  We study the scattering of electromagnetic waves in anisotropic energetic
materials. Nonlinear light-matter interactions in molecular crystals result in
frequency-conversion and polarization changes. Applied electromagnetic fields
of moderate intensity can induce these nonlinear effects without triggering
chemical decomposition, offering a mechanism for non-ionizing identification of
explosives. We use molecular dynamics simulations to compute such
two-dimensional Raman spectra in the terahertz range for planar slabs made of
PETN and ammonium nitrate. We discuss third-harmonic generation and
polarization-conversion processes in such materials. These observed far-field
spectral features of the reflected or transmitted light may serve as an
alternative tool for stand-off explosive detection.
