Recent advances in ultrafast optical laser technology have improved generation and detection of energy within the
terahertz (THz) portion of the electromagnetic (EM) spectrum. One promising application of THz spectroscopy
is the detection of explosive materials and chemical or biological agents. This application has been motivated by
initial measurements that indicate that explosives may have unique spectral characteristics in the THz region thus
providing a discernible fingerprint. However, since THz wavelengths are 10's to 100's of microns in scale, rough
interfaces between materials as well as the granular nature of explosives can cause frequency-dependent scattering
that has the potential to alter or obscure these signatures. For reflection spectroscopy in particular the measured
response may be dominated by rough surface scattering, which is in turn influenced by a number of factors
including the dielectric contrast, the angle of incidence and scattering, and the operating frequency. In this paper,
we present measurements of THz scattering from rough surfaces and compare these measurements with analytical
and numerical scattering models. These models are then used to predict the distortion of explosive signatures
due to rough surface interfaces with varying surface height deviations and correlation lengths. Implications of
scattering effects on the performance of THz sensing of explosive materials are presented and discussed.
The effects of surface scattering on terahertz reflection spectrum for explosive detection are studied by measuring
terahertz reflection pulses from sandpapers with different roughness coated with gold. The experimental results show that
the amplitude decrease and pulse broadening of the detected signal caused by the surface scattering result in the width
reduction of Gaussian distribution of the specular scattering coefficient spectrum. A simple analytical model is applied to
the analysis of experimental results and good agreements are obtained.
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