) as an analytical technique to detect a suite
of elements in water samples. LIBS has real time monitoring capabilities and can be applied for elemental and isotopic
analysis of solid, liquid, and gas samples. The flexibility of probe design and use of fiber optics make it a suitable
technique for real time measurements in harsh conditions and in hard to reach places. The laboratory scale experiments
to measure Li, K, Ca, and Sr composition of water samples indicate that the technique produces rapid and reliable data.
Since CO2 leakage from saline aquifers may accompany a brine solution, we studied the effect of sodium salts on the
accuracy of LIBS analysis. This work specifically also details the fabrication and application of a miniature ruggedized
remotely operated diode pumped solid state passively Q-switched laser system for use as the plasma excitation source
for a real time LIBS analysis. This work also proposes the optical distribution of many laser spark sources across a wide
area for widespread leak detection and basin monitoring.
Laser-Induced Breakdown Spectroscopy (LIBS) technique combined with Laser-Induced Fluorescence (LIF) is known
to be a high sensitivity and high selectivity analytical technique. Although sub-ppm limits of detection (LoD) have
already been demonstrated, there is still a constant and urgent need to reach lower LoDs. Here, we report results obtained
for the detection of lead trace in brass samples. The plasma was produced by a Q-switched Nd:YAG laser at 1064 nm
and then re-excited by a nanosecond optical parametric oscillator (OPO) laser tuned at 283.31 nm. Emission from Pb
atoms was then observed at 405.78 nm. The experiments were performed in air at atmospheric pressure. We found out
that the optimal conditions were obtained for an ablation fluence of 2-3 J/cm2 and inter-pulse delay of 8-10 μs. Also,
excitation energy of about 200 μJ was required to maximize the Pb(I) 405.78 nm emission. Using the LIBS-LIFS
technique, the LoD was estimated to be about 180 ppb over 100 laser shots, which corresponds to an improvement of
about two orders of magnitude with that obtained using conventional LIBS.
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