Guided wave terahertz characterization of fingerprint lines in threat materials

摘要

The underlying THz vibrational spectrum of explosives and related threat materials consists of a highly detailed fingerprint due to the interaction of internal and external vibrations in the crystalline environment. However, the underlying spectrum has been difficult to resolve, even at cryogenic temperatures, because of line broadening processes. In this paper we use the technique of waveguide terahertz time-domain spectroscopy (THz-TDS) to measure the underlying THz vibrational spectrum of three threat-related materials: 2,4-dintrotoleuene (2,4-DNT), 4-amino-dintrotoluene (4A-DNT), and pentaerythritol dinitrotoluene (PETN). These materials are characterized as polycrystalline layers in the 50 micron gap of a metal parallel plate waveguide. For each material, we show that waveguide THz-TDS measurements at cryogenic temperature resolve, at least partially, the underlying THz vibrational spectrum. We suggest that these narrow-line waveguide THz-TDS measurements may be used as rigorous input for theoretical computations to predict THz vibrational spectra.