Advanced detection of concealed white powders in security applications using terahertz spectroscopy

To meet the growing demands of public security screening in transportation systems, this study utilizes terahertz time-domain spectroscopy (THz-TDS) to analyze six visually indistinguishable white powdery substances and evaluate their purity within the 0-1.5 THz frequency range. The analysis incorporates both time-domain and frequency-domain spectra alongside three key optical parameters: transmittance, refractive index, and absorption coefficient. Experimental results reveal that each substance, irrespective of purity, exhibits different spectral signatures in the terahertz range. These distinctions are evident through variations in main pulse delay, signal attenuation, and the position of absorption peaks (i.e., enabling high-accuracy material differentiation). This research not only expands the spectral database of chemicals within the terahertz region but also provides robust experimental evidence supporting the practical application of THz-TDS in public security and transportation safety screening.