Abstract
Optical signatures of fresh and aged explosives are measured and compared to determine whether there exist differences
in the signatures that can be exploited for detection. The explosives examined are RDX, TNT, and HMX, which have
been heated for two weeks at 75 degrees centigrade or irradiated for two weeks with a 15-Watt ultraviolet lamp (254nm).
The optical signatures are obtained by illuminating the samples with a sequence of laser wavelengths between 420nm
and 620nm in 10 nm steps and measuring the spectra of light scattered from the sample at each laser wavelength. The
measurements are performed on the Naval Research Laboratory's SWOrRD instrument. SWOrRD is capable of
illuminating a sample with laser wavelength between 210nm and 2000nm, in steps of 0.1nm, and measuring the
spectrum of light scattered from the sample at each wavelength. SWOrRD's broad tuning range, high average power (1-
300mW), narrow line width (< 4cm-1), and rapid wavelength tunability enable these measurements.
Results, based on more than 80 measurements - each at 21 sequential laser wavelengths, indicate that the variation in
spectral line amplitude observed when altering laser illumination wavelength differs between fresh and aged explosives.
Thus, an instrument for rapid and reagent-less differentiation between aged and fresh explosives, based on illumination
with a few appropriately chosen laser wavelengths appears feasible.
