A novel approach to optical detection of airborne explosive vapor using a combination of cavity enhanced ab-
sorption spectroscopy (CEAS) and diusion time of
ight (DiTOF) is reported. The direct optical detection of
explosive vapors by absorption presents a number of unique challenges due to low vapor pressures of explosive
compounds, a lack of resolved spectral features, and the presence of interfering species with overlapping absorp-
tion spectra. By recording the changing optical absorption as sampled atmosphere diuses into an explosive-free
buer gas, the concentration of explosive molecules may be determined using a Bayesian statistical signal process-
ing technique. This technique avoids the need for laser wavelength scans while simultaneously providing robust
background rejection. The use of xed laser wavelengths allows for the use of cavity-locked cavity ring-down or
cavity-locked direct cavity transmission absorption measurements with high data acquisition rates and signi-
cantly reduces the complexity of the laser system by eliminating the need for precision wavelength monitoring.
This allows for the development of compact, eld deployable sensors based on this technique. Experimental
demonstration of the simultaneous detection of multiple species of hydrocarbon tracer molecules at 4295 cm<sup>−1</sup>
will be reported. The results of the current work will be applied to the detection of TNT vapor to show a
projected sensitivity of 2 pptv in a diesel exhaust background.