Resonance-Enhanced Raman Spectroscopy on Explosives Vapor at Standoff Distances

Table 1

Apparent maximum enhancements, 𝐹_max, compared to the Raman cross section at 532 nm for NM, DNT, and TNT at the given concentrations. 𝜆_max is the incident wavelength resulting in the highest cross section, 𝜔 is the Raman wave number of the observed Raman peak, and 𝜎_HE,app is the apparent Raman cross section. The Raman signal for TNT at a concentration of 26 ppm is only measured at 248 nm; a higher value might be found at another wavelength. The apparent cross section is included in the table to facilitate comparison with other measurements and should not be mistaken for an absolute Raman cross section.

Substance	𝜆max (nm)	𝜔 (cm^−1)	𝜎HE,app(cm^2 str^−1)	Temp. (K)	Conc. (ppm)	F max
NM	232	1378/1401	3.4×10^−27	291	32,500	9,300
2,4-DNT	262	1347	1×10^−26	383	1,445	24,000
2,4-DNT	252	1347	1×10^−25	354	126	240,000
2,4,6-TNT	250	1358	8×10^−27	401	341	17,000
2,4,6-TNT	248	1358	3×10^−26	369	26	61,000