Nonlinear multi-photon laser wave-mixing spectroscopic method is demonstrated as an ultrasensitive detection method for explosives including ammonium nitrate, trinitrotoluene and triacetone-triperoxide. These analytes can be detected based on direct optical absorption in their native form label-free using UV lasers or by using convenient visible lasers when combined with specific labels or agents. Wave mixing offers inherent advantages as compared to currently available methods including ion mobility spectrometers and mass spectrometers including a rugged, compact and portable design, excellent sensitivity and specificity levels, and standoff detection capability. Laser wave mixing is an unusually sensitive optical absorption-based detection method that offers significant inherent advantages including excellent sensitivity, small sample requirements, short optical path lengths, high spatial resolution, and high spectral resolution. Wave mixing allows for reliable monitoring of small changes in the analyte properties since the signal has a quadratic dependence on analyte concentration. The wave-mixing signal is a laser-like coherent beam, and hence, it can be collected with virtually 100% efficiency with excellent signal-to-noise ratio. The wave-mixing signal also has its own propagation direction and it can be spatially filtered and detected away from all the input beams. Laser excitation wavelengths can be tuned to detect multiple analytes in their native forms. We have detected ammonium nitrate, trinitrotoluene and triacetone-triperoxide in different sample configurations (liquid, thin film, solid) and obtained excellent preliminary detection limits that are comparable or better than currently available detection methods while using a compact design.

Sensitive and selective detection of explosives by nonlinear optical laser wave-mixing spectroscopy

253rd National Meeting (2017)

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