Surface roughness impacts terahertz signal from explosives
It makes sense that if the performance of a terahertz emitter is directly impacted by its surface structure (see “Black silicon emits terahertz radiation,” p.46)
It makes sense that if the performance of a terahertz emitter is directly impacted by its surface structure (see “Black silicon emits terahertz radiation,” p. 46), then the surface structure of a material could also impact the signal level of its emitted terahertz radiation. This is precisely what researchers at Berliner Elektronenspeicherringgesellschaft für Synchrotronstrahlung (BESSY) and Deutsches Zentrum für Luft-und Raumfahrt (DLR), both in Berlin, Germany, have demonstrated: that surface roughness of a pure explosive material has a significant effect on its terahertz reflectance, severely limiting the applicability of terahertz detection systems for many substances.
Reflectance spectra of prepared octogen and hexogen explosive pellets at different incidence angles and for different surface-structure sizes were gathered using Fourier-transform infrared spectroscopy with a mercury source and a silicon bolometer in the 1.5 to 20 THz range. The researchers found that realistic surface roughness can significantly reduce the reflected terahertz spectral signature of a sample due to high-frequency rolloff of the specular reflectance, especially at normal incidence. Fortunately, multiple measurements at various (and oblique) incidence angles can improve the measured results if classical scattering theory is included in the data analysis. Contact Michele Ortolani at email@example.com.