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A thermal luminescence (TL) spectroscopy method for detecting organic impurities in water solution is presented. Infrared emissions by the dissolved organic matter are measurable, once a thermal gradient between it and the water medium is established, at those TL frequencies that are absorbed by the contaminant, following irradiation by a pulsed microwave beam. This detection window of opportunity closes as the liquid reaches thermal equilibrium at elevated temperatures and on collapse of the gradient. TL radiance liberated by a suspected contaminated water sample is scanned interferometrically about the maximum thermal gradient event, where N interferograms are acquired and grouped into contiguous sets of two, with N/2 interferogram elements per set. The coadded averages of these sets enhance the sensitivity of measurement to a small variance in emissivity and are Fourier transformed, and the adjacent spectra are subtracted. The difference spectrum is preprocessed with linear baseline, noise filtration, scaling, and parity operators to reveal a clear emissions band signature of the solute of dimethylmethylphosphonate to concentrations of parts per 103 and less. An artificial neural network facilitates detection of the contaminant by pattern recognition of the contaminant’s infrared band signature.
© 2001 Optical Society of America
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