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Pulsed terahertz bi-directional reflection distribution function (BRDF) measurements of materials and obscurants

A pulsed terahertz imaging system modified to perform angular detection of light for quantitatively characterizing reflection and scattering from samples is reported. Reflection from a gold mirror shows that the full width half maximum (FWHM) of the terahertz beam angular spread is < 1° with signal-to-noise of 65 dB. Two samples, a paper index card and a corduroy cloth sample were tested. The index card reflects ca. 1% of the incident terahertz energy with similar angular spreading while the corduroy sample reflected approximately 0.01% of the incident terahertz energy with FWHM of 5 - 10°. The corduroy sample also exhibits temporal pulse scattering as a function of angle which correlates with direct frequency domain measurements.